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Salicylic acid application modulates physiological and hormonal changes in Eucalyptus globulus under water deficit
Abstract
Eucalyptus genus is the most widely planted hardwood tree, which productivity and development are limited by low water availability. Plant drought tolerance can be managed by adopting strategies, such as the exogenous application of salicylic acid. The main objective of the present study was to assess whether the exogenous foliar salicylic acid application would ameliorate the damages of water deficit on Eucalyptus globulus plants. Plants were watered at 70% (well water) or 15% (water deficit) of field capacity and four concentrations of salicylic acid (0, 0.75, 2.5 and 5.0 mM) were applied. Water potential, total chlorophylls and carotenoids contents, chlorophyll fluorescence parameters, leaf gas exchange, malondialdehyde, total soluble sugars, starch and total phenols contents were measured. The global hormonal content was quantified by ultra-performance liquid chromatography-mass spectrometry and specific local dynamics of indolacetic acid and abcisic acid were detected by immunolocalization in leaves. A multivariate statistical approach was used to get an overview of the plant physiological status. E. globulus water deficit response included growth rate decline associated with reduced in both water potential and leaf gas exchange parameters. Plant water deficit defence strategies led to an increase in total chlorophylls and carotenoids contents, lipid peroxidation, phenols and total soluble sugars. Six from the 18 hormones detected increased in water deficit plants. Exogenous salicylic acid application improved water deficit tolerance of E. globulus by improving water potential with a positive impact in primary metabolism (photosynthetic rate, soluble sugars) but also in secondary metabolism and defence mechanisms (higher total phenols and less lipid peroxidation) in the highest salicylic acid concentrations. Also, changes in endogenous levels of abscisic and salicylic acids, gibberellins 4 and 7, and specific cytokinins were found in water deficit plants with salicylic acid application. Our results indicated that salicylic acid application could be a potential chemical priming strategy to ameliorate water deficit effects on E. globulus plants.
... This process is also related to the 50.5% increase in the concentration of ABA observed in plants under drought at 08 DAP, compared to the WW control (p < 0.05 - Table 1 and Figure S3E). Gibberellic acid (GA) is also important for the modulation of plant growth induced by stressors (Colebrook et al. 2014;Jesus et al. 2015). Specifically, GA4 was elucidated to be responsive in E. globulus under drought stress, with more than 2-fold increase after 14 days of stress (Jesus et al. 2015). ...
... Gibberellic acid (GA) is also important for the modulation of plant growth induced by stressors (Colebrook et al. 2014;Jesus et al. 2015). Specifically, GA4 was elucidated to be responsive in E. globulus under drought stress, with more than 2-fold increase after 14 days of stress (Jesus et al. 2015). Similarly, we found an increase of almost 6-fold in GA4 concentration in plants kept under DC at 14 DAP (Table 1 and Figure S3E). ...
... Similarly, we found an increase of almost 6-fold in GA4 concentration in plants kept under DC at 14 DAP (Table 1 and Figure S3E). Relatively few studies have been published emphasizing the influence of water deficiency on the metabolism of gibberellins and their relationship with other hormones in eucalypt (Jesus et al. 2015). However, GA4-increase concentrations in response to soil drying may vary across evaluation time, as similar results to those found here at 8 DAP (no difference comparing to control - Table 1 and Figure S3E) were also noted for Glycine max (Castro-Valdecantos et al. 2021), Cucumis sativus (Kang et al. 2014) and Solanum lycopersicum (Gaion et al. 2018) at 7 days or less after drought. ...
... In this study, foliar application of SA reduced the harmful impact of soil water deficit on the plant growth and biomass production of M. alba saplings (Table 1 and Figure 1). Our findings were in accordance with different other studies on Torreya grandis and Eucalyptus globulus, Conocarpus erectus, Populus deltoides, Olea europaea and Syzygium sumini [23,24,[55][56][57], in which a similar increase in growth and biomass production was reported in response to SA under water deficit treatments, respectively. The increment in growth parameters after the foliar application of SA has been associated previously with enhanced cell division in tissues in the meristematic parts of the plants which thus promotes growth and development [58]. ...
... In this experiment, phenolic compounds and soluble proteins significantly increased under both water deficit (MS and HS) treatments, respectively ( Table 2). Similar findings were reported in previous studies [23,55,57], where phenolic compounds and soluble proteins increased under a limited supply of water. Multiplies studies have demonstrated that plants upregulate the expression of phenolics synthesis enzymes; for example, phenylalanine ammonia-lyase, results in the increased production of phenolic compounds that are antioxidants enzymes in stressful conditions [68]. ...
... In this experiment, an increase in H 2 O 2 and O 2 − was noticed in M. alba saplings under both soil water deficit treatments (Figure 3). Our results are consistent with previous research reporting increased production of H 2 O 2 and O 2 − under water stress [23,24,55,57]. Multiple studies have demonstrated that an increase in ROS production alters the redox equilibrium, which ultimately affects plant development in a water-scarce environment [38]. ...
Morus alba L. is a multipurpose and fast-growing tree species. However, its growth and productivity are susceptible to water stress. Therefore, a study was conducted to check the effectiveness of foliar application of salicylic acid (SA) in improving the water stress tolerance of M. alba. A pot experiment was conducted and the morphological, physiological and biochemical attributes of young M. alba saplings were assessed under control (CK, 90% of field capacity (FC)), moderate (MS, 60% of FC) and high soil water deficits (HS, 30% of FC), along with MS and HS + foliar application of SA 0.5 and 1.0 mM (MS + 0.5; HS + 0.5; MS + 1.0, and HS+1.0, respectively). Results demonstrated that the highest decrease in plant growth, leaf, stems and roots' dry biomass, chlorophyll a, b, carotenoid contents and leaf gas exchange parameters was observed under HS, whereas the lowest decrease was evidenced for HS + 1.0 mM SA. Electrolyte leakage, malondialdehyde contents, hydrogen peroxide and superoxide radicals significantly increased under HS, while the lowest increase was evidenced for HS + 1.0 mM SA. The highest increase in proline content, total soluble sugar, total phenolic content, soluble protein and superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase was also found under HS + 1.0 mM SA. Based on the results, it can be concluded that foliar application of SA can help improve the water deficit tolerance of Morus alba saplings, especially under high soil water deficit.
... The lowest carotenoid content values were also observed in less restrictive water regimes for plant growth (IR3, IR4, and IR5), similar to the results obtained for chlorophyll contents (Figure 4). Higher chlorophyll and carotenoid contents were found under a lower water availability (RI1), which agrees with the results obtained by Jesus et al. (2015) with E. globulus plants submitted to water deficit. Chlorophyll is the main element of pigment-protein complexes and plays an important role in photosynthesis (Chen et al., 2018). ...
... Chlorophyll is the main element of pigment-protein complexes and plays an important role in photosynthesis (Chen et al., 2018). The increased chlorophyll content under water deficit may be related to a decrease in leaf area, with a protective role of carotenoids or other mechanisms, which protect these pigments from degradation to protect photosynthetic capacity (Jesus et al., 2015), and a reduction of cell expansion can lead to the concentration of the accumulation of chlorophyll and carotenoids. ...
... The lower photosynthetic capacity related to more restrictive water regimes (IR1 and IR2), as well as the increase in MDA and proline contents, indicates that the lower water availability favored an increase in reactive oxygen species (ROS) levels. Plants under oxidative stress show an accumulation of MDA, resulting from lipid oxidation (Pompelli et al., 2010;Silva et al., 2010;Arcoverde et al., 2011;Jesus et al., 2015;Yalcinkaya et al., 2019). It indicates that both the enzymatic and non-enzymatic antioxidant defense system was affected by water deficit, which may be associated with reduced photosynthesis and increased total chlorophyll contents recorded in this experiment. ...
... In the present study, the production of phenolic compounds increased significantly under water deficit treatment in both C. erectus and M. alba saplings ( Table 2). These results are in line with the previous studies where an increase in phenolic compound and soluble protein has been observed in Salix and Acacia [47], Portulaca oleracea [60], Eucalyptus globulus [61] Syzygium cumini [13], under water stress conditions. ...
... In this study, the production of H 2 O 2 and O 2 − increased significantly in C. erectus and M. alba saplings under MS and HS treatments (Figure 3). These results are similar to the previous findings where an increase in the production of H 2 O 2 and O 2 − have been reported in Salix, Acacia, Portulaca, Quercus and other woody tree species under water deficit treatments [47,60,63,64]. Various studies have elaborated that an increase in the accumulation of ROS disrupts the redox balance and this ultimately decreases the productivity of plants under limited supply of water [65]. ...
... Our study also showed that the significant increase in ROS and resulted in a significant decrease in dry weight production in C. erectus and M. alba saplings under HS. It has been reported that the cell membrane is highly sensitive to different abiotic stress and increase in the concentration of malondialdehyde (MDA) contents and electrolyte leakage (EL%) indicates the extent of cellular damage [47,60]. In this study, we noticed a significant increase in MDA content and EL% in both C. erectus and M. alba under MS and HS ( Figure 2). ...
Mitigating climate change requires the identification of tree species that can tolerate water stress with fewer negative impacts on plant productivity. Therefore, the study aimed to evaluate the water stress tolerance of young saplings of C. erectus and M. alba under three soil water deficit treatments (control, CK, 90% field capacity, FC, medium stress MS, 60% FC and high stress, HS, 30% FC) under controlled conditions. Results showed that leaf and stem dry weight decreased significantly in both species under MS and HS. However, root dry weight and root/shoot ratio increased, and total dry weight remained similar to CK under MS in C. erectus saplings. Stomatal conductance, CO2 assimilation rate decreased, and intrinsic water use efficiency increased significantly in both species under MS and HS treatments. The concentration of hydrogen peroxide, superoxide radical, malondialdehyde and electrolyte leakage increased in both the species under soil water deficit but was highest in M. alba. The concentration of antioxidative enzymes like superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase also increased in both species under MS and HS but was highest in C. erectus. Therefore, results suggest that C. erectus saplings depicted a better tolerance to MS due to an effective antioxidative enzyme system.
... In this study, foliar application of SA significantly increased total dry weight (D T ) in both species under MS + SA and HS + SA ( Figure 1D). These results are in agreement with previous studies on Rosmarinus officinalis L., Oryza sativa L., Olea europaea L., and Eucalyptus globulus where the application of SA resulted in an increase in biomass production under water stress [22,28,30,57,58]. Previously, improvements in growth after SA application have been related to the increased plant water potential and cell division in the meristematic parts of the plant [30,59]. ...
... Therefore, an increase in Pc and TSS under SA application may help to regulate the water balance reducing water stress-induced loss in productivity. Similar results have been reported in a previous study in which a significant increase in proline and soluble sugar contents after the application of SA has been linked to the growth sustainability in Eucalyptus globulus under water stress [22]. Phenolic compounds are important secondary metabolites that also play an important role in water stress tolerance in plants as they act as antioxidants and protect the plants against drought induced oxidative stress [33]. ...
... In this study, this argument was supported by the observed increase in TPC under water stress concurrent with the decrease in MDA under MS + SA and HS + SA. Similar results are reported in previous studies where SA application significantly decreased the concentration of MDA indicating reduced membrane damage [22]. Based on these results, it can be concluded that the application of SA resulted in an increased production of various osmolytes (Pc, TSS, and TPC) that may have helped in improving the cellular osmotic status and productivity of both species under MS + SA and HS + SA. ...
Reforestation efforts are being challenged as water stress is hampering the sapling growth and survival in arid to semiarid regions. A controlled experiment was conducted to evaluate the effect of foliar application of salicylic acid (SA) on water stress tolerance of Conocarpus erectus and Populus deltoides. Saplings were watered at 90%, 60%, and 30% of field capacity (FC), and half of the saplings under 60% and 30% FC were sprayed with 1.0 mM SA. Results indicated that dry weight production decreased significantly in Populus deltoides under both water deficit conditions, and leaf gas exchange parameters decreased significantly in both the species under both soil water deficit conditions. Foliar application of SA resulted in a significant increase in leaf gas exchange parameters, and compatible solutes, thereby increasing the dry weight production in both of the species under soil water deficit. Oxidative stress (hydrogen peroxide and superoxide anions) increased under soil water deficit and decreased after the foliar application of SA and was parallel to the increased antioxidant enzymes activity (superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase). Therefore, it can be concluded that foliar application of 1.0 mM SA can significantly improve the water stress tolerance in both species, however, positive impacts of SA application were higher in Conocarpus erectus due to improved photosynthetic capacity and increased antioxidant enzyme activity.
... Application of Tre and/or SA mitigated the drought effects in basil through the partial recovery of chlorophyll levels and photosynthetic activity. Similar results have been reported in several plant species, such as sunflower [44], sesame [45], sweet basil [27], squash [46], Eucalyptus globulus L. [47], and maize (Zea mays L.) [48]. SA and Tre probably acted through the maintenance of the structural integrity of the thylakoid membrane and protected PSII from over-excitation and oxidative stress, as clearly shown by the increased Fv/Fm ratio and the reduced NPQ, especially when Tre and SA were used in combination. ...
... SA and Tre probably acted through the maintenance of the structural integrity of the thylakoid membrane and protected PSII from over-excitation and oxidative stress, as clearly shown by the increased Fv/Fm ratio and the reduced NPQ, especially when Tre and SA were used in combination. Similar effects were reported in E. globulus [47]. Taken together, our results support a role for SA and Tre in the protection of photosynthetic apparatus [44] through increased chlorophyll synthesis and photosynthetic activity, which support increased plant growth during drought stress. ...
... Sweet basil plants subjected to drought stress showed increased EL, potentially due to increased H 2 O 2 and MDA concentrations, compared to well-watered control plants. This result was consistent with previous studies in safflower (Carthamus tinctorius L.) [48] and E. globulus [47]. Spraying the foliage of drought-stressed sweet basil plants with Tre and/or SA reduced H 2 O 2 and MDA concentrations, as well as EL, indicating that Tre and SA alleviate the oxidative stress associated with drought stress. ...
Trehalose (Tre) and salicylic acid (SA) are increasingly used to mitigate drought stress in
crop plants. In this study, a pot experiment was performed to study the influence of Tre and SA
applied individually or in combination on the growth, photosynthesis, and antioxidant responses
of sweet basil (Ocimum basilicum L.) exposed to drought stress. Basil plants were watered to 60% or
100% field capacity with or without treatment with 30 mM Tre and/or 1 mM SA. Drought negatively
affected growth, physiological parameters, and antioxidant responses. Application of Tre and/or SA
resulted in growth recovery, increased photosynthesis, and reduced oxidative stress. Application
of Tre mitigated the detrimental effects of drought more than SA. Furthermore, co-application of
Tre and SA largely eliminated the negative impact of drought by reducing oxidative stress through
increased activities of antioxidant enzymes superoxide dismutase, peroxidase, and catalase, as well
as the accumulation of the protective osmolytes proline and glycine betaine. Combined Tre and SA
application improved water use efficiency and reduced the amount of malondialdehyde in droughtstressed
plants. Our results suggested that combined application of Tre and SA may trigger defense
mechanisms of sweet basil to better mitigate oxidative stress induced by drought stress, thereby
improving plant growth.
... In the present study, foliar application of SA increased growth rate and biomass accumulation in S. cumini saplings under water deficit treatments (Table 1 and Figure 1). Our observation was in agreement with previous studies on Rosmarinus officinalis [46], Portulaca oleracea [47], Euclayptus globulus [19] and Torreya grandis [48] where a similar increase in growth and biomass accumulation has been reported in response to SA application under water deficit treatments. Furthermore, the increase in growth attributes after the application of SA has been related to an increase in cell division in the meristematic regions of the plant sapling, thus promoting plant growth and productivity [49]. ...
... Similar results have been found in Quercus, Torreya grandis and Olea europaea saplings under water deficit [48,56,57]. Similarly, increase in soluble sugars has also been found in Portulaca oleracea, Populus nigra and Eucalyptus globulus plants under water deficit treatments [19,47,58]. Increase in proline concentration plays a key role in osmotic adjustment and protects the plant cell from ROS damage under water stress [59]. ...
... Moreover, foliar application of SA resulted in a decrease in EL% and MDA content in S. cumini saplings under water stress ( Figure 3). These results are in agreement with previous findings where application of SA application resulted in a decrease in EL% and MDA content in Lippia citriodora, Portulaca oleracea, and Eucalyptus globulus plants under water deficit treatments [19,47,66], thus highlighting the protective role of foliar application of SA under water deficit. Therefore, it can be concluded that the foliar application of SA significantly decreased the concentration of H 2 O 2 , O 2 − , MDA and EL% which was mediated by the increased production of antioxidant enzymes. ...
Fruit tree culture is at the brink of disaster in arid to semi-arid regions due to low water availability. A pot experiment was carried out to analyze whether foliar application of salicylic acid (SA) can improve water stress tolerance in Syzygiumcumini. Saplings were subjected to control (CK, 90% of field capacity, FC), medium stress (MS, 60% of FC) and high stress (HS, 30% of FC) along with foliar application of 0.5 and 1.0 mM of SA. Results showed that soil water deficit significantly decreased leaf, stem and total dry weight, leaf gas exchange attributes and chlorophyll a, b. However, root dry weight and root/shoot ratio increased under MS and HS, respectively. Contrarily, foliar application of SA significantly improved chlorophyll a, b, leaf gas exchange attributes, and dry weight production under soil water deficit. Concentration of oxidants like hydrogen peroxide and superoxide radicals, along with malondialdehyde and electrolyte leakage increased under soil water deficit; however, decreased in plants sprayed with SA due to the increase in the concentration of antioxidant enzymes like superoxide dismutase, peroxidase, catalase and ascorbate peroxidase. Results suggest that the foliar application of SA can help improve water stress tolerance in Syzygiumcumini saplings; however, validation of the results under field conditions is necessary.
... The effects of exogenous SA on plant resistance to abiotic stress depend on a set of factors: (i) applied SA concentration (Kang et al. 2012;Agami et al. 2013;Jesus et al. 2015;Brito et al. 2018b), the dose for maximum stress tolerance ranging between 0.1 mM and 0.5 mM (Hara et al. 2012); (ii) method of SA administration, including pre-soaking, addition to the growth medium or foliar spray (Singh and Usha 2003;Kang et al. 2012); (iii) plant species and cultivars (Umebese, Olatimilehin and Ogunsusi 2009;Khalil et al. 2012); (iv) plant developmental stage (Umebese, Olatimilehin and Ogunsusi 2009;Ahmad, Murali and Marimathu 2014); (v) kind of stress Fayez and Bazaid 2014); (vi) stress level (El-Tayeb 2005;Alam et al. 2013;Hashempour et al. 2014); (vii) system in which the study was carried out, from cell suspensions to the whole plant (Pál et al. 2013) and (viii) frequency of application (Shaaban, Abd El-Aal and Ahmed 2011). Still, an accurate SA application improves abiotic stress tolerance in plants by the modulation of several important aspects of plant function and structure, with relevant consequences on growth, yield and harvest quality (Brito et al. 2018b(Brito et al. , 2018c(Brito et al. , 2019. ...
... The available evidence supports the theory that SA pre-treatment is related to the lower accumulation of ROS under water-deficit conditions (Alam et al. 2013;Nazar et al. 2015). Moreover, SA also improved the cell membrane integrity of droughted plants, a signal of lower oxidative stress (Agami et al. 2013;Alam et al. 2013 Jesus et al. 2015;Nazar et al. 2015). Additionally, there is also evidence that SA prevents photosynthetic pigment stress-induced degradation (Agami et al. 2013;Alam et al. 2013;Ahmad, Murali and Marimathu 2014;Fayez and Bazaid 2014;Brito et al. 2018b). ...
... SA was also found to increase the transcription of certain ascorbateglutathione cycle-related genes, allowing the maintenance of higher concentrations of ascorbate and glutathione Alam et al. 2013;Li et al. 2013;Khan, Asgher and Khan 2014), and the improvement of reduced-to-oxidized ascorbate and reduced-to-oxidized glutathione ratios (Wang and Li 2006;Alam et al. 2013). On the other hand, while the increase in the concentration of phenolic compounds in response to SA application was reported under drought conditions (Jesus et al. 2015), no influence and/or its decline seems to prevail (Agami et al. 2013;Fayez and Bazaid 2014), suggesting that other defense mechanisms might be activated. Meanwhile, the synthesis of stress proteins also plays a crucial role in drought-tolerance development (Farooq et al. 2009). ...
... Chlorophyll fluorescence kinetics were measured on needles of all the plants in Phase II of the experiment using a pulse-amplitude modulation fluorimeter (Mini-PAM, Walz) according to Jesus et al. (2015). For the same plants, total contents of soluble sugars (TSS) and phenolic compounds were determined using 10 mg of lyophilized samples following the anthrone and Folin-Ciocalteu methods, respectively, as described by Jesus et al. (2015). ...
... Chlorophyll fluorescence kinetics were measured on needles of all the plants in Phase II of the experiment using a pulse-amplitude modulation fluorimeter (Mini-PAM, Walz) according to Jesus et al. (2015). For the same plants, total contents of soluble sugars (TSS) and phenolic compounds were determined using 10 mg of lyophilized samples following the anthrone and Folin-Ciocalteu methods, respectively, as described by Jesus et al. (2015). ...
... The plants that were being subjected to their first exposure to stress suffered more photosynthetic damage in comparison with thermoprimed plants (Fig. 8a). The contents of total soluble sugars and total phenolics were significantly higher in primed plants (Fig. 8b, c), which indicates a physiological preconditioning to stress (Jesus et al., 2015). These results therefore provided indications of a stable acquired thermotolerance. ...
Despite it being an important issue in the context of climate change, for most plant species it is not currently known how abiotic stresses affect nuclear proteomes and mediate memory effects. This study examines how Pinus radiata nuclei respond, adapt, ‘remember’, and ‘learn’ from heat stress. Seedlings were heat-stressed at 45 °C for 10 d and then allowed to recover. Nuclear proteins were isolated and quantified by nLC-MS/MS, the dynamics of tissue DNA methylation were examined, and the potential acquired memory was analysed in recovered plants. In an additional experiment, the expression of key gene genes was also quantified. Specific nuclear heat-responsive proteins were identified, and their biological roles were evaluated using a systems biology approach. In addition to heat-shock proteins, several clusters involved in regulation processes were discovered, such as epigenomic-driven gene regulation, some transcription factors, and a variety of RNA-associated functions. Nuclei exhibited differential proteome profiles across the phases of the experiment, with histone H2A and methyl cycle enzymes in particular being accumulated in the recovery step. A thermopriming effect was possibly linked to H2A abundance and over-accumulation of spliceosome elements in recovered P. radiata plants. The results suggest that epigenetic mechanisms play a key role in heat-stress tolerance and priming mechanisms.
... Drought stress and further recovery performance in Eucalyptus spp. are well documented: changes in biomass (Pita et al. 2003;Susiluoto and Berninger 2007), water potential and osmotic adjustment (Costa et al. 2004;Susiluoto and Berninger 2007), gas-exchange parameters (Costa et al. 2004;Correia et al. 2014b), pigments content (Correia et al. 2014b), hormones (Correia et al. 2014a;Jesus et al. 2015), redox status (Shvaleva et al. 2006;Correia et al. 2016), as well as in proteomic and metabolomic profiles (Warren et al. 2011;Correia et al. 2016;McKiernan et al. 2016). Altogether, these studies confirm that stress induces changes in primary and secondary plant metabolism, which impact energy production (e.g. ...
... All FRM underwent an increase in chlorophyll content under WS. In E. nitens and the hybrid, this high chlorophyll content might be explained by carotenoids protective role, preventing chlorophyll degradation and maintaining plants photosynthetic capacity (Santakumari and Berkowitz 1991) as observed in other studies with Eucalyptus (Michelozzi et al. 1995;Rui-ling 2009;Correia et al. 2014b;Jesus et al. 2015). In E. globulus, the decrease observed in the TLA supports that chlorophyll content increase under WS may result from reduction in leaf mass expansion, as discussed by Correia et al. (2014b) and Jesus et al. (2015). ...
... In E. nitens and the hybrid, this high chlorophyll content might be explained by carotenoids protective role, preventing chlorophyll degradation and maintaining plants photosynthetic capacity (Santakumari and Berkowitz 1991) as observed in other studies with Eucalyptus (Michelozzi et al. 1995;Rui-ling 2009;Correia et al. 2014b;Jesus et al. 2015). In E. globulus, the decrease observed in the TLA supports that chlorophyll content increase under WS may result from reduction in leaf mass expansion, as discussed by Correia et al. (2014b) and Jesus et al. (2015). The lack of lipid peroxidation changes in E. nitens does not necessarily imply that an increase in ROS production did not occur. ...
Key message
Eucalyptus forest reproductive material responded differently to the imposed water scenarios through different water resistance mechanisms.
Abstract
Eucalyptus is amongst the most planted genera in the world. The focus of this study was to evaluate the ability of different forest reproductive material to withstand the occurrence of drought under different possible climate scenarios, both experienced by plants in the field: a long-term water deficit period (WS) and a short-term water deficit period followed by recovery, in comparison with a well-watered condition. The performance of two Eucalyptus species (Eucalyptus globulus and Eucalyptus nitens) and one hybrid (Eucalyptus globulus × Eucalyptus cypellocarpa), under such conditions, was assessed through several morphological and physiological traits. Under prolonged water stress, E. globulus, which experienced the lowest water potential values, suffered a decrease in CO2 assimilation rates as a result of stomatal limitations that, together with high oxidative damage, led to growth impairment. It also exhibited the slowest recovery from a short-term water stress period. The hybrid reacted to the prolonged water stress period through an active antioxidant system which allowed a higher photosynthetic assimilation rate and overall growth. Though it experienced a decrease in CO2 assimilation rate, due to non-stomatal limitations, E. nitens was able to maintain its growth under a prolonged water deficit period. Furthermore, under short-term drought stress followed by recovery, E. nitens was able to completely recover its gas-exchange parameters and increase overall growth production conferring a physiological advantage under the tested conditions. Our data demonstrate that, under the experimentally imposed water stress scenario, plants have different adaptive mechanisms to cope with continuous water deficit and recovery after a short-term stress situation.
... The effects of drought at the physiological, biochemical and molecular levels in E. globulus have been deeply studied (Correia, Pintó-Marijuan, Castro, et al., 2014;Correia, Pintó-Marijuan, Neves, et al., 2014;Correia, Valledor, Hancock, Jesus, et al., 2016;Correia, Valledor, Hancock, Renaut, et al., 2016). This response is characterized by a decline in photosynthesis and stomatal conductance and an accumulation of osmoprotectants and abscisic acid (ABA) (Correia, Pintó-Marijuan, Castro, et al., 2014;Correia, Pintó-Marijuan, Neves, et al., 2014;Jesus et al., 2015). The disturbance in energy balance caused by photosynthesis impairment under drought may compromise the synthesis of defence-related components, as this is an energydemanding process (Hossain et al., 2019). ...
... Proline content increased under water stress in comparison to well-watered plants; and its role as osmoprotectant has been previously reported in response to drought in Picea abies seedlings (Ditmarová et al., 2009) and E. globulus . Also, SA has a role beyond plant immunity and its increase is recognized to improve drought stress tolerance via SA-mediated control of major plant-metabolic processes, including in eucalypts (Jesus et al., 2015). ...
The contribution of Eucalyptus globulus plantations to timber production for pulp, paper and energy production may be hampered by climate change. It is expected that Eucalyptus productivity may be affected through drought stress and changes to both pathogen distribution/pathogenicity and host-pathogen interactions. The impact of the fungal pathogen Neofusicoccum kwambonambiense on E. globulus, causing can-kers and dieback, is well known but the impact of drought on disease development is still understudied. Our aim was to study the effect of drought on N. kwambon-ambiense infection by inoculating E. globulus plants under well-watered conditions or with water limitation. Non-infected plants for both water regimes were also analysed. Morphophysiological, biochemical and hormonal parameters were assessed 65 days post-inoculation. Inoculation under conditions of water stress decreased water potential and photosynthetic efficiency and increased abscisic acid, jasmonic acid and lipid peroxidation. Water-stressed infected plants also showed higher fungal colonization and external lesion length in comparison with well-watered inoculated plants. Our results indicate that drought increased E. globulus predisposition to N. kwambonam-biense infection and may also have promoted a change in the lifestyle of the fungus. Identifying host-pathogen interaction responses under different stress conditions is necessary to provide knowledge for decision-making in the management of forest systems in general and of Eucalyptus production in particular.
... Gas exchange data collected from field-grown immature tea plants also exhibited similar trends, with higher photosynthetic rates and stomatal conductance observed in SA-treated plants compared to the WS treatment. These findings align with the results of studies conducted by Yao et al. (2016) on G. jasminoides plants, Jesus et al. (2015) on E. globulus plants, and Khalvandi et al. (2021) on T. aestivum. The maintenance of a relatively higher photosynthetic rate under moisture stress conditions serves as an indicator of increased productivity under such conditions. ...
... The promotion of osmolyte accumulation using SA has been reported in G. jasminoides, E. globulus, T. aestivum, Zea mays, and L. esculentum plants (Hayat et al., 2008;Jesus et al., 2015;Manzoor et al., 2015;Marcinska et al., 2015;Yao et al., 2016). The SA-induced sugar accumulation partially contributes to osmotic adjustment, aiding in better survival under drought conditions. ...
Salicylic acid (SA) has been known to induce drought tolerance in many plant species. In this study, we investigated the potential of exogenous application of SA to enhance drought tolerance in immature tea plants under glasshouse conditions at the Tea Research Institute in Talawakelle, Sri Lanka. One-year-old potted tea cultivars known for drought tolerance were used in the study. The plants were subjected to a drying cycle while being foliar sprayed with different concentrations of SA along with well-watered (WW), water-spray (WS) and no-spray (NS) treatments. Data were collected at 18 hours, 14 days after spraying (DAS), 21 DAS, and during the recovery after re-watering at 21 DAS. Based on the results obtained from the glasshouse study, the effective concentration of 150 mg L-1 SA was selected for further testing under field conditions in Talawakelle using three-year-old tea plants. The field experiment followed a randomized complete block design (RCBD) with three blocks. When the plants reached a moderate moisture stress level, they were foliar-sprayed with 150 mg L-1 SA, WS and NS treatments were included as controls. Data were collected at 7 DAS, 14 DAS, 21 DAS, and during the recovery phase after rain. The results showed that drought stress led to a decline in gas exchange parameters, relative water content, and an increase in the accumulation of osmolytes. However, the exogenous application of 150 mg L-1 SA significantly improved physiological processes such as gas exchange, osmolyte accumulation, and antioxidant activity, thus effectively enhancing drought tolerance in immature tea plants.
... Phenolic compounds can act as a substrate for GPX and GST enzymes and also function as metal chelators, hence protecting plant cells from the harmful effects of oxidative stress by reducing cell membrane peroxidation (Edwards et al. 2000;Sakihama et al. 2002;Kulbat 2016). It has been reported that the application of SA induced a higher accumulation of phenolic compounds in Eucalyptus globulus (Jesus et al. 2015) and young olive trees (Brito et al. 2019) in response to water limitation. Our findings also show that the application of SA induces the activity of PAL in Pistachio leaves under drought stress (Fig. 3d). ...
... SA application reduced the amount of H2O2 under drought stress (Fig. 2a), probably resulting in the alleviation of lipid peroxidation (Fig. 2b), indicating the effect of SA in reducing stress-induced damage in association with decreasing H2O2 content. The MDA content, as the end-product of lipid peroxidation, increases under environmental stresses and this increase is a symptom of extent organelle and cell membrane damage resulting in cell death (Jesus et al. 2015;Sedaghat et al. 2017). Previous studies have shown that SA treatment resulted in increased antioxidant activity, leading to a reduction of oxidative stress as indicated by lower MDA content (Agarwal et al. 2005;Saruhan et al. 2012;Sedaghat et al. 2017). ...
Pistachio (Pistacia vera L.) is an economically important nut crop that is prone to drought stress since it is mainly produced in arid and semi-arid regions. Considering the possible impact of salicylic acid (SA) on drought tolerance of pistachio, several physiological and biochemical responses of pistachio seedlings to foliar application of SA under progressive drought treatment were investigated. Application of SA increased the content of pigments, chlorophyll, and carotenoids, and improved the accumulation of osmolytes such as proline and total soluble carbohydrates leading to preserve photosynthetic apparatus and relative water content. Moreover, SA application reduced the drought-induced levels of H2O2 and lipid peroxidation in pistachio seedlings by increasing the activity of antioxidant enzymes. According to our findings, ascorbate peroxidase and glutathione reductase play a major role in the antioxidative salicylic acid-induced defense against oxidative stress in pistachio. Taken together, our results show that the foliar application of SA could significantly enhance drought tolerance of pistachio seedlings through protecting photosynthetic apparatus, improving osmoregulation, and inducing the antioxidant defense system.
... Moreover, exogenous SA application on leaves increased tolerance to heat and cold stress in grapevine, promoting Ca 2+ homeostasis and antioxidant activity (Wang and Li, 2006). Mitigation of negative effects of drought was also ascertained in case of SA application in Eucalyptus globulus Labill (Jesus et al., 2015) and annual crops such as maize (Saruhan et al., 2012) and barley (Habibi, 2012). ...
... The current investigation affirmed the decline in leaf water potential under water deficit stress, but the application of salicylic acid (SA) spray ameliorated this, improving leaf water potential amid water stress. Previous research has established SA's beneficial role in mitigating water stress impacts on Eucalyptus globule by enhancing antioxidants and osmolytes, thereby sustaining water potential (Jesus et al., 2015). Similarly, in Vigna radiate, osmotic stress induced a water potential decrease, whereas SA administration resulted in an increase (Syeed et al., 2021). ...
Rapid environmental fluctuations, particularly water deficit stress, significantly hinder a plant’s growth by constraining primary metabolic processes. Salicylic acid (SA), a recognized plant hormone, exhibits a noteworthy role in alleviating water stress impacts on leaf gas exchange. This study investigates the interaction between SA and water deficit (WD) stress in Bacopa monnieri (L.). Different SA doses (50, 75, 100, and 125 mg/l) were foliar-sprayed, with water deficit imposed by reduced irrigation (well-watered, water deficit 1, and water deficit 2). Pooled data from 2 years indicated increased electrolyte leakage and decreased photosynthetic pigments, photosynthesis rate, and protein content in WD2-stressed plants. Moderate SA concentrations with WD1 and WD2 stress positively impacted photosynthesis-related traits and enhanced defense mechanisms, reflected in increased total protein, leaf water potential, and chlorophyll stability index. Positive correlations between photosynthesis rate and antioxidants suggests SA’s role in fortifying plant defense mechanisms against stress. Overall, this research underscores SA’s resilient role in mitigating water deficit stress effects by regulating various physiological and metabolic processes, ultimately supporting plant growth.
... In this concern, NABF supported IAA, CK, and GA 3 contents in drought-stressed tomato plants. This may be due to the accumulated macro-and micronutrients necessary for protoplasm formation and phytohormone biosynthesis [85,86]. The reports [80,[87][88][89] point out that plants treated with fertilizers (i.e., urea and potassium) or antioxidants (i.e., glutathione or salicylic acid) led to higher levels of CKs, IAA, and GA 3 while reducing ABA. ...
... In this concern, NABF supported IAA, CK, and GA 3 contents in drought-stressed tomato plants. This may be due to the accumulated macro-and micronutrients necessary for protoplasm formation and phytohormone biosynthesis [85,86]. The reports [80,[87][88][89] point out that plants treated with fertilizers (i.e., urea and potassium) or antioxidants (i.e., glutathione or salicylic acid) led to higher levels of CKs, IAA, and GA 3 while reducing ABA. ...
As a result of the climate changes that are getting worse nowadays, drought stress (DS) is a major obstacle during crop life stages, which ultimately reduces tomato crop yields. So, there is a need to adopt modern approaches like a novel nutrient- and antioxidant-based formulation (NABF) for boosting tomato crop productivity. NABF consists of antioxidants (i.e., citric acid, salicylic acid, ascorbic acid, glutathione, and EDTA) and nutrients making it a fruitful growth stimulator
against environmental stressors. As a first report, this study was scheduled to investigate the foliar application of NABF on growth and production traits, physio-biochemical attributes, water use efficiency (WUE), and nutritional, hormonal, and antioxidative status of tomato plants cultivated under full watering (100% of ETc) and DS (80 or 60% of ETc). Stressed tomato plants treated with NABF had higher DS tolerance through improved traits of photosynthetic efficiency, leaf integrity,
various nutrients (i.e., copper, zinc, manganese, calcium, potassium, phosphorus, and nitrogen), and hormonal contents. These positives were a result of lower levels of oxidative stress biomarkers as a result of enhanced osmoprotectants (soluble sugars, proline, and soluble protein), and non-enzymatic and enzymatic antioxidant activities. Growth, yield, and fruit quality traits, as well as WUE, were improved. Full watering with application of 2.5 g NABF L1 collected 121 t tomato fruits per hectare as the best treatment. Under moderate DS (80% of ETc), NABF application increased fruit yield by 10.3%, while, under severe DS (40% of ETc), the same fruit yield was obtained compared to full irrigation without NABF. Therefore, the application of 60% ETc � NABF was explored to not only give a similar yield with higher quality compared to 100% ETc without NABF as well as increase WUE.
... Such responses may result in maintenance of photosynthetic apparatus and membrane cell integrity. The increased levels of phenolic compounds in UFTS seedlings may serve in activating defense mechanisms via up-regulating phenolics-synthesizing enzymes, such as phenylalanine ammonia-lyase [83] which supports the findings on Salix and Acacia [84], Portulaca oleracea [85], Eucalyptus globulus [86], Syzygium cumini [87] and canola [88] in suboptimal watering condition. ...
Aims: This study was designed to examine the effects of watering regime and biochar on soil properties and performance of seedlings of urban forest tree species (UFTS) in the nursery. Study Design: The experiment was a 5 by 3 by 2 factorial scheme involving urban forest tree species, watering regimes and biochar amendment or not. Place and Duration of Study: seedlings of five UFTS were raised in the Nursery and Screenhouse of Wesley University, Ondo, a rainforest zone of Nigeria. Methodology: Seedlings of five Urban Forest Tree Species (UFTS) were subjected to watering at 80, 60 and 35% field capacity (FC) with or without biochar amendment. UFTS evaluated are: Bauhinia monandra, Delonix regia, Terminalia catappa, Dypsis lutescens and Veitchia merrillii. Results: Watering regime and biochar amendment exerted significant effects on soil physical and chemical properties, physiological attributes and biochemical constituents and performance o the UFTS evaluated. Watering at 60 and 35% FC increased bulk and particle densities but reduced significantly (P<.05) soil moisture content at field capacity compare with watering at 80% FC. Further, the 60 and 35% FC watering exhibited low N, available K+, Ca2+ and Mg2+. Addition of biochar to the variously watered soil considerably reduced bulk density but remarkably increased porosity, field capacity moisture and plant available moisture. Biochar amendment increased soil pH, total and volatile organic matter contents, available K+ and Ca2+, extractable Mg2+ and dissolved phosphate (PO43+). The responses of growth traits and biochemical constituents of UFTS to watering regimes was species specific. Relative to 80 % FC watering, seedling growth attributes reduced significantly under deficit water application (60 and 35% FC) in addition to remarkable accumulation of osmolytes (osmoprotectants) and enzymatic activities. Biochar amendment enhanced accumulation of osmolytes and activities of superoxide dismutase, guaiacol peroxidase and catalase enzymes of UFTS seedlings. Conclusion: Differential watering and biochar amendment affected soil physical and chemical properties and growth of UFTS seedlings evaluated. Biochar amendment of the variously watered soil enhanced seedling growth, and appear as effective strategy for improving soil properties and UFTS performance, and for mitigation of adverse effects of suboptimal watering.
... Chlorophyll fluorescence was determined in situ on the same leaves as used for the gas-exchange measurements with a portable fluorometer (Mini-PAM; Walz, Effeltrich, Germany). Light-adapted components of chlorophyll fluorescence were measured as described in Jesus et al. [53]: steady-state fluorescence (F), maximal fluorescence (F'm), variable fluorescence (F'v, equivalent to F'm-F), and quantum yield of PSII photochemistry [Φ PSII, equivalent to (F'm-F)/F'm)]. Leaves were then dark adapted for at least 20 min to obtain F0 (minimum fluorescence), Fm (maximum fluorescence), Fv (variable fluorescence, equivalent to Fm-F0), and Fv/Fm (maximum quantum yield of PSII photochemistry). ...
Tamarillo (Solanum betaceum Cav.) is a subtropical solanaceous tree with increasing agronomic interest due to its nutritious edible fruits. Growing demand for tamarillo plants and fruits requires optimization of existing propagation methods and scaled-up systems for large-scale cloning of selected germplasm. Three in vitro protocols have been used to micropropagate tamarillo: (1) axillary shoot proliferation in a semisolid medium, (2) organogenesis, and (3) somatic embryogenesis procedures. Variables such as the age of the established shoot cultures and rooting treatments were also analyzed. The morphological and physiological quality of acclimatized plants derived from all the methodologies were compared, with seed-derived plants used as a control group. Overall, the results show that in vitro-derived plants have a similar development to seed-derived plants. Micropropagation by axillary shoot proliferation was highly efficient, with rooting rates above 80% in most treatments. Organogenesis induction was more effective from lamina explants using MS media with 2.0 mg·L−1 6-benzylaminopurine. Both organogenesis and somatic embryogenesis-derived plants were also morphologically and physiologically equivalent to seed and axillary shoot-derived plants. The specificities of each micropropagation method are discussed.
... It leads to the inhibition of cell division, cell expansion, gas-exchange rates, stomatal conductance, biomass accumulation, and leaf area. It also causes an imbalance in several plant hormones and growth regulators; increases leaf temperature, which reduces RWC and increases transpiration rates; reduces the uptake and translocation of macronutrients; and induces oxidative damage, which may affect leaf water status and leaf pigments [8][9][10][11][12]15,16,35,37,38]. Consequently, decrease in wheat growth, yield, and yield components is the LM regime's expected outcome. ...
As water deficit in arid countries has already become the norm rather than the exception, water conservation in crop production processes has become very critical. Therefore, it is urgent to develop feasible strategies to achieve this goal. Exogenous application of salicylic acid (SA) has been proposed as one of the effective and economical strategies for mitigating water deficit in plants. However, the recommendations concerning the proper application methods (AMs) and the optimal concentrations (Cons) of SA under field conditions seem contradictory. Here, a two-year field study was conducted to compare the effects of twelve combinations of AMs and Cons on the vegetative growth, physiological parameters, yield, and irrigation water use efficiency (IWUE) of wheat under full (FL) and limited (LM) irrigation regimes. These combinations included seed soaking in purified water (S0), 0.5 mM SA (S1), and 1.0 mM SA (S2); foliar spray of SA at concentrations of 1.0 mM (F1), 2.0 mM (F2), and 3.0 mM (F3); and combinations of S1 and S2 with F1 (S1F1 and S2F1), F2 (S1F2 and S2F2), and F3 (S1F3 and S2F3). The results showed that the LM regime caused a significant reduction in all vegetative growth, physiological, and yield parameters, while it led to an increase in IWUE. The application of SA through seed soaking, foliar application, and a combination of both methods increased all of the studied parameters in all the evaluated times, resulting in higher values for all parameters than the treatment without SA (S0). The multivariate analyses, including principal component analysis and heatmapping, identified the foliar application method with 1–3 mM SA alone or in combination with seed soaking with 0.5 mM SA as the best treatments for the optimal performance of wheat under both irrigation regimes. Overall, our results indicated that exogenous application of SA has the potential to greatly improve growth, yield, and IWUE under limited water application, while optimal coupling combinations of AMs and Cons were required for positive effects in field conditions.
... Intrinsic ABA signalling has been proposed as a potential mediator of plant stress tolerance induced by SA (Jesus et al., 2015). The majority of researchers have found a link between SA and ABA levels through stress (Fig. 2). ...
Salicylic acid (SA) is one of the potential plant growth regulators (PGRs) that regulate plant growth and development by triggering many physiological and metabolic processes. It is also known to be a crucial component of plant defense mechanisms against environmental stimuli. In stressed plants, it is documented that it can effectively modulate a myriad of metabolic processes including strengthening of oxidative defense system by directly or indirectly limiting the buildup of reactive nitrogen and oxygen radicals. Although it is well recognized that it performs a crucial role in plant tolerance to various stresses, it is not fully elucidated that whether low or high concentrations of this PGR is effective to achieve optimal growth of plants under stressful environments. It is also not fully understood that to what extent and in what manner it cross-talks with other potential growth regulators and signalling molecules within the plant body. Thus, this critical review discusses how far SA mediates crosstalk with other key PGRs and molecular components of signalling pathways mechanisms, particularly in plants exposed to environmental cues. Moreover, the function of SA exogenously applied in regulation of growth and development as well as reinforcement of oxidative defense system of plants under abiotic stresses is explicitly elucidated.
... SA application under salt stress enhancing synthesis of chl a, b and carotenoids, maintained membrane integrity also led to less contents of Ca2+ and act to accumulate K+ and soluble sugars which caused increasing of photosynthesis process [172,173], Arabidopsis tolerance salinity with SA by restoring membrane potential and preventing saltinduced K+ loss from guard cell outward rectifying K(+) (GORK) also SA can upregulation of H+-ATPase activity, which improving K+ retention during salt stress moreover pretreatment of SA can reduce the concentration of accumulated Na+ in the shoot [174], also SA caused accumulation of ABA and IAA [175], another methods as (soaking the seeds prior to sowing, adding to the hydroponic solution, irrigating, or spraying with SA solution) have been shown to protect various plant species against abiotic stress by inducing a wide range of processes involved in stress tolerance mechanisms via enhancing activity of antioxidant enzymes Salicylic acid can enhancing antioxidant enzymes activity i.e. POD, DOD and SOD in tomato as spraying under drought and salinity stress A foliar spray of SA at 1.00 mM promoted the plant growth under 50, 100, or 200 mM NaCl , activity of antioxidant enzymes, as catalase [176][177][178][179][180][181], peroxidase, and superoxide dismutase, were enhanced by SA treatment Aftab, et al. [182], Habibi [183], Misra & Misra [184]on Rauwolfia serpentina ), [185][186], salicylic acid application 0.75, 2.5 and 5.0 mM improved tolerance of Eucalyptus globulus by improving water potential with increasing photosynthetic rate, soluble sugars under water deficit 5% and chlorophyll a Jesusa, et al. [187], Nimir, et al. [188] on Sorghum bicolor), in this respect proved that, salicylic acid at 400 ppm and IAA at 30 ppm were enhanced growth estimations i.e. plant height, leaves numbers, fresh and dry weights of leaves. Whereas these parameters were significant reduced under salts 14000 ppm NaCl, chlorophyll a and b was decreased, At saline conditions, increasing of, proteins, catalase activities (CAT) and peroxidase activities (POD) which act as defense effects in the plants exposed to salinity stress, Na+, Ca2+, Cl-and K+ leaf concentrations were rising under 14000 ppm NaCl [189]. ...
Salt stress soil or water come to be the most problem and deficiency the crop yields, in spite of the fact that date palm (Phoenix dactylifera L.) can be tolerate high levels of salts, the acclimatized plantlets in the early stage facing stress just planted in the open field, however in the pre-acclimatization stage in vitro , also after acclimatization stage in the greenhouse these plantlets were adapted with different concentrations of salts NaCl, CaCl2 for helping them facing bad effects of salts in the fields, as well as many treatments can be done to ameliorate the bad effects of salts on the plantlets as hormons (IAA, GA3, cytokinins), yeast, amino acids, potassium K+ or Ca2+ and some of growth retardants, all of these treatments have important role to adverse bad effects of salts, enhancing growth as well as improving productivity of plants under salts stress.
... Various studies on different crops have shown that SA can improve plant resistance to major abiotic stresses, including salinity [47,68]. SA was applied to stressed plants via different methods such as seed soaking, irrigation, spraying, or being adding to the nutrient solution, suggesting that SA induced an abiotic stress tolerance mechanism [69][70][71][72][73][74]. It has been demonstrated that a reasonable exogenous application of SA can enhance the growth and photosynthesis activity of cotton seedlings under salt stress and help the plants to withstand stressful conditions [75]. ...
The presence of phyto-hormones in plants at relatively low concentrations plays an indispensable role in regulating crop growth and yield. Salt stress is one of the major abiotic stresses limiting cotton production. It has been reported that exogenous phyto-hormones are involved in various plant defense systems against salt stress. Recently, different studies revealed the pivotal performance of hormones in regulating cotton growth and yield. However, a comprehensive understanding of these exogenous hormones, which regulate cotton growth and yield under salt stress, is lacking. In this review, we focused on new advances in elucidating the roles of exogenous hormones (gibberellin (GA) and salicylic acid (SA)) and their signaling and transduction pathways and the cross-talk between GA and SA in regulating crop growth and development under salt stress. In this review, we not only focused on the role of phyto-hormones but also identified the roles of GA and SA responsive genes to salt stress. Our aim is to provide a comprehensive review of the performance of GA and SA and their responsive genes under salt stress, assisting in the further elucidation of the mechanism that plant hormones use to regulate growth and yield under salt stress.
... The role of epigenetic mechanisms, like DNA methylation in many genes and histone acetylation is vital in managing acclimation, and therefore in plants adaptation to high temperatures (Correia et al., 2013) associated to increased solar radiation and low water availability, which leads to a DNA hypermethylation (Bernardo et al., 2017). The prompt response of hormones is crucial for plant physiology and biochemistry acclimation, being a serious condition for their survival (Jesus et al., 2015). One of the most important phytohormones due to their multiple functions is the abscisic acid (ABA) which activates a wide range of cellular and adaptive physiological and hydraulic responses and is a key regulator in the activation of plant cellular adaptation strategies to abiotic stresses (Takahashi et al., 2020), having a crucial function as a growth inhibitor (Golldack et al., 2014). ...
Foreseen climate change points to shifts in viticultural production patterns worldwide, leading to some major impacts in the economy of the wine industry. In a climate change scenario, combination of water scarcity, high temperature, and radiation and salinity, experienced in many regions will be strengthened, worsening the negative effects on plant growth, berry composition, and yield. Hence, the interaction between several factors, such as terroir features, climate, grapevine stress responses, and management practices used, represents a real challenge for sustainable Mediterranean viticulture. The processed kaolin particle film (PKPF) application in vineyards has been renowned as a favorable short-term strategy for sustainable mitigation of adverse abiotic summer stress. Nevertheless, the mechanisms underlying stress alleviation by PKPF application continue minimally discussed, and far from consensus on its effects on different variables, including berry composition and wine quality. This short review illustrates some of the main PKPF functions and evaluates its impact on leaves and berry traits.
... Exogenous application of SA was reported to improve growth and photosynthetic traits in several crop plants including lead (Pb) exposed Oryza sativa, Cd exposed Zea mays El Dakak RA. and Cu-exposed Phaseolus vulgaris [18]. The efficacy of SA as foliar supplement on two mentha cultivars, namely, Kosi and Kushal grown under Cd (50 μM) stress conditions was tested by Zaid [32][33][34]. Out of three foliar applications of plant growth regulators, the application of SA at different growth stages proved best in alleviating Cd toxicity. Application of SA was also found to tolerate as toxicity in two varieties of Artemisia annua L. [35]. ...
Abiotic stresses have been recognized as the potential threat for
agricultural production across the globe. Anthropogenic activities related
to industrialization and urbanization also have aggravated the degradation
of agricultural system as they are experiencing increasing impact of abiotic
stresses. These stresses potentially induce various adverse effects on plants
affecting their physiological, biochemical and molecular processes ultimately leading huge loss in crop productivity. Plant hormones are recognized
amongst the handiest tools to mitigate the abiotic stress. Salicylic acid (SA) is
one of most essential and multifaceted plant hormone that not only play vital
role in plant defense but also have active participation in conferring abiotic
stress tolerance. The present review deals with the illustrations of studies
carried out by different workers on the role of SA in combating various types
of abiotic stresses like metal stress, salinity stress, temperature stress and
water stress in different crops
... These results indicated that exogenous application of SA may cause osmotic adjustment due to the accumulation of compatible solutes such as proline. Foliar application of SA can improve chlorophyll content under drought conditions, as reported in sweet basil (Kordi et al. 2013), olive trees (Brito et al. 2018), star fruit and Eucalyptus (Jesus et al. 2015). However, the activities of antioxidant enzymes such as POD, SOD, and CAT increase in response to DR and SD, which protected plants from oxidative damaged. ...
Floral initiation is a critical developmental mechanism associated with external factors, and citrus flowering is mainly regulated by drought stress. However, little is known about the intricate regulatory network involved in stress-induced flowering in citrus. To understand the molecular mechanism of floral initiation in citrus, flower induction was performed on potted Citrus sinensis trees under the combined treatment of salicylic acid (SA) and drought (DR). Physiological analysis revealed that SA treatment significantly normalized the drastic effect of drought stress by increasing antioxidant enzyme activities (SOD, POD, and CAT), relative leaf water content, total chlorophyll, and proline contents and promoting more flowering than drought treatment. Analysis of transcriptome changes in leaves from different treatments showed that 1135, 2728 and 957 differentially expressed genes (DEGs) were revealed in response to DR, SD (SA + DR), and SA (SA + well water) treatments in comparison with the well watered plants, respectively. A total of 2415, 2318 and 1933 DEGs were
expressed in DR, SD, and SA in comparison with water recovery, respectively. Some key flowering genes were more highly expressed in SA-treated drought plants than in DR-treated plants. GO enrichment revealed that SA treatment enhances the regulation and growth of meristem activity under drought conditions, but no such a pathway was found to be highly enriched in the control. Furthermore, we focused on various hormones, sugars, starch metabolism, and biosynthesis-related genes. The KEGG analysis demonstrated that DEGs enriched in starch sucrose metabolism and hormonal signal transduction pathways probably account for stress-induced floral initiation in citrus. In addition, a citrus LIPOYLTRANSFERSAE 2A
homologous (LIP2A) gene was upregulated by SD treatment. Ectopic expression of CsLIP2A exhibited early flowering in transgenic Arabidopsis. Taken together, this study provides new insight that contributes to citrus tree floral initiation under the SA-drought scenario as well as an excellent reference for stress-induced floral initiation in woody trees.
... the plants produce defence responses to a given elicitor. The concentration of an elicitor play a major role in the production of secondary metabolites [41]. Salicylic Acid (SA) (0,75-5 mM) produced drought tolerance in Eucalyptus globulus and this effect was linked with the concentration of elicitor, showing highest dosage produced tremendous effects. ...
Plant's secondary metabolites, produced usually under stress, are one of the promising sources for food additives, pharmaceuticals, food flavors and other industrial materials. The comprehensive probing of metabolite's production mechanism, stress signal transduction pathway, would be great push toward in commercial production. Higher plants inevitably encounter stresses and sustain themselves by producing various secondary metabolites which, the secondary metabolites, have various industrial application that's why are promising candidates for commercialization. Due to certain limitations of natural plant extraction, plant cell/tissue culture is considered a best alternative way for in-vitro production of bioactive secondary metabolites. Elicitation can be employed to overcome the constraints of plant cell technology that retard the process of commercialization. A way to enhance the secondary metabolite's production in plants is Elicitation. In which an exogeneous elicitor, biotic or abiotic, is exposed in growth medium to trigger the production of secondary metabolite. During this phenomenon, several defense/ non-defenses related genes, activated/ deactivated. Furthermore, transient phosphorylation or dephosphorylation of proteins, expression of enzymes occurs through which biosynthetic pathways of several secondary metabolites can be ascertained. Additionally, a push toward advancement of metabolic engineering and gene manipulation to increase the productivity of secondary metabolites can be gained through integration of proteomics, transcriptomics, and metabolomics with system biology.
... Before of exogenous application of JA, because JA (Sigma-Aldrich) has low solubility in water, it was dissolved in 0.02 percent (v/v) ethanol and diluted with distilled water (Złotek et al., 2016). Also, SA (Merck, Germany) solutions prepare with dissolved in distilled water (Jesus et al., 2015). The concentrations of SA and JA were selected based on previous reports on diff ;erent plants (Idrees et al., 2013;Drazic and Mihailovic, 2005;Ding et al., 2002;Wang et al., 2006). ...
Drought stress affects plant growth and is considered as one of the most important issues in In Middle East. In order to manage the critical water, it is essential to develop strategies to improve plant growth and biochemical characteristics. Plant growth regulators may afford a safe solution to increasing crop productivity via several mechanisms. Thus, the current study investigated the influence of salicylic acid and jasmonic acid on some physiological and antioxidant responses of Catharanthus roseus to drought stress under field conditions in Ahvaz and Tehran, Iran. The results indicated drought stress decreased total fresh and dry weights, relative water content, and concentration of photosynthetic pigments. In contrast, the activity of antioxidant enzymes and alkaloid contents would be increased. Foliar application of salicylic acid had a significant impact on all studied traits, but jasmonic acid had an effect only on total fresh and dry weights, concentration of photosynthetic pigments, and alkaloid contents. The activity of antioxidant enzymes including peroxidase, ascorbate peroxidase, superoxide dismutase, and polyphenol oxidase enhanced by spraying salicylic acid in deficit and good irrigation conditions. Foliar application of salicylic acid 10 mM on activity of antioxidant enzymes and salicylic acid 1 mM on relative water content and photosynthetic pigment content were more effective than other salicylic acid concentrations. Foliar application of jasmonic acid increased total fresh and dry weights also carotenoid content, but decreased total chlorophyll contents under stress conditions, in both places. Application of salicylic acid 0.1 mM + jasmonic acid increased total fresh and dry weights in any irrigation regimes, while this treatment increased carotenoid contents only under drought conditions in Ahvaz. Application of salicylic acid alone and with jasmonic acid significantly increased the alkaloid contents under severe drought stress. Salicylic acid improved C. roseus physiological performance and alkaloid contents, also it could be a way for periwinkle to alleviate the adverse effects of drought stress.
... Recent studies have shown that rootstock-induced changes in ABA content play an important role in defining the drought tolerance of grafted plants (Allario et al., 2013;Liu et al., 2016;Santana-Vieira et al., 2016;Silva et al., 2018). Salicylic acid (SA) and jasmonates (JAs) are phytohormones that are well known for regulating plant defence against pests and pathogens (Martín et al., 2010;Vivas et al., 2012;López-Villamor et al., 2021), but their involvement in plant drought responses is increasingly recognised (De Diego et al., 2012;Jesus et al., 2015;Shenxie et al., 2015;De Ollas and Dodd, 2016). In citrus trees under severe drought, SA was reported to increase along with ABA, presumably promoting stomatal closure jointly (Santana-Vieira et al., 2016;Neves et al., 2017). ...
Nut production by the European sweet chestnut (Castanea sativa Mill.) in grafted orchards is under threat of increased drought stress associated with current global warming. To explore whether drought tolerance in C. sativa could be improved using drought tolerant scions and rootstocks, trees from humid (H) and xeric (X) populations in Spain were used to generate intra-family (H/H and X/X) and reciprocal inter-location (X/H and H/X) grafts. We studied the effects of the (i) scion, (ii) rootstock and (iii) the grafting itself as a wounding stress
on the vegetative budbreak, secondary growth and drought tolerance of C. sativa trees. Drought tolerance was assessed by measuring leaf gas exchange, chlorophyll fluorescence, water status and leaf wilting two weeks after water deprivation. Hormone (ABA, SA, JA and JA-Ile) and proline quantification in tree leaves and fine roots were assessed, as well as tree and scion mortality. Rootstocks and scions of xeric origin induced earlier flushing and improved drought tolerance of scions and rootstocks of humid origin. Tree mortality after drought was 57 % lower in H/X than in H/H trees, and scion loss after drought was 47 % lower in H/X than in X/H trees. The ‘grafting’ (i.e., wounding) effect delayed vegetative budbreak and reduced secondary growth of trees but did not predispose trees to drought. We report for the first time differences in hormone and proline content in leaves and fine roots of chestnut trees of humid and xeric origins exposed to drought. The results suggest the use of scions and rootstocks from xeric areas to improve drought tolerance in chestnut.
... Nitrogen addition increased maximum photosynthetic rate with the increase of leaf nitrogen content but had no effect on leaf specific hydraulic conductivity of E. grandis trees (Clearwater and Meinzer, 2001). Moreover, drought stress would limit Eucalyptus height growth, and reduce net CO 2 assimilation rate, stomatal conductance and transpiration rate, and then increase phenols content, total soluble sugars (Zhou et al., 2014;Jesus et al., 2015). For hormonal dynamics, drought caused an increase in abscisic acid (ABA) and abscisic acid glucose ester (ABA-GE) levels in all plant parts of E. globulus (Correia et al., 2014). ...
Eucalyptus is widely planted in South China and has high economic and ecological values. However, the seasonal drought in southern China severely limits the productivity of Eucalyptus plantation. In this study, the dry-season irrigation was carried out after the conventional production and planting of Eucalyptus. The diurnal changes of photosynthetic characteristics of Eucalyptus plantations were measured in explore the diurnal and seasonal variations and their responses to both dry-season irrigation and environmental factors. The results showed that during the first-year growth of Eucalyptus urophylla × E. grandis plantation, (1) the diurnal changes of the trees under different treatments showed single-peak curves with the varied occurrence time of the highest photosynthetic characteristics in different months; the E. urophylla × E. grandis without dry-season irrigation (CK and F) had transpiration midday depression in January and that with the only dry-season irrigation (W) exhibited both photosynthetic and transpiration midday depression in May. (2) The trees of CK and F were subjected to mild drought stress in the dry season and their maximum photo-synthetic and transpiration rate were lower than those of W and WF treatment respectively, but they had higher maximum WUE. The trees of W had significantly higher daily net CO 2 assimilation and daily water transpiration in dry season. (3) The diurnal changes of photosynthetic characteristics were mainly influenced by water vapor pressure deficit (VPD) at the corresponding time of the month. (4) In the short-term treatments, dry-season irrigation and fertilization significantly increased the biomass of E. urophylla × E. grandis. Dry-season irrigation alleviated the mild drought stress for gas exchange in the dry season and further promote the biomass of E. urophylla × E. grandis. This study provided an important practical exploration for improving the productivity of E. urophylla × E. grandis plantation in seasonal arid areas.
... Elicitor concentration JOJ Horticulture & Arboriculture is another important factor to be taken into account; ca. Jesús [19] found that foliar treatments with Salicylic Acid (SA) (0,75-5 mM) increased drought tolerance in Eucalyptus globulus and this effect was dependent on the dosage applied, highest dosage being more effective. Similar effects had previously been observed by Singh & Usha [20] in wheat seedlings, where decreased transpiration rate and improved photosynthesis were linked to improved behaviour under water stress conditions. ...
... Moreover, supplying exogenous protectants under salinity led to much higher concentrations of phenolic compounds and promoting effects were more pronounced in proline and salicylic acid treatments (Fig. 3A). These results agree with the earlier reports which indicated the elevating effects of exogenous protectants on the phenolic content of different stressed plants (Rasheed et al. 2014;Jesus et al. 2015;Khalil et al. 2018). Supplementation of exogenous protectants to NaClstressed plants also had enhancing effects on antioxidant capacities and the highest values were observed in those treated by salicylic acid (Fig. 4A, B). ...
Worldwide, salt stress is one the major limiting factors of crop production particularly in arid and semi-arid areas. Here, responses of salt-stressed lemon balm (Melissa officinalis L.) to exogenously applied protective substances including reduced glutathione (GSH), proline and salicylic acid were studied to elucidate the regulatory roles of these protectants at the physiochemical and molecular levels. Under salinity, supplying exogenous protectants improved the contents of photosynthetic pigments and proline, triggered accumulation of phenolic compounds and expression of related biosynthetic genes, enhanced antioxidant capacity and modulated stress-induced lipid peroxidation which indicate the regulatory functions of applied protectants in lemon balm plant in this condition. In addition, there were strong correlations between the expression levels of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) genes, as key components of the phenylpropanoid pathway and the contents of total phenolics and flavonoids. In this study, a partial-length of lemon balm CHS gene was also cloned and sequenced for the first time.
... Exogenously applied SA can also be effectively used to improve the stress tolerance of various plant species. SA has been applied in different ways, for example by spraying the leaves, irrigating the plants with SA [6][7][8], or soaking seeds in SA solution before sowing [9][10][11][12]. The transport of endogenous SA has been characterised at several levels, such as in short-and long-distance transport processes [13], although changes in various biochemical and physiological stress acclimation processes have been described in SAtreated plants, the uptake mechanism, mode of action and further fate of exogenously applied SA is still not fully understood. ...
Salicylic acid (SA) plays a role in several physiological processes in plants. Exogenously applied SA is a promising tool to reduce stress sensitivity. However, the mode of action may depend on how the treatment was performed and environmental conditions may alter the effects of SA. In the present study the physiological and biochemical effects of different modes of application (soaking seeds prior sowing; spraying leaves with 0.5 mM NaSA) were compared at normal and moderately elevated temperatures (4 h; 35°C) in Brachypodium distachyon (L.) P. Beauv. plants. While soaking the seeds stimulated plant growth, spraying caused mild stress, as indicated by the chlorophyll-a fluorescence induction parameters and changes in certain protective compounds, such as glutathione, flavonoids or antioxidant enzymes. Elevated temperature also caused an increase in the glutathione-S-transferase activity, and this increase was more pronounced in plants pre-treated with NaSA. Both seed soaking or spraying with NaSA and exposure to heat treatment at 35°C reduced the abscisic acid levels in the leaves. In contrast to abscisic acid, the jasmonic acid level in the leaves were increased by both spraying and heat treatment. The present results suggest that different modes of application may induce different physiological processes, after which plants respond differently to heat treatment. Since these results were obtained with a model plants, further experiments are required to clarify how these changes occur in crop plants, especially in cereals.
... However, till date, most of the studies have been conducted on crop species while only a few studies have been done on tree species. For example, Jesus et al. (2015) used salicylic acid to treat E. globulus kept under water-deficit conditions. Eucalyptus spp. ...
Salinity is one of the primary issues causing a gradual reduction of fertile lands, especially in the arid and semiarid regions. With an increasing human population and demand for raw materials derived from tree species, it poses a threat for sustainability of such agricultural practices. Deep-rooted species like Eucalyptus can be used to reclaim such lands but seedling establishment in extremely saline conditions can be a challenge and an enhancement of salt tolerance is necessary through chemical treatment. This study attempts to quantify the effect of treating two commercially available Eucalyptus hybrid (H4 and H28) seedlings with chemicals, to increase their chances of survival in highly saline (40 dS m⁻¹ of NaCl solution) inland environments of Thailand. This is most likely the first investigation of using chemicals to enhance the salt tolerance of Eucalyptus seedlings. After a month, no H28 seedlings could survive, while an average of 40% H4 seedlings survived. H4 seedlings treated with 30 μM selenium had the highest survival percentage (60%) along with the highest relative weight and lowest electrical leakage, suggesting a higher growth and low cell damage, or an increased salt tolerance under this chemical treatment. Prior to planting in salt-affected areas, application of selenium through root uptake is recommended, to increase the chances for seedling growth in the field.
... Principal physiological mechanisms in response to stress and later adaptation have been described in many forestry species. Good examples of well-described physiological stress response and acclimation are heat and UV stress response in Pinus radiata (Escandón et al. 2017(Escandón et al. , 2018Pascual et al. 2017) and drought and heat stress response in Eucalyptus globulus (Jesus et al. 2015;Correia et al. 2018). In contrast, the regulation of these processes at chromatin level and those mechanisms that are implied in long-term stress responses and acclimation are still poorly described in most cases. ...
Trees are sessile and long-lived organism so they have to rapidly adapt to dynamic and unfavorable environments (drought, soil salinity, heat, …) for ensure their survival. Acclimation is mostly related to epigenetic regulation mechanisms that act responding to environmental stimuli and thus regulating gene expression during leaf development, floral transition, bud dormancy, and climate change induced abiotic stress response. Also, environmental stresses have been related to the transgenerational inheritance of epigenetic marks, called epigenetic memory. Epigenetic variation complements natural genetic variation as a source of phenotypic and functional diversity in plants, resulting in a phenotypic plasticity including also traits of transgenerational inheritance. This chapter provide an overview about how epigenetic mechanisms act, the memory role and new epi-variates definition that combined will help us to create new biotechnological tools for forest trees productivity improvement.
... A Chl a fluorescence was determined in situ in fully expanded leaves, with a portable fluorimeter Mini-PAM (Walz, Effeltrich, Germany) as described by Jesus et al. (2015). Values of F v /F m. .= ...
... Acting as a membrane protector, farnesol may present the same protective effect against other stresses, such as other metals, water and salt stress, since these are known to also induce ROS generation and lipid peroxidation (Abogadallah, 2010;Jesus et al., 2015;Taïbi et al., 2016). At higher concentrations, farnesol is also capable of decreasing Cd uptake. ...
Soil acts as a repository for many metals that human activity releases into the environment. Cadmium enters agricultural soils primarily from application of phosphate fertilizers and sewage sludge. Among soil bacteria, rhizobia have a great agronomic and environmental significance and are major contributors to a sustainable maintenance of soil fertility. However, the services that this group of microorganisms provides are affected by environmental constraints, such as Cd contamination. Bioactive compounds also influence soil microorganisms. Farnesol is a phytocompound with recognized bioactivity, inducing both beneficial and harmful effects. In this study, Rhizobium sp. strain E20-8 was exposed to sole or combined exposure to Cd and farnesol. Results showed that farnesol (25 and 200 µM) did not affect rhizobia; exposure to Cd (µM) inhibited rhizobia growth and induced several biomarkers of oxidative stress; exposure to the combination of farnesol and Cd reduced oxidative damage, and the highest concentration of farnesol tested reduced Cd accumulation and allowed a significant growth recovery. Farnesol protective effects on rhizobia exposed to Cd is novel information which can be used in the development of microbe-based environmental engineering strategies for restoration of metal contaminated areas.
... Salicylic acid-induced plant stress tolerance has been considered to be mediated by endogenous ABA signal (Szepesia et al., 2009;Jesus et al., 2015). Exogenous SA induces ABA accumulation by up-regulating of ABA biosynthesis related genes (Horvath et al., 2015). ...
Salicylic acid (SA) can induce plant resistance to biotic and abiotic stresses through cross talk with other signaling molecules, whereas the interaction between hydrogen peroxide (H2O2) and abscisic acid (ABA) in response to SA signal is far from clear. Here, we focused on the roles and interactions of H2O2 and ABA in SA-induced freezing tolerance in wheat plants. Exogenous SA pretreatment significantly induced freezing tolerance of wheat via maintaining relatively higher dark-adapted maximum photosystem II quantum yield, electron transport rates, less cell membrane damage. Exogenous SA induced the accumulation of endogenous H2O2 and ABA. Endogenous H2O2 accumulation in the apoplast was triggered by both cell wall peroxidase and membrane-linked NADPH oxidase. The pharmacological study indicated that pretreatment with dimethylthiourea (H2O2 scavenger) completely abolished SA-induced freezing tolerance and ABA synthesis, while pretreatment with fluridone (ABA biosynthesis inhibitor) reduced H2O2 accumulation by inhibiting NADPH oxidase encoding genes expression and partially counteracted SA-induced freezing tolerance. These findings demonstrate that endogenous H2O2 and ABA signaling may form a positive feedback loop to mediate SA-induced freezing tolerance in wheat.
... Net photosynthetic rate (A, μmol CO 2 m −2 s −1 ) and stomatal conductance (gs, mol H 2 O m −2 s −1 ) were measured in all plants using a portable infrared gas analyser (LCpro-SD, ADC BioScientific Ltd., UK) equipped with a broad leaf chamber (Jesus et al. 2015). To find out the saturation light intensity A/PPFD (photosynthetic photon flux density; light response curves of CO 2 assimilation), curves were performed with the following PPFD: 2,000, 1,500, 1,000, 750, 500, 250, 100, 50 and 0 μmol m −2 s −1 . ...
Diplodia corticola is one of the most aggressive fungal pathogens of Quercus species and is involved in the decline of Mediterranean cork oak forests and Californian oaks.
Information regarding variation in virulence between strains is scarce. We hypothesize that D. corticola strains differ in virulence and consequently induce different symptoms in infected plants. To test this, infection assays were carried out on Quercus suber half-sib
seedlings with seven strains of D. corticola. Visual symptoms of infection (external lesions, leaf wilting, exudation and others) were recorded in parallel with physiological and biochemical parameters. All strains were able to cause lesions but at differing levels of aggressiveness. We show that internal lesion length did not correlate
directly with strain aggressiveness and this agrees with physiological parameters that should be taken into account to infer about strain pathogenicity. Infection by all strains induced an overall negative impact on the net photosynthetic rate and an increase in the oxidative stress status of plants; however, significant differences were found when the effects of different strains were compared. Results also suggest that being under optimum growth conditions, prior to and during infection, allowed plants to respond to the pathogen. At the end of the experiment, some strains of D. corticola established a latent pathogen-like relationship with cork oak. This is the first study to show that D. corticola virulence is strain-dependent.
... A Chl a fluorescence was determined in situ in fully expanded leaves, with a portable fluorimeter Mini-PAM (Walz, Effeltrich, Germany) as described by Jesus et al. (2015). Values of F v /F m. .= ...
Strawberry tree (Arbutus unedo) is a small perennial tree that grows spontaneously in Europe and North Africa. It is a very important species in Mediterranean ecosystems, as its regenerates after forest fires avoiding erosion and helping recover marginal lands. Strawberry tree is also a very atractive ornamental and can be used for honey production. The fruit is a spherical edible berry that is commonly used in the manufacture of traditional products such as jam and jelly. However, its main application is the production of an alcoholic distillate. Once considered a “Neglected or UnderuDlized Crop” (www.cropsforthefuture.org/), the demanding for strawberry tree by producers and stakeholders is increasing, as an alternative to other forest species, such as pine and eucalyptus, that are suffering from several diseases. In order to make this species more atractive, an intensive propagation and breeding program is being carried out. Because it is essential to assure plant quality and drought tolerance of the micropropagated plants, especially on a changing climate context, plants produced in vitro through different methods were submited to drought stress and several physiological parameters evaluated.
Abiotic stresses are major constraints in crop production, and are accountable for more than half of the total crop loss. Plants overcome these environmental stresses using coordinated activities of transcription factors and phytohormones. Pearl millet an important C4 cereal plant having high nutritional value and climate resilient features is grown in marginal lands of Africa and South-East Asia including India. Among several transcription factors, the basic leucine zipper (bZIP) is an important TF family associated with diverse biological functions in plants. In this study, we have identified 98 bZIP family members (PgbZIP) in pearl millet. Phylogenetic analysis divided these PgbZIP genes into twelve groups (A-I, S, U and X). Motif analysis has shown that all the PgbZIP proteins possess conserved bZIP domains and the exon-intron organization revealed conserved structural features among the identified genes. Cis-element analysis, RNA-seq data analysis, and real-time expression analysis of PgbZIP genes suggested the potential role of selected PgbZIP genes in growth/development and abiotic stress responses in pearl millet. Expression profiling of selected PgbZIPs under various phytohormones (ABA, SA and MeJA) treatment showed differential expression patterns of PgbZIP genes. Further, PgbZIP9, a homolog of AtABI5 was found to localize in the nucleus and modulate gene expression in pearl millet under stresses. Our present findings provide a better understanding of bZIP genes in pearl millet and lay a good foundation for the further functional characterization of multi-stress tolerant PgbZIP genes, which could become efficient tools for crop improvement.
Under the changing climate due to global warming, various abiotic stresses including drought (D) and salinity (S) are expected to further trigger their devastating effects on the already vulnerable crop production systems. This experiment was designed to unravel and quantify the potential role of exogenous application of salicylic acid (SA) in mitigating both D and S stresses and their combination (D+S), with three replications using CRD (Completely Randomized Design). The obtained results of the current study demonstrated significant effects of all three types of stresses (D, S, and D+S) on various parameters in Brassica napus plants. Quantifying these parameters provides a more informative and precise understanding of the findings. Current results revealed that all three stress types (D, S, and D+S) resulted in a reduction in leaf area (13.65 to 21.87%), chlorophyll levels (30 to 50%), gaseous exchange rate (30 to 54%) and the concentration of mineral ions compared to non-stressed plants. However, application of SA helped in mitigating these stresses by ameliorating the negative effects of these stresses. Moreover, Malondialdehyde (MDA) contents, an indicator of lipid per-oxidation and oxidative stress, the levels of antioxidants, proline content, an osmolyte associated with stress tolerance, and sugar content in the leaves were elevated in response to all stress conditions. In addition, the ultra-structures within the leaves were negatively affected by the stresses, while an application of SA considerably minimized the deterioration of these structures thus providing protection to the brassica plants against the stresses. In a nutshell, the findings of this study suggest that SA application in S, D and S+ D stresses provides evasion to the plants by improving different physiological and growth indices. The application of Salicylic Acid (SA) mitigated the negative effects of the stresses on all the above parameters, reducing MDA contents (47%), antioxidants (11 to 20%), proline (28%), sugar contents (20.50%), and minimizing the deterioration of ultra-structures. The findings emphasize the potential mitigatory role of SA in mitigating D and S stresses and highlight the need for further research to understand the underlying mechanisms in detail and explore its practical application in farming practices.
This study investigated the effects of exogenous salicylic acid (SA) treatment (0, control; 3 mmol L⁻¹) on the antioxidant and hormone levels of winter jujube during shelf life (20 d) at 4 °C. The results showed that 3 mmol L⁻¹ SA treatment preferably maintained firmness, color, titratable acidity, and total soluble solids, and effectively reduced the respiratory intensity and TSS/TA value (13.08%) of the fruit. Compared with the control group, the SA group had a higher content of sucrose (14.03%) and malic acid (29.13%). Meanwhile, SA reduced the accumulation of H2O2 (27.73%) and O2·- (45.44%) by enhancing the activity of antioxidant enzymes (superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and the content of antioxidant substances (ascorbic acid, total phenols, total flavonoids, and glutathione) in the fruit. In addition, 3 mmol L⁻¹ SA treatment led to higher levels of endogenous abscisic acid (18.49%) and SA (20.47%) in fruit, and lower concentration of jasmonic acid (42.68%), but had a weak effect on indole acetic acid levels.
Background and objectives: Paulownia fortunei (Seem.) Hemsl is one of the fastest growing tree species of Paulownia genus, which is a suitable option for wood farming and agroforestry in north of Iran. Drought is one of the most important factors limiting the growth and survival of this species, which can cause severe damage to its performance in the nursery and planting area. This study intends while to investigate the growth and survival response of this species seedling to changes in soil moisture, to consider the possibility of using foliar spray of salicylic acid and ascorbic acid to increase drought resistance of P. fortunei in seedling stage.
Materials and Methods: In this study, 225 seedlings were selected, and were transplanted in 3 liter pots filled with suitable soil, and were examined after establishment under 3 levels of soil moisture (90%, 60% and 30% of field capacity) and 5 levels of foliar spray (control, 1 and 10 mM ascorbic acid, 100 and 150 mg.l-1 salicylic acid), using two-factor factorial experiment with 3 replications for 4 month. Survival of seedlings and growth characteristics, including stem height, collar root diameter, chlorophyll, and specific area of leaves, and also length and number of main and lateral roots for each seedling were measured at the end of the study. Collected data were analyzed using two-way analysis of variance, Duncan multiple comparison of means, and simple linear regression method at 95% confidence level.
Results: The results showed that in all foliar spraying treatments, a decreasing and significant linear relationship was observed between soil moisture and seedling survival. So that at 30% moisture level (severe drought) salicylic acid foliar spray treatment increased the survival of seedlings by 7 times. Also, lessening of soil moisture from 90% to 60% caused a significant reduction in growth traits of stems and leaves of seedlings, The results showed that the effects of foliar spray on seedling root properties are strongly affected by soil moisture, so that at 90% moisture level, foliar spray reduces root area and number of first order lateral roots, nevertheless, at 30% moisture level, seedlings were treated with foliar spray of salicylic acid at a concentration of 150 mg.l-1 and ascorbic acid at a concentration of 10 mM, showed the highest mean values of root area, total root length and number of first order lateral roots.
Conclusion: P. fortunei seedlings are very sensitive to changes in soil moisture. Also, the use of foliar spray, especially in the treatment of salicylic acid with a concentration of 150 mg.l-1 improves the survival and growth characteristics of this species seedling under water scarcity conditions.
Pistachio orchards in Iran are exposed to many abiotic and biotic stresses; the most
important are drought and herbivory of the common pistachio psyllid. These two stress factors, either in combination or individually, cause secondary oxidative stress and, consequently, plant cell damages due to lipid peroxidation, resulting in the reduction of the yield. In this study, salicylic acid was used as an inducer of the plant defense system against the adverse effect of drought and herbivory stresses. In the first experiment, the influence of exogenous salicylic acid on the antioxidative system of 75 days old pistachio seedlings subjected to water deficits is explored on days 0, 1, 3, 6, and 10 after the start of water deprivation. Variations of photosynthetic pigments content, relative water content, osmolyte accumulation (proline and total soluble carbohydrates), total phenolic compounds and the activities of polyphenol oxidase (PPO), phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), glutathione s-transferase (GST) and guaiacol peroxidase (GPX) are assayed in four treatments, including control (C), drought (D), salicylic acid (1mM) (SA), salicylic acid+drought (SD). The results show that salicylic acid can increase the efficiency of the plant antioxidant system, which in turn enhances the tolerance against drought stress, and the maximum activity occurs on the sixth day after treatment. In the second series of experiments, on the 6th day, pistachio psyllid is placed on the seedlings treated with salicylic acid and/or drought stress. Accordingly, the plant response to herbivory stress as well as the effect of this response on pistachio psyllid is investigated by the evaluation of antioxidant systems (SOD, CAT, APX, GPX, phenolics, H2O2, and MDA), detoxification enzymes activity (GST and carboxylesterases), energy reserves (carbohydrate, glycogen, lipid, protein) alternation and occurred mortality (%). The results indicate a decrease in the adverse effects of pistachio psyllid feeding on pistachio seedlings due to the improvement of the antioxidant system and reduction of lipid peroxidation. Having altered the antioxidant and detoxification enzymes activity and disrupted the allocation of energy reserves in the insect, salicylic acid shows the possible potential anti-nutritional resistance traits in SD treatment. Therefore, we concluded that salicylic acid could be used in pistachio orchards to decrease the negative effects of drought stress, induce plant tolerance against pistachio psyllid feeding, and reduce the simultaneous influence of these two stress factors on the plant.
Salicylic acid (SA) is a pharmaceutical drug that may exert toxic effects by its own; however, simultaneous exposure of plants to SA and to other substances, often results in the significant changes in the patterns of toxic response/resistance to these other sources of chemical stress. Thus, the aim of this work was to investigate the capacity of SA of modulating Lemna minor responses co-exposed to the pharmaceutical drug, diclofenac - DCF. To attain this objective, L. minor was exposed for 7 days, to DCF alone, and to combinations of DCF with SA. After exposure, biochemical, physiological and population endpoints were analyzed as follow: catalase (CAT) and glutathione S-transferases (GSTs) activities, pigments content (chlorophyll a (Chl a), b (Chl b) and total (TChl), carotenoids (Car) and [Chl a]/[Chl b] and [TChl]/[Car] ratios), and growth specific rate, fresh weight and root length. Single exposures to DCF were capable of causing effects in all analyzed endpoints. However, co-exposure of DCF with SA partially reverted these effects. Finally, we may suggest that SA is capable to prevent the toxicity of DCF in macrophytes, by modulating the toxic response of exposed plants.
This study investigated the effects of foliar applications, such as brassinosteroid (BR), methyl jasmonate (JA), salicylic acid (SA), and sodium nitroprusside (SNP), on the growth, yield, photosynthetic characteristics, and antioxidant enzyme activity of Kimchi cabbage (Brassica rapa L. ssp. pekinensis) exposed to heat stress. Kimchi cabbages were grown in extreme weather growth chambers under controlled conditions (air temperature, relative humidity, and solar radiation of the Daegwanryeong region, 37° 40′ N, 128° 32′ E). At 18 days after transplanting, Kimchi cabbages were treated with foliar application of biostimulants (vs. non-sprayed control) and exposed to heat stress (air temperature 30/25 °C) and mean daily air temperature under normal conditions (21.2 ± 1.6 °C day/night, respectively) for 5 days. The foliar application concentrations were 50, 100, and 200 nM BR; 50, 100, and 200 μM JA; 1, 2, and 4 mM SA; and 0.25, 0.50, and 1.00 mM SNP. At 38 days after foliar application, the shoot fresh weight of Kimchi cabbages treated with 200 nM BR was 2123 versus 1422 g plant⁻¹ (control). The head weight and yield were the greatest with 2 mM SA treatment, which produced 3806 versus 2184 kg ha⁻¹ (control). Heat stress induced a low photosynthetic rate in Kimchi cabbage, while foliar application of biostimulants enhanced photosynthesis recovery. During the 3 days after heat stress, catalase and peroxidase enzyme activities of Kimchi cabbage increased by 1.76- to 2.08-fold on average compared to the control. Results indicated that foliar application of biostimulants reduced physiological damage and enhanced the activity of the antioxidant enzymes, thereby improving heat stress tolerance in Kimchi cabbage.
In a changing world, the search for new agronomic practices that help crops to maintain and/or increase yields and quality is a continuous challenge. We aim to evaluate kaolin (KL) and salicylic acid (SA) effectiveness as summer stress alleviating agents through physiological, biochemical and immunohistochemical analysis. Olive trees (Olea europaea L. cv. Cobrançosa) grown under rainfed conditions were sprayed with 5% KL and 100 μM SA, at the beginning of summer, during two consecutive years. KL enhanced relative water content (RWC), stomatal conductance (gs) net photosynthesis (A) and leaf indole-3-acetic acid (IAA) signal, and decreased leaf sclerophylly, secondary metabolites and non-structural carbohydrates accumulation and abscisic acid (ABA).The trees treated with SA showed changes on IAA and ABA dynamics, and an enhancement in RWC, gs, A, soluble proteins, and leaf P and Mg concentrations during the summer. Notably, KL and SA also allowed a faster restauration of the physiological functions during stress relief. In sum, KL and SA foliar sprays alleviated the negative effects induced by summer stress in olive trees performance, by modulation of distinct physiological and biochemical responses.
The foliar exogenous application of kaolin, a radiation-reflecting inert mineral, has proven to be an effective short-term climate change mitigation strategy for Mediterranean vineyards. In this work, we address the hypothesis that kaolin could improve both the hormonal dynamics and physiological responses of grapevines growing in Douro Region, northern Portugal. For this purpose, the leaf water potential, gas exchange and chlorophyll a fluorescence parameters were monitored, as well as the abscisic acid (ABA) and indole-3-acetic acid (IAA) quantification and immunolocalization were assessed. The study revealed a slight decrease in ABA and an increase in IAA in the kaolin treatment, which in turn were associated with the improvement of physiological performance. A month after spraying, kaolin improves the water potential respectively, 30% and 17% in the predawn and midday periods. Besides, plants treated with kaolin showed higher values of stomatal conductance, net CO2 assimilation rate and intrinsic water use efficiency. Kaolin also ameliorates the effective PSII efficiency (67%), as well as the maximum quantum efficiency of photosystem II and the photosynthetic electron transport rate (>73%). These results were consistent with the higher photochemical quenching and the lower non-photochemical quenching observed in treated leaves and with the better performance obtained by the JIP test parameters. Physiological and hormonal analysis confirmed that kaolin effectively enhance grapevine summer stress tolerance.
Phytohormones play critical roles in regulating plant responses to stress. The present study investigates the effect of cytokinin, abscisic acid and cytokinin/abscisic acid interaction on some osmoprotectants and antioxidant parameters induced by drought stress in two wheat cultivars (Triticum aestivum L.) of ‘Pishgam’ and ‘MV-17’ as tolerant and sensitive to drought during post-anthesis phase, respectively grown in field conditions. The most considerable effect of the treatments was exhibited 21 days after anthesis. Under drought conditions, the flag leaf soluble carbohydrate content increased in both cultivars while starch content was remarkably decreased in ‘Pishgam’ as compared to ‘MV-17’. Abscisic acid increased total soluble sugar and reduced starch more than other hormonal treatments, although it decreased studied monosaccharaides in ‘Pishgam’, especially. Drought stress induced high proportion of gylycinebetain and free proline in ‘Pishgam’ cultivar. Application of abscisic acid and cytokinin/abscisic acid interaction increased gylycinebetain and proline content in both cultivars under irrigation and drought conditions. The tolerant cultivar exhibited less accumulation of hydrogen peroxide and malondialdehyde in relation to significant increase of catalase and peroxidase activities and α-tocpherol content under drought conditions. All hormonal treatments increased the named enzyme activities under both irrigation and drought conditions, while higher accumulation of α-tocopherol was only showed in case of cytokinin application. Also, abscisic acid and cytokinin/abscisic acid could decrease drought-induced hydrogen peroxide and malondialdehyde level to some extent, although abscisic acid increased both of hydrogen peroxide andmalondialdehyde content in irrigation phase, especially.
Phytohormones play critical roles in regulating plant responses to stress. The present study investigates the effect of cytokinin, abscisic acid and cytokinin/abscisic acid interaction on some osmoprotectants and antioxidant parameters induced by drought stress in two wheat cultivars (Triticum aestivum L.) of ‘Pishgam’ and ‘MV-17’ as tolerant and sensitive to drought during post-anthesis phase, respectively grown in field conditions. The most considerable effect of the treatments was exhibited 21 days after anthesis. Under drought conditions, the flag leaf soluble carbohydrate content increased in both cultivars while starch content was remarkably decreased in ‘Pishgam’ as compared to ‘MV-17’. Abscisic acid increased total soluble sugar and reduced starch more than other hormonal treatments, although it decreased studied monosaccharaides in ‘Pishgam’, especially. Drought stress induced high proportion of gylycinebetain and free proline in ‘Pishgam’ cultivar. Application of abscisic acid and cytokinin/abscisic acid interaction increased gylycinebetain and proline content in both cultivars under irrigation and drought conditions. The tolerant cultivar exhibited less accumulation of hydrogen peroxide and malondialdehyde in relation to significant increase of catalase and peroxidase activities and α-tocpherol content under drought conditions. All hormonal treatments increased the named enzyme activities under both irrigation and drought conditions, while higher accumulation of α-tocopherol was only showed in case of cytokinin application. Also, abscisic acid and cytokinin/abscisic acid could decrease drought-induced hydrogen peroxide and malondialdehyde level to some extent, although abscisic acid increased both of hydrogen peroxide andmalondialdehyde content in irrigation phase, especially.
Plants growing in their natural habitats are often challenged simultaneously by multiple stress factors, both abiotic and biotic. Research has so far been limited to responses to individual stresses, and understanding of adaptation to combinatorial stress is limited, but indicative of non-additive interactions. Omics data analysis and functional characterization of individual genes has revealed a convergence of signaling pathways for abiotic and biotic stress adaptation. Taking into account that most data originate from imposition of individual stress factors, this review summarizes these findings in a physiological context, following the pathogenesis timeline and highlighting potential differential interactions occurring between abiotic and biotic stress signaling across the different cellular compartments and at the whole plant level. Potential effects of abiotic stress on resistance components such as extracellular receptor proteins, R-genes and systemic acquired resistance will be elaborated, as well as crosstalk at the levels of hormone, reactive oxygen species, and redox signaling. Breeding targets and strategies are proposed focusing on either manipulation and deployment of individual common regulators such as transcription factors or pyramiding of non- (negatively) interacting components such as R-genes with abiotic stress resistance genes. We propose that dissection of broad spectrum stress tolerance conferred by priming chemicals may provide an insight on stress cross regulation and additional candidate genes for improving crop performance under combined stress. Validation of the proposed strategies in lab and field experiments is a first step toward the goal of achieving tolerance to combinatorial stress in crops.
Growth and physiological activities of barley (Hordeum vulgare L. cv. Gustoe) grown in soil cultures were evaluated to recognize the ameliorative role of salicylic acid (SA) and KNO3 against the negative effects of salt and water deficit stresses. Barley plants were subjected to three levels of NaCl (50, 100 and 150 mM), three levels of water stress (80%, 70% and 50% of the soil water content (SWC) and the combination of 150 mM NaCl + 50 μM SA, 150 mM NaCl + 10 mM KNO3, 50% SWC + 50 μM SA and 50% SWC + 10 mM KNO3 for two weeks. Salt and water deficit stresses reduced the shoot growth, leaf photosynthetic pigments, K+ contents and provoked oxidative stress in leaves confirmed by considerable changes in soluble carbohydrate, proline, malondialdehyde (MDA), total phenolic compounds, antioxidant activity and Na+ contents. Leaf soluble protein of salt and water deficit treated plants was unaffected. The Na+/K+ ratio increased with increasing salt and water deficit treated plants. Application of 50 μM SA or 10 mM KNO3 to150 mM NaCl and/or 50% SWC treated plants improved these attributes under salt and water stresses. Soluble carbohydrates in stressed plants may have a significant role in osmotic adjustment. It can be concluded that the addition of SA or KNO3 can ameliorate the oxidative stress in barley stressed plants. This ameliorative effect might be maintained through low MDA contents and decreased Na+/K+ ratio in leaves. This study also provided evidence for the ability of barley cultivation in salt and water deficit soils due to its capacity for osmotic adjustment.
Plant hormones are small molecules that regulate plant growth and development, as well as responses to changing environmental conditions. By modifying the production, distribution or signal transduction of these hormones, plants are able to regulate and coordinate both growth and/or stress tolerance to promote survival or escape from environmental stress. A central role for the gibberellin (GA) class of growth hormones in the response to abiotic stress is becoming increasingly evident. Reduction of GA levels and signalling has been shown to contribute to plant growth restriction on exposure to several stresses, including cold, salt and osmotic stress. Conversely, increased GA biosynthesis and signalling promote growth in plant escape responses to shading and submergence. In several cases, GA signalling has also been linked to stress tolerance. The transcriptional regulation of GA metabolism appears to be a major point of regulation of the GA pathway, while emerging evidence for interaction of the GA-signalling molecule DELLA with components of the signalling pathway for the stress hormone jasmonic acid suggests additional mechanisms by which GA signalling may integrate multiple hormone signalling pathways in the response to stress. Here, we review the evidence for the role of GA in these processes, and the regulation of the GA signalling pathway on exposure to abiotic stress. The potential mechanisms by which GA signalling modulates stress tolerance are also discussed.
The present paper alms at determining how carbon (C) and nitrogen (N) compounds are redistributed from leaves to harvesting organs during maturation in several major field crops. In order to illustrate these processes in the case of C and N compounds, 6 major crops in Hokkaido were grown and compared during maturation. The results obtained were as follows. 1) The N-redistribution rate during maturation was in the order of wheat, soybean and potato > maize > rice. The percentage of distributed nitrogen among the different nitrogenous fractions in leaves and stems was remained constant during maturation, suggesting that each nitrogen compound was equally decomposed. 2) The composition of protein amino acids was similar regardless of organs or crops. The composition of free amino acids differed widely among organs and crops, and differed from that of protein amino acids. Therefore during the translocation of amino acids from leaves to harvesting organs through stems, the composition of free amino acids was almost reconstructed in all the crops. 3) Dry weight of leaves and stems during maturation increased in rice, wheat and maize, but decreased in soybean and potato. The proportion of cellulose and heniicellulose in leaves was high in rice, wheat and maize and low in soybean and potato, whereas that of stems was high in all the crops. The amount of cell wall components in leaves and stems decreased during maturation only in soybean and potato.
Drought stress is a major factor in reduce growth, development and production of plants. Stress was applied with polyethylene glycol (PEG) 6000 and water potentials were: zero (control), -0.15 (PEG 10%), -0.49 (PEG 20%), -1.03 (PEG 30%) and -1.76 (PEG40%) MPa. The solutes accumulation of two maize (Zea mays L. ) cultivars -704 and 301- were determined after drought stress. In our experiments, a higher amount of soluble sugars and a lower amount of starch were found under stress. Soluble sugars concentration increased (from 1.18 to 1.90 times) in roots and shoots of both varieties when the studied varieties were subjected to drought stress, but starch content were significantly (p
The effect of a moderate (PEG −0.75 MPa) and severe (PEG −1.5 MPa) water deficit on SA content in leaves and roots as well
as the effect of pre-treatment with SA on reaction to water stress were evaluated in two barley genotypes — the modern cv.
Maresi and a wild form of Hordeum spontaneum.
Water deficit increased SA content in roots, whereas SA content in leaves did not change. The level of SA in the roots of
control plants was about twofold higher in ‘Maresi’ than in H. spontaneum. After 6 hours of a moderate stress the level of SA increased about twofold in H. spontaneum and about two and a half-fold in ‘Maresi’. Under severe stress conditions the level of SA increased about twofold in the
both genotypes, but not before 24 hrs of the stress.
Plant treatment with SA before stress reduced a damaging action of water deficit on cell membrane in leaves. A protective
effect was more noticeable in H. spontaneum than in ‘Maresi’. SA treatment increased ABA content in the leaves of the studied genotypes. An increase of proline level
was observed only in H. spontaneum. The obtained results suggest that ABA and proline can contribute to the development of antistress reactions induced by SA.
Anatomical, physiological and phytohormonal changes involved in drought tolerance were examined in different Pinus radiata D. Don breeds subjected to soil drying and rewatering. Breeds with the smallest stomatal chamber size had the lowest transpiration rate and the highest intrinsic water-use efficiency. Xylem cell size was positively correlated with leaf hydraulic conductance and needle indole-3-acetic acid (IAA) concentrations, whereas transpiration rate was negatively correlated with needle abscisic acid (ABA) levels. Since these two phytohormones seem important in regulating the P. radiata drought response, they were simultaneously immunolocalized in roots and needles of the most tolerant breed (P. radiata var. radiata × var. cedrosensis) during two sequential drought cycles and after rewatering. During drought, IAA was unequally distributed into the pointed area of the needle cross-section and mainly located in mesophyll and vascular tissue cells of needles, possibly inducing needle epinasty, whereas ABA was principally located in guard cells, presumably to elicit stomata closure. In the roots, at the end of the first drought cycle, while strong IAA accumulation was observed in the cortex, ABA levels decreased probably due to translocation to the leaves. Rewatering modified the distribution of both IAA and ABA in the needles, causing an accumulation principally in vascular tissue, with residual concentrations in mesophyll, likely favouring the acclimatization of the plants for further drought cycles. Contrarily, in the roots IAA and ABA were located in the exodermis, a natural barrier that regulates the phytohormone translocation to other plant tissues and hormone losses to the soil solution after rewatering. These results confirm that immunolocalization is an efficient tool to understand the translocation of IAA and ABA in plants subjected to different water stress situations, and clarify their role in regulating physiological responses such as stomata closure and epinasty in needles and root development.
Two important role players in plant defence response are the phytohormones salicylic acid (SA) and jasmonic acid (JA); both of which have been well described in model species such as Arabidopsis thaliana. Several pathogenesis related (PR) genes have previously been used as indicators of the onset of SA and JA signaling in Arabidopsis. This information is lacking in tree genera such as Eucalyptus. The aim of this study was to characterize the transcriptional response of PR genes (EgrPR2, EgrPR3, EgrPR4, EgrPR5, and EgrLOX) identified in Eucalyptus grandis to SA and methyl jasmonate (MeJA) treatment as well as to qualify them as diagnostic for the two signaling pathways. Using the genome sequence of E. grandis, we identified candidate Eucalyptus orthologs EgrPR2, EgrPR3, EgrPR4, EgrPR5, and EgrLOX based on a co-phylogenetic approach. The expression of these genes was investigated after various doses of SA and MeJA (a derivative of JA) treatment as well as at various time points. The transcript levels of EgrPR2 were decreased in response to high concentrations of MeJA whereas the expression of EgrPR3 and EgrLOX declined as the concentrations of SA treatment increased, suggesting an antagonistic relationship between SA and MeJA. Our results support EgrPR2 as potentially diagnostic for SA and EgrPR3, EgrPR4, and EgrLOX as indicators of MeJA signaling. To further validate the diagnostic potential of the PR genes we challenged E. grandis clones with the fungal necrotrophic pathogen Chrysoporthe austroafricana. The tolerant clone showed high induction of EgrPR2 and decreased transcript abundance of EgrPR4. Pre-treatment of the susceptible genotype with 5 mM SA resulted in lesion lengths comparable to the tolerant genotype after artificial inoculation with C. austroafricana. Thus expression profiling of EgrPR2 and EgrPR4 genes could serve as a useful diagnostic approach to determine which of the two signaling pathways are activated against various pathogens in Eucalyptus.
Growth and productivity of banana is seriously restricted by water deficit. Salicylic acid (SA) induces biotic and abiotic stress tolerance in crops. To study the ameliorative effects of SA on water stress in banana (Musa acuminata cv. 'Berangan', AAA), shoot tip explants with 8 mm in size were treated with varying SA concentrations (0, 1, 2 and 3 mM) and incubated on MS media containing different levels (0, 1, 2 and 3 %) of PEG in vitro. After 2 months, proliferation rate, fresh weight increase, relative water content, chlorophyll level, proline accumulation, malondialdehyde (MDA) and H 2 O 2 contents were measured and analyzed. The results indicated that with increasing levels of PEG, proliferation rate, fresh weight increase, relative water content and chlorophyll concentrations were significantly decreased. The SA concentrations improved shoot tips performance by increasing proliferation rate, fresh weight increase and relative water content. Although non SA – treated shoot tips were not significantly responsive to increasing levels of PEG in terms of elevated proline content, they responded positively to supply of SA by showing significant increase in proline and chlorophyll contents under water stressed conditions. SA treatments also enhanced plant tolerance against oxidative stress. This was observed through significant reduction in H 2 O 2 and MDA contents of SA – treated shoot tips under water stress conditions. The results revealed that exogenous application of SA helped to reduce the harmful effects of water deficit on banana regenerants in vitro.
Plants of Lycopersicon esculentum L. cv. K-25 were subjected to water stress by withholding water for 10 days at 20 (WS I) and 30 (WS II) days after sowing (DAS). Seedlings were sprayed with double distilled water (DDW) or 10-5M salicylic acid (SA) at 45 DAS. The water stress at earlier stage of growth (20 day stage) was more inhibitory as compared to the later stage (30 day stage). The plants exposed to water stress exhibited a significant (p<0.05) decline in photosynthetic parameters, membrane stability index (MSI), leaf water potential, activity of nitrate reductase (NR), carbonic anhydrase (CA), chlorophyll and relative water content (RWC). A follow-up treatment with SA protected against the stress generated by water and significantly improved the above parameters. However, proline content and antioxidant enzymes increased under drought as well as under SA treatments.
It is possible to determine the optimum time for permanence of vegetative propagules (mini-cuttings) inside a greenhouse for rooting, and this value can be used to optimize the structure of the nursery. The aim of this study was to determine the dynamics of adventitious rooting in mini-cuttings of three clones of Eucalyptus benthamii x Eucalyptus dunnii. Sprouts of H12, H19 and H20 clones were collected from mini-stumps that were planted in gutters containing sand and grown in a semi-hydroponic system. The basal region of the mini-cuttings was immersed in 2,000 mg L-1 indole-3-butyric acid (IBA) solution for 10 seconds. The rooting percentage of the mini-cuttings, the total length of the root system and the rooting rate per mini-cutting were also evaluated at 0 (time of planting), 7, 14, 21, 28, 35, 42, 49 and 56 days. We used logistic and exponential regression to mathematically model the speed of rhizogenesis. The rooting percentage was best represented as a logistic model, and the total length of the root system was best represented as an exponential model. The clones had different speeds of adventitious rooting. The optimum time for permanence of the mini-cuttings inside the greenhouse for rooting was between 35 and 42 days, and varied depending on the genetic material.
Drought stress encumbers the rice growth predominantly by oxidative damage to biological membranes and disturbed tissue water status. In this study, the role of salicylic acid (SA) to induce drought tolerance in aromatic fine grain rice cultivar Basmati 2000 was evaluated. SA was applied as seed and foliar treatments. For seed treatment, rice seeds were soaked in 50, 100 and 150 mg l−1 aerated solution of SA for 48 h and then dried back. Treated and untreated seeds were sown in plastic pots in a phytotron. At four leaf stage, one set of plants was subjected to drought stress, while the other remained well watered. Drought was maintained at 50 % of field capacity by watering every alternate day. For exogenous application, SA was applied 50, 100 and 150 mg l−1 at five leaf stage. In the control, SA was neither applied exogenously nor as seed treatment. Drought stress severely affected the seedling fresh and dry weight, photosynthesis, stomatal conductance, plant water relations and starch metabolism; however, SA application improved the performance of rice under both normal and stress conditions. Drought tolerance in rice was well associated with the accumulation of compatible solutes, maintenance of tissue water potential and enhanced potency of antioxidant system, which improved the integrity of cellular membranes and facilitated the rice plant to sustain photosynthesis and general metabolism. Foliar treatments were more effective than the seed treatments. Foliar application with 100 mg l−1 (FA 100) was the best treatment to induce the drought tolerance and improve the performance under normal and stress conditions compared with the control or other treatments used in this study.
Fiji is a distribution of the popular open-source software ImageJ focused on biological-image analysis. Fiji uses modern software engineering practices to combine powerful software libraries with a broad range of scripting languages to enable rapid prototyping of image-processing algorithms. Fiji facilitates the transformation of new algorithms into ImageJ plugins that can be shared with end users through an integrated update system. We propose Fiji as a platform for productive collaboration between computer science and biology research communities.
It emerged recently that there is an inter-relationship between drought and ultraviolet-B (UV-B) radiation in plant responses, in that both stresses provoke an oxidative burst. The purpose of this investigation was to compare the effects and interaction of drought and UV-B in wheat and pea. The absence of changes in relative leaf water content (RWC) after UV-B treatments indicate that changes in water content were not involved. RWC was the main factor resulting in reduced growth in response to drought. Increases in anthocyanin and phenols were detected after exposure to UV-B. The increases do not appear to be of sufficient magnitude to act as a UV-B screen. UV-B application caused greater membrane damage than drought stress, as assessed by lipid peroxidation as well as osmolyte leakage. An increase in the specific activities of antioxidant enzymes was measured after UV-B alone as well as after application to droughted plants. Proline increased primarily in drought-stressed pea or wheat. Proline may be the drought-induced factor which has a protective role in response to UV-B. The physiological and biochemical parameters measured indicate the UV-B light has stronger stress effectors than drought on the growth of seedlings of both species. The two environmental stresses acted synergistically to induce protective mechanisms in that pre-application of either stress reduced the damage caused by subsequent application of the other stress.
The dynamic responses of stomatal conductance (g
s) net photosynthesis (A) and leaf water potential (Ψleaf) to a progressive drought were examined in nine poplar clones (Populus spp.) with contrasting drought tolerance from the Canadian Prairies, a region prone to frequent droughts. Plants were grown
in a greenhouse and either well-watered or drought preconditioned (5–6 cycles of drought) for 8weeks. At the end of the last
cycle, plants were watered to saturation then progressively dried-down (−1.25MPa Ψsoil) during which A, g
s and Ψleaf were measured. Drought tolerant Okanese reached the lowest combined Ψleaf while sensitive clones (Assiniboine and Imperial) had the highest (−1.6 vs. −1.1MPa). Steady state g
s (measured under well watered conditions) was lower in tolerant (Okanese and Tristis SBC#1) than in sensitive clones. Preconditioning
reduced steady state g
s in all clones, lowered the threshold Ψleaf for stomatal closure and the minimum Ψleaf in most clones but did not affect the steady state A. Tolerant and some moderately tolerant clones maintained higher A at lower Ψleaf than the other clones. Stomatal closure was gradual in tolerant clones and in moderately tolerant Northwest but rapid in
the other clones. Stomata in the sensitive clones closed at the highest Ψleaf, Okanese closed at the lowest. The substantial range in gas exchange and Ψleaf responses observed here represented both drought tolerance and taxonomic (Aegiros or Tacamahaca sections) traits which could play a role in the survival and productivity in environments with limited water or during periods
of drought.
Salicylic acid (SA) is an important signal molecule modulating plantresponses to stress. It is recently reported to induce multiple stresstolerancein plants including drought. An experiment was, therefore, conducted toascertain the effect of salicylic acid on the growth and metabolic profile ofwheat seedlings under water stress. Irrespective of the SA concentration(1–3 mM) and water stress, SA treated plants showed, ingeneral, a higher moisture content, dry mass, carboxylase activity of Rubisco,superoxide dismutase (SOD) activity and total chlorophyll compared to those ofuntreated seedlings. SA treatment, under water stress, protected nitratereductase (NR) activity and maintained, especially at 3 mM SAconcentration, the protein and nitrogen content of leaves compared to watersufficient seedlings. Results signify the role of SA in regulating the droughtresponse of plants and suggest that SA could be used as a potential growthregulator, for improving plant growth under water stress.
It is almost impossible to find a single process in plant life that is not affected by both stress and hormones directly or indirectly. This minireview is focused on the interactions between water stress and cytokinins (CKs). The attention was paid mainly to changes in endogenous CK content and composition under water stress, involvement of CK in plant responses to water stress mainly in stomatal regulation of gas exchange, water relations of transgenic plants with elevated CK content, and possibilities to ameliorate the negative effects of water stress by application of exogenous CKs.
Canonical correspondence analysis (CCA) is a multivariate method to elucidate the relationships between biological assemblages of species and their environment. The method is designed to extract synthetic environmental gradients from ecological data-sets. The gradients are the basis for succinctly describing and visualizing the differential habitat preferences (niches) of taxavia an ordination diagram. Linear multivariate methods for relating two set of variables, such as two-block Partial Least Squares (PLS2), canonical correlation analysis and redundancy analysis, are less suited for this purpose because habitat preferences are often unimodal functions of habitat variables. After pointing out the key assumptions underlying CCA, the paper focuses on the interpretation of CCA ordination diagrams. Subsequently, some advanced uses, such as ranking environmental variables in importance and the statistical testing of effects are illustrated on a typical macroinvertebrate data-set. The paper closes with comparisons with correspondence analysis, discriminant analysis, PLS2 and co-inertia analysis. In an appendix a new method, named CCA-PLS, is proposed that combines the strong features of CCA and PLS2.
Seedlings of two barley genotypes (‘Maresi’ and wild form of Hordeum spontaneum) were treated with jasmonic acid (JA 5 µM and 15 µM) for 24 h, and then subjected to water stress (PEG 6000 solution of −
1.5 MPa). JA caused an increase in the content of ABA but not in that of proline and spermidine in the two studied genotypes.
The effect of the treatment did not depend on the applied JA concentration. The pre-stress treatment with JA changed plant
response to water deficit with regard to membrane injury. Treatment with a lower JA concentration (5 µM) caused a substantial
reduction of the stress-induced membrane damage in the both genotypes. A higher JA concentration (15 µM) caused the reduction
of membrane injury only in H. spontaneum and was ineffective in ‘Maresi’. JA had no influence on the leaf water status in water-stressed plants. A possible role of
JA in leaf ABA accumulation and alleviation of cell membrane injury under water deficit is discussed.
In order to assess drought tolerance mechanism in cotton, short-term drought-induced biochemical responses were monitored
in two cotton (Gossypium hirsutum L.) genotypes contrasting their tolerance to water deficit. The seeds of two genotypes, namely GM 090304 (moderately drought
tolerant) and Ca/H 631 (drought sensitive), were sown in pots containing soil, sand and peat in the ratio of 1:1:1, and irrigated
every alternate day up to 45days after sowing when each genotype was subjected to a cycle of water stress by withholding
irrigation for 7days. The stress cycle was terminated by re-watering the stressed plants for 7days. The leaf of the drought
tolerant genotype (GM 090304) maintained higher relative water content under water stress than that of the drought sensitive
genotype (Ca/H 631). The levels of biochemical components, such as chlorophylls, carotenoids, total protein, free proline,
total free amino acids, sugars, starch and polyphenols, were measured during the stress as well as the recovery periods. The
chlorophylls, carotenoids, protein and starch contents decreased in drought stressed plants as compared to control and tended
to increase when the plants were recovered from stress. The degree of decrease in chlorophylls, carotenoids and protein contents
under drought was higher in the sensitive genotype (Ca/H 631) as compared to the moderately tolerant genotype (GM 090304).
However, proline, total free amino acids, total sugars, reducing sugars and polyphenol contents were increased in drought
stressed plants and tended to decrease during the period of recovery. Drought-induced increases in total free amino acids,
proline, sugars and polyphenols were significantly higher in the moderately tolerant genotype (GM 090304) than in the sensitive
genotype (Ca/H 631). These results suggest that proline, sugars and polyphenols act as main compatible solutes in cotton in
order to maintain osmotic balance, to protect cellular macromolecules, to detoxify the cells, and to scavenge free radicals
under water stress condition.
The floral transition includes a complex system of factors that interact and involve various biochemical signals, including
plant growth regulators. The physiological signals involved in the control of the floral transition have been sparsely studied
and mainly in plant species whose genetics are poorly known. In this work, the role of polyamines, gibberellins, and cytokinins
was investigated by analyzing their endogenous content in vegetative and floral buds of azalea. The results showed that there
is a clear distinction between floral and vegetative buds with respect to the levels of these plant hormones, with floral
buds containing higher amounts of conjugated polyamines, gibberellins (GAs) from the non-13-hydroxylation pathway (GA9, GA7, and GA4), and cytokinins (particularly isopentenyl-type species), and vegetative buds containing higher amounts of free polyamines
and gibberellins from the early 13-hydroxylation pathway and fewer cytokinins. In conclusion, there is a specific pattern
of endogenous hormone profiles in both vegetative and floral bud development in azalea, which may be relevant for future research
on the control of flowering by exogenous hormone applications.
Keywords
Rhododendron sp.–Polyamines–Gibberellins–Cytokinins–Flowering
Pinus radiata D. Don is one of the most abundant species in the north of Spain. Knowledge of drought response mechanisms is essential to
guarantee plantation survival under reduced water supply as predicted in the future. Tolerance mechanisms are being studied
in breeding programs, because information on such mechanisms can be used for genotype selection. In this paper, we analyze
the changes of leaf water potential, hydraulic conductance (Kleaf), stomatal conductance and phytohormones under drought in P. radiata breeds (O1, O2, O3, O4, O5 and O6) from different climatology areas, hypothesizing that they could show variable drought
tolerance. As a primary signal, drought decreased cytokinin (zeatin and zeatin riboside—Z + ZR) levels in needles parallel
to Kleaf and gas exchange. When Z + ZR decreased by 65%, indole-3-acetic acid (IAA) and abscisic acid (ABA) accumulation started as
a second signal and increments were higher for IAA than for ABA. When plants decreased by 80%, Z + ZR and Kleaf doubled their ABA and IAA levels, the photosystem II yield decreased and the electrolyte leakage increased. At the end of
the drought period, less tolerant breeds increased IAA over 10-fold compared with controls. External damage also induced jasmonic
acid accumulation in all breeds except in O5 (P. radiata var. radiata × var. cedrosensis), which accumulated salicylic acid as a defense mechanism. After rewatering, only the most tolerant plants recovered their
Kleaf, perhaps due to an IAA decrease and 1-aminocyclopropane-1-carboxylic acid maintenance. From all phytohormones, IAA was the
most representative ‘water deficit signal’ in P. radiata.
Salicylic acid (SA), an endogenous plant growth regulator has been found to generate a wide range of metabolic and physiological responses in plants thereby affecting their growth and development. In the present review, we have focused on various intrinsic biosynthetic pathways, interplay of SA and MeSA, its long distance transport and signaling. The effect of exogenous application of SA on bio-productivity, growth, photosynthesis, plant water relations, various enzyme activities and its effect on the plants exposed to various biotic and abiotic stresses has also been discussed.
Leaf pigment content can provide valuable insight into the physiological performance of leaves. Measurement of spectral reflectance provides a fast, nondestructive method for pigment estimation. A large number of spectral indices have been developed for estimation of leaf pigment content. However, in most cases these indices have been tested for only one or at most a few related species and thus it is not clear whether they can be applied across species with varying leaf structural characteristics. Our objective in this study was to develop spectral indices for prediction of leaf pigment content that are relatively insensitive to species and leaf structure variation and thus could be applied in larger scale remote-sensing studies without extensive calibration. We also quantified the degree of spectral interference between pigments when multiple pigments occur within the same leaf tissue. We found that previously published spectral indices provided relatively poor correlations with leaf chlorophyll content when applied across a wide range of species and plant functional types. Leaf surface reflectance appeared to be the most important factor in this variation. By developing a new spectral index that reduces the effect of differences in leaf surface reflectance, we were able to significantly improve the correlations with chlorophyll content. We also found that an index based on the first derivative of reflectance in the red edge region was insensitive to leaf structural variation. The presence of other pigments did not significantly affect estimation of chlorophyll from spectral reflectance. Previously published carotenoid and anthocyanin indices performed poorly across the whole data set. However, we found that the photochemical reflectance index (PRI, originally developed for estimation of xanthophyll cycle pigment changes) was related to carotenoid/chlorophyll ratios in green leaves. This result has important implications for the interpretation of PRI measured at both large and small scales. Our results demonstrate that spectral indices can be applied across species with widely varying leaf structure without the necessity for extensive calibration for each species. This opens up new possibilities for assessment of vegetation health in heterogeneous natural environments.
Increased endogenous plant cytokinin (CK) content through transformation with an adenine isopentyl transferase (ipt) gene has been associated with improved plant drought tolerance. The objective of this study is to determine metabolic changes
associated with elevated CK production in ipt transgenic creeping bentgrass (Agrostis stolonifera L.) with improved drought tolerance. Null transformants (NTs) and plants transformed with ipt controlled by a stress- or senescence-activated promoter (SAG12-ipt) were exposed to well-watered conditions or drought stress by withholding irrigation in an environmental growth chamber.
Physiological analysis confirmed that the SAG12-ipt line (S41) had improved drought tolerance compared with the NT plants. Specific metabolite changes over the course of drought
stress and differential accumulation of metabolites in SAG12-ipt plants compared with NT plants at the same level of leaf relative water content (47% RWC) were identified using gas chromatography–mass
spectroscopy. The metabolite profiling analysis detected 45 metabolites differentially accumulated in response to ipt expression or drought stress, which included amino acids, carbohydrates, organic acids, and organic alcohols. The enhanced
drought tolerance of SAG12-ipt plants was associated with the maintenance of accumulation of several metabolites, particularly amino acids (proline, γ-aminobutyric
acid, alanine, and glycine) carbohydrates (sucrose, fructose, maltose, and ribose), and organic acids that are mainly involved
in the citric acid cycle. The accumulation of these metabolites could contribute to improved drought tolerance due to their
roles in the stress response pathways such as stress signalling, osmotic adjustment, and respiration for energy production.
Plant growth and development is influenced by mutual interactions among plant hormones. The five classical plant hormones are auxins, cytokinins, gibberellins, abscisic acid and ethylene. They are small diffusible molecules that easily penetrate between cells. In addition, newer classes of plant hormones have been identified such as brassinosteroids, jasmonic acid, salicylic acid and various small proteins or peptides. These hormones also play important roles in the regulation of plant growth and development. This review begins with a brief summary of the current findings on plant hormones. Based on this knowledge, a conceptual model about interactions among plant hormones is built so as to link and develop an understanding of the diverse functions of different plant hormones as a whole in plants.
The results from toxicity test indicated that salicylic acid (SA) at 1 ∼ 20 mmol had no direct inhibition over the growth of Ralstonia solanacearum grown on modified Kelman agar plates. SA within range of 1 ∼ 5 mmol was capable of inducing systemic acquired resistance (SAR) against eucalypt bacterial wilt by root pouring, but the best induction of disease resistance could only be obtained with 5 mmol salicylic acid 7 days prior to inoculation of the pathogen. Correspondingly, the activities of peroxidase (POX) and polyphenol oxidase (PPO) increased when SA was more than 0.1 mmol, and reached the highest level at the concentration of 5 mmol. Within 3 ∼ 9 days between SA application and challenge inoculation on decapitated shoot tip with R. solanacearum, 5 mmol SA was able to induce systemic resistance against the pathogen, but the best inducing results could be gained within intervals of 5 ∼ 7 days. The activities of POX and PPO were positively correlated to the enhance disease resistance, by increasing to their maxima at the 7th day, with 2 times and 1 time higher, respectively, than those from the controlled plants. Concerning the sensitivity, POX was better than PPO to reflect the physiological change of eucalypt seedlings upon application of SA. Infiltration with SA into lower leaves could not induce SAR against bacterial wilt upon challenge inoculation on wounded shoot tips.
Common histidine-to-aspartate (His→Asp) phosphorelay is a paradigm of signal transduction in both prokaryotes and eukaryotes for the propagation of certain environmental stimuli, in which histidine (His)-kinases play central roles as sensors for environmental signals. For the higher plant, Arabidopsis thaliana, it was recently suggested that the His-kinase (AHK4 / CRE1 / WOL) is a sensor for cytokinins, which are a class of plant hormones important for the regulation of cell division and differentiation. Interestingly, AHK4 is capable of functioning as a cytokinin sensor in the eubacterium, Escherichia coli (Suzuki et al. 2001, Plant Cell Physiol. 42: 107). Here we further show that AHK4 is a primary receptor that directly binds a variety of natural and synthetic cytokinins (e.g. not only N⁶-substituted aminopurines such as isopentenyl-adenine, trans-zeatin, benzyl-adenine, but also diphenylurea derivatives such as thidiazuron), in a highly specific manner (Kd = 4.55±0.48×10–9 M). AHK4 has a presumed extracellular domain, within which a single amino acid substitution (Thr-301 to Ile) was shown to result in loss of its ability to bind cytokinins. This particular mutation corresponds to the previously reported wol allele (wooden leg) that causes a striking phenotype defective in vascular morphogenesis. Collectively, evidence is presented that AHK4 and its homologues (AHK3 and possibly AHK2) are receptor kinases that can transduce cytokinin signals across the plasma membrane of A. thaliana.
Drought is a limiting environmental stress that represents a growing constraint to the forestry sector. Eucalyptus globulus is a widely planted coppice species, which capacity to cope with water deficit has already been described. However, the capacity of this species to recover is still poorly understood. In this study, we aimed to investigate the changes in abscisic acid (ABA), ABA-glucose ester (ABA-GE) and jasmonic acid (JA) content in leaves, xylem sap and roots of two genotypes (AL-10 and AL-18) during rewatering (2 h, 4 h, 24 h, and 168 h), after a drought stress period (0 h). We wished to clarify the role of these hormones in the recovery from drought and to determine whether these hormonal relations were related to specific genotype metabolisms. Our results showed that drought caused an increased in ABA and ABA-GE levels in all analysed plant parts, while JA content decreased in leaves, increased in xylem sap and did not change in roots. Some of these responses were genotype specific. During rewatering, ABA and ABA-GE content decreased in both genotypes and all plant parts, but at different time scales, and JA levels did not greatly change. Again, the genotypes responded differently. Altogether, our results characterised the response pattern of clone AL-10 as more responsive and defended that leaf should be used in preliminary screening methods of stress tolerance. The hormonal dynamics were related to the previously documented responses of these genotypes and sustain further physiological and molecular studies of water stress in this and other tree species.
In Mediterranean areas, plants are concomitantly exposed to various abiotic stresses such as light intensity, water deficit, extremes in air temperature, air pollutants, etc. These environmental pressures adversely affect plant development. Changes in photosystem activity are an early response of plants to abiotic stresses. Therefore, chlorophyll (Chl) fluorescence and gas exchange, two non-invasive, rapid and inexpensive techniques for measuring photosynthesis in leaves, have been widely used by plant ecophysiologists to analyze plant responses to stressful conditions. Chl a fluorescence and gas exchange parameters can be indeed used to evaluate changes in photochemical and non-photochemical processes in photosystems associated with electron transport, CO2 fixation, and heat dissipation.In this review, we focus our analysis on the effects of different abiotic stresses on the photochemistry of Mediterranean plants using Chl a fluorescence and gas exchange measurements. Since changes in photosynthetic parameters are observed in the absence of visual injuries, these methodologies constitute fundamental tools to predict and evaluate the extent to which abiotic stresses damage photosynthesis.
Eucalyptus plantations are among the most productive forest stands in Portugal and Spain, being mostly used for pulp production and, more recently, as an energy crop. However, the region's Mediterranean climate, with characteristic severe summer drought, negatively affects eucalypt growth and increases mortality. Although the physiological response to water shortage is well characterized for this species, evidence about the plants' recovery ability remains scarce. In order to assess the physiological and biochemical response of E. globulus during the recovery phase, two genotypes (AL-18 and AL-10) were submitted to a three-week water stress period at two different intensities (18% and 25% of field capacity), followed by one week of rewatering. Recovery was assessed one day and one week after rehydration. Drought reduced height, biomass, water potential, NPQ and gas exchange in both genotypes. Contrarily, the levels of pigments, chlorophyll fluorescence parameters (Fv /Fm and ɸPSII ), MDA and ABA increased. During recovery, the physiological and biochemical profile of stressed plants showed a similar trend: they experienced reversion of altered traits (MDA, ABA, E, gs , pigments), while other parameters did not recover (ɸPSII , NPQ). Furthermore, an overcompensation of CO2 assimilation was achieved one week after rehydration, which was accompanied by greater growth and re-establishment of oxidative balance. Both genotypes were tolerant to the tested conditions, although clonal differences were found. AL-10 was more productive and showed a more rapid and dynamic response to rehydration (namely in carotenoid content, ɸPSII and NPQ) compared to clone AL-18.
There is currently much interest in phytochemicals as bioactive components of food. The roles of fruit, vegetables and red wine in disease prevention have been attributed, in part, to the antioxidant properties of their constituent polyphenols (vitamins E and C, and the carotenoids). Recent studies have shown that many dietary polyphenolic constituents derived from plants are more effective antioxidants in vitro than vitamins E or C, and thus might contribute significantly to the protective effects in vivo. It is now possible to establish the antioxidant activities of plant-derived flavonoids in the aqueous and lipophilic phases, and to assess the extent to which the total antioxidant potentials of wine and tea can be accounted for by the activities of individual polyphenols.
More than 2.5 million ha of Eucalyptus globulus are now planted across the globe including approximately 500 000 ha in southern Australia. In this region average annual rainfall has declined since 1960 and this trend is predicted to continue in the coming decades. E. globulus is a premium species for paper manufacture and grows well under moderate seasonal water stress. The traits that underpin this rapid early growth also make the species vulnerable to prolonged water stress. We established nitrogen rate and nitrogen-by-stocking experiments in five 2-year-old E. globulus plantations along a climatic gradient in south-western Australia. We measured volume growth, predawn leaf water potential and leaf area index over 7 years or until the plantations were 9 years old. These data were used to explore the relationship between growth and water stress, to understand the mechanistic basis for the relationship and to identify best-bet management strategies for E. globulus plantations in southern Australia.
Senescence of plant tissues is a natural process that may be accelerated by unfavourable environmental factors, including disbalanced mineral nutrition. During plant senescence, the concentration of reactive oxygen species (ROS) increases in the cells, whereas the concentration of cytokinins declines. Negative correlation between ROS, such as hydroxyl radical ((OH)-O-center dot), and concentration of cytokinins triggers the question whether the addition of cytokinins can reduce ROS production and/or its concentration. This would also reduce the level of lipid peroxidation (LP) in the senescing tissue, which is the final phase in the destruction of cell membranes by ROS. With the aim to address these questions, the effects of cytokinins (trans-zeatin, TZ, and benzyladenine, BA) on the concentration of (OH)-O-center dot and LP were studied in wheat subjected to nitrogen deficiency. Foliar application of TZ reduced the concentration of (OH)-O-center dot and the intensity of LP in the leaves of young wheat plants insufficiently supplied with nitrogen.
Inhibition of root elongation and modification of membrane properties are sensitive responses of plants to aluminium. The present paper reports on the effect of AI on lipid peroxidation and activities of enzymes related to production of activated oxygen species. Soybean seedlings (Glycine max L. cv. Sito) were precultured in solution culture for 3–5 days and then treated for 1–72 h with Al (AICI3) concentrations ranging from 10 to 75 μM at a constant pH of 4.1. In response to Al supply, lipid peroxidation in the root tips (< 2 cm) was enhanced only after longer durations of treatment. Aluminium-dependent increase in lipid peroxidation was intensified by Fe2+ (FeSO4). A close relationship existed between lipid peroxidation and inhibition of root-elongation rate induced by Al and/or Fe toxicity and/or Ca deficiency. Besides enhancement of lipid peroxidation in the crude extracts of root tips due to Al, the activities of superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) increased, whereas catalase (EC 1.11.1.6) activity decreased. This indicates a greater generation of oxygen free radicals and related tissue damage. The results suggest that lipid peroxidation is part of the overall expression of Al toxicity in roots and that enhanced lipid peroxidation by oxygen free radicals is a consequence of primary effects of Al on membrane structure.
Susceptibility of alfalfa (Medicago saliva L. cv. Aragón) nodules and leaves to water stress has been investigated. Nodule acetylene reduction activity (ARA), leaf CO2 exchange rate (CER) as well as soluble protein, proline and total soluble sugar (TSS) contents were determined during drought. Water status was estimated as water potential (Ψw) and Relative water content (RWC) of the respective tissues. Maximum rates of ARA required higher Ψw than CER. Nodules had lower RWC for a given Ψw than leaves. Water stress reduced soluble protein content in both tissues; however, the decline in soluble protein content was detected at greater Ψw in nodules than in leaves. Proline and TSS increased in leaves and nodules, and again the threshold Ψw triggering such accumulation was higher in nodule tissues. Oior results suggest that alfalfa nodules are more susceptible to water shortage than leaves. Effects of accumulated TSS and proline upon leaf and nodule physiology are discussed in relation to protein stability (proline), pH control (proline) and osmotic adjustment (proiine and TSS). The TSS accumulation induced by water stress suggests that substrate shortage would not be the primary effect of drought on nodule activity.
A new report, "The Global Eucalyptus Wood Products Industry", describes how this fast-growing hardwood is impacting international markets through substituting for more valuable hardwoods, especially tropical hardwood species. The following article highlights some of the findings of this report, looking at changes in forest management, manufacturing, and marketing of Eucalyptus for "higher-value utilization." Forest management The Eucalyptus genus, which includes more than 500 species, is by far the most commonly planted fast-growing hardwood in the world. Only a relatively few species have been planted outside of Australia, but today the total area of Eucalyptus plantations is estimated at between 16 and 19 million hectares (40-47 million acres). While the overwhelming majority of this resource has been managed to produce either pulpwood or fuelwood, a number of companies, including some large multi-national companies, are changing their focus. Rather than targeting pulpwood as the objective, these companies are extending rotations, and pursuing aggressive management regimes including early thinnings and prunings, to produce higher value sawlogs with a maximum amount of clear wood. In this paradigm, the pulpwood produced – in the form of thinnings or conversion residues—is a by-product. Most of the Eucalyptus roundwood produced in the world from plantations today is in South America. Despite wide-spread planting in parts of Asia and Australia, South America is still expected to produce 55% of the world's Eucalyptus roundwood in 2010. Sawlogs make up only a small share of the Eucalyptus harvest today, approximately 6 million m 3 of sawlogs in total. Of this, just over half are logs from native Eucalyptus forests in Australia, while the balance are from plantations worldwide. Brazil produces just over a third of all the plantation-grown Eucalyptus sawlogs in the world. By 2015, the volume of sawlogs from native forests in Australia will be substantially smaller, but the total sawlog harvest will be nearly double the current amount. Of the total production in 2015, an estimated 1.4 million m 3 are expected to be pruned sawlogs.
The relationship between the bulk abscisic acid (ABA) content, ABA compartmental redistribution, and chloroplast ultrastructural changes was studied in leaves of lavender (Lavandula stoechas L.) plants subjected to water stress. ABA was uniformly distributed in the cytosol, nucleus, chloroplasts, and cell walls of mesophyll cells in well-watered plants. In plants subjected to water stress (−2.6 MPa water potential) the bulk leaf ABA increased from 900 to 3 600 pmol g−1 fresh weight. At the ultrastructural level, the first indication of this rise in ABA was a 4-fold increase in ABA immunolabeling in the cell wall in which the highest labeling values were recorded. This increase in apoplastic ABA in lavender was not attributable to ABA release from the chloroplast, because a simultaneous increase in ABA labeling was observed in both the chloroplast and nucleus (2- and 3-fold, respectively). Water stress induced a progressive increase in bulk leaf ABA concentration to 13 600 pmol g−1 fresh weight coincident, with the highest immunolabeling of ABA in the nucleus and chloroplast. Under severe water stress, the chloroplast membrane broke down, resulting in leakage of ABA from the chloroplast. The stress-induced increase of ABA in chloroplasts and nuclei may serve a function other than affecting stomatal movement.
The choice to become dormant versus continuing to grow is observed in a variety of organisms in response to specific developmental
and environmental signals. In higher plants this is most obvious during both the establishment and breaking of seed dormancy.
With the advent of molecular genetic analysis, particularly in Arabidopsis, genes involved in the establishment and breaking of seed dormancy have been identified. Genetic analysis suggests a web
of hormone-derived information is required in the regulation of these processes. In this review we focus on examples of where
hormones, and in particular cross-talk between hormones, is used to regulate both the establishment and release of seed dormancy.
The use of multiple hormones that overlap in their control of specific developmental programs allows seeds to be flexible
in making decisions in response to specific developmental and environmental cues.
KeywordsHormone mutants–
Arabidopsis
–Gibberellins–Abscisic acid–Ethylene–Brassinosteroid–Seed development–Signal transduction–Hormone interaction
Effects of progressive soil drought on leaf growth, the rate of photosynthesis, and phytohormone contents were followed in the experiments with cucumber (Cucumis sativus L.) plants. Suppression of photosynthesis by drought did not immediately cause growth retardation, because the latter was observed one day earlier than the inhibition of photosynthesis. In the meantime, growth retardation could be caused by a decline in IAA and cytokinin contents, rather than ABA accumulation, because ABA accumulated when the growth has been already suppressed.
The interplay between jasmonic acid (JA) and abscisic acid (ABA) in plant responses to water stress and in water-stress-enhanced oxidative stress was investigated in Arabidopsis thaliana plants subjected to water stress by water deprivation. For this purpose a drought assay was conducted using Arabidopsis mutants impaired in ABA (aba2), JA (aos), and ascorbate (vtc1) biosynthesis. Our results show an interaction between ABA and JA during their biosynthesis. Moreover, the coordinated action of ABA and JA protected wild-type, aba2, and aos plants from the effects of stress. However, this effect was not observed in the vtc1 mutant, which showed a distinct decrease in the F
v/F
m ratio, concomitant with a marked fall in relative water content (RWC), despite high endogenous concentrations of JA and ABA. This finding indicates the relevance of ascorbate metabolism in plant acclimation to stress. Despite the interaction between the two phytohormones, drought-associated stomatal closure is regulated mainly by ABA and weakly by JA, whereas JA plays a role in the formation of antioxidants regulating ascorbate and glutathione metabolism. A time course analysis revealed the relevance of plant age and stress duration in the responses of the mutants compared to wild-type plants. Here we discuss the relationship between ABA, JA, ascorbate, and glutathione in plants under water stress.
The treatment of wheat plants with 0.05 mM salicylic acid (SA) increased the level of cell division within the apical meristem of seedling roots causing an increase in plant growth and an elevated wheat productivity. It was found that SA treatment caused accumulation of both abscisic acid (ABA) and indoleacetic acid (IAA) in the wheat seedlings but did not influence cytokinin content. SA treatment reduced the damaging action of salinity on seedling growth and accelerated reparation of the growth processes. SA-treatment diminished changes in phytohormones levels in wheat seedlings under salinity. It prevented any decrease in IAA and cytokinin contents and thus reduced stress-induced inhibition of plant growth. A high ABA level was also maintained in SA-treated wheat seedlings providing the development of antistress reactions, for example, maintenance of proline accumulation. Thus SA's protective action includes the development of antistress programs and acceleration of growth processes recovery after the removal of stress factors.
It is well known that abscisic acid (ABA) antagonizes gibberellin (GA)-promoted seed germination. Recent circumstantial evidence suggests that salicylic acid (SA) also inhibits seed germination in maize and Arabidopsis. Our study shows that SA blocks barley seed germination in a dosage dependent manner. As an initial effort to addressing the mechanism controlling the crosstalk of SA, GA and ABA signaling in barley, we studied the regulation of alpha-amylases by SA and a WRKY gene whose expression is modulated by these hormones. Assays of alpha-amylase activity reveal that GA-induced alpha-amylase production in aleurone cells is inhibited by bioactive SA, but not its analogs, 3-hydroxybenzoic acid and 4-hydroxybenzoic acid. This inhibitory effect is unlikely due to repressing alpha-amylase secretion or inhibiting alpha-amylase enzyme activities. Northern blot analyses indicate that SA suppresses GA-induced expression of a barley low pI alpha-amylase gene (Amy32b). Because our previous data indicate that ABA-inducible and GA-suppressible WRKY genes inhibit the expression of alpha-amylase genes in rice, we studied the steady state mRNA levels of a barley WRKY gene, HvWRKY38. The expression of HvWRKY38 in barley aleurone cells is down-regulated by GA, but up-regulated by SA and ABA. However, the regulation of HvWRKY38 by SA appears to be different from that of ABA in term of the kinetics and levels of induction. Over-expression of HvWRKY38 in aleurone cells by particle bombardment blocks GA induction of the Amy32b promoter reporter construct (Amy32b-GUS). Therefore, HvWRKY38 might serve as a converging node of SA and ABA signal pathways involved in suppressing GA-induced seed germination.
In recent years salicylic acid (SA) has been the focus of intensive research due to its function as an endogenous signal mediating
local and systemic plant defence responses against pathogens. It has also been found that SA plays a role during the plant
response to abiotic stresses such as drought, chilling, heavy metal toxicity, heat, and osmotic stress. In this sense, SA
appears to be, just like in mammals, an ‘effective therapeutic agent’ for plants. Besides this function during biotic and
abiotic stress, SA plays a crucial role in the regulation of physiological and biochemical processes during the entire lifespan
of the plant. The discovery of its targets and the understanding of its molecular modes of action in physiological processes
could help in the dissection of the complex SA signalling network, confirming its important role in both plant health and
disease. Here, the evidence that supports the role of SA during plant growth and development is reviewed by comparing experiments
performed by exogenous application of SA with analysis of genotypes affected by SA levels and/or perception.
Photosynthesis is one of the key processes to be affected by water deficits, via decreased CO2 diffusion to the chloroplast and metabolic constraints. The relative impact of those limitations varies with the intensity of the stress, the occurrence (or not) of superimposed stresses, and the species we are dealing with. Total plant carbon uptake is further reduced due to the concomitant or even earlier inhibition of growth. Leaf carbohydrate status, altered directly by water deficits or indirectly (via decreased growth), acts as a metabolic signal although its role is not totally clear. Other relevant signals acting under water deficits comprise: abscisic acid (ABA), with an impact on stomatal aperture and the regulation at the transcription level of a large number of genes related to plant stress response; other hormones that act either concurrently (brassinosteroids, jasmonates, and salycilic acid) or antagonistically (auxin, cytokinin, or ethylene) with ABA; and redox control of the energy balance of photosynthetic cells deprived of CO2 by stomatal closure. In an attempt to systematize current knowledge on the complex network of interactions and regulation of photosynthesis in plants subjected to water deficits, a meta-analysis has been performed covering >450 papers published in the last 15 years. This analysis shows the interplay of sugars, reactive oxygen species (ROS), and hormones with photosynthetic responses to drought, involving many metabolic events. However, more significantly it highlights (i) how fragmented and often non-comparable the results are and (ii) how hard it is to relate molecular events to plant physiological status, namely photosynthetic activity, and to stress intensity. Indeed, the same data set usually does not integrate these different levels of analysis. Considering these limitations, it was hard to find a general trend, particularly concerning molecular responses to drought, with the exception of the genes ABI1 and ABI3. These genes, irrespective of the stress type (acute versus chronic) and intensity, show a similar response to water shortage in the two plant systems analysed (Arabidopsis and barley). Both are associated with ABA-mediated metabolic responses to stress and the regulation of stomatal aperture. Under drought, ABI1 transcription is up-regulated while ABI3 is usually down-regulated. Recently ABI3 has been hypothesized to be essential for successful drought recovery.