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Vermicompost humic acids modulate the accumulation and metabolism of ROS in rice plants
Abstract
This work aims to determine the reactive oxygen species (ROS) accumulation, gene expression, anti-oxidant enzyme activity, and derived effects on membrane lipid peroxidation and certain stress markers (proline and malondialdehyde-MDA) in the roots of unstressed and PEG-stressed rice plants associated with vermicompost humic acid (VCHA) application. The results show that the application of VCHA to the roots of unstressed rice plants caused a slight but significant increase in root ROS accumulation and the gene expression and activity of the major anti-oxidant enzymes (superoxide dismutase and peroxidase). This action did not have negative effects on root development, and an increase in both root growth and root proliferation occurred. However, the root proline and MDA concentrations and the root permeability results indicate the development of a type of mild stress associated with VCHA application. When VCHA was applied to PEG-stressed plants, a clear alleviation of the inhibition in root development linked to PEG-mediated osmotic stress was observed. This was associated with a reduction in root ROS production and anti-oxidant enzymatic activity caused by osmotic stress. This alleviation of stress caused by VCHA was also
reflected as a reduction in the PEG-mediated concentration of MDA in the root as well as root permeability. In summary, the beneficial action of VCHA on the root development of unstressed or PEG-stressed rice plants clearly involves the modulation of ROS accumulation in roots.
... 10:123 Humic substances (HS) are dominant components of soil organic matter and one of the most efficient antioxidants found in nature. Typically HS bear functional groups that contain oxygen (O), primarily in carboxyl (C(= O)OH) and carbonyl (− C = O), attached to an R group, and hydroxyl (-OH) groups in alcohols and phenols, related to their reducing capacities or electrondonating capacities [10], probably resulting in the HS ability to regulate ROS accumulation and metabolism [11][12][13][14]. ...
... The effect of HS in mitigating different plant stresses is well known and generally described as a result of enzymatic and nonenzymatic antioxidant defence rise and increase in compatible solutes production [15]. The potential role of humic acids (HA) in preventing oxidative stress in plants was previously described, including enhancement of peroxidase activity, reduction of H 2 O 2 concentration and increase of cell proline levels, leading to decreased ROS contents and thereby restoring the cytosolic redox homeostasis [13,14]. Antioxidant activities of superoxide dismutase (SOD), peroxidases (POX) and catalase (CAT), which are omnipresent in all aerobic organisms, were promoted by HS, diminishing the injurious effects of ROS [16][17][18]. ...
... We presented evidence that HS enriched (or not) with plant growth-promoting bacteria can be used as a prime agent to induce citrus defence. HS can attenuate oxidative stress due to their antioxidant properties, hormonal regulation and enzymatic and not enzymatic antioxidant response elicitor [14]. Antioxidative systems, both enzymatic and nonenzymatic, play an essential role in balancing and preventing oxidative damage [26]. ...
Background
Huanglongbing (HLB) is a devastating citrus disease. Before callose deposition, the bacterial infection causes oxidative stress, starting cell damage. Humic substances are among the most efficient antioxidants found in nature. Furthermore, it is also previously reported that humic substances can induce a phenylpropanoid metabolism contributing to the production of antimicrobial compounds. It has been noted by technicians and growers in the Brazil's main citrus belt that orchards continuously treated with humic substances can live well with the symptoms of HLB.
Methods
We treated two young citrus orchards (Citrus sinensis cultivars Baía and Pera) with soluble humic substances (HS) isolated from peat either combined or not with a plant growth-promoting bacteria consortium. The activity of key enzymes related to the response against biotic stresses, such as peroxidase (POX), β-1,3-glucanase (PR) and phenylalanine ammonia-lyase (PAL), as well as the differential transcription level of target genes linked to plant stress response by qRT-PCR was monitored for six months.
Results
No differences were obtained between sole humic substances and their application combined with plant growth-promoting bacteria, indicating that the microbial consortium had no modulatory effect on HS-treated plants. The treatments promoted the activities of POX, PAL and β-1,3-glucanase, which remained significantly higher concerning the control throughout the evaluation period. In addition, treatments positively regulated the transcription levels of CsPR-7, CsPR-3 and CsPR-11 genes. The experimental data were qualitatively similar to those found in commercial orange orchards treated continuously for 12 and 6 years with humic substances, where the activity and transcription levels were also more significant than for untreated plants.
Conclusion
Our results indicate that humic substances can trigger immune-mediated responses in plants and they can be used as a natural chemical priming agent to mitigate disease symptoms and contribute to more resilient citrus cultivation.
Graphical Abstract
... Moreover, the best performance of humic substances was observed under stress conditions [10]. It was previously reported that HS significantly improves plant resistance to abiotic stresses [11][12][13][14][15]. This HS ability can be attributed to the interaction of multiple effects among which biosynthesis and concentration of secondary metabolites directly involved in stress alleviation, like phenols [16], expression of genes involved in plant responses to abiotic stress [17][18][19], including protective enzymes include catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and polyphenol oxidase (PPO) [15,20], and regulation of reactive oxygen species accumulation and metabolism [11][12][13][14]. ...
... It was previously reported that HS significantly improves plant resistance to abiotic stresses [11][12][13][14][15]. This HS ability can be attributed to the interaction of multiple effects among which biosynthesis and concentration of secondary metabolites directly involved in stress alleviation, like phenols [16], expression of genes involved in plant responses to abiotic stress [17][18][19], including protective enzymes include catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), and polyphenol oxidase (PPO) [15,20], and regulation of reactive oxygen species accumulation and metabolism [11][12][13][14]. Furthermore, it is well known that HS promotes several interconnected, hormone-mediated signalling pathways related to plant growth and defence [21]. ...
... The second plant hormone with a transcriptional level modified by HA was ethylene (50 genes), of which 28 was down-and 22 up-regulated. ABA [39] was another plant hormone with more genes [25] down-regulated than up-regulated [14] by HA treatment in respect to control. There were 22 genes involved in gibberellin synthesis, signalling and metabolism with high transcript levels, compared to the control, with 13 down-and 9 up-regulated. ...
Background
The reliance on chemical inputs to support high yields is the Achilles’ heel of modern crop production. The soil organic matter management is as old as agriculture itself. Recently, the use of soluble humic substances as plant growth promoters has been brought to attention due to their effects on nutrient uptake and water use efficiency. Humic substances applied directly at low concentrations can trigger different molecular, biochemical, and physiological processes in plants. However, how humic substances exert this plethoric regulatory action remains unclear. The objective of this study was to evaluate changes in the transcription level of genes coding cell receptors, phosphatases, synthesis, and function of different plant hormones and transcription factors.
Materials and methods
After seven days of humic acid treatment, we used RNAseq in maize root seedlings. The level of gene transcription was compared with control plants.
Results
Plant kinase receptors and different phosphatases were regulated by humic acids. Likewise, genes related to plant hormones (auxin, gibberellin, ethylene, cytokinin, abscisic acid, brassinosteroids, jasmonic and salicylic acids) were transcript in differential levels in maize root seedlings as well as the expression of a hundred of transcription factors modifying the signal transduction pathway via alterations of the subsequent gene response.
Conclusion
We showed a general mechanism for simultaneously regulating the activity of several hormones where humic acids act as a key regulatory hub in plant responses integrating hormonal signalling and response pathways.
... HPs are excellent organic soil amendments known to enhance plant growth and crop yield in several different plant species, including maize (Zea mays), wheat (T. aestivum), rice (Oryza sativa), millet (Setaria italica), soybean (Glycine max), and canola (Brassica napus) (Arslan et al., 2021;Canellas et al., 2019;García, Santos, et al., 2016b;Jannin et al., 2012;Malik et al., 2023;Nunes et al., 2019;Shen, Guo, Wang, Yuan, Dong, et al., 2020;Shen, Guo, Wang, Yuan, Wen, et al., 2020). HPs can improve plant growth through direct and indirect effects. ...
... compounds have gained considerable attention in recent years due to their bio-stimulatory effects in improving plant growth and crop yield. Several researchers have observed and documented the plant growth-promoting effect of HPs in different plant species using HPs from a variety of sourcesCanellas & Olivares, 2014;García, Santos, et al., 2016b; García-Mina et al., 2004;Jannin et al., 2012;Nardi et al., 2018Nardi et al., , 2021Nunes et al., 2019;Scaglia et al., 2016; Shen, Guo, Wang, Yuan, Wen, et al., 2020;Zanin et al., 2018). ...
Background
The application of synthetic chemical inputs in current agricultural practices has significantly increased crop production, but their use has caused severe negative consequences on the environment. Humalite is an organic soil amendment that is rich in humic acid and found in large deposits in southern Alberta, Canada. Humic products can enhance nutrient uptake and assimilation in plants by reducing nutrient losses and enhancing bioavailability in the soil.
Aim
Here, we evaluated the effects of different humalite rates in the presence of nitrogen, phosphorus, potassium (NPK) at recommended rates on soil nitrogen availability, wheat growth, grain yield, seed nutritional quality, and nitrogen use efficiency (NUE) under controlled environmental conditions.
Methods
A series of studies were conducted by applying five different rates of humalite (0, 200, 400, 800, and 1600 kg ha ⁻¹ ) with NPK at recommended rates. Soil nitrogen availability and shoot and root growth parameters were recorded at flowering stage. NUE was calculated based on the grain yield at maturity stage.
Results
Plants grown in the presence of humalite augmented root morphological parameters (root length, volume, and surface area), plant biomass (shoot and root), and nutrient uptake (N, P, K, and S) compared to the plants supplied with recommended fertilizer alone. Furthermore, humalite application significantly increased grain yield (14%–19%), seed protein content (23%–30%), and NUE (14%–60%) compared to the fertilizer application alone.
Conclusion
These findings suggest that humalite can be used as an organic soil amendment to reduce synthetic fertilizer application and improve plant growth and yield while enhancing fertilizer use efficiency.
... nteractions promote pore clogging and modify their functioning, creating a perception of mild stress called "eustress" in plants. Under this physiological condition, plants regulate the levels of reactive oxygen species (ROS) through the synthesis of redox enzymes. This mechanism of action promotes root growth in plants and protects against stress (García et al,. 2016;Castro et al., 2021aCastro et al., , 2022. Studies conducted by de showed that the beneficial effects of HSs when applied to both foliar and root tissues were due to adaptation to mild stress that is regulated mainly by the action of jasmonic acid. ...
... The action of HSs in plants is directly related to the HS structure (Fig. 3). Studies performed with 37 fractions of humified organic matter showed that when applied to rice plants via the roots, the C-aliphatic, substituted C-aromatic, and C-carboxylic structures in HSs are responsible for root growth, while in HAs, the C-aliphatic, unsubstituted C-aromatic, and Ccarboxyl structures account for the bioactivity in plants (García et al., 2016). As previously noted, HSs are able to stimulate plant growth through eustress, a type of mild, beneficial stress that promotes biomass increase, improves plant nutrition, and protects against abiotic stress. . ...
... The effect of HS on the induction of catalase activity (CAT) was shown by Cordeiro et al. [118]. Plants treated with HA showed increased activity of SOD, CAT, and APX [119][120][121]. ...
... De Hita et al. [131] reported the increase of SA and JA in cucumber plants, 24 and 72 h after HA foliar application, respectively, indicating a possible effect on the activation of SA and JA signaling pathways as plant defense response. Based on the evidence found in literature, humified organic matter may be involved with RAS [17,88,119,120,131], but further studies are needed to prove it. ...
Background
Pesticides have become a central public health problem and a source of environmental contamination. The use of organic matter is an important strategy to reduce synthetic agrochemicals, improve soil conditions, and increase nutrient uptake by plants. Organic matter can also induce plant resistance against biotic stress in some circumstances. However, the results reported for different types of organic matter applications are often very different form each other, thus making difficult their interpretation and hindering and discouraging their use as valuable alternative. Identifying the main factors involved in the efficacy of these sustainable methodologies and the associated research gaps is important to increase the efficiency of organic matter and reduce the use of pesticides.
Materials and methods
We performed a comprehensive meta-analysis of the current recent scientific literature on the use of organic matter as control method for pest and disease, using data reduction techniques, such as principal component analysis. We found 695 articles listing the keywords in the databases between 2010 and 2021 and selected 42 that met inclusion criteria.
Results
In general, all organic matter reported showed a high inhibition of pests and diseases. Control effectiveness was close to 75% for fungal diseases and 67% for the pest control. The source of organic matter most frequently reported was the vermicompost. However, humic substances showed the greatest effectiveness of 74% when compared to both fungal and bacterial disease control. The concentration of humic substances ranged from 1 to 500 mg L ⁻¹ , with the highest concentrations used in case of soil application.
Conclusions
The study demonstrated the potential role of organic matter as a resistance elicitor in plants, thus allowing a partial/total reduction of pesticides in crops. Despite the efficiency reported in the works, the mechanisms of induction of pest and disease control remains poorly studied.
Graphical Abstract
... As an example, HA have been shown to reduce negative effects of low water availability in different plant species. The application of HA in plants subjected to these conditions influences the oxidative defense system, plant growth, root development, the concentrations of photosynthetic pigments and the concentrations of proline (García et al. , 2014(García et al. , 2016bAguiar et al. 2016;Castro et al. 2021). ...
... The application of HAVC under water deficit conditions (HAVC + PEG-6000) resulted in plants with a significantly greater amount, length, area, volume and diameter than those observed in plants under water deficit (PEG-6000); thus, the contribution of vermicompost humic acid to the development of the root system of plants under adverse water conditions is evident. García et al. (2016b) suggested that the effect mediated by the application of HAVC in the roots, by the slight increase in the production of ROS in the roots, may result from a type of mild stress caused by the interaction of HAVC with the root cells, suggesting that ROS play an important role in the mechanism by which HA affects the development of the plant root system. ...
Agriculture is responsible for consuming the largest amount of water in the world. Water availability is the environmental factor that most limits the sustainability of agricultural systems. The adoption of sustainable technologies that improve plant water use efficiency has become increasingly important in modern agriculture. Humic acids (HA) acts as a rhizospheric bioeffector, stimulating the biochemical and physiological activities of plants. The objective of this study was to evaluate the potential of humic acids from vermicompost (HAVC), previously characterized by ATR-FTIR and 1 H-NMR, in stimulating the emission kinetics of the transient fluorescence of chlorophyll a, the concentrations of photosynthetic pigments and soluble metabolites, development of the root system and accumulation of fresh and dry biomass in rice (Oryza sativa L.) under normal growth conditions and water deficit. The experimental design was completely randomized, with four treatments (Control; HAVC; PEG-6000; HAVC + PEG-6000). The application of HAVC in plants under water deficit was efficient in maintaining photosynthesis, with an effect as an eustressor. HAVC triggered the increase of plant biomass and root development of plants under water deficit. HAVC acted on osmotic regulation and the influx and remobilization of different forms of nitrogen, enhancing protection against stress. HAVC in the rhizosphere induced plants with higher root biomass, partially due to better photosynthetic performance.
... The increase WEC concentrations stimulated maize RDM, since a correlation was observed between C of nutrient solution and RDM (Table S1). The WEC chemical structure recorded by the ATR-FTIR spectrum showed aliphatic C and aromatic C groups, as well as other stretching and bending vibrations (Fig. S1) that can be associated with root growth, as related by García et al. (2016). Linking humic compounds chemical structure with their biostimulant action is not an easy task (Carletti et al. 2021;Conselvan et al. 2017). ...
... Linking humic compounds chemical structure with their biostimulant action is not an easy task (Carletti et al. 2021;Conselvan et al. 2017). However, the functional HA groups -OH, -CH, C = O, C = C, aromatic-CH, and C-O evidenced in the FTIR spectrum of WEC have been found to correlate with root growth parameters in rice (García et al. 2016), confirming their possible role in the plant responses to WEC treatment. ...
Water extract of compost (WEC) can be used to develop eco-friendly fertilizers and presents plant biostimulant effects. The aim of this study was to evaluate WEC bioactivity effects on maize growth and root organic acid exudation. Maize plants were cultivated 24 days in nutrient solution with WEC addition at the concentrations of 0, 2, 5, 15, 40, and 75 mg L−1 of C. The SPAD index, shoot dry matter (SDM), root dry matter (RDM), and nutrient accumulation in maize shoot were measured, and organic acid root exudate was determined. WEC application increased maize growth in 30%, compared to control plants. Furthermore, SPAD index, N, K, S, and Mn shoot accumulation; K and Mn uptake efficiency; and S, Fe, and Mn translocation efficiency increased over WEC concentrations. Root organic acid exudation of isocitric, oxalic, and tartaric increase about 100%, citric and malic about 200%, and succinic was more than four times higher, in relation to maize plants not treated with WEC. WEC augmented maize growth and stimulated root organic acid exudation. The optimum WEC concentration was about 40 mg L−1 of C in nutrient solution.
... What most likely gives the ability of HSs to alleviate abiotic stresses is the interaction with plant roots. While in optimal conditions HSs induce the production of ROS in plants to the point of which excessive doses may actually be detrimental to plant growth [49], it seems that under high stress conditions, they balance excessive ROS response by modulating antioxidant enzymes such as SOD, APX, and POD and determine increases in osmolites such as proline [103][104][105]. As Garcia and collaborators [99] summarized, the effect of HSs on plant development due to their structure may depend on the induction of signaling networks composed of phytohormones and messengers such as ROS and Ca 2+ . ...
... Cucumber (Cucumis sativus L.), the model cucurbit and a Si accumulating species [106], has shown to be responsive to silicon treatments. An addition to the nutrient solution of either sodium silicate (Na 2 SiO 3 ), sodium silicate-derived metasilicic acid (H 2 SiO 3 ), or engineered nanosilica at the rate of 0.3 [43,107], 0.8 mM [104], and 200 ppm [108], respectively, have proven to significantly increase the germination rates, fresh and dry weights, decrease the sodium content in roots or leaves, and increase the root hydraulic conductivity of salinized cucumber plants. Moreover, a better physiological status, as in higher photosynthetic rate and F v /F m , was recorded than the untreated salt-stressed controls, and comparable results were also obtained when combined heat and salinity stresses were applied [109][110][111]. ...
Climate change is a pressing matter of anthropogenic nature to which agriculture contributes by abusing production inputs such as inorganic fertilizers and fertigation water, thus degrading land and water sources. Moreover, as the increase in the demand of food in 2050 is estimated to be 25 to 70% more than what is currently produced today, a sustainable intensification of agriculture is needed. Biostimulant substances are products that the EU states work by promoting growth, resistance to plant abiotic stress, and increasing produce quality, and may be a valid strategy to enhance sustainable agricultural practice. Presented in this review is a comprehensive look at the
scientific literature regarding the widely used and EU-sanctioned biostimulant substances categories of silicon, seaweed extracts, protein hydrolysates, and humic substances. Starting from their origin, the modulation of plants’ hormonal networks, physiology, and stress defense systems, their in vivo effects are discussed on some of the most prominent vegetable species of the popular plant groupings of cucurbits, leafy greens, and nightshades. The review concludes by identifying several research areas relevant to biostimulant substances to exploit and enhance the biostimulant action of these
substances and signaling molecules in horticulture.
... Rather, they stimulate the capacity of plants to better acquire nutrients and use them for primary and secondary metabolism, and biomass production. They also aid plants to overcome stress conditions by eliciting the upregulation of enzymatic and non-enzymatic antioxidant systems [8][9][10][11]. ...
... A study testing 37 humic fractions-characterized by isotopic composition, structural characteristics, and chemical properties responsible for stimulation of root traits-showed that the fractions shared some structural similarity although differing in their stimulation activity on plant roots [8]. In this context, the lability (N, O aliphatic chains, and carboxyl group) and recalcitrance (unsubstituted aromatic and aliphatic structures) of HS were associated with the nature and strength of their biological activity on the root. ...
Humic substances (HS) are dominant components of soil organic matter and are recognized as natural, effective growth promoters to be used in sustainable agriculture. In recent years, many efforts have been made to get insights on the relationship between HS chemical structure and their biological activity in plants using combinatory approaches. Relevant results highlight the existence of key functional groups in HS that might trigger positive local and systemic physiological responses via a complex network of hormone-like signaling pathways. The biological activity of HS finely relies on their dosage, origin, molecular size, degree of hydrophobicity and aromaticity, and spatial distribution of hydrophilic and hydrophobic domains. The molecular size of HS also impacts their mode of action in plants, as low molecular size HS can enter the root cells and directly elicit intracellular signals, while high molecular size HS bind to external cell receptors to induce molecular responses. Main targets of HS in plants are nutrient transporters, plasma membrane H+-ATPases, hormone routes, genes/enzymes involved in nitrogen assimilation, cell division, and development. This review aims to give a detailed survey of the mechanisms associated to the growth regulatory functions of HS in view of their use in sustainable technologies.
... K is a crucial element that could increase plant dry matter and enhance productivity [10]. Humic substances generally impact the bioavailability of nutrients through their ability to form compounds with metallic ions, which promote micronutrient availability and macronutrients, especially when these nutrients in the soil are rare [11]. ...
... This is related to the existence of hydrophilic and hydrophobic sites that promote surface activity. Hence, the humic substances react with the cell membrane structures and interact as a carrier of nutrients [11]. These outcomes are in accordance with the authors in [38], who indicated that humic substances may improve nutrient uptake. ...
Several agronomic factors, including planting density, affect plant growth and final yield. New soil suffers from severe fertility shortage and crop productivity. Potassium humate (KH) application improves soil fertility and plant performance under new soil conditions. Therefore, this investigation was performed in two seasons of 2018/2019 and 2019/2020 to study the impact of KH application at the rate of 50 kg hectare−1 (ha−1) on growth, yield, physio-biochemical attributes, plant water status and nutrients in faba bean plants grown in newly reclaimed soil under three planting densities, i.e., D1 = 222.222 plants ha−1 (15 × 60 cm), D2 = 166.666 plants ha−1 (20 × 60 cm) and D3 = 133.333 plants ha−1 (25 × 60 cm). The results showed that KH application enhanced tissue water status by increasing the membrane stability index (MSI%) and relative water content (RWC%), while electric leakage (EL%) was reduced, alongside increased growth attributes physio-biochemical properties and nutrients. These results were positively reflected by the improved yield and its components (i.e., number of pods plant−1, 100-seed weight, seed yield plant−1 and seed yield ha−1) in favor of the medium planting density (166.666 plants ha−1). The results of the current study showed that the application of KH with the medium planting density (20 × 60 cm) was the best treatment combination to enhance the performance and productivity (2.97 ton ha−1) of faba bean plants grown under newly reclaimed soil conditions.
... Thus, HS may enhance root growth and water uptake, nutrient bioavailability and absorption, photosynthesis performance, compatible solutes accumulation, and enzymatic and non-enzymatic antioxidant activity (Ramadan et al. 2023a;Lasheen et al. 2024). All of this translates into ROS scavenging, photosynthetic activity maintenance, preventing cytoplasmic ionic imbalances, and ensuring adequate cellular water status (García et al. 2016;Khaleda et al. 2017;Man-hong et al. 2020;Souza et al. 2021;Abu-Ria et al. 2023;Ramadan et al. 2023b). In this way, several researchers and companies extract HS from various sources such as leonardite, coal, and peat to develop HS-based products and improve plant growth and abiotic stress tolerance in different crops such as lettuce (Lactuca sativa L.). ...
Salinity stress constitutes one of the main abiotic stresses that considerably reduces crop yield. An approach to enhance plant growth under salt stress involves the addition of humic substances (HS) to roots or leaves. Here, we evaluated the potential use of BLACKJAK®, an HS-based product, to enhance salt tolerance in lettuce (Lactuca sativa L.). For this aim, plants were exposed to salinity (100 mM NaCl), salinity + HS: radicular (R)-HS (0.40 mL/L and 0.60 mL/L) and foliar (F)-HS (7.50 mL/L and 10.00 mL/L), along with a control (without NaCl). Parameters related to plant growth, Na⁺ and K⁺ accumulation, photosynthetic activity, oxidative stress, enzymatic and non-enzymatic antioxidants, as well as proline levels were evaluated. Results showed that R and F-HS considerably enhanced salinity tolerance. In addition, F-HS offered a greater improvement of plant growth in relation to shoot fresh weight, shoot relative growth rate, and foliar area, being 10.00 mL/L the best dose. This tolerance could be associated with reduced Na⁺ translocation to the shoot and enhanced shoot K⁺ accumulation, decreasing Na⁺/K⁺ ratio. Furthermore, HS improved the net photosynthetic rate, Rubisco carboxylation efficiency, and photosystem II performance, and reduced ROS levels and lipid peroxidation. Hence, our data show the potential use of BLACKJAK® to improve lettuce tolerance to salinity, with foliar application slightly better than radicular to achieve this aim, especially at 10.00 mL/L dose.
... Other polar functional groups in nano humus structure may also contribute to the interaction and penetration. Hydrophilic components in the structure of humic materials could trigger nitrogen metabolism related enzymatic activities after penetration and therefore positively affect root growth and biomass production [43][44][45]. Further investigations on the biological effects of functional groups in humic fragments will be needed. ...
Increasing pressures on land resources requires increased land use efficiency. Over 900 million ha of sandy soils throughout the world are extensively used for agricultural crop production, most requiring nutrient inputs. Although use of humic substances together with inorganic fertilizer as soil amendments has been introduced, their synergistic effects on plant growth in sandy soils are not well addressed. We assessed the efficacy of a lignite waste derived humic substance on barley (Hordeum vulgare L.) growth, with and without inorganic fertilizer. Ten treatments were applied to sandy soils, comprising sole application of the humic product at four rates (NH1, NH2, NH3, NH4), sole application of fertilizer (F), and their combinations (F + NH1, F + NH2, F + NH3, F + NH4). Synergistic effects of nano humus and fertilizer were more notable than the corresponding sole application, particularly on plant biomass and seed production. Combined application with inorganic fertilizer increased root biomass by 92 % (0.1 g per plant), shoot biomass by 80 % (0.5 g per plant), root length by 24 % (3.6 cm), and seed production by 38 % (5 seeds per head) averagely relative to the untreated control, suggesting a strong synergistic effect. The increased seed production was particularly important from an agricultural perspective. Four application rates of nano humus all showed beneficial effects on barley growth with no significant differences. The most distinct positive effect of the humic product as a sole application was on root growth. Our study confirmed that a lignite waste derived humic product, nano humus, together with fertilizer may be an effective soil amendment to enhance agricultural plant growth in sandy soil regions.
... Given these challenges, providing appropriate supplements like humic and chitosan can enhance drought resilience, thereby improving crop productivity and contributing to global food security. Humic substances, resulting from the decomposition of plant and animal matter, improve nutrient availability, membrane permeability, enzyme and hormone activity, and water retention, positively affecting plant metabolism and yield [28][29][30][31][32][33][34][35][36] . ...
The current decline in freshwater resources presents a significant global challenge to crop production, a situation expected to intensify with ongoing climate change. This underscores the need for extensive research to enhance crop yields under drought conditions, a priority for scientists given its vital role in global food security. Our study explores the effects of using humic and chitosan treatments to alleviate drought stress during critical growth phases and their impact on crop yield and water efficiency. We employed four different irrigation strategies: full irrigation, 70% irrigation at the early vine development stage, 70% irrigation during the storage root bulking stage, and 85% irrigation across both stages, complemented by full irrigation in other periods. The plants received either humic treatments through foliar spray or soil application, or chitosan foliar applications, with tap water serving as a control. Our findings highlight that the early vine development stage is particularly vulnerable to drought, with a 42.0% decrease in yield observed under such conditions. In normal growth scenarios, foliar application of humic substances significantly improved growth parameters, resulting in a substantial increase in yield and water efficiency by 66.9% and 68.4%, respectively, compared to the control treatment under full irrigation. For sweet potatoes irrigated with 70% water at the storage root bulking stage, ground application of humic substances outperformed both foliar applications of chitosan and humic in terms of yield results. The highest tuber yield and water efficiency were attained by combining chitosan and humic ground applications, regardless of whether 70% irrigation was used at the storage root bulking stage or 85% irrigation during both the early vine development and storage root bulking stages.
... The presence of hydrophilic and hydrophobic areas that encourage surface activity is connected to this. As a result, the humic compounds interact as carriers of nutrients with the cell membrane structures (Garca et al., 2016). ...
Ammonium humate (AH) is a substance that applied in agriculture as a fertilizer and soil conditioner. It
is created when humic acid, reacts with ammonium hydroxide. So, it is considered a useful tool because it has
various advantages for plant growth and development. A field trial was conducted on sandy soil at the Ismailia
Agriculture Research Station farm in Ismailia Governorate, Egypt, during the winter season of 2021–2022 to
study the influence of three forms of 3% ammonium humate (AH1, AH2, and AH3) and two methods of
application (foliar on the plant (M1) and spraying on the soil (M2)) on the growth of cultivated crops (wheat, faba
beans, and lupine) and some soil properties. Obtained results indicated that adding different forms of AH
significantly increased crop productivity, macronutrient total content, and protein percent. The AH2 form was
superior in yield, and the soil application was positive compared to foliar application on the plant. The interaction
between AH form and method of application indicated that AH2M2 treatment was the best for all tested crop
productivity. Macronutrient availability increased with all experiment treatments, and the highest available N
values were with the AH1M2 treatment. Organic matter content in the soil was highest when different ammonium
humate forms were applied to the soil compared to foliar application.
Keywords: Ammonium humate; Application method; Yield production; Soil chemical properties.
... The presence of hydrophilic and hydrophobic areas that encourage surface activity is connected to this. As a result, the humic compounds interact as carriers of nutrients with the cell membrane structures (Garca et al., 2016). ...
... The biostimulatory effects of HSs are evaluated by quantifying plant growth and crop yield under different growth conditions. In the last 20 years, tremendous efforts have been made to understand the mode of action of HSs to improve plant growth (Calvo et al. 2014;Canellas et al. 2008aCanellas et al. , 2015Canellas and Olivares 2014;García et al. 2016c;Mora et al. 2010;Nardi et al. 2009Nardi et al. , 2017Olaetxea et al. 2018;Rose et al. 2014;Yakhin et al. 2017). Analysis of the results from several reports suggests that the bio-stimulatory effects of HSs on plant growth involve different but integrated mechanisms that are regulated at transcriptional and post-transcriptional levels ( Figs. 1 and 2). ...
Background
The global population is increasing at a pace that food security has become a major concern. The 20th-century Green Revolution saved billions of people from starvation, but the continuous widespread utilization of pesticides and synthetic fertilizers to boost yields has negatively impacted arable lands, water resources, and the environment. Moreover, the production and use of chemical inputs contribute to global climate change. But this impact could be reduced by replacing synthetic chemical inputs with sustainable resources. A promising and environmentally friendly approach to reduce synthetic chemicals is to incorporate biostimulants from sustainable resources. Humic substances (HSs) are composed of humic, fulvic, and ulmic acids and are the most abundant organic matter on earth. They are well known for their beneficial effects on plant growth and development.
Scope
This review encompasses the most recent findings related to the bio-stimulatory effects of HSs in modulating phytohormone biosynthesis, nutrient uptake and assimilation, primary and secondary metabolism, and tolerance to biotic and abiotic stresses.
Conclusion
Existing evidence shows that HSs have multifaceted actions that are attributed to different functional groups and other bioactive compounds enclosed in their macrostructure. Studies have shown that HSs possess auxin-like properties that alter plant metabolism which results in beneficial effects on plant growth and productivity, such as improved nutrient use efficiency and increased abiotic and biotic stress tolerance. In future studies, delineating the mechanisms that can pave the way to further refine these products and increase their efficacy to amplify beneficial effects is required to develop novel products.
... However, it decreased the content of non-enzymatic antioxidants (total phenols and flavonoids) ( Figure 3A,B) in the leaves under non-saline and saline conditions. The humic acid application to rice root increased both the ROS production and the activities of antioxidant enzymes, and such increases in ROS were not associated with a negative effect on plants but rather with the beneficial effect of increasing root growth [75]. In addition, humic acid enhanced CAT activity and the production of ROS in maize plants [76]. ...
The sensitivity of rice plants to salinity is a major challenge for rice growth and productivity in the salt-affected lands. Priming rice seeds in biostimulants with stress-alleviating potential is an effective strategy to improve salinity tolerance in rice. However, the mechanisms of action of these compounds are not fully understood. Herein, the impact of priming rice seeds (cv. Giza 179) with 100 mg/L of humic acid on growth and its underlaying physiological processes under increased magnitudes of salinity (EC = 0.55, 3.40, 6.77, 8.00 mS/cm) during the critical reproductive stage was investigated. Our results indicated that salinity significantly reduced Giza 179 growth indices, which were associated with the accumulation of toxic levels of Na+ in shoots and roots, a reduction in the K+ and K+/Na+ ratio in shoots and roots, induced buildup of malondialdehyde, electrolyte leakage, and an accumulation of total soluble sugars, sucrose, proline, and enzymic and non-enzymic antioxidants. Humic acid application significantly increased growth of the Giza 179 plants under non-saline conditions. It also substantially enhanced growth of the salinity-stressed Giza 179 plants even at 8.00 mS/cm. Such humic acid ameliorating effects were associated with maintaining ionic homeostasis, appropriate osmolytes content, and an efficient antioxidant defense system. Our results highlight the potential role of humic acid in enhancing salt tolerance in Giza 179.
... The potential role of HA to mitigate drought-induced oxidative damages in rice was reported by García et al. (2016). They observed a significant increase in the activity of peroxidase (POD) and proline levels as well as decreased H 2 O 2 accumulation to restore cytosolic redox homeostasis in water-stressed plants. ...
Plant biostimulants (BS), also termed bioeffectors, are viable microorganisms or active natural compounds applied to stimulate growth, nutrients uptake and stress tolerance in crop plants. The agricultural use of BS is discussed as a sustainable and resource-efficient approach to make optimal use of the biological potential that supports soil fertility, plant health and stress resilience of crops, contributing to profitable and sustained yield level. The use of BS-containing products (e.g. plant-beneficial microbes, seaweed, plant and compost extracts, protein hydrolysates, peptides, chitosan, and humic acids) as commercial formulations to enhance stress tolerance in plants provides a continuously increasing market potential with current annual growth rates of 12%. However, although the principal effectiveness of BS products is well documented, limited reproducibility of the expected effects, particularly under field conditions, still remains a major challenge. Therefore, it is essential to understand the physiological and functional basis of BS and their interactions in complex environments to get maximum benefit from these biological agents. This chapter provides a broad overview of the bio-protective effects of BS with the aim to make agriculture more sustainable and resilient to water limitations and salt stress. The positive effects of BS on physiological and metabolic events such as photosynthetic activity, phytohormonal balances, acquisition of nutrients and scavenging of reactive oxygen species to strengthen the defense mechanisms in water and salt-stressed plants are reviewed and discussed.
... H2O2 são o resultado de um aumento da expressão de genes responsivos da síntese de enzimas superóxido dismutase (SOD) em nível citosólico (CuZnSOD1 e CuZnSOD2) e de peroxidases (POX1) (Figura 6). 60 As evidências científicas nos mostram hoje que quando os AH são aplicados via radicular e em solução para as plantas, ocorre uma desfragmentação da supramolécula, 47,52, possivelmente em regiões próximas da raiz onde o valor de pH pode ser inferior a 3.0. A este valor de pH, alguns fragmentos de SHs podem se aglomerar na superfície radicular, causando entupimento de poros e modificando a funcionalidade da raiz. ...
The understanding of humic substances (HS) chemistry in soil science faces new challenges at present. Theories alternative to humification (HS formation process) have been presented to scientific community propagating uncertainty about the existence of these compounds as a structural entity located in the soil. In this review, we aim to show in a compressible manner that HS have a structural pattern independent of its origin, which allows us the characterization by means of techniques common to other groups of compounds (13 C NMR CP/MAS). These characteristics (C-aliphatic, C-aromatic, carboxyl, carbonyl) allow the obtaining and quantification of HS properties (aromaticity, aliphaticity, hydrophobicity, recalcitrance) that define different functions in the soil (plant bioactivity). The preservation of the structure-property-function relationship of HS qualifies them as a chemical compounds groups that are formed in the soil and are widely distributed in nature. The relevance of the supramolecularity concept to explain chemical and organizational characteristics of the humic structure, as well as, the use of spectroscopic techniques combined with chemometrics to understand the complex behavior of HS and its various functions is highlighted in this review. Resumo O entendimento da química das substâncias húmicas (SHs) na ciência do solo enfrenta hoje novos desafios. Teorias alternativas à humificação (processo de formação das SH) têm sido apresentadas à comunidade científica gerando questionamentos sobre a existência destes compostos como uma entidade estrutural presente no solo. Esta revisão tem como objetivo mostrar de forma compreensível que as SHs possuem um padrão estrutural independente da fonte de origem, que permite a caracterização por meio de técnicas comuns a outros grupos de compostos (13 C NMR CP/MAS). As características que as SHs apresentam (C-alifáticos, C-aromáticos, carboxilas, carbonilas) permitem a obtenção e quantificação de propriedades (aromaticidade, alifaticidade, hidrofobicidade, recalcitrância) que definem as diferentes funções que as mesmas exercem no solo (bioatividade em plantas). A preservação da relação estrutura-propriedade-função das SHs as qualifica como compostos químicos que são formados no solo e que estão amplamente distribuídos na natureza. Destaca-se nesta revisão a importância do conceito de supramolecularidade para explicar as características químicas e organizacionais da estrutura húmica e o uso de técnicas espectroscópicas aliadas à quimiometria para entender o comportamento complexo das SHs e suas diversas funções. Palavras-chave: Ácidos húmicos; espectroscopia; quimiometria; estresse oxidativo.
... The aromaticity was calculated according to the formula (C Aromatic -H,R) + (C Aromatic -O) * 100/total area, and the aliphaticity was calculated as 100-aromaticity (%). The hydrophobicity index (HB/HI) was calculated as (0 ppm-46 ppm) + (110 ppm-156 ppm)/ (46 ppm-110 ppm) + (156 ppm-240 ppm) (García et al., 2016a). ...
Salinity induces salt uptake by plant cells, which hinders plant growth and results in decreased agronomic crop yields. Humic substances (HSs) have been shown to be ecological agricultural alternatives to stimulate plant development under both normal and abiotic stress conditions. At the same time, arbuscular mycorrhizal fungi (AMF) provide nutrients and provide salinity tolerance through the osmotic balance between Na⁺ and K⁺. This study aimed to evaluate the effects of the combination of AMF and HSs on the growth of rice plants under salinity stress. The experiment was carried out in a greenhouse: Pots filled with sand were treated with a nutrient solution (as a control), 40 mg HS L⁻¹ or 200 mM NaCl and inoculated with Acaulospora mellea, Glomus formosanum, Rhizoglomus clarum, or Glomus spp. The HSs and AMF stimulated biomass production and root growth compared to those of uninoculated plants. The leaf P content increased in the presence of HSs and AMF under stress conditions. The sodium concentration was higher in the shoots of plants not treated with HSs than in those of the control plants. The potassium concentration decreased in the shoots under saline conditions. HSs and AMF alone or in combination promoted mycorrhizal colonization, especially that of A. mellea. AMF and HSs stimulated plant growth, improved root morphological characteristics, and increased P accumulation in rice plants under salt-stress conditions. These results support the production of biofertilizers with protective effects for sustainable agriculture.
... Enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) are activated in plants to reduce the concentration of hydrogen peroxide and superoxide (Canellas et al. 2020). In this regard, Cordeiro et al. (2011) showed that the treatment with HS stimulated catalase activity in plants, whereas García et al. (2016) have shown the role of humic extracts in the upregulation of peroxidase that is capable to reduce ROS concentration in cell, thereby restoring the cytosolic redox homeostasis. In the latter study, the antioxidant defence induced in plants by HS was shown to be related to their biostimulant activity, as HS led to a state of eustress whose final effect is somehow beneficial to plants. ...
Background and aims
Biostimulants of natural origin represent a growing ecological strategy to increase crops productivity, especially when applied in combination with microbial bioeffectors. We studied the effect of biostimulants such as Potassium Humates (KH) from Leonardite and Compost Tea (CT) from green compost on both productivity and nutritional status of lettuce plants, as well as on the primary and secondary metabolism of treated plants, when amended either alone or in combination with a commercial microbial inoculum (M+), mainly based on arbuscular mycorrhizal fungi (Micosat TabPlus).
Results
The biomass production as well as the uptake of both macro- and micronutrients by lettuce plants significantly increased when amended by the mixture of both humic materials (MIX) combined with the microbial inoculum. Similarly, the synergic MIX_M+ treatment significantly affected both the primary and secondary metabolism of lettuce more than their individual applications, by increasing, respectively, the biosynthesis of essential amino acids and carbohydrates, and that of antioxidant polyphenolic compounds, such as hydroxycinnamic acids, flavonols and coumarins.
Conclusions
Our findings suggest that a calibrated mixture of humic bioactive molecules in combination with microbial consortia represents a potential tool to improve crop productivity and its nutritional and metabolic status.
... Glutathione is broadly distributed in many plant tissues and has a contributing role in ROS biotransformation. Furthermore, it aids in the sequestration of heavy metals in vacuoles by the creation of phytochelatins (Sharma and Dietz 2006 Esringü et al. (2016) and García et al. (2016) also discovered a reduction in MDA levels in Hungarian vetch and Oryza sativa after treatment with vermicompost-generated humic acid, respectively. Similarly, 35.60 and 12.47% reduction was observed in MDA and H 2 O 2 levels after tomato seeds were primed with vermicompost extract (Tikoria et al., 2022). ...
In addition to chemical pesticides and fertilizers, the use of vermicompost can help in the management of root-knot nematodes (RKN) while also augmenting plant growth. The present study is carried out to determine the role of neem-based vermicompost on plant growth during stress produced by Meloidogyne incognita. Vermicompost (Vcom) and soil were mixed in various proportions (0, 20, 40, 60, 80, and 100%) and used to treat tomato plants against nematode infestation. After 10 days of inoculation of second-stage juveniles of M. incognita, several morphological parameters such as root length, shoot length, root weight, shoot weight, number of galls, and number of leaves were evaluated to investigate the plant growth. Various photosynthetic pigments (chlorophyll a and b, total chlorophyll, and carotenoid content) and gaseous exchange parameters (photosynthesis rate, intercellular carbon dioxide intensity, stomatal conductance, and transpiration rate) were also investigated in order to better understand plant respiration and response to nematode stress. In biochemical studies, the protein content and unit activity of antioxidative enzymes such as catalase, superoxide dismutase, guaiacol peroxidase, glutathione-s-transferase, ascorbate peroxidase, and polyphenol oxidase were investigated. The analyses of malondialdehyde (MDA) and hydrogen peroxide (H2O2) contents were also performed to examine the stress caused by nematodes and the effect of vermicompost in overcoming that stress. Aside from that, the influence of vermicompost on several bioactive components of plants was investigated by quantifying non-antioxidative enzymes (ascorbic acid, glutathione, and tocopherol levels) and secondary metabolites (total phenolic, total flavonoid, and anthocyanin contents). The results of the foregoing experiments reveal a significant increase in all morphological, biochemical, and photosynthetic parameters except MDA and H2O2, which tend to decrease with increasing vermicompost concentration as compared to untreated and nematode-infected plants. The current study reveals that vermicompost has a high potential for lowering the nematode stress and enhancing plant growth and development through the augmentation of different bioactive components in plants.
... Knowledge of ROS accumulation in plants exposed to BTEX is still lacking. However, in a few studies, exposure of plants to organic compounds such as organic matter, vermicompost, humic acid, and organic pollutants induced significant ROS production, disrupted gene expression and activity of major antioxidant enzymes such as superoxide dismutase and peroxidase, and also damaged the leaf subcellular structure and organelles (García et al., 2016, Ahammed et al., 2013, Shen et al., 2018, Wei et al., 2014, Kreslavski et al., 2017, Liu et al., 2009, Zhang et al., 2016, Dogan et al., 2010. In our study, the accumulation of H 2 O 2 was higher in Ct-1 than in the tolerant Kn-0 in all treatments ( Figure 2A). ...
Benzene, toluene, ethylbenzene, and xylenes (BTEX) are important environmental pollutants around the world. The uptake and transformation of BTEX by plants are well understood, but not the molecular mechanisms for BTEX stress response. In the current study, we combined transcriptomic and physiology analysis of two Arabidopsis thaliana accessions with contrasting BTEX tolerance and a reverse genetic approach to identify BTEX-tolerance related genes. Physiology and gene expression were analyzed in seedlings exposed for 5 days to BTEX compounds separately and combined. Our results showed reduced root length, high proline accumulation, and decreased chlorophyll content in the susceptible accession (Ct-1) after BTEX exposure, whereas the tolerant accession (Kn-0) did not show a statistically significant difference. RNA-seq revealed 1593, and 717 DEGs in Ct-1, and Kn-0, respectively, under BTEX stress, with 234 genes in common. DEGs were associated with pathways such as “glutathione transferase activity”, “photosynthesis light harvesting in photosystem I”, “cellular response to ethylene”, and “cellular amino acid catabolic process and found to be upregulated in Kn-0 in stress . DEGs partaking to “response to chitin”, “cellular response to hypoxia”, “plant-pathogen interaction”, and “anthocyanin-containing compound biosynthetic process” were noted to be downregulating in stress mitigation. Moreover, compared with the wild type, BTEX sensitivity increased in T-DNA knockout (KO) lines for two genes, including basic region/leucine zipper motif 60 (BZIP60) (At1G42990) and a hypothetical protein (At2G16190). Our study explored mechanisms underlying the stress involving BTEX compounds in Arabidopsis and the identification of genes responsible for BTEX stress tolerance.
... HSs are known to interact with calcium-phosphate precipitation and thereby increasing phosphorus solubility for plant uptake [42,43]. Additionally, HSs were reported to regulate reactive oxygen species (ROS) concentration and superoxide dismutase (SOD) genes in cytosol, promoting cell growth and differentiation [44]. The biostimulatory actions of HSs were found to be effective in increasing root uptake of sulphate as well as gene expression of primary sulphate transporters in roots [45]. ...
Demand for organically grown food crops is rising substantially annually owing to their contributions to human health. However, organic farm production is still generally lower compared to conventional farming. Nutrient availability, content consistency, uptake, assimilation, and crop responses to various stresses were reported as critical yield-limiting factors in many organic farming systems. In recent years, plant biostimulants (BSs) have gained much interest from researchers and growers, and with the objective of integrating these products to enhance nutrient use efficiency (NUE), crop performance, and delivering better stress resilience in organic-related farming. This review gave an overview of direct and indirect mechanisms of microbial and non-microbial BSs in enhancing plant nutrient uptake, physiological status, productivity, resilience to various stressors, and soil-microbe-plant interactions. BSs offer a promising, innovative and sustainable strategy to supplement and replace agrochemicals in the near future. With greater mechanistic clarity, designing purposeful combinations of microbial and non-microbial BSs that would interact synergistically and deliver desired outcomes in terms of acceptable yield and high-quality products sustainably will be pivotal. Understanding these mechanisms will improve the next generation of novel and well-characterized BSs, combining microbial and non-microbial BSs strategically with specific desired synergistic bio-stimulatory action, to deliver enhanced plant growth, yield, quality, and resilience consistently in organic-related cultivation.
... Biologically, they improve growth of useful soil micro-organisms by acting as source of nutrients and energy to soil biota. HS mainly affect nutrient bioavailability via their ability to form complexes with metallic ions, which enhances the availability of micronutrients (zinc, manganese, copper, and iron); and macronutrients (phosphorus), and particularly when these nutrients are scarce in the soil [2]. The present study was carried out in a view to observe the influence of humic acid and inorganic nitrogen on chemical properties of soil under direct sown rice. ...
A field experiment was carried out to study the influence of different levels of humic acid (10, 20, 30 kg ha-1) and inorganic N fertilizer viz., 100 % of recommended dose and 75 % of recommended dose on chemical properties of soil under direct sown rice at Agricultural college farm, Bapatla during 2019. The experiment was laid out in RBD with ten treatments replicated thrice with BPT-5204 variety of rice as test crop. Soil samples collected at tillering, panicle initiation and harvest stages of crop were analyzed for chemical properties like available N, P 2 O 5 , K 2 O, Sulphur and cationic micro-nutrients (Fe, Mn, Zn, Cu). Results indicated that increased availability of N, P 2 O 5 , K 2 O, Sulphur and cationic micro-nutrients (Fe, Mn, Zn, Cu) were observed with the treatment T 6 involving 100% RDN and HA @ 30 kg ha-1 .
... Vermicompost humic acids modulate H2O2, nitric oxide, and both calcium and proton fluxes. It is also associated with root growth [25,42,43], affecting mineral nutrient concentration [44,45]. On the other hand, mineral deficiency is a common symptom in plants infected with RKN [8,9]. ...
Root-knot nematode (RKN) is a serious threat to crops worldwide due to the difficulty in controlling it and the limited eco-friendly alternatives to deal with the biotic stress it causes. In the present work, water-extractable fractions obtained from vermicompost (WSFv), vermicompost enriched with Trichoderma asperellum (WSFta) and T. virens (WSFtv) were tested as biotechnological tools to reduce the impacts of RKN on gas exchange, water use efficiency (WUE) and nutrient concentration in tomato and bell pepper plants. The plants were infected with 5000 eggs and eventual J2 of RKN and then treated with the water-extractable fractions for seven weeks. It was observed that the addition of WSFta, WSFtv and WSFv increased the CO2 assimilation, stomatal conductance and WUE in the tomato plants. In the bell pepper plants, WSFta, WSFtv, WSFv increased the stomatal conductance, while WUE was higher in the treatment with WSFtv. In fact, the parameters associated with the gas exchange were usually higher in the bell pepper than in the tomato plants. Overall, higher contents of N, Mg, B and Mn were detected when the extracts were applied in both bell pepper and tomato plants. The application of the water-extractable fractions, inoculated or not with Trichoderma, attenuates the RKN damage on the gas exchange parameters and successfully enhanced the nutrient concentration in the infected tomato and bell pepper plants, showing that it could be an important and promising tool for reducing the damage caused by this pathogen. We suggest that both the tomato and pepper plants can cope with the dilemma between growth and stress response via stomata regulation that are modulated by the WSF and Trichoderma.
... Plant growthpromoting bacteria can trigger the salicylic acid (SA)dependent SAR and SA-independent ISR pathway [18]. Humic substances can increase the concentration of phenolic compounds [19] and peroxidase activity [20], as well as phenylalanine ammonia-lyase (PAL) activity [21] in leaves tissues. PAL is the key enzyme involved in synthesising phenolics and lignin compounds via the phenylpropanoid pathway. ...
Background
The bacterial-spot disease caused by different Xanthomonas species is one of the major tomato diseases that reduce crop production and quality. Pesticides indiscriminate usage has resulted in an increase in resistant bacterial strains as well as contamination of farmers, consumers and the environment. Plant growth-promoting bacteria and humic acids can act as elicitors of plant defence mechanism causing extensive transcriptional and metabolic reprogramming which, in turn, produce a range of plant chemical defences. The purpose of this study was to study how humic acids and plant growth-promoting bacteria, when applied to the substrate, affected the severity of bacterial spot symptoms in tomato leaves.
Materials and methods
One-month-old Micro-Tom tomato ( Solanum lycopersicum L.) were transferred to 3 L pots filled with a sterile mixture of sand and vermiculite (2:1, v:v) and treated or not (control) with 250 mL of 4.5 mmol C. L ⁻¹ of humic acids, Herbaspirillum seropedicae (10 ⁸ CFU. mL ⁻¹ ) and the combination of humic acids plus H. seropedicae . One day after substrate treatment, the leaves were inoculated (or not) with X. euvesicatoria ( Xe ) . The area below the disease progression curve based on severity scores and the number of symptomatic leaflets was used to assess phytopathogen virulence. The concentration of oxalic, citric and succinic acids in leaf extracts were determined using HPLC analysis.
Results
Sole or combined H. seropedicae (BAC) and humic acids (HA) application promoted shoot and root growth related to control when plants were challenged with Xe pathogen. For plants inoculated with Xe , more significant plant-growth promotion results were obtained for HA + BAC treatment. The first visible symptoms were observed 16 days after inoculation with 2 × 10 ⁴ CFU. g ⁻¹ of Xe cells in leaves of control plants. HA and BAC applied alone or combined reduced disease severity. Only plants treated with HA were able to reduce disease incidence (number of the leaflets with symptoms). Organic acids, such as oxalic, citric and succinic acids, rose in Xe-inoculated leaves. The reduced amount of organic acids in diseased leaves treated with HA + BAC may be linked to a decrease in disease progression.
Conclusion
Humic acids and H. seropedicae increased growth by modulating the content of organic acids in leaf tissue, attenuating the symptoms of the bacterial spot disease.
Graphic abstract
... HA, as a significant constituent of soil organic matter, is a natural heterogeneous aggregate that contains organic molecules at different degrees of transformation (Olaetxea et al. 2018). HA is also a common organic fertilizer due to its indirect effects (improving soil porosity, aggregation, and texture; increasing respiration; enlarging the pool of bioavailable nutrients; promoting microbiota activity; etc.) and direct effects (its interaction with cell membranes at the root surface) on crop growth (García et al. 2012(García et al. , 2014(García et al. , 2016Olaetxea et al. 2018). Furthermore, HA can also be used as an in situ amendment to reduce Cd uptake in crops by reducing Cd bioavailability through coprecipitation and/or complexation (Ondrasek et al. 2018). ...
Selenium (Se), iron (Fe), and humic acid (HA) are beneficial fertilizers that inhibit cadmium (Cd) uptake in crops and are crucial for agricultural yields as well as human health. However, the joined effect of Se, Fe, and HA on Cd uptake in rice are still poorly understood. Therefore, a hydroponic culture experiment was established to evaluate the combined effect of Se (Se⁴⁺ or Se⁶⁺), Fe, and HA on the biomass, Cd uptake, and Cd translocation of/in rice seedlings. Compared to Se⁶⁺ application, Se⁴⁺ application in most treatments resulted in lower Cd translocations from roots to shoots, leading to a significant decrease in shoot Cd concentrations. Compared to the treatments with Se⁴⁺ or Fe²⁺ application, joined application of Se⁴⁺ and Fe²⁺ inhibited Cd uptake in shoots by decreasing Cd adsorption onto (iron plaque) and uptake by roots, and alleviating Cd translocation from root to shoot. Compared to the treatments with Se⁶⁺ or Fe²⁺ application, joined application of Se⁶⁺ and Fe²⁺ inhibited Cd uptake in shoots by sequestering (retaining) Cd onto root surface (iron plaque). HA inhibited Cd uptake in all treatments by decreasing the bioavailability of Cd in the nutrient solution through complexation. The simultaneous application of Se, Fe, and HA decreased the shoot Cd concentrations the most, followed by the combined application of two fertilizers and their individual application; the mean shoot Cd concentration in the Fe-SeIV-HA2 treatment was the lowest among all the treatments, at only 11.39 % of those in the control treatments. The 3-way ANOVA results indicated that the Cd concentrations in shoots were significantly affected by Se, Fe, HA, and certain of their interactions (Fe×Se and Se×HA) (p< 0.05). The above findings suggest that the joined application of Se, Fe, and HA ameliorated Cd uptake mainly by inhibiting Cd adsorption onto (iron plaque) and uptake by roots and the translocation from roots to shoots (Fe×Se⁴⁺), retaining (sequestering) Cd in iron plaque (Fe×Se⁶⁺), and decreasing Cd availability in nutrient solution (HA).
Graphical abstract
... In order to survive in an unfavorable living environment, organisms have evolved a set of strategies to outwit their adversaries. One of them is the antioxidant enzyme system (García et al., 2016). Under normal circumstances, the process of cell metabolism to complete all kinds of life activities can produce reactive oxygen species (ROS). ...
... Similarly, Mehrasbi et al. (2018) found that HA affected ROS production in algae. However, the pre-teatment with HA has been found to mitigate the presence of major abiotic stresses induced by PEG (García et al., 2016b) as well as salinity, drought and heavy metals (Canellas et al., 2020), resulting in higher transcription level of genes involved in stress perception. ...
The increasing demands for biostimulants in the agricultural market over the last years have posed the problem of regulating this product category by requiring the industry to make available the information about efficacy and safety, including the explanation of mode of action and the definition of bioactive constituents. In the present study, we tested the biostimulant proprieties of a sedimentary shale ore-extracted humic acid (HA) on Micro Tom tomato plants under increasing nutritional stress and investigated the correlation with the chemical features of HA by means of ultra-high resolution FT-ICR MS, FT-ATR, and ¹³C-NMR. Humic acid application proved effective in alleviating the nutritional stress by improving nutrient use efficiency, with results comparable to the control treatment supplied with higher NPK nutrition. Increased yield (up to +19%) and fruit quality (in the range +10–24%), higher ascorbic acid content and a better root growth were the main parameters affected by HA application. Molecular-level characterization identified the possible chemical drivers of bioactivity, and included flavonoids, quinones, and alkaloids among the most represented molecules, some of which exhibiting antioxidant, pro-oxidant, and antimicrobial activity. The redox effect was discussed as a determinant of the delicate homeostasis balance, capable of triggering plant defense response and eventually inducing a protective priming effect on the plants.
... HS can stimulate plant growth by improving the absorption of nutrients through releasing hormone-like effectors such as IAA [2,61]. Canellas et al. [62] and Nardi et al. [63] observed that plants treated with HS of different origin were able to induce the proliferation of lateral roots and root hairs, which could be related to the activation of signaling pathways of phytohormones, especially auxin, nitric oxide, Ca 2+ and reactive oxygen species (ROS) [36,38,[64][65][66][67][68]. HS also stimulate shoot elongation and an increase in the accumulation of leaf nutrients and chlorophyll biosynthesis [2,69,70]. ...
Nowadays, farmers and entrepreneurs strive to obtain higher and better quality seeds and plant products containing fibre by providing plants with optimal growth conditions using agrotechnical methods such as crop rotation, enhancing soil quality and protection against diseases. The use of biostimulants, substances that promote plant growth and resistance, seems to be the best way to achieve satisfying results. Biostimulants are included in the modern plant industry and environment-friendly crop management as they enhance the quality of crops while reducing chemical inputs. In textile plants, biostimulants can affect fibre structures regardless of the part of the plant they come from-seed, bast or leaf. The possible positive influence may be related to the increase in fibre length, shape, diameter, strength, flexibility, abrasion resistance, moisture absorbency, and antimicrobial properties. The purpose of this review is to better understand the unique characteristics of different biostimulants, which have a great influence on crop and fibrous plant properties.
Background
Traditional agriculture is on the front line of climate change, being most impacted by the increase in the intensity and frequency of extreme events, such as floods, drought and rising temperatures. Local ecological knowledge is a recognized keystone of successfully managed socioecological systems, but loss of soil fertility, water scarcity, incidence of diseases and decreased production due to climate change are linked to the greater vulnerability experienced by traditional farmers. Plant biostimulants are natural products used to stimulate nutrient uptake and efficiency by crops, increase tolerance to abiotic/biotic stress and improve quality without negative impacts on the environment if obtained from renewed sources. Humic substances are some of the most used plant biostimulants in agriculture and play a central role in plant adaptation.
Materials and methods
We reviewed and discussed a sample set of papers (n = 52) about humic substances to mitigate abiotic stress in crops using data basis from Web of Science (Clarivate Analytics), Scopus—IBM (International Business Machines Corporation), and Scielo (Scientific Electronic Library Online).
Results
The predominance of authors in the global south is notable, but it is not a coincidence, since this is where the effects of climate change will have the greatest impact. The mechanisms involved in the stress mitigation involve the activation of signaling factors, gene response induction, the accumulation of osmoprotective and anti-oxidant compounds, the induction of antioxidative metabolism, ion homeostasis, membrane transport and adjustment of hormonal balance. The intriguing question is: how can a complex mixture of molecules affect so many distinct effects on plants responsible for plant adaptation?
Conclusions
The complexity of humic substances challenges our knowledge method, but supramolecular chemistry may provide answers that enable us to broaden our understanding of the plant defense mechanisms modulated by these substances.
Graphical Abstract
Humified organic matter has been shown to decrease Pb toxicity in plants. However, there are still gaps in our understanding of the mechanism by which this phenomenon occurs. In this study, we aimed to assess the ability of humic substances (HSs), humic acids (HAs), and fulvic acids (FAs) to enhance defense mechanisms in rice plants under lead (Pb)-stressed conditions. HS fractions were isolated from vermicompost using the chemical fractionation methodology established by the International Humic Substances Society. These fractions were characterized by solid-state NMR and FTIR. Chemometric analysis was used to compare humic structures and correlate them with bioactivity. Three treatments were tested to evaluate the protective effect of humic fractions on rice plants. The first experiment involved the application of humic fractions along with Pb. The second comprised pretreatment with humic fractions followed by subsequent exposure to Pb stress. The third experiment involved Pb stress and subsequent treatment with humic fractions. The root morphology and components of the antioxidative defense system were evaluated and quantified. The results showed that HS + Pb, HA + Pb, and FA + Pb treatment preserved root growth and reduced the levels of O2⁻ and malondialdehyde (MDA) in the roots by up to 5% and 2%, respectively. Pretreatment of the plants with humic fractions promoted the maintenance of root growth and reduced the contents of O2⁻, H2O2, and MDA by up to 48%, 22%, and 20%, respectively. Combined application of humic fractions and Pb reduced the Pb content in plant tissues by up to 60%, while pretreatment reduced it by up to 80%. The protective capacity of humic fractions is related to the presence of peptides, lignin, and carbohydrate fragments in their molecular structures. These results suggest that products could be developed that can mitigate the adverse effects of heavy metals on agricultural crops.
This investigate was conducted during the summer seasons of 2021 and 2022 to study the beneficial role of humic acid as biostimulant for reducing the harmful effect of water deficit on sorghum plant. Results show that water deficit at 75% FC and 50% FC caused decreases in vegetative growth parameters; grains yield and yield components, carbohydrate content of the yielded grains accompanied by increases in total soluble sugar and proline of the dry leaf tissues and protein content of the yielded grains. Regarding the interaction between water deficit and humic acid treatments, it was noted that humic acid at 50 mg/L and 100 mg/L markedly increased vegetative growth parameters, total soluble sugar and protein of the dry leaf tissues, grains yield and yield components, carbohydrate content and protein content of the yielded grains of sorghum grown under 95% FC, 75% FC and 50% FC relative to corresponding controls. It was noted that humic acid at 50mg/L and 100mg/L significantly increased weight of the yielded grains/plant by 11.46% and 34.50% respectively in plant irrigated with 95%FC, and by 17.25% and 24.37% respectively in plants irrigated with 75% FC and by 9.16% and 38.50% respectively in plants irrigated with 50% FC relative to corresponding controls. Clearly, humic acid treatment at 100mg/L was more effective than humic acid at 50mg/L under all conditions.
The use of pesticides in food cultivation appears to be very positive for the economy, but how do consumers view this from a health and environmental perspective? This study aims to a) assess Brazilian consumers’ risk perception and trust in conventionally produced foods and b) assess predictors of purchase intention of conventionally produced foods. A hypothesis model was created based on trust in food toolkit, risk perception, purchase intention, and price consciousness. The data collection was conducted in person in three cities in Brazil. Consumer trust in the consumption of conventionally produced food was analyzed using 27 indicators divided into six constructs: Trust in Organization, Trust in Product, Interpersonal Trust, Trust in Food Chain, Distrust in Organization, and Interpersonal Distrust. Risk perception, purchase intention, and price consciousness was analyzed using three, three, and four indicators, respectively. The sample consisted of 262 consumers, most of whom were female (65.3%). Purchase intention for conventionally produced food was predicted by trust in the product and risk perception, but not by price consciousness. Finally, risk perception was a partially competitive mediator between trust in the product and purchase intention for conventionally produced vegetables. Since consumers trust the organization (government health agency), the product, and the food chain, regulators must enforce safety in this context. Risk perception is an essential cognitive factor to improve consumers’ awareness of pesticide risk and thus reduce their intention to consume conventionally produced vegetables.
This study aimed to investigate the influence of chemical and structural characteristics of biochar on the development of rice plants grown in fragile sandy soil. An experiment was carried out in pots with the application of four doses (0 ton ha−1; 10 ton ha−1; 20 ton ha−1; 30 ton ha−1) of eucalyptus biochar from four artisanal sources (B1, B2, B3, and B4). Fresh root mass increased by 0.56% with the application of biochar B4 and decreased with the application of biochars B1, B2, and B3 (23.3%; 18.3%; 19.9%). The fresh mass of sheath and leaves decreased by an average of 23.6% and 27%, respectively, with the application of all biochars. Root dry mass increased by 7.8% with the application of biochar B4 and decreased with the application of B1, B2, and B3. The sheath dry mass and leaf dry mass decreased by an average of 20.2% and 25.1%, respectively, with the application of all biochars. The nutrient content, specifically P, K, and N, increased with the application of B1, B2, and B3. The application of biochar B4 (30 ton ha−1) lessened the damage to the photosynthetic apparatus and promoted physiological recovery. The beneficial effect of biochar B4 occurred at a dose of 30 ton ha−1 in the reaction centers, increasing photochemical efficiency in photosystem II. Root development was stimulated by the application of biochar B4, increasing root area by 55% (10 ton ha−1) and 56% (20 ton ha−1 and 30 ton ha−1). The total length increased by 48% with the application of biochar B4 and by 27% with biochar B2 (30 ton ha−1). The length of thick roots and the total root volume were less affected by the treatments, with increases of approximately 11% and 7%, respectively. Although most treatments did not result in higher biomass production compared to the control, there was a notable increase in nutrient content in the aboveground portion, particularly with the application of biochar B2. Furthermore, improvements in photosynthetic parameters and root morphology were observed, particularly when biochar B4 was applied. Overall, the findings of this study indicate that biochars B2 and B4, at rates of 20 and 30 ton ha−1, respectively, hold promise for enhancing cultivation in vulnerable Planosols in the Rio de Janeiro region of Brazil. However, to fully understand the effects on soil properties in different crops and the economic implications of implementing biochar in agriculture, further long-term and large-scale research is necessary.
The use of humified organic matter (HOM)-based plant biostimulants and plant growth-promoting rhizobacteria (PGPR) has emerged as a promising approach to enhance agricultural productivity in arid and semiarid environments. However, the bioactivity of humic stimulants varies based on their chemical composition, and the synergistic effects of co-applying these biostimulants remain to be fully elucidated. In this research, we investigated the structural and bioactive characteristics of humic acids derived from goat manure vermicompost (HAVC) and lignite coal (HAC). Additionally, we explored the plant growth-promoting effects of each humic acid (HA) in conjunction with the Bacillus mycoides strain BSC25 (Bm) on corn plants in arid conditions. To assess the relationship between structure and bioactivity, we determined the supramolecular composition of the HAs and evaluated their effectiveness through a corn coleoptile elongation test. Subsequently, we conducted biostimulation tests on maize seedlings in a growth chamber and performed a field-based biostimulation test in a semi-arid region. Notably, HACs exhibited coleoptile elongation at lower concentrations (25-50 mg LC) compared to HAVCs, which required higher concentrations (100-200 mg LC) to achieve the same effect. These outcomes correlated with the supramolecular composition of HAs. The bioactivity of HACs was linked to their oxygen content, aromatic and carboxylic groups, whereas HAVCs' bioactivity was associated with their carbohydrate, aliphatic carbon, and hydrogen content. The application of both HAs, together with Bm, resulted in enhanced corn leaf biomass production in the growth chamber and under field conditions. This effect can be attributed to the hormone-like actions of HA and the PGPR activity of Bm. Interestingly, despite foliar application, HAs displayed bioactivity at the root level, as evidenced by increased root biomass in the field. These results indicate a PGPR effect of Bm that remained unaltered with co-application of HAVC. However, the joint application of Bm-HAC and Bm-HAVC reversed the positive effect of Bm on corn production under field conditions. This outcome likely relates to the hormone-like effects of HA and potential additive effects following Bm inoculation.
Background
Humic acid (HA) is an organic acid that is naturally present in soil organic matter and improves nutrient availability and the mechanisms involved in plant growth and development. Likewise, salicylic acid (SA) is an important plant hormone involved in the regulation of plant growth and development. A pot experiment was carried out to determine the effects of individual or combined HA and SA application on growth and yield of maize (Zea mays L.) under drought stress conditions. Two maize hybrids, namely, 30T60 (drought tolerant) and 75S75 (drought sensitive), were grown in semi‐controlled conditions and foliar applied with SA (1 mM), HA (100 mg L⁻¹) and their combination (HA + SA). The plants were exposed to drought stress at the tasseling stage (R1, 60 days after sowing) for 2 weeks, while control plants were given normal irrigation.
Results
The results showed that HA and SA applications significantly enhanced the gas exchange characteristics (photosynthetic rate, transpiration rate, and stomatal conductance), and antioxidant activity (catalase, guaiacol peroxidase, and superoxide dismutase) of water stressed maize plants. Foliar SA spray significantly increased the photosynthetic efficiency and activity of enzymatic antioxidants closely followed by HA + SA application that ultimately improved the yield and net benefit cost ratio of maize under water deficit conditions.
Conclusion
Our findings suggest that foliar spraying of SA at the initiation of the reproductive stage is a cost‐effective strategy to obtain a high maize yield under limited water conditions.
The aim of this study was to investigate the effects of humic acid (HA) applications on rapeseed (Brassica napus L.) growth, heavy metal uptake, bioconcentration factor (BCF), translocation factor (TF), tolerance index (TI), catalase (CAT), ascorbate peroxidase (APX) enzyme activities and hydrogen peroxide (H2O2) content in polluted soil with lead (Pb), chromium (Cr), cadmium (Cd), and zinc (Zn). Three doses of HA (Control, HA1:500 mg kg-1, HA2:1000 mg kg-1, HA3:2000 mg kg-1) were applied in pots. HA1, HA2, and HA3 applications increased plant growth parameters compared to polluted soil. Compared to the control, HA applications in polluted soil increased the Pb, Cr, Cd, and Zn concentrations in the plant. However, HA applications in polluted soil significantly decreased the heavy metal content in roots and shoots of the plant compared to polluted soil. BCF in both roots and shoots of the plants were greater than 1 for Pb, Cr, Cd, and Zn. However, specifically HA2 application decreased the shoot and root BCF values in polluted soil. TF was smaller than 1 in Pb, Cr, Cd, and Zn in polluted soil. On the other hand, HA applications for Cd increased TF values. Shoot TI decreased 17.37 %, and root TI decreased 9.09% in polluted soil. CAT and APX enzyme activities and H2O2 increased significantly in polluted soil. However, HA applications decreased CAT and APX enzyme activities and H2O2 content in rapeseed. It is concluded that HA application in Pb, Cr, Cd, and Zn polluted soil has a remedial effect on the development of rapeseed by reducing heavy metal content and oxidative stress.
Extreme temperatures are predicted to become increasingly common due to climate change, threatening the sustainability and profitability of global rice production. Manure amendment is a common agricultural practice to improve soil fertility and increase crop yields, but whether this practice modulates the effect of extreme temperatures on crop yield is unclear. Here we show through a series of experiments and meta-analysis that long-term manure amendment reduces losses of rice yield due to extreme temperatures. We propose that by increasing soil fertility, manure amendment increased net photosynthetic rate and plant physiological resistance to extreme temperatures. Without considering the impact of other global change factors, we estimate that manure amendment could potentially reduce global losses of rice yield due to extreme temperatures from 33.6 to 25.1%. Thus, our findings indicate that manure amendment may play a key role in improving food security in a changing climate. Heat resilience and tolerance of rice crops is enhanced by manure amendment and could improve yield stability under projected climate change, suggest a meta-analysis and long term manure amendment experiments.
PurposeWithania somnifera is a widely used herb due to its multi-health benefits. There is a growing interest to improve the growth and chemical profile of this plant because a large gap exists in the supply and demand of the quality raw material. The present study focused on using organic amendments to enhance the health and quality of this herb.Methods
Seeds pre-soaked in distilled water (DW) and vermicompost leachate (Vcom-L) were sown in 10-cm diameter pots having 0, 40, and 60% vermicompost. After 45 days of sowing, seedlings were transplanted to 25-cm diameter pots with the respective vermicompost proportions and divided into vermicompost group (without supplementation of Vcom-L) and vermicompost + Vcom-L group (weekly supplementation of Vcom-L). Sixty days post-transplantation, the plants were used for the analysis of gas exchange and biochemical parameters.ResultsSeed pre-soaking in Vcom-L and combined application of vermicompost + Vcom-L caused a significant enhancement in the biochemical parameters of the plant. In the vermicompost group, sulfur, hydrogen, chlorophyll b, total chlorophyll, photosynthetic rate, transpiration rate, stomatal conductance, total phenolics, flavonoids, antioxidant potential, proline, protein, and activity of ascorbate peroxidase were higher at 40% vermicompost while carbon, nitrogen, chlorophyll a, polyphenols, and activity of guaiacol peroxidase and glutathione reductase were higher at 60% vermicompost. The activity of superoxide dismutase and catalase declined with the Vcom application. In the vermicompost + Vcom-L group, an increase in most of the parameters was maximum at 40% vermicompost and significantly more than the vermicompost group.Conclusions
Vcom-L pre-soaking and the combination of 40% vermicompost + Vcom-L were found to be more effective in enhancing the nutrient profile, medicinal constituents, and antioxidant potential of W. somnifera. Hence, this amendment could prove useful for the production of quality raw material for the pharmaceutical industry.
Background
Due to the severe cadmium (Cd) pollution of farmland soil, effective measures need to be taken to reduce the Cd content in agricultural products. In this study, we added α-Fe 2 O 3 nanoparticles (NPs) and biochar into Cd-contaminated soil to investigate physiological responses of muskmelon in the whole life cycle.
Results
The results showed that Cd caused adverse impacts on muskmelon ( Cucumis melo ) plants. For instance, the chlorophyll of muskmelon leaves in the Cd alone treatment was reduced by 8.07–32.34% in the four periods, relative to the control. The treatments with single amendment, α-Fe 2 O 3 NPs or 1% biochar or 5% biochar, significantly reduced the soil available Cd content, but the co-exposure treatments (α-Fe 2 O 3 NPs and biochar) had no impact on the soil available Cd content. All treatments could reduce the Cd content by 47.64–74.60% and increase the Fe content by 15.15–95.27% in fruits as compared to the Cd alone treatment. The KEGG enrichment results of different genes in different treatments indicated that single treatments could regulate genes related to anthocyanin biosynthesis, glutathione metabolism and MAPK signal transduction pathways to reduce the Cd toxicity.
Conclusions
Overall the combination of biochar and α-Fe 2 O 3 NPs can alleviate Cd toxicity in muskmelon. The present study could provide new insights into Cd remediation in soil using α-Fe 2 O 3 NPs and biochar as amendments.
Graphic Abstract
O Brasil é o maior produtor de cana-de-açúcar do mundo. Com as mudanças nos sistemas de colheita da cana-de-açúcar, há uma quantidade expressiva de palhada que fica depositada sobre o solo, podendo contribuir para o aumento da matéria orgânica do solo (MOS). No entanto, no Brasil já existem diversas Unidades Industriais que processam toda a biomassa da cana para fabricar álcool de segunda geração e/ou gerar energia elétrica, tornando-se assim, uma nova fonte de renda das Usinas e Destilarias. Ao processar toda a biomassa gerada pela cana-de-açúcar, os possíveis efeitos favoráveis sobre as propriedades químicas, físicas e biológicas do solo serão retardados. Vale destacar que a matéria orgânica determina os principais atributos que definem a qualidade do solo, sendo diretamente afetada pelas práticas de manejo. Por meio do estudo da qualidade da matéria orgânica, pode-se além de avaliar a qualidade do solo, ter uma maior compreensão do sistema de produção que este solo comporta. Diante do exposto, o objetivo do presente trabalho, foi de estudar os principais efeitos da retirada da palhada da superfície dos solos no conteúdo de matéria orgânica do solo, indicando estudos que apontam a quantidade ideal de palhada a ser deixada no solo, sem afetar o conteudo de matéria orgânica. Para isto, foi realizado uma intensa busca em bases de dados, de estudos que avaliaram as possíveis implicações da retirada total e parcial da palhada de cana.
Seed germination is one of the most crucial and complex physiological phenomena in the lifecycle of a plant, which often falls prey to environmental and biological stress that leads to erratic germination. Priming is a traditional method, generally used for synchronized seedling growth and stable crop stand, but priming has emerged as a potent tool for sustainable agriculture in recent times. It is used to tide over many abiotic stresses, such as salinity, drought, cold, heavy metal stresses, and also escalate the growth of the crop plants. Priming is even found to be beneficial against biotic stress agents like pathogenic bacteria and fungi. In this review, we have tried to summarize different successful reports of priming that had brought remarkable results in terms of growth, yield, disease resistance, abiotic and biotic stress tolerance. It also identifies the subcellular changes induced by priming highlighting the molecular and physiological aspects. The specific proteomic changes during imbibition and seed dehydration processes associated with a priming that helps in uplifting the seed vigor are also summarized. In the wake of the soaring demand of the food supply due to continuous surge in population and excessive use of chemical fertilizers to achieve higher yield, soil health is compromised. As an alternative, seed priming can serve as a cost-effective, environment-friendly, and pragmatic approach to address global food security through sustainable agricultural innovation.
Organic and biological fertilizers are considered as a very important source of plant nutrients. A field experiment was conducted during 2017−2018 in paddy soil to investigate the effect of vermicomposting of cattle manure mixture with Azolla and rice straw on soil microbial activity, nutrient uptake, and grain yield under inoculation of N 2 -fixing bacteria. Experimental factors consisted of organic amendments at six levels (vermicomposts prepared from manure (VM); manure + rice straw (VRM); manure + Azolla mixture (VAM); manure + rice straw + Azolla mixture (VRAM); raw manure without vermicomposting (M), and a control) and N 2 -fixing bacteria at three levels ( Azotobacter chroococcum , Azospirillum brasilence , and non−inoculation). The results showed that, vermicompost treatments compared to control and raw manure significantly increased the number and biomass−C of soil microorganisms, urease activity, number of tillers hill ⁻¹ , phosphorus (P) and potassium (K) uptake, and grain and protein yield. Inoculation of plants with N 2 -fixing bacteria, especially Azotobacter increased the efficiency of organic amendments, so that the maximum urease activity, soil microbial activity, P and N uptake, and grain yield (4,667 (2017) and 5,081 (2018) kg/h) were observed in vermicompost treatments containing Azolla (VAM and VRAM) under inoculation with Azotobacter . The results of the study suggested that, using an organic source along with inoculation with appropriate N 2 -fixing bacteria for vermicompost has a great effect on enzyme activity, soil biology, nutrient uptake and grain yield has a synergistic interaction on agronomic traits under flooded conditions. Therefore, this nutrient method can be used as one of the nutrient management strategies in the sustainable rice production.
Histochemistry is an essential analytical tool interfacing extensively with plant science. The literature is indeed constellated with examples showing its use to decipher specific physiological and developmental processes, as well as to study plant cell structures. Plant cell structures are translucent unless they are stained. Histochemistry allows the identification and localization, at the cellular level, of biomolecules and organelles in different types of cells and tissues, based on the use of specific staining reactions and imaging. Histochemical techniques are also widely used for the in-vivo localization of promoters in specific tissues, as well as to identify specific cell wall components such as lignin and polysaccharides. Histochemistry also enables the study of plants’ reactions to environmental constraints, for example, the production of reactive oxygen species (ROS) can be traced by applying histochemical staining techniques. The possibility of detecting ROS and localizing them at the cellular level is vital in establishing the mechanisms involved in the sensitivity and tolerance to different stress conditions in plants.
This review comprehensively highlights the additional value of histochemistry as a complementary technique to high-throughput approaches for the study of the plant response to environmental constraints. Moreover, here we have provided and extensive survey of the available plant histochemical staining methods used for the localization of metals, minerals, secondary metabolites, cell wall components, as well as the detection of ROS production in plant cells. The use of recent technological advances like CRISPR/Cas9 based genome-editing for histological application is also addressed. This review also surveys the availale literature data on histochemical techniques used to study the response of plants to abiotic stresses and to identify the effects at the tissue and cell-level.
The humic acid (HA) fraction of soil organic matter (SOM) exerts an effective plant growth promotion through a complex mechanism involving a coordinated activation of several key ion transport and signaling systems. We investigated the effects of HA on H+ and Ca2+ cellular dynamics at the early stages of lateral plant root development.
Emergence of lateral root in rice seedlings were related to specific H+ and Ca2+ fluxes in the root elongation zone underlying an activation of the plasma membrane H+-ATPase and of the Ca2+-dependent protein kinase (CDPK). The latter was coupled with an increased expression of the voltage-dependent OsTPC1 Ca2+channels and two stress responsive CDPK isoforms, such as OsCPK7 and OsCPK17.
HA act as molecular elicitors of H+ and Ca2+ fluxes, which seem to be upstream of a complex CDPK cell-signaling cascade. These findings shed light on the first ion signaling events involved in the mechanism of action of HA on plant growth and development.
Background
Plant biostimulants are diverse substances and microorganisms used to enhance plant growth. The global market for biostimulants is projected to increase 12 % per year and reach over $2,200 million by 2018. Despite the growing use of biostimulants in agriculture, many in the scientific community consider biostimulants to be lacking peer-reviewed scientific evaluation.
Scope
This article describes the emerging definitions of biostimulants and reviews the literature on five categories of biostimulants: i. microbial inoculants, ii. humic acids, iii. fulvic acids, iv. protein hydrolysates and amino acids, and v. seaweed extracts.
Conclusions
The large number of publications cited for each category of biostimulants demonstrates that there is growing scientific evidence supporting the use of biostimulants as agricultural inputs on diverse plant species. The cited literature also reveals some commonalities in plant responses to different biostimulants, such as increased root growth, enhanced nutrient uptake, and stress tolerance.
Drought-induced changes in the activities of superoxide dismutase (SOD) and catalase, level of lipid peroxidation, and membrane permeability (solute leakage) have been studied in two mosses, the drought-tolerant Tortula ruralis and the drought-sensitive Cratoneuron filicinum. In T. ruralis the activities of SOD and catalase increase during slow drying. The level of lipid peroxidation consequently declines. On subsequent rehydration the enzyme activities decline and the level of lipid peroxidation rises gradually to normal levels. The leakage of preloaded 86Rb on rehydration of slowly dried T. ruralis is similar to that in turgid moss, i.e. leakage of about 20% of tissue 86Rb. When T. ruralis is subjected to rapid drying there is no change in the enzyme activities or in lipid peroxidation. However, when this moss is rehydrated there is a large immediate increase in lipid peroxidation. Half of the tissue 86Rb is leaked into the bathing medium during the first hour of rehydration. But within the next hour, when SOD and catalase activities have increased to high levels, lipid peroxidation quickly declines to a level lower than that in the turgid control moss, and the 86Rb leaked earlier is partly reabsorbed indicating that membrane repair is well underway. On prolonged rehydration the enzyme activities decline and the level of lipid peroxidation rises gradually to reach normal levels found in control turgid moss. In the case of drought-sensitive C. filicinum the activities of SOD and catalase decline during drying as well as during subsequent rehydration. There is a rapid increase in lipid peroxidation during rehydration and most of the preloaded 86Rb leaks into the bathing medium irreversibly. The changes in lipid peroxidation during drying and subsequent rehydration of both the mosses appear to coincide in time with the reported changes in O2 uptake, indicating that the drought-induced membrane damage may be due to free radical-induced lipid peroxidation which is known to require active O2 uptake. Furthermore, there appears to be a good correlation between an ability of the tissue to control lipid peroxidation and its ability to retain solutes. It is suggested that ability of plant tissues to mobilize enzymatic defence against uncontrolled lipid peroxidation may be an important facet of their drought tolerance.
Humic acids are ubiquitous, organic-end-products of the chemical and microbial degradation of dead biota in soils throughout
the world. Humic acids can be transported in soil water as heterogeneous, supra-molecular, colloidal-agglomerates. Humic acid
accumulation in the rhizosphere of transpiring plants may chemically stimulate development by increasing root availability
of mineral nutrients and/or growth regulatory biomolecules. This report introduces novel, physical mechanisms by which humic
acid can also reduce plant development. Effects of humic acid addition to the root media of intact maize plants (Zea mays
L.) on their growth, transpiration and resistance to water deficits were assayed, as were the effects of external humic acid
on the hydraulic conductivity of excised primary-roots. Humic acid reduced shoot growth, transpiration and resistance to water
stress but not root growth. Root hydraulic conductivity was reduced by up to 44% via a time-, concentration- and size-dependent
fouling mechanism resulting from humic acid accumulation at root cell-walls. Thus, humic acid is shown, apparently for the
first time, to be able to exert novel physical effects in addition to its known chemical effects on plant development.
KeywordsRhizosphere-Humic acid-Cell-wall-fouling-Hydraulic-conductivity-Water-stress-resistance
It is well known that abscisic acid (ABA) promotes reactive oxygen species (ROS) production through plasma membrane-associated NADPH oxidases during ABA signaling. However, whether ROS from organelles can act as second messengers in ABA signaling is largely unknown. Here, we identified an ABA overly sensitive mutant, abo6, in a genetic screen for ABA-mediated inhibition of primary root growth. ABO6 encodes a DEXH box RNA helicase that is involved in regulating the splicing of several genes of complex I in mitochondria. The abo6 mutant accumulated more ROS in mitochondria, as established using a mitochondrial superoxide indicator, circularly permuted yellow fluorescent protein. Two dominant-negative mutations in ABA insensitive1 (abi1-1) and abi2-1 greatly reduced ROS production in mitochondria. The ABA sensitivity of abo6 can also be compromised by the atrbohF mutation. ABA-mediated inhibition of seed germination and primary root growth in abo6 was released by the addition of reduced GSH and exogenous auxin to the medium. Expression of auxin-responsive markers ProDR5:GUS (for synthetic auxin response element D1-4 with site-directed mutants in the 5'-end from soybean):β-glucuronidase) and Indole-3-acetic acid inducible2:GUS was greatly reduced by the abo6 mutation. Hence, our results provide molecular evidence for the interplay between ABA and auxin through the production of ROS from mitochondria. This interplay regulates primary root growth and seed germination in Arabidopsis thaliana.
It is widely reported that some humic substances behave as exogenous auxins influencing root growth by mechanisms that are not yet completely understood. This study explores the hypothesis that the humic acids' effects on root development involve a nitric oxide signaling. Maize seedlings were treated with HA 20 mg C L(-1), IAA 0.1 nM, and NO donors (SNP or GSNO), in combination with either the auxin-signaling inhibitor PCIB, the auxin efflux inhibitor TIBA, or the NO scavenger PTIO. H(+)-transport-competent plasma membrane vesicles were isolated from roots to investigate a possible link between NO-induced H(+)-pump and HA bioactivity. Plants treated with either HA or SNP stimulated similarly the lateral roots emergence even in the presence of the auxin inhibitors, whereas NO scavenger diminished this effect. These treatments induced H(+)-ATPase stimulation by threefold, which was abolished by PTIO and decreased by auxin inhibitors. HA-induced NO synthesis was also detected in the sites of lateral roots emergence. These data depict a new scenario where the root development stimulation and the H(+)-ATPase activation elicited by either HA or exogenous IAA depend essentially on mechanisms that use NO as a messenger induced site-specifically in the early stages of lateral root development.
Besides being essential for plant structure and metabolism, soluble carbohydrates play important roles in stress responses. Sucrose has been shown to confer to Arabidopsis seedlings a high level of tolerance to the herbicide atrazine, which causes reactive oxygen species (ROS) production and oxidative stress. The effects of atrazine and of exogenous sucrose on ROS patterns and ROS-scavenging systems were studied. Simultaneous analysis of ROS contents, expression of ROS-related genes and activities of ROS-scavenging enzymes gave an integrative view of physiological state and detoxifying potential under conditions of sensitivity or tolerance.
Toxicity of atrazine could be related to inefficient activation of singlet oxygen (1O2) quenching pathways leading to 1O2 accumulation. Atrazine treatment also increased hydrogen peroxide (H2O2) content, while reducing gene expressions and enzymatic activities related to two major H2O2-detoxification pathways. Conversely, sucrose-protected plantlets in the presence of atrazine exhibited efficient 1O2 quenching, low 1O2 accumulation and active H2O2-detoxifying systems.
In conclusion, sucrose protection was in part due to activation of specific ROS scavenging systems with consequent reduction of oxidative damages. Importance of ROS combination and potential interferences of sucrose, xenobiotic and ROS signalling pathways are discussed.
Extracellular ATP regulates higher plant growth and adaptation. The signalling events may be unique to higher plants, as they lack animal purinoceptor homologues. Although it is known that plant cytosolic free Ca2+ can be elevated by extracellular ATP, the mechanism is unknown. Here, we have studied roots of Arabidopsis thaliana to determine the events that lead to the transcriptional stress response evoked by extracellular ATP. Root cell protoplasts were used to demonstrate that signalling to elevate cytosolic free Ca2+ is determined by ATP perception at the plasma membrane, and not at the cell wall. Imaging revealed that extracellular ATP causes the production of reactive oxygen species in intact roots, with the plasma membrane NADPH oxidase AtRBOHC being the major contributor. This resulted in the stimulation of plasma membrane Ca2+-permeable channels (determined using patch-clamp electrophysiology), which contribute to the elevation of cytosolic free Ca2+. Disruption of this pathway in the AtrbohC mutant impaired the extracellular ATP-induced increase in reactive oxygen species (ROS), the activation of Ca2+ channels, and the transcription of the MAP kinase3 gene that is known to be involved in stress responses. This study shows that higher plants, although bereft of purinoceptor homologues, could have evolved a distinct mechanism to transduce the ATP signal at the plasma membrane.
Earthworms (Eisenia foetida) produce humic substances that can influence plant growth by mechanisms that are not yet clear. In this work, we investigated the effects of humic acids (HAs) isolated from cattle manure earthworm compost on the earliest stages of lateral root development and on the plasma membrane H(+)-ATPase activity. These HAs enhance the root growth of maize (Zea mays) seedlings in conjunction with a marked proliferation of sites of lateral root emergence. They also stimulate the plasma membrane H(+)-ATPase activity, apparently associated with an ability to promote expression of this enzyme. In addition, structural analysis reveals the presence of exchangeable auxin groups in the macrostructure of the earthworm compost HA. These results may shed light on the hormonal activity that has been postulated for these humic substances.
Cell expansion is a central process in plant morphogenesis, and the elongation of roots and root hairs is essential for uptake of minerals and water from the soil. Ca2+ influx from the extracellular store is required for (and sets the rates of) cell elongation in roots. Arabidopsis thaliana rhd2 mutants are defective in Ca2+ uptake and consequently cell expansion is compromised--rhd2 mutants have short root hairs and stunted roots. To determine the regulation of Ca2+ acquisition in growing root cells we show here that RHD2 is an NADPH oxidase, a protein that transfers electrons from NADPH to an electron acceptor leading to the formation of reactive oxygen species (ROS). We show that ROS accumulate in growing wild-type (WT) root hairs but their levels are markedly decreased in rhd2 mutants. Blocking the activity of the NADPH oxidase with diphenylene iodonium (DPI) inhibits ROS formation and phenocopies Rhd2-. Treatment of rhd2 roots with ROS partly suppresses the mutant phenotype and stimulates the activity of plasma membrane hyperpolarization-activated Ca2+ channels, the predominant root Ca2+ acquisition system. This indicates that NADPH oxidases control development by making ROS that regulate plant cell expansion through the activation of Ca2+ channels.
Root hairs are tip-growing tubes that emerge from trichoblasts (hair-forming epidermal cells) along the length of the root. Signalling events involved in the formation of root hairs are largely unknown. However, two recent studies have revealed that signalling enzymes such as NADPH oxidase and phospholipase D are crucial for root hair growth and development. Reactive oxygen species (ROS) produced by NADPH oxidase activate calcium ion channels in the apical plasma membrane leading to the tip-focused calcium gradient, an inherent feature of growing root hairs.
A protein determination method which involves the binding of Coomassie Brilliant Blue G-250 to protein is described. The binding of the dye to protein causes a shift in the absorption maximum of the dye from 465 to 595 nm, and it is the increase in absorption at 595 nm which is monitored. This assay is very reproducible and rapid with the dye binding process virtually complete in approximately 2 min with good color stability for 1 hr. There is little or no interference from cations such as sodium or potassium nor from carbohydrates such as sucrose. A small amount of color is developed in the presence of strongly alkaline buffering agents, but the assay may be run accurately by the use of proper buffer controls. The only components found to give excessive interfering color in the assay are relatively large amounts of detergents such as sodium dodecyl sulfate, Triton X-100, and commercial glassware detergents. Interference by small amounts of detergent may be eliminated by the use of proper controls.
Despite substantial evidence showing the ammonium-altered redox homeostasis in plants, the involvement and molecular mechanism of heme-heme oxygenase1 (heme-HO1), a novel antioxidant system, in the regulation of ammonium tolerance remain elusive. To fill in these gaps, the biological function of rice HO1 (OsSE5) was investigated. Results showed that NH4 Cl up-regulated rice OsSE5 expression. Oxidative stress and subsequent growth inhibition induced by excess NH4 Cl was partly mitigated by pretreatment with carbon monoxide (CO, a by-product of HO1 activity) or intensified by zinc protoporphyrin (ZnPP, a potent inhibitor of HO1 activity). Pretreatment with HO1 inducer hemin, not only up-regulated OsSE5 expression and HO activity, but also rescued the down-regulation of antioxidant transcripts, total and related isozymatic activities, thus significantly counteracting the excess NH4 Cl-triggered reactive oxygen species overproduction, lipid peroxidation, and growth inhibition. OsSE5 RNAi-transgenic rice plants revealed NH4 Cl-hypersensitive phenotype with impaired antioxidant defence, both of which could be rescued by CO but not hemin. Transgenic Arabidopsis plants over-expressing OsSE5 also exhibited enhanced tolerance to NH4 Cl, which might be attributed to the up-regulation of several antioxidant transcripts. Altogether, these results illustrated the involvement of heme-HO1 system in ammonium tolerance by enhancing antioxidant defence, which may improve plant tolerance to excess ammonium fertilizer.
The increase in root growth is one of the major effects of humic substances, but the mechanisms involved in humic acid-mediated changes in root growth, morphology and architecture are poorly known. Probably, humic substances may act on plant development through an action on the hormonal balance within the plant, either directly or indirectly by affecting the root uptake of some nutrients. In this study we investigate in cucumber plants the effects of a purified sedimentary humic acid (PHA), without detectable concentrations of the main phytoregulators in its structure, on root architecture, and its relationships with the functional action of three phytoregulators, indole-acetic acid, ethylene and nitric oxide, which are also affected by the root application of this humic acid. The results obtained using inhibitors of auxin transport or action, inhibitors of ethylene biosynthesis or action, and a scavenger of nitric oxide indicate that the increase in the root concentration of these phytoregulators caused by the root application of PHA does not play an essential role in the expression of the main changes on root architecture caused by PHA in developed cucumber plants. Other factors, which could act in coordination or independently of those phytoregulators affected by PHA root application, must be involved in the whole action on this humic acid on root architecture in cucumber.
Humic substances (HS), as component of soil organic matter, have been widely studied. Their positive effects on plant physiology have been further demonstrated, but there are no clear evidences about the direct as well as indirect mechanisms regulating these processes.In this paper a transcriptomic approach based on the detection of cDNA-AFLP markers was used to identify candidate genes potentially involved in the regulation of the response to HS in Arabidopsis thaliana.Using 160 primer combinations, the cDNA-AFLP enabled to identify 133 genes putatively involved in plant–HS interaction. Sequence analysis and Gene Ontology classification indicated that a large number of genes involved in developmental and metabolic processes, as well as in transcription regulation or RNA metabolism were identified as HS-regulated. Real-Time PCR analyses confirmed transcription levels of 32 HS-regulated genes.This study demonstrates that HS exert their effects on plant physiology by means of complex transcriptional networks. From the overall transcriptomic results we may hypothesize that HS exert their function through a multifaceted mechanism of action, partially connected to their well demonstrated auxin activity, but involving also IAA-independent signalling pathways.
Humic substances (HS) contained in the vermicompost, are environmentally friendly materials that
restore the chemical and physical properties of soils and improve plant growth. The work described
herein was aimed at studying the HA–root interactions and their relationship with some components of
antioxidative metabolism in rice (Oryza sativa L.). These studies encompassed aspects ranging from the
activity of enzymes in antioxidative metabolism and the relationship between these enzymes and the
reactive oxygen species (ROS) content in rice to the expression of genes encoding rice tonoplast intrinsic
proteins (OsTIP), a sub-family of aquaporins. The HA–root interactions were also characterized. The
results from these studies demonstrate that the interaction of HA with the radicular system in plants activates
antioxidative enzymatic function, thus controlling the ROS content and modifying OsTIP expression.
Microscopic and spectroscopic techniques confirmed the interactions between HA fragments of lower
structural complexity and the radicular system. It appears that HA act in plants via a specific form of
stress that is detected by anti-stress defense systems in plants. These HA applied to plants can protect
against water stress in degraded soils.
Publisher Summary This chapter discusses the assay of catalases and peroxidases are: (1) catalase assay by disappearance of peroxide; (2) method for crude cell extracts; (3) direct spectrophotometric assay of catalase and peroxidase in cells and tissues; and (4) peroxidase assay by spectrophotometric measurements of the disappearance of hydrogen donor or the appearance of their colored oxidation products. Two methods are described for the catalase assay by disappearance of peroxide are: ultraviolet spectrophotometry and permanganate titration. Ultraviolet spectrophotometryis a method devised, on the basis of the absorption curves for peroxide solutions, for determining the activity of catalase by direct measurements of the decrease of light absorption in the region 230 to 250 mμ caused by the decomposition of hydrogen peroxide by catalase. In the case of method for crude cell extracts, oxygen evolution caused by the decomposition of hydrogen peroxide is measured with the conventional manometric technique. Peroxidase assay by spectrophotometric measurements of the disappearance of hydrogen donor or the appearance of their colored oxidation products includes the guaiacol test and the pyrogallol test.
Proline, which increases proportionately faster than other amino acids in plants under water stress, has been suggested as an evaluating parameter for irrigation scheduling and for selecting drought-resistant varieties. The necessity to analyze numerous samples from multiple replications of field grown materials prompted the development of a simple, rapid colorimetric determination of proline. The method detected proline in the 0.1 to 36.0 moles/g range of fresh weight leaf material.
The potential role of superoxide dismutase (SOD) in the protection against salt stress was examined using transgenic rice plants. The coding region of the yeast mitochondrial Mn-SOD gene was fused with the chloroplast targetting signal of glutamine synthetase gene and introduced into rice protoplasts by electroporation. Immunogold labeling experiments revealed that the yeast Mn-SOD was accumulated in the chloroplasts of transgenic rice. The total SOD activity in the control plant was mostly attributed to the activity of cytosolic and chloroplastic Cu/Zn-SOD. Total SOD activity in the transformant was about 1.7-fold that of the control under non-stressed conditions. The photosynthetic electron transport rates of control and transgenic rice were similar under non-stressed conditions. Upon salt stress (100 mM NaCl), the SOD activities decreased in both plants, but the decrease was faster in the control plant. The activities of overexpressed Mn-SOD and cytosolic Cu/Zn-SOD did not change upon salt stress in either the transgenic or control plants, whereas the chloroplastic Cu/Zn-SOD activity in control rice decreased significantly. At high salinity, the ascorbate peroxidase activity of the transformant was about 1.5-fold higher than that in the control. These results suggest that increased levels of ascorbate peroxidase and high levels of chloroplastic SOD in the transformant are important factors for salt resistance in rice.
The redox state of the chloroplast and mitochondria, the two main powerhouses of photosynthesizing eukaryotes, is maintained by a delicate balance between energy production and consumption, and affected by the need to avoid increased production of reactive oxygen species (ROS). These demands are especially critical during exposure to extreme environmental conditions, such as high light (HL) intensity, heat, drought or a combination of different environmental stresses. Under these conditions, ROS and redox cues, generated in the chloroplast and mitochondria, are essential for maintaining normal energy and metabolic fluxes, optimizing different cell functions, activating acclimation responses through retrograde signalling, and controlling whole-plant systemic signalling pathways. Regulation of the multiple redox and ROS signals in plants requires a high degree of coordination and balance between signalling and metabolic pathways in different cellular compartments. In this review, we provide an update on ROS and redox signalling in the context of abiotic stress responses, while addressing their role in retrograde regulation, systemic acquired acclimation and cellular coordination in plants.
Reactive oxygen species (ROS) play a multitude of signaling roles in different organisms from bacteria to mammalian cells. They were initially thought to be toxic byproducts of aerobic metabolism, but have now been acknowledged as central players in the complex signaling network of cells. In this review, we will attempt to address several key questions related to the use of ROS as signaling molecules in cells, including the dynamics and specificity of ROS signaling, networking of ROS with other signaling pathways, ROS signaling within and across different cells, ROS waves and the evolution of the ROS gene network.
The balance between cellular proliferation and differentiation is a key aspect of development in multicellular organisms. Using high-resolution expression data from the Arabidopsis root, we identified a transcription factor, UPBEAT1 (UPB1), that regulates this balance. Genomewide expression profiling coupled with ChIP-chip analysis revealed that UPB1 directly regulates the expression of a set of peroxidases that modulate the balance of reactive oxygen species (ROS) between the zones of cell proliferation and the zone of cell elongation where differentiation begins. Disruption of UPB1 activity alters this ROS balance, leading to a delay in the onset of differentiation. Modulation of either ROS balance or peroxidase activity through chemical reagents affects the onset of differentiation in a manner consistent with the postulated UPB1 function. This pathway functions independently of auxin and cytokinin plant hormonal signaling. Comparison to ROS-regulated growth control in animals suggests that a similar mechanism is used in plants and animals.
Various abiotic stresses lead to the overproduction of reactive oxygen species (ROS) in plants which are highly reactive and toxic and cause damage to proteins, lipids, carbohydrates and DNA which ultimately results in oxidative stress. The ROS comprises both free radical (O(2)(-), superoxide radicals; OH, hydroxyl radical; HO(2), perhydroxy radical and RO, alkoxy radicals) and non-radical (molecular) forms (H(2)O(2), hydrogen peroxide and (1)O(2), singlet oxygen). In chloroplasts, photosystem I and II (PSI and PSII) are the major sites for the production of (1)O(2) and O(2)(-). In mitochondria, complex I, ubiquinone and complex III of electron transport chain (ETC) are the major sites for the generation of O(2)(-). The antioxidant defense machinery protects plants against oxidative stress damages. Plants possess very efficient enzymatic (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR; monodehydroascorbate reductase, MDHAR; dehydroascorbate reductase, DHAR; glutathione peroxidase, GPX; guaicol peroxidase, GOPX and glutathione-S- transferase, GST) and non-enzymatic (ascorbic acid, ASH; glutathione, GSH; phenolic compounds, alkaloids, non-protein amino acids and α-tocopherols) antioxidant defense systems which work in concert to control the cascades of uncontrolled oxidation and protect plant cells from oxidative damage by scavenging of ROS. ROS also influence the expression of a number of genes and therefore control the many processes like growth, cell cycle, programmed cell death (PCD), abiotic stress responses, pathogen defense, systemic signaling and development. In this review, we describe the biochemistry of ROS and their production sites, and ROS scavenging antioxidant defense machinery.
Water deficit and salinity, especially under high light intensity or in combination with other stresses, disrupt photosynthesis and increase photorespiration, altering the normal homeostasis of cells and cause an increased production of reactive oxygen species (ROS). ROS play a dual role in the response of plants to abiotic stresses functioning as toxic by-products of stress metabolism, as well as important signal transduction molecules. In this review, we provide an overview of ROS homeostasis and signalling in response to drought and salt stresses and discuss the current understanding of ROS involvement in stress sensing, stress signalling and regulation of acclimation responses.
Nitro blue tetrazolium has been used to intercept O2− generated enzymically or photochemically. The reduction of NBT by O2− has been utilized as the basis of assays for superoxide dismutase, which exposes its presence by inhibiting the reduction of NBT. Superoxide dismutase could thus be assayed either in crude extracts or in purified protein fractions. The assays described are sensitive to ng/ml levels of super-oxide dismutase and were applicable in free solution or on polyacrylamide gels. The staining procedure for localizing superoxide dismutase on polyacrylamide electrophoretograms has been applied to extracts obtained from a variety of sources. E. coli has been found to contain two superoxide dismutases whereas bovine heart, brain, lung, and erthrocytes contain only one.
Previous studies suggest that salicylic acid (SA) plays an important role in influencing plant resistance to ozone (O3). To further define the role of SA in O3-induced responses, we compared the responses of two Arabidopsis genotypes that accumulate different amounts of SA in response to O3 and a SA-deficient transgenic Col-0 line expressing salicylate hydroxylase (NahG). The differences observed in O3-induced changes in SA levels, the accumulation of active oxygen species, defense gene expression, and the kinetics and severity of lesion formation indicate that SA influences O3 tolerance via two distinct mechanisms. Detailed analyses indicated that features associated with a hypersensitive response (HR) were significantly greater in O3-exposed Cvi-0 than in Col-0, and that NahG plants failed to exhibit these HR-like responses. Furthermore, O3-induced antioxidant defenses, including the redox state of glutathione, were greatly reduced in NahG plants compared to Col-0 and Cvi-0. This suggests that O3-induced cell death in NahG plants is due to the loss of SA-mediated potentiation of antioxidant defenses, while O3-induced cell death in Cvi-0 is due to activation of a HR. This hypothesis is supported by the observation that inhibition of NADPH-oxidases reduced O3-induced H2O2 levels and the O3-induced cell death in Cvi-0, while no major changes were observed in NahG plants. We conclude that although SA is required to maintain the cellular redox state and potentiate defense responses in O3 exposed plants, high levels of SA also potentiate activation of an oxidative burst and a cell death pathway that results in apparent O3 sensitivity.
The two most commonly used methods to analyze data from real-time, quantitative PCR experiments are absolute quantification and relative quantification. Absolute quantification determines the input copy number, usually by relating the PCR signal to a standard curve. Relative quantification relates the PCR signal of the target transcript in a treatment group to that of another sample such as an untreated control. The 2(-Delta Delta C(T)) method is a convenient way to analyze the relative changes in gene expression from real-time quantitative PCR experiments. The purpose of this report is to present the derivation, assumptions, and applications of the 2(-Delta Delta C(T)) method. In addition, we present the derivation and applications of two variations of the 2(-Delta Delta C(T)) method that may be useful in the analysis of real-time, quantitative PCR data.
Reactive oxygen species (ROS) control many different processes in plants. However, being toxic molecules, they are also capable of injuring cells. How this conflict is resolved in plants is largely unknown. Nonetheless, it is clear that the steady-state level of ROS in cells needs to be tightly regulated. In Arabidopsis, a network of at least 152 genes is involved in managing the level of ROS. This network is highly dynamic and redundant, and encodes ROS-scavenging and ROS-producing proteins. Although recent studies have unraveled some of the key players in the network, many questions related to its mode of regulation, its protective roles and its modulation of signaling networks that control growth, development and stress response remain unanswered.
Shoots, roots, and seeds of corn (Zea mays L., cv. Michigan 500), oats (Avena sativa L., cv. Au Sable), and peas (Pisum sativum L., cv. Wando) were analyzed for their superoxide dismutase content using a photochemical assay system consisting of methionine, riboflavin, and p-nitro blue tetrazolium. The enzyme is present in the shoots, roots, and seeds of the three species. On a dry weight basis, shoots contain more enzyme than roots. In seeds, the enzyme is present in both the embryo and the storage tissue. Electrophoresis indicated a total of 10 distinct forms of the enzyme. Corn contained seven of these forms and oats three. Peas contained one of the corn and two of the oat enzymes. Nine of the enzyme activities were eliminated with cyanide treatment suggesting that they may be cupro-zinc enzymes, whereas one was cyanide-resistant and may be a manganese enzyme. Some of the leaf superoxide dismutases were found primarily in mitochondria or chloroplasts. Peroxidases at high concentrations interfere with the assay. In test tube assays of crude extracts from seedlings, the interference was negligible. On gels, however, peroxidases may account for two of the 10 superoxide dismutase forms.
Characteristics of pyrroline-5-carboxylate reductase (P5CR) from Bradyrhizobium japonicum bacteroids and cultured rhizobia were compared with those of the enzyme in soybean nodule host cytosol. Reductase from host cytosol differed from that in bacteroids in: (a) the effect of pH on enzymic activity, (b) the capacity to catalyze both reduction of pyrroline-5-carboxylic acid and NAD(+)-dependent proline oxidation, (c) apparent affinities for pyrroline-5-carboxylic acid, and (d) sensitivities to inhibition by NADP(+) and proline. The K(1) for proline inhibition of P5CR in bacteroid cytosol was 1.8 millimolar. The properties of P5CR in B. japonicum and bacteroid cytosol were similar. The specific activities of P5CR in the cytosolic fractions of the nodule host and the bacteroid compartment were also comparable.
For accurate and reliable gene expression results, normalization of real-time PCR data is required against a control gene, which displays highly uniform expression in living organisms during various phases of development and under different environmental conditions. We assessed the gene expression of 10 frequently used housekeeping genes, including 18S rRNA, 25S rRNA, UBC, UBQ5, UBQ10, ACT11, GAPDH, eEF-1alpha, eIF-4a, and beta-TUB, in a diverse set of 25 rice samples. Their expression varied considerably in different tissue samples analyzed. The expression of UBQ5 and eEF-1alpha was most stable across all the tissue samples examined. However, 18S and 25S rRNA exhibited most stable expression in plants grown under various environmental conditions. Also, a set of two genes was found to be better as control for normalization of the data. The expression of these genes (with more uniform expression) can be used for normalization of real-time PCR results for gene expression studies in a wide variety of samples in rice.
Aldehyde dehydrogenases (ALDHs) play a major role in the detoxification processes of aldehydes generated in plants when exposed to abiotic stress. In previous studies, we have shown that the Arabidopsis thaliana ALDH3I1 gene is transcriptionally activated by abiotic stress, and over-expression of the ALDH3I1 gene confers stress tolerance in transgenic plants. The A. thaliana genome contains 14 ALDH genes expressed in different sub-cellular compartments and are presumably involved in different reactions. The purpose of this study was to compare the potential of a cytoplasmic and a chloroplastic stress-inducible ALDH in conferring stress tolerance under different conditions. We demonstrated that constitutive or stress-inducible expression of both the chloroplastic ALDH3I1 and the cytoplasmic ALDH7B4 confers tolerance to osmotic and oxidative stress. Stress tolerance in transgenic plants is accompanied by a reduction of H2O2 and malondialdehyde (MDA) derived from cellular lipid peroxidation. Involvement of ALDHs in stress tolerance was corroborated by the analysis of ALDH3I1 and ALDH7B4 T-DNA knockout (KO) mutants. Both mutant lines exhibited higher sensitivity to dehydration and salt than wild-type (WT) plants. The results indicate that ALDH3I1 and ALDH7B4 not only function as aldehyde-detoxifying enzymes, but also as efficient reactive oxygen species (ROS) scavengers and lipid peroxidation-inhibiting enzymes. The potential of ALDHs to interfere with H2O2 was also shown for recombinant bacterial proteins.
Hydrogen peroxide is an important regulatory agent in plants. This study demonstrates that exogenous H2O2 application to Arabidopsis thaliana root epidermis results in dose-dependent transient increases in net Ca2+ influx. The magnitude and duration of the transients were greater in the elongation zone than in the mature epidermis. In both regions, treatment with the cation channel blocker Gd3+ prevented H2O2-induced net Ca2+ influx, consistent with application of exogenous H2O2 resulting in the activation of plasma membrane Gd3+-sensitive Ca2+-influx pathways. Application of 10 mm H2O2 to the external plasma membrane face of elongation zone epidermal protoplasts resulted in the appearance of a hyperpolarization-activated Ca2+-permeable conductance. This conductance differed from that previously characterized as being responsive to extracellular hydroxyl radicals. In contrast, in mature epidermal protoplasts a plasma membrane hyperpolarization-activated Ca2+-permeable channel was activated only when H2O2 was present at the intracellular membrane face. Channel open probability increased with intracellular [H2O2] and at hyperpolarized voltages. Unitary conductance decreased thus: Ba2+ > Ca2+ (14.5 pS) > Mg2+ > Zn2+ (20 mM external cation, 1 mM H2O2). Lanthanides and Zn2+ (but not TEA+) suppressed the open probability without affecting current amplitude. The results suggest spatial heterogeneity and differential sensitivity of Ca2+ channel activation by reactive oxygen species in the root that could underpin signalling.
The respective distribution of superoxide (O(2) (.-)) and hydrogen peroxide (H(2)O(2)), two reactive oxygen species (ROS) involved in root growth and differentiation, was determined within the Arabidopsis root tip. We investigated the effect of changing the levels of these ROS on root development and the possible interactions with peroxidases. H(2)O(2) was detected by confocal laser-scanning microscopy using hydroxyphenyl fluorescein (HPF). Both O(2) (.-) accumulation and peroxidase distribution were assessed by light microscopy, using nitroblue tetrazolium (NBT) and o-dianisidine, respectively. Root length and root hair length and density were also quantified following ROS scavenging. O(2) (.-) was predominantly located in the apoplast of cell elongation zone, whereas H(2)O(2) accumulated in the differentiation zone and the cell wall of root hairs in formation. Treatments that decrease O(2) (.-) concentration reduced root elongation and root hair formation, while scavenging H(2)O(2) promoted root elongation and suppressed root hair formation. The results allow to precise the respective role of O(2) (.-) and H(2)O(2) in root growth and development. The consequences of their distinct accumulation sites within the root tip are discussed, especially in relation to peroxidases.
Reactive oxygen species (ROS) play a dual role in plant biology acting on the one hand as important signal transduction molecules and on the other as toxic by-products of aerobic metabolism that accumulate in cells during different stress conditions. Because of their toxicity as well as their important signaling role, the level of ROS in cells is tightly controlled by a vast network of genes termed the 'ROS gene network'. Using mutants deficient in key ROS-scavenging enzymes, we have defined a signaling pathway that is activated in cells in response to ROS accumulation. Interestingly, many of the key players in this pathway, including different zinc finger proteins and WRKY transcription factors, are also central regulators of abiotic stress responses involved in temperature, salinity and osmotic stresses. Here, we describe our recent findings and discuss how ROS integrate different signals originating from different cellular compartments during abiotic stress.
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