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Drought-Induced Changes in Leaf Morphology and Anatomy: Overview, Implications and Perspectives
... Dicot plants, in particular, may exhibit different responses in stomatal density based on their adaptation mechanisms. While some dicots reduce stomatal density to minimize water loss, others maintain higher stomatal densities to continue photosynthesis and development despite limited water availability (Yavas et al. 2024). The results showed that the two olive cultivars had good adaptations against water deficit since they had a maximum of 465 ST/mm 2 and could even reach less than 400 ST/mm 2 . ...
... Notably, olive cultivars native to arid regions tend to excel in adapting to drought compared to those originating from more temperate locations (Bacelar et al. 2007;Brito et al. 2019). In terms of morphology, leaves with higher trichome density per leaf area exhibit greater resistance to abiotic degradation, as they facilitate transpiration regulation, preventing excessive water loss and regulating temperature (Chen et al. 2022;Yavas et al. 2024). Same authors noted a significant increase in trichome numbers during the dry season compared to the wet season, impacting plant physiological processes. ...
... Trichomes play a crucial role in directing water droplets away from the stem and soil towards them, aiding in water absorption. They also contribute to decreased transpiration, alteration of energy balance, and reduced light absorption, thereby enhancing water storage (Yavas et al. 2024). A previous works reports that under normal watering conditions, stomatal density ranges from 267.41 to 232.63 per mm 2 , and trichome density ranges from 85.50 to 55.55 per mm 2 of leaf area. ...
In olive-growing regions, climate change exacerbates challenges like high temperatures and water scarcity, necessitating a deeper understanding of its impact on olive trees behaviour to cope with drought. This study assesses the ecophysiological performance of 12-year-old olive trees ‘Chemlali Sfax’ (local) and ‘Koroneiki’ (Greek) and drought response mechanisms for developing agronomic strategies that ensure sustainable yields despite adverse climatic conditions in the Mediterranean region (Tunisia). Leaf water content declined from February, with ‘Chemlali Sfax’ and ‘Koroneiki’ maintaining higher content (59%) in June 2012. ‘Koroneiki’ exhibited significantly reduced relative water content (48.09%), leaf area (396.82 mm2), stomatal (346.59 ST/mm2), and trichomic densities (135.66 TR/mm2) compared to ‘Chemlali Sfax’. Soil moisture in the 40–80 cm horizon was higher in April, with ‘Koroneiki’ reaching 5.40% compared to ‘Chemlali Sfax’ at 4.42%. ‘Chemlali Sfax’ significantly outperformed ‘Koroneiki’ in yield, yielding 1129.2 kg/ha compared to 956.9 kg/ha during the 2011–2012 period. Despite these differences, both cultivars showed promising productivity potential under arid, rain-fed conditions, with an average water utilization of 0.8 kg/m3. ‘Chemlali Sfax’ and ‘Koroneiki’ demonstrated favourable adaptability and yield stability in arid conditions, suggesting its potential suitability for cultivation in such environments. Future research directions include exploring the effects of planting both cultivars at identical densities and combinations on olive oil and fruit qualities, as well as exploring additional ecophysiological parameters to enhance understanding of olive tree responses to water stress and drought tolerance mechanisms.
Enhancing the water-use efficiency (WUE) of barley cultivars may safeguard yield deficits during periods of low rainfall. Reduced stomatal density is linked to enhanced WUE, leading to improved drought resistance across plant genera. In this study, 10 barley varieties exhibiting a range of stomatal density phenotypes were grown under differing soil water contents to determine whether stomatal density influences the capacity of genotypes to resist low water availability. The low-stomatal-density genotype Hindmarsh showed the least impact on biomass production during early development, with a 37.13% decrease in dry biomass during drought treatment. Low-stomatal-density genotypes additionally outcompeted high-stomatal-density genotypes under water-deprivation conditions during the reproductive phase of development, exhibiting 19.35% greater wilting resistance and generating 54.62% more heads relative to high-stomatal-density genotypes (p < 0.05). Finally, a correlation analysis revealed a strong negative linear relationship between stomatal density and the traits of head number (r = −0.71) and the number of days until wilting symptoms (r = −0.67) (p < 0.05). The combined results indicate that low-stomatal-density genotypes show promising attributes for high WUE, revealing novel barley varieties that may be useful to future breed improvement for drought tolerance.
Life on Earth depends on the conversion of solar energy to chemical energy by plants through photosynthesis. A fundamental challenge in optimizing photosynthesis is to adjust leaf angles to efficiently use the intercepted sunlight under the constraints of heat stress, water loss and competition. Despite the importance of leaf angle, until recently, we have lacked data and frameworks to describe and predict leaf angle dynamics and their impacts on leaves to the globe. We review the role of leaf angle in studies of ecophysiology, ecosystem ecology and earth system science, and highlight the essential yet understudied role of leaf angle as an ecological strategy to regulate plant carbon–water–energy nexus and to bridge leaf, canopy and earth system processes. Using two models, we show that leaf angle variations have significant impacts on not only canopy‐scale photosynthesis, energy balance and water use efficiency but also light competition within the forest canopy. New techniques to measure leaf angles are emerging, opening opportunities to understand the rarely‐measured intraspecific, interspecific, seasonal and interannual variations of leaf angles and their implications to plant biology and earth system science. We conclude by proposing three directions for future research.
Background: Climate change and depleting water sources demand scarce natural water supplies like air moisture to be used as an irrigation water source. Wheat production is threatened by climate variability and extreme climate events especially heat waves and drought. The present study focused to develop the wheat plant for self-irrigation by optimizing leaf architecture and surface properties for precise irrigation.
Methods: Thirty-four genotypes were selected from 1796 genotypes with all combinations of leaf angle and leaf rolling. These genotypes were characterized for morpho-physiological traits and soil moisture content at stem elongation and booting stages. Further, a core set of ten genotypes was evaluated for stem flow efficiency and leaf wettability.
Results: Biplot, heat map, and correlation analysis indicated wide diversity and traits association. The environmental parameters indicated a substantial amount of air moisture (> 60% relative humidity) at these critical wheat growth stages. Leaf angle showed a negative association with leaf rolling, physiological and yield traits, adaxial and abaxial contact angle while leaf angle showed a positive association with the stem flow water. The wettability and air moisture harvesting indicated that the genotypes (coded as 1, 7, and 18) having semi-erect to erect leaf angle, spiral rolling,
and hydrophilic leaf surface (<90o) with contact angle hysteresis less than 10o
had higher soil moisture content (6-8%) and moisture harvesting efficiency (3.5 ml).
Conclusions: These findings can provide the basis to develop self-irrigating, drought-tolerant wheat cultivars as an adaptation to climate change.
Osmotic stress that is induced by salinity and drought affects plant growth and development, resulting in significant losses to global crop production. Consequently, there is a strong need to develop stress-tolerant crops with a higher water use efficiency through breeding programs. Water use efficiency could be improved by decreasing stomatal transpiration without causing a reduction in CO2 uptake under osmotic stress conditions. The genetic manipulation of stomatal density could be one of the most promising strategies for breeders to achieve this goal. On the other hand, a substantial amount of water loss occurs across the cuticle without any contribution to carbon gain when the stomata are closed and under osmotic stress. The minimization of cuticular (otherwise known as residual) transpiration also determines the fitness and survival capacity of the plant under the conditions of a water deficit. The deposition of cuticular wax on the leaf epidermis acts as a limiting barrier for residual transpiration. However, the causal relationship between the frequency of stomatal density and plant osmotic stress tolerance and the link between residual transpiration and cuticular wax is not always straightforward, with controversial reports available in the literature. In this review, we focus on these controversies and explore the potential physiological and molecular aspects of controlling stomatal and residual transpiration water loss for improving water use efficiency under osmotic stress conditions via a comparative analysis of the performance of domesticated crops and their wild relatives.
Leaf rolling is a common response to drought among members of the grass family. A detailed understanding of the structural changes that occur when rice leaves roll in response to drought may assist in determining the physiological mechanisms underlying this feature and determining its potential utility in plant breeding. The anatomical characteristics of rice cultivars native to northeastern Thailand in response to drought stress were evaluated in this study. Polyethylene glycol (PEG) treatments were applied to seedlings of 28 native rice cultivars and two rice breeding cultivars for 10 d. When cultivated in drought-prone environments, the native rice cultivars had a leaf rolling index between 4 and 7, which was classified as moderate to high leaf rolling. Rice leaf anatomy exhibited profound changes in response to drought, with smaller bulliform cells (36.8%), thicker epidermis (10.98%), smaller vascular bundles (7.41%), and smaller bundle sheath cells (11.95%). Decision trees were used to explore the association between the degree of leaf rolling and anatomical traits. According to the decision tree models generated on the basis of the gain ratio, information gain, and Gini index, the epidermis, leaf thickness, and bulliform cells were the major factors of the root nodes, and the maximum accuracy of the models was 70.90%. Overall, the models indicated that rice leaves with a thin epidermis, large bulliform cells, thin leaves, and small vascular bundles are more likely to display high leaf rolling adaptations under drought stress conditions.
Stomata are specialized portals in plant leaves to modulate water loss from plants to the atmosphere by control of the transpiration, thereby determining the water-use efficiency and drought resistance of plants. Despite that the stomata developmental progression is well-understood at the molecular level, the experimental evidence that miRNA regulates stomata development is still lacking, and the underlying mechanism remains elusive. This study demonstrates the involvement of stu-miR827 in regulating the drought tolerance of potato due to its control over the leaf stomatal density. The expression analysis showed that stu-miR827 was obviously repressed by drought stresses and then rapidly increased after rewatering. Suppressing the expression of stu-miR827 transgenic potato lines showed an increase in stomatal density, correlating with a weaker drought resistance compared with wildtype potato lines. In addition, StWRKY48 was identified as the target gene of stu-miR827, and the expression of StWRKY48 was obviously induced by drought stresses and was greatly upregulated in stu-miR827 knockdown transgenic potato lines, suggesting its involvement in the drought stress response. Importantly, the expression of genes associated with stomata development, such as SDD (stomatal density and distribution) and TMM (too many mouths), was seriously suppressed in transgenic lines. Altogether, these observations demonstrated that suppression of stu-miR827 might lead to overexpression of StWRKY48, which may contribute to negatively regulating the drought adaptation of potato by increasing the stomatal density. The results may facilitate functional studies of miRNAs in the process of drought tolerance in plants.
Using cryo scanning electron microscopy, the surface micromorphology of vegetative (leaf blade and ligule) and generative (pedicel and outer glume) organs in Deschampsia antarctica , one of the only two flowering plants native to Antarctica, was examined. Whereas the pedicel and outer glume were wax-free, both leaf sides had a prominent epicuticular wax coverage consisting of two superimposed layers: polygonal rodlets formed by fused irregular platelets (the lower wax layer) and membraneous platelets (the upper wax layer). Although the adaxial (inner) and abaxial (outer) leaf surfaces showed a similar microstructure of the wax coverage, they differed in the thickness ratio between lower and upper wax layer. The ligule bore a very loose wax coverage composed of separate scale-like projections or clusters of them. We suppose that the two-layered wax densely covering both leaf surfaces might contribute to the plant adaptation to severe environmental conditions in Antarctica due to an increase of its resistance against cold temperatures, icing, harmful UV radiation, and dehydration. The presence of the epicuticular wax on the abaxial leaf side and the ligule as well as the hierarchical structure of the wax coverage on both leaf surfaces is described in D. antarctica for the first time.
Background
Water deficit (WD) has serious effect on the productivity of crops. Formation of cuticular layer with increased content of wax and cutin on leaf surfaces is closely related to drought tolerance. Identification of drought tolerance associated wax components and cutin monomers and the genes responsible for their biosynthesis is essential for understanding the physiological and genetic mechanisms underlying drought tolerance and improving crop drought resistance.
Result
In this study, we conducted comparative phenotypic and transcriptomic analyses of two Gossypium hirsutum varieties that are tolerant (XL22) or sensitive (XL17) to drought stress. XL17 consumed more water than XL22, particularly under the WD conditions. WD significantly induced accumulation of most major wax components (C29 and C31 alkanes) and cutin monomers (palmitic acid and stearic acid) in leaves of both XL22 and XL17, although accumulation of the major cutin monomers, i.e., polyunsaturated linolenic acid (C18:3n-3) and linoleic acid (C18:2n-6), were significantly repressed by WD in both XL22 and XL17. According to the results of transcriptome analysis, although many genes and their related pathways were commonly induced or repressed by WD in both XL22 and XL17, WD-induced differentially expressed genes specific to XL22 or XL17 were also evident. Among the genes that were commonly induced by WD were the GhCER1 genes involved in biosynthesis of alkanes, consistent with the observation of enhanced accumulation of alkanes in cotton leaves under the WD conditions. Interestingly, under the WD conditions, several GhCYP86 genes, which encode enzymes catalyzing the omega-hydroxylation of fatty acids and were identified to be the hub genes of one of the co-expression gene modules, showed a different expression pattern between XL22 and XL17 that was in agreement with the WD-induced changes of the content of hydroxyacids or fatty alcohols in these two varieties.
Conclusion
The results contribute to our comprehending the physiological and genetic mechanisms underlying drought tolerance and provide possible solutions for the difference of drought resistance of different cotton varieties.
Rice (Oryza sativa L.) is one of the main food crops for human survival, and its yield is often restricted by abiotic stresses. Drought and soil salinity are among the most damaging abiotic stresses affecting today’s agriculture. Given the importance of abscisic acid (ABA) in plant growth and abiotic stress responses, it is very important to identify new genes involved in ABA signal transduction. We screened a drought-inducing gene containing about 158 amino acid residues from the transcriptome library of rice exposed to drought treatment, and we found ABA-related cis-acting elements and multiple drought-stress-related cis-acting elements in its promoter sequence. The results of real-time PCR showed that OsMLP423 was strongly induced by drought and salt stresses. The physiological and biochemical phenotype analysis of transgenic plants confirmed that overexpression of OsMLP423 enhanced the tolerance to drought and salt stresses in rice. The expression of OsMLP423-GFP fusion protein indicated that OsMLP423 was located in both the cell membrane system and nucleus. Compared with the wild type, the overexpressed OsMLP423 showed enhanced sensitivity to ABA. Physiological analyses showed that the overexpression of OsMLP423 may regulate the water loss efficiency and ABA-responsive gene expression of rice plants under drought and salt stresses, and it reduces membrane damage and the accumulation of reactive oxygen species. These results indicate that OsMLP423 is a positive regulator of drought and salinity tolerance in rice, governing the tolerance of rice to abiotic stresses through an ABA-dependent pathway. Therefore, this study provides a new insight into the physiological and molecular mechanisms of OsMLP423-mediated ABA signal transduction participating in drought and salt stresses.
To address the demand for food by a rapidly growing human population, agricultural scientists have carried out both plant breeding and genetic engineering research. Previously, we reported that the constitutive expression of a pea apyrase (Nucleoside triphosphate, diphosphohydrolase) gene, psNTP9, under the control of the CaMV35S promoter, resulted in soybean plants with an expanded root system architecture, enhanced drought resistance and increased seed yield when they are grown in greenhouses under controlled conditions. Here, we report that psNTP9-expressing soybean lines also show significantly enhanced seed yields when grown in multiple different field conditions at multiple field sites, including when the gene is introgressed into elite germplasm. The transgenic lines have higher leaf chlorophyll and soluble protein contents and decreased stomatal density and cuticle permeability, traits that increase water use efficiency and likely contribute to the increased seed yields of field-grown plants. These altered properties are explained, in part, by genome-wide gene expression changes induced by the transgene.
Many arid lands across the globe are experiencing more frequent and extreme droughts due to warmer temperatures resulting from climate change, less predictable precipitation patterns, and decreased soil moisture. Approximately 60–90% of household water is used for urban landscape irrigation in the western United States, necessitating the establishment of landscapes using drought-tolerant plants that conserve water. Shepherdia ×utahensis (hybrid buffaloberry) is a drought-tolerant plant with dense leaf trichomes (epidermal appendages) that may limit excessive water loss by transpiration. However, little is known about how S. ×utahensis regulates leaf heat balance when transpirational cooling is limited. The objective of this research was to investigate the effects of substrate water availability on plant growth and development and trichome density of S. ×utahensis. Ninety-six clonally propagated plants were grown using an automated irrigation system, and their substrate volumetric water contents were controlled at 0.05–0.40 m³·m⁻³ for 2 months. Results showed that water stress impaired plant growth and increased the proportion of visibly wilted leaves. Shepherdia ×utahensis acclimates to drought by reducing cell dehydration and canopy overheating, which may be accomplished through decreased stomatal conductance, smaller leaf development, leaf curling, increased leaf thickness, and greater root-to-shoot ratio. Leaf trichome density increased when stem water potential decreased, resulting in greater leaf reflectance of visible light. Cell and leaf expansion were restricted under water stress, and negative correlations were exhibited between epidermal cell size and trichome density. According to our results, plasticity in leaves and roots aids plants in tolerating abiotic stresses associated with drought. Acclimation of S. ×utahensis to water stress was associated with increased trichome density due to plasticity in cell size. Dense trichomes on leaves reflected more lights which appeared to facilitate leaf temperature regulation.
Epidermal Patterning Factor Like 9 (EPFL9), also known as STOMAGEN, is a cysteine-rich peptide that induces stomata formation in vascular plants, acting antagonistically to other epidermal patterning factors (EPF1, EPF2). In grapevine there are two EPFL9 genes, EPFL9-1 and EPFL9-2 sharing 82% identity at protein level in the mature functional C-terminal domain. In this study, CRISPR/Cas9 system was applied to functionally characterize VvEPFL9-1 in ‘Sugraone’, a highly transformable genotype. A set of plants, regenerated after gene transfer in embryogenic calli via Agrobacterium tumefaciens, were selected for evaluation. For many lines, the editing profile in the target site displayed a range of mutations mainly causing frameshift in the coding sequence or affecting the second cysteine residue. The analysis of stomata density revealed that in edited plants the number of stomata was significantly reduced compared to control, demonstrating for the first time the role of EPFL9 in a perennial fruit crop. Three edited lines were then assessed for growth, photosynthesis, stomatal conductance, and water use efficiency in experiments carried out at different environmental conditions. Intrinsic water-use efficiency was improved in edited lines compared to control, indicating possible advantages in reducing stomatal density under future environmental drier scenarios. Our results show the potential of manipulating stomatal density for optimizing grapevine adaptation under changing climate conditions.
All land plants seal their above ground body parts with a lipid-rich hydrophobic barrier called the cuticle to protect themselves from dehydration and other terrestrial threats. Mutational studies in several model species have identified multiple loci regulating cuticular metabolism and development. Of particular importance are the eceriferum (cer) mutants characterized by a loss of cuticular wax. Some barley cer mutants, including cer-x, show defects in the distinctive β-diketone-enriched wax bloom on reproductive stage leaf sheaths, stems, and spikes. We exploited extensive allelic populations, near-isogenic lines, and powerful genotyping platforms to identify variation in the HvWAX INDUCER1 (HvWIN1) gene, encoding a SHINE transcription factor, as underlying cer-x. Comparing the cer-x allelic glossy sheath4.l Bowman Near Isogenic Line BW407 to cv. Bowman revealed an increased cuticular permeability in tissues showing reduced accumulation of β-diketones and altered cuticular metabolic gene expression in BW407. Analyses across the barley pangenome and hundreds of exome-capture datasets revealed high sequence conservation of HvWIN1 and two non-synonymous variants exclusive to the cultivated germplasm. Taken together, we suggest that variation in HvWIN1 controls multiple cuticular features in barley.
Waxes are critical in limiting non-stomatal water loss in higher terrestrial plants by making up the limiting barrier for water diffusion across cuticles. Using a differential extraction protocol, we investigated the influence of various wax fractions on the cuticular transpiration barrier. Triterpenoids (TRPs) and very long-chain aliphatics (VLCAs) were selectively extracted from isolated adaxial leaf cuticles using methanol (MeOH) followed by chloroform (TCM). The water permeabilities of the native and the solvent-treated cuticles were measured gravimetrically. Seven plant species (Camellia sinensis, Ficus elastica, Hedera helix, Ilex aquifolium, Nerium oleander, Vinca minor, and Zamioculcas zamiifolia) with highly varying wax compositions ranging from nearly pure VLCA- to TRP-dominated waxes were selected. After TRP removal with MeOH, water permeability did not or only slightly increase. The subsequent VLCA extraction with TCM led to increases in cuticular water permeabilities by up to two orders of magnitude. These effects were consistent across all species investigated, providing direct evidence that the cuticular transpiration barrier is mainly composed of VLCA. In contrast, TRPs play no or only a minor role in controlling water loss.
Background
Leaf hydraulic and economics traits are critical for balancing plant water and CO2 exchange, and their relationship has been widely studied. Leaf anatomical traits determine the efficiency of CO2 diffusion within mesophyll structure. However, it remains unclear whether leaf anatomical traits are associated with leaf hydraulic and economics traits acclimation to long-term drought.
Results
To address this knowledge gap, eight hydraulic traits, including stomatal and venation structures, four economics traits, including leaf dry mass per area (LMA) and the ratio between palisade and spongy mesophyll thickness (PT/ST), and four anatomical traits related to CO2 diffusion were measured in tomato seedlings under the long-term drought conditions. Redundancy analysis indicated that the long-term drought decreased stomatal conductance (gs) mainly due to a synchronized reduction in hydraulic structure such as leaf hydraulic conductance (Kleaf) and major vein width. Simultaneously, stomatal aperture on the adaxial surface and minor vein density (VDminor) also contributed a lot to this reduction. The decreases in mesophyll thickness (Tmes) and chlorophyll surface area exposed to leaf intercellular air spaces (Sc/S) were primarily responsible for the decline of mesophyll conductance (gm) thereby affecting photosynthesis. Drought increased leaf density (LD) thus limited CO2 diffusion. In addition, LMA may not be important in regulating gm in tomato under drought. Principal component analysis revealed that main anatomical traits such as Tmes and Sc/S were positively correlated to Kleaf, VDminor and leaf thickness (LT), while negatively associated with PT/ST.
Conclusions
These findings indicated that leaf anatomy plays an important role in maintaining the balance between water supply and CO2 diffusion responses to drought. There was a strong coordination between leaf hydraulic, anatomical, and economical traits in tomato seedlings acclimation to long-term drought.
To ensure global food security under the changing climate, there is a strong need for developing ‘climate resilient crops’ that can thrive and produce better yields under extreme environmental conditions such as drought, salinity, and high temperature. To enhance plant productivity under the adverse conditions, we constitutively overexpressed a bifunctional wax synthase/acyl-CoA:diacylglycerol acyltransferase (WSD1) gene, which plays a critical role in wax ester synthesis in Arabidopsis stem and leaf tissues. The qRT-PCR analysis showed a strong upregulation of WSD1 transcripts by mannitol, NaCl, and abscisic acid (ABA) treatments, particularly in Arabidopsis thaliana shoots. Gas chromatography and electron microscopy analyses of Arabidopsis seedlings overexpressing WSD1 showed higher deposition of epicuticular wax crystals and increased leaf and stem wax loading in WSD1 transgenics compared to wildtype (WT) plants. WSD1 transgenics exhibited enhanced tolerance to ABA, mannitol, drought and salinity, which suggested new physiological roles for WSD1 in stress response aside from its wax synthase activity. Transgenic plants were able to recover from drought and salinity better than the WT plants. Furthermore, transgenics showed reduced cuticular transpirational rates and cuticle permeability, as well as less chlorophyll leaching than the WT. The knowledge from Arabidopsis was translated to the oilseed crop Camelina sativa (L.) Crantz. Similar to Arabidopsis, transgenic Camelina lines overexpressing WSD1 also showed enhanced tolerance to drought stress. Our results clearly show that the manipulation of cuticular waxes will be advantageous for enhancing plant productivity under a changing climate.
Drought is one of the major environmental stresses that negatively affect the maize ( Zea mays L.) growth and production throughout the world. Foliar applications of plant growth regulators, micronutrients or osmoprotectants for stimulating drought-tolerance in plants have been intensively reported. A controlled pot experiment was conducted to study the relative efficacy of salicylic acid (SA), zinc (Zn), and glycine betaine (GB) foliar applications on morphology, chlorophyll contents, relative water content (RWC), gas-exchange attributes, activities of antioxidant enzymes, accumulations of reactive oxygen species (ROS) and osmolytes, and yield attributes of maize plants exposed to two soil water conditions (85% field capacity: well-watered, 50% field capacity: drought stress) during critical growth stages. Drought stress significantly reduced the morphological parameters, yield and its components, RWC, chlorophyll contents, and gas-exchange parameters except for intercellular CO 2 concentration, compared with well water conditions. However, the foliar applications considerably enhanced all the above parameters under drought. Drought stress significantly (p < 0.05) increased the hydrogen peroxide and superoxide anion contents, and enhanced the lipid peroxidation rate measured in terms of malonaldehyde (MDA) content. However, ROS and MDA contents were substantially decreased by foliar applications under drought stress. Antioxidant enzymes activity, proline content, and the soluble sugar were increased by foliar treatments under both well-watered and drought-stressed conditions. Overall, the application of GB was the most effective among all compounds to enhance the drought tolerance in maize through reduced levels of ROS, increased activities of antioxidant enzymes and higher accumulation of osmolytes contents.
Drought stress, being the inevitable factor that exists in various environments without recognizing borders and no clear warning thereby hampering plant biomass production, quality, and energy. It is the key important environmental stress that occurs due to temperature dynamics, light intensity, and low rainfall. Despite this, its cumulative, not obvious impact and multidimen-sional nature severely affects the plant morphological, physiological, biochemical and molecular attributes with adverse impact on photosynthetic capacity. Coping with water scarcity, plants evolve various complex resistance and adaptation mechanisms including physiological and biochemical responses, which differ with species level. The sophisticated adaptation mechanisms and regularity network that improves the water stress tolerance and adaptation in plants are briefly discussed. Growth pattern and structural dynamics, reduction in transpiration loss through altering stomatal conductance and distribution, leaf rolling, root to shoot ratio dynamics, root length increment, accumulation of compatible solutes, enhancement in transpiration efficiency, osmotic and hormonal regulation, and delayed senescence are the strategies that are adopted by plants under water deficit. Approaches for drought stress alleviations are breeding strategies, molecular and genomics perspectives with special emphasis on the omics technology alteration i.e., metabo-lomics, proteomics, genomics, transcriptomics, glyomics and phenomics that improve the stress tolerance in plants. For drought stress induction, seed priming, growth hormones, osmoprotect-ants, silicon (Si), selenium (Se) and potassium application are worth using under drought stress conditions in plants. In addition, drought adaptation through microbes, hydrogel, nanoparticles applications and metabolic engineering techniques that regulate the antioxidant enzymes activity for adaptation to drought stress in plants, enhancing plant tolerance through maintenance in cell homeostasis and ameliorates the adverse effects of water stress are of great potential in agriculture.
Morpho-anatomical characters supporting the resilience of a plant under certain environmental conditions cannot be interpreted individually but thoroughly along with the physiological factors to determine the ability of plants to survive in the drought environment. In this study, we conducted a selection of Nusa Tenggara Timur (NTT) local drought-tolerant rice through the assessment of leaf anatomical characters and their correlation with physiological mechanisms. Materials used in this study were 18 local rice cultivars and 2 control cultivars. The characters of leaf includes epidermal thickness, stomatal density and size, bundle-sheath size, vascular-bundle size and bulliform-cell size were found to be negatively correlated with the changes of chlorophyll, carotenoid, and anthocyanin contents. Moreover the change in anatomical characters is positively correlated with relative water content and cell membrane stability index based on two-way ANOVA test with 95% confidence level. Although most of the cultivars undergo decreasing in all characters measured, several cultivars includes Boawae 100-Malam, Gogo Sikka, Gogo Jak, Hare Tora, Pak Mutin and Gogo Fatuhao showed high potential to be drought tolerant cultivars as found with low reduction percentage of parameters measured.
Significance
Heading, which facilitates harvest and contributes to taste and shelf life, is an important trait in some vegetable crops. However, litter is known about its genetic and molecular mechanism. Here, we report the genetic cloning of a key regulator ( LsKN1 ) of heading in lettuce, which is homologous to the knotted 1 ( KN1 ) gene in maize. The LsKN1 gene is upregulated by the insertion of a CACTA-like transposon. Its enhanced expression suppressed the LsAS1 gene and consequently altered leaf polarity and led to a heading phenotype.
Introduction:
Drought is an important stress factor for sugarcane production in many areas of the world. Water proportion and moisture indices are applicable information for agronomic planning to forecast water excess or deficit during the crop cycle.
Objective:
Leaf anatomical features of two different sugarcane Saccharum ‘UT12’ (drought susceptible cultivar) and Saccharum ‘UT13’ (drought tolerant cultivar) were compared under early drought stress situation between 30 and 90 days after planting.
Methods:
Forty leaf anatomical features were investigated using peeling and free hand sectioning technique.
Results:
Some anatomical characteristics showed response to drought stress. Saccharum ‘UT12’ demonstrated higher sensitivity toward anatomical characteristics than Saccharum ‘UT13’. A total of 23 and 15 out of the 40 anatomical characteristics showed significance in Saccharum ‘UT12’ and Saccharum ‘UT13’, respectively. Some anatomical features such as cell wall and cuticle thickness, vascular bundle size, stomatal size and density can be used as important markers for drought stress assessment in sugarcane leaf.
Conclusions:
This is the first report describing comparative leaf anatomy of sugarcane Saccharum ‘UT12’ and Saccharum ‘UT13’ in Thailand under drought stress. Results will provide important information to improve adaptation mechanisms of tolerant sugarcane cultivars under initial drought stress situations.
The hydrophobic cuticle of plant shoots serves as an important interaction interface with the environment. It consists of the lipid polymer cutin, embedded with and covered by waxes, and provides protection against stresses including desiccation, UV radiation, and pathogen attack. Bulliform cells form in longitudinal strips on the adaxial leaf surface, and have been implicated in the leaf rolling response observed in drought-stressed grass leaves. In this study, we show that bulliform cells of the adult maize leaf epidermis have a specialized cuticle, and we investigate its function along with that of bulliform cells themselves. Bulliform cells displayed increased shrinkage compared to other epidermal cell types during dehydration of the leaf, providing a potential mechanism to facilitate leaf rolling. Analysis of natural variation was used to relate bulliform strip patterning to leaf rolling rate, providing further evidence of a role for bulliform cells in leaf rolling. Bulliform cell cuticles showed a distinct ultra-structure with increased cuticle thickness compared to other leaf epidermal cells. Comparisons of cuticular conductance between adaxial and abaxial leaf surfaces, and between bulliform-enriched mutants versus wild-type siblings, showed a correlation between elevated water loss rates and presence or increased density of bulliform cells, suggesting that bulliform cuticles are more water-permeable. Biochemical analysis revealed altered cutin composition and increased cutin monomer content in bulliform-enriched tissues. In particular, our findings suggest that an increase in 9,10-epoxy-18-hydroxyoctadecanoic acid content, and a lower proportion of ferulate, are characteristics of bulliform cuticles. We hypothesize that elevated water permeability of the bulliform cell cuticle contributes to the differential shrinkage of these cells during leaf dehydration, thereby facilitating the function of bulliform cells in stress-induced leaf rolling observed in grasses.
Maize belongs to a tropical environment and is extremely sensitive to drought and chilling stress, particularly at early developmental stages. The present study investigated the individual and combined effects of drought (15% PEG-Solution) and chilling stress (15/12 • C) on morpho-physiological growth, osmolyte accumulation, production of reactive oxygen species (ROS), and activities/levels of enzymatic and non-enzymatic antioxidants in two maize hybrids (i.e., "XD889" and "XD319") and two inbred cultivars (i.e., "Yu13" and "Yu37"). Results revealed that individual and combined exposure of drought and chilling stresses hampered the morpho-physiological growth and oxidative status of maize cultivars, nevertheless, the interactive damage caused by drought + chilling was found to be more severe for all the studied traits. Between two individual stress factors, chilling-induced reductions in seedling length and biomass of maize cultivars were more compared with drought stress alone. Greater decrease in root length and biomass under chilling stress ultimately decreased the volume and surface area of the root system, and restricted the shoot growth. All the stress treatments, particularly chilling and drought + chilling, triggered the oxidative stress by higher accumulation of superoxide anion, hydrogen peroxide, hydroxyl ion, and malondialdehyde contents compared with the control. Variations in response of maize cultivars were also apparent against different stress treatments, and XD889 performed comparatively better than the rest of the cultivars. The better growth and greater stress tolerance of this cultivar was attributed to the vigorous root system architecture, as indicated by higher root biomass, root surface area, and root volume under drought and chilling stresses. Moreover, efficient antioxidant defense system in terms of higher total antioxidant capability, superoxide dismutase, peroxidase, catalase, and glutathione reductase activities also contributed in greater stress tolerance of XD889 over other cultivars.
In the context of climatic change, more severe and long-lasting droughts will modify the fitness of plants, with potentially worse consequences on the relict trees. We have investigated the leaf phenotypic (anatomical, physiological and biochemical) plasticity in well-watered, drought-stressed and re-watered plants of two populations of Platanus orientalis, an endangered species in the west of the Mediterranean area. The two populations originated in contrasting climate (drier and warmer, Italy (IT) population; more humid and colder, Bulgaria (BG) population). The IT control plants had thicker leaves, enabling them to maintain higher leaf water content in the dry environment, and more spongy parenchyma, which could improve water conductivity of these plants and may result in easier CO2 diffusion than in BG plants. Control BG plants were also characterized by higher photorespiration and leaf antioxidants compared to IT plants. BG plants responded to drought with greater leaf thickness shrinkage. Drought also caused substantial reduction in photosynthetic parameters of both IT and BG plants. After re-watering, photosynthesis did not fully recover in either of the two populations. However, IT leaves became thicker, while photorespiration in BG plants further increased, perhaps indicating sustained activation of defensive mechanisms. Overall, our hypothesis, that plants with a fragmented habitat (i.e., the IT population) lose phenotypic plasticity but acquire traits allowing better resistance to the climate where they became adapted, remains confirmed.
Many plants can modify their leaf profile rapidly in response to environmental stress. Image-based data are increasingly used to retrieve reliable information on plant water status in a non-contact manner that has the potential to be scaled to high-throughput and repeated through time. This paper examined the variation of leaf angle as measured by both 3D images and goniometer in progressively drought stressed grapevine. Grapevines, grown in pots, were subjected to a 21-day period of drought stress receiving 100% (CTRL), 60% (IRR60%) and 30% (IRR30%) of maximum soil available water capacity. Leaf angle was (i) measured manually (goniometer) and (ii) computed by a 3D reconstruction method (multi-view stereo and structure from motion). Stomatal conductance, leaf water potential, fluorescence (Fv/Fm), leaf area and 2D RGB data were simultaneously collected during drought imposition. Throughout the experiment, values of leaf water potential ranged from −0.4 (CTRL) to −1.1 MPa (IRR30%) and it linearly influenced the leaf angle when measured manually (R² = 0.86) and with 3D image (R² = 0.73). Drought was negatively related to stomatal conductance and leaf area growth particularly in IRR30% while photosynthetic parameters (i.e., Fv/Fm) were not impaired by water restriction. A model for leaf area estimation based on the number of pixels of 2D RGB images developed at a different phenotyping robotized platform in a closely related experiment was successfully employed (R² = 0.78). At the end of the experiment, top view 2D RGB images showed a ∼50% reduction of greener fraction (GGF) in CTRL and IRR60% vines compared to initial values, while GGF in IRR30% increased by approximately 20%.
In grapevine, the anatomy of xylem conduits and the non-structural carbohydrates (NSCs) content of the associated living parenchyma are expected to influence water transport under water limitation. In fact, both NSC and xylem features play a role in plant recovery from drought stress. We evaluated these traits in petioles of Cabernet Sauvignon (CS) and Syrah (SY) cultivars during water stress (WS) and recovery. In CS, the stress response was associated to NSC consumption, supporting the hypothesis that starch mobilization is related to an increased supply of maltose and sucrose, putatively involved in drought stress responses at the xylem level. In contrast, in SY, the WS-induced increase in the latter soluble NSCs was maintained even 2 days after re-watering, suggesting a different pattern of utilization of NSC resources. Interestingly, the anatomical analysis revealed that conduits are constitutively wider in SY in well-watered (WW) plants, and that water stress led to the production of narrower conduits only in this cultivar.
River runoff is a key attribute of the land surface, that additionally has a strong influence on society by the provision of freshwater. Yet various environmental factors modify runoff levels, and some trends could be detrimental to humanity. Drivers include elevated CO 2 concentration, climate change, aerosols and altered land-use. Additionally, nitrogen deposition and tropospheric ozone changes influence plant functioning, and thus runoff, yet their importance is less understood. All these effects are now included in the JULES-CN model. We first evaluate runoff estimates from this model against 42 large basin scales, and then conduct factorial simulations to investigate these mechanisms individually. We determine how different drivers govern the trends of runoff over three decades for which data is available. Numerical results suggest rising atmospheric CO 2 concentration is the most important contributor to the global mean runoff trend, having a significant mean increase of +0.18 ± 0.006 mm yr ⁻² and due to the overwhelming importance of physiological effects. However, at the local scale, the dominant influence on historical runoff trends is climate in 82% of the global land area. This difference is because climate change impacts, mainly due to precipitation changes, can be positive (38% of global land area) or negative (44% of area), depending on location. For other drivers, land use change leads to increased runoff trends in wet tropical regions and decreased runoff in Southeast China, Central Asia and the eastern USA. Modelling the terrestrial nitrogen cycle in general suppresses runoff decreases induced by the CO 2 fertilization effect, highlighting the importance of carbon–nitrogen interactions on ecosystem hydrology. Nitrogen effects do, though, induce decreasing trend components for much of arid Australia and the boreal regions. Ozone influence was mainly smaller than other drivers.
Each organ plant has been formed perfectly to support physiological processes in an unfavorable environmental condition. Rice (Oryza sativa L.) be included plants sensitive to drought conditions during a stage of growth and development. This will cause pressure (stress) resulting in a decrease in rate metabolism in leaf cells. Leaf anatomical characteristics are criteria that can be used to identify plants that are tolerant to drought. Anatomical response leaves in drought conditions inform the development of leaf photosynthetic parts carrying out changes in anatomical structure morphology includes changes in cell walls, organ size, changes in direction growth, including dropping leaves and enhancing the life cycle. The research aimed to determine the anatomic response leaves rice varieties (Oryza sativa L.) to drought stress. Five rice varieties used were given drought-stress treatment for 12 days. Identification leaf anatomical structures using microscopic slices of transverse was made according to the paraffin method. Changes in the anatomical structure of leaves of drought-stress have decreased bulliform cells increase in size, the thickness epidermis cells in an effort to retain the water content in cells, and reducing the size and total stomata with purpose process control flow of transpiration and water use efficiency.
Trait integration arises through both selection on functional coordination and shared developmental pathways. Different anatomical components must both work well and develop together to generate individuals with the appropriate physiology to survive and reproduce in their environment. In this study, we used a common garden experiment and Bayesian multilevel models to test whether stomatal anatomy coordinates leaf gas exchange, Rubisco kinetics, and leaf size across 10 closely related species of Limonium from the Balearic Islands. The results indicate that the anatomical determinants of maximum stomatal conductance, stomatal density and size, were functionally coordinated with Rubisco kinetics – species whose stomatal anatomy was correlated with low stomatal conductance have evolved Rubisco enzymes better adapted to low operational chloroplastic CO2 concentrations. Lower stomatal density was associated with greater leaf size, which can be explained by a greater proportion of pavement cells in large-leaved species. These results suggest that both selection for functional coordination (stomata and Rubisco kinetics) and shared development pathways (stomatal density and leaf area) likely shape patterns of trait integration between species.
Cuticular waxes, which cover the aboveground parts of land plants, are essential for plant survival in terrestrial environments. However, little is known about the regulatory mechanisms underlying cuticular wax biosynthesis in response to changes in ambient humidity. Here, we report that the Arabidopsis (Arabidopsis thaliana) Kelch repeat F-box protein SMALL AND GLOSSY LEAVES1 (SAGL1) mediates proteasome-dependent degradation of ECERIFERUM3 (CER3), a biosynthetic enzyme involved in the production of very long chain alkanes (the major components of wax), thereby negatively regulating cuticular wax biosynthesis. Disruption of SAGL1 led to severe growth retardation, enhanced drought tolerance, and increased wax accumulation in stems, leaves, and roots. Cytoplasmic SAGL1 physically interacts with CER3 and targets it for degradation. β‑glucuronidase (GUS) expression was observed in the roots of pSAGL1:GUS plants but was barely detected in aerial organs. High humidity-induced GUS activity and SAGL1 transcript levels were reduced in response to abscisic acid treatment and water deficit. SAGL1 levels increase under high humidity, and the stability of this protein is regulated by the 26S proteasome. These findings indicate that the SAGL1-CER3 module negatively regulates cuticular wax biosynthesis in Arabidopsis in response to changes to humidity, and they highlight the importance of permeable cuticle formation in terrestrial plants under high humidity conditions.
Wheat is a staple crop, frequently cultivated in water-restricted environments. Improving crop water-use efficiency would be desirable if grain yield can be maintained. We investigated whether a decrease in wheat stomatal density via the manipulation of Epidermal Patterning Factor (EPF) gene expression, could improve water-use efficiency. Our results show that severe reductions in stomatal density in EPF over-expressing wheat plants have a detrimental outcome on yields. However, wheat plants with a more moderate reduction in stomatal density (i.e. <50% reduction in stomatal density on leaves prior to tillering) had yields indistinguishable from controls, coupled with an increase in intrinsic water-use efficiency. Yields of these moderately reduced stomatal density plants were also comparable to control plants under conditions of drought and elevated CO2. Our data demonstrate that EPF-mediated control of wheat stomatal development follows that observed in other grasses, and we identify the potential of stomatal density as a tool for breeding wheat plants that are better able to withstand water-restricted environments without yield loss.
The density and architecture of leaf veins determine the network and efficiency of water transport within laminae and resultant leaf gas exchange and vary widely among plant species. Leaf hydraulic conductance (Kleaf) can be regulated by vein architecture in conjunction with the water channel protein aquaporin. However, our understanding of how leaf veins and aquaporins affect leaf hydraulics and stomatal conductance (gs) remains poor. By inducing blockage of the major veins and inhibition of aquaporin activity using HgCl2, we examined the effects of major veins and aquaporins on Kleaf and gs in species with different venation types. A vine species, with thick first-order veins and low vein density, displayed a rapidly declined gs with high leaf water potential in response to vein blockage and a greatly reduced Kleaf and gs in response to aquaporin inhibition, suggesting that leaf aquaporins are involved in isohydric/anisohydric stomatal behaviour. Across species, the decline in Kleaf and gs due to aquaporin inhibition increased linearly with decreasing major vein density, possibly indicating that a trade-off function between vein architecture (apoplastic pathway) and aquaporin activity (cell-to-cell pathway) affects leaf hydraulics.
This is an open-access publication and can be downloaded at:
https://doi.org/10.1098/rspb.2019.0799
The frequent occurrence of prolonged droughts has become a very negative factor in the sugarcane crop production worldwide. Ratoon sugarcane, after second crop cycle, can response to drought stress is different as first crop cycle. Thus, this study aimed to investigate the biometric and physiological responses of sugarcane varieties under drought stress conditions of ratoon crop sugarcane. Our hypothesis is that some biometric and physiological characteristics of sugarcane are correlated with its drought tolerance. Six sugarcane varieties were used: 1-RB72910, 2-RB99382, 3-RB72454, 4-RB92579, 5-RB855536 and 6-RB931011, and three water treatments based on soil available water content (SAWC) and defined as: 1-control, 80 to 100% SAWC; 2-moderate water stress, 40 to 60% SAWC and 3-severe water stress, 0 to 20% SAWC. The RB92579 variety was the most tolerant to drought, with less alteration in its biometric and physiological characteristics under drought stress. On the other hand, RB72454 variety was the most affected by drought stress, with high reduction in gas exchange and plant growth. Sugarcane leaf width, specific leaf area, stomatal conductance, transpiration, photosynthesis and carboxylation efficiency were quite sensitive to changes in soil moisture and can be used by breeding programs to discriminate sugarcane varieties more tolerant to drought stress.
Maize is a sensitive crop to drought and heat stresses, particularly at the reproductive stages of development. The present study investigated the individual and interactive effects of drought (50% field capacity) and heat (38°C/30°C) stresses on morpho-physiological growth, yield, nutrient uptake and oxidative metabolism in two maize hybrids i.e., ‘Xida 889’ and ‘Xida 319’. The stress treatments were applied at tasseling stage for 15 days. Drought, heat and drought + heat stress caused oxidative stress by the over-production of ROS (O2‒, H2O2, OH‒) and enhanced malondialdehyde contents, which led to reduced photosynthetic components, nutrients uptake and yield attributes. The concurrent occurrence of drought and heat was more severe for maize growth than the single stress. However, both stresses induced the metabolites accumulation and enzymatic and non-enzymatic antioxidants to prevent the oxidative damage. The performance of Xida 899 was more prominent than the Xida 319. The greater tolerance of Xida 889 to heat and drought stresses was attributed to strong antioxidant defense system, higher osmolyte accumulation, and maintenance of photosynthetic pigments and nutrient balance compared with Xida 319.
Significance
We use a coupled photosynthesis–hydraulic optimal physiology model in conjunction with paleoclimate modeling to examine the primary selective pressures along the ecological trajectory of C 4 photosynthesis and to confirm and revise likely geographical points of dominance and expansion. Water limitation was the primary driver for the initial ecological advantage of C 4 over C 3 in the mid-Oligocene until CO 2 became low enough to, along with light intensity, drive the global expansion of C 4 in the Miocene. Our integrated modeling framework also predicts C 4 evolution should be followed by a decrease in hydraulic conductance, an increase in the leaf–turgor-loss point, and CO 2 -dependent reallocation of nitrogen between dark and light reactions.
Rapid detection of allelic variation and identification of advantage haplotypes responsible for spike related traits play a crucial role in wheat yield improvement. The released genome sequence of hexaploid wheat (Chinese Spring) provides an extraordinary opportunity for rapid detection of natural variation and promotes breeding application. Here, selection signals detection and genome-wide association study (GWAS) were conducted for spike related traits. Based on the genotyping results by 90K SNP chip, 192 common wheat samples from southwest China were analyzed. One hundred and forty-six selective windows and one hundred and eighty-four significant SNPs (51 for spike length, 28 for kernels per spike, 39 for spikelet number, 30 for thousand kernel weight, and 36 for spike number per plant) were detected. Furthermore, tightly linkage and environmental stability window clusters and SNP clusters were also obtained. As a result, four SNP clusters associated with spike length were detected on chromosome 2A, 2B, 2D, and 6A. Two SNP clusters correlated to kernels per spike were detected on 2A and 2B. One pleiotropy SNP cluster correlated to spikelet number and kernels per spike was detected on 7B. According to the genome sequence, these SNP clusters and their overlapped/flanking QTLs which have been reported previously were integrated to a physical map. The candidate genes responsible for spike length, kernels per spike and spikelet number were predicted. Based on the genotypes of cultivars in south China, two advantage haplotypes associated with spike length and one advantage haplotype associated with kernels per spike/spikelet number were detected which have not been effectively transited into cultivars. According to these haplotypes, KASP markers were developed and diagnosed across landraces and cultivars which were selected from south and north China. Consequently, KASP assay, consistent with the GWAS results, provides reliable haplotypes for MAS in wheat yield improvement.
Flag leaf-related traits (FLRTs) are determinant traits affecting plant architecture and yield potential in wheat (Triticum aestivum L.). In this study, three related recombinant inbred line (RIL) populations with a common female parent were developed to identify quantitative trait loci (QTL) for flag leaf width (FLW), length (FLL), and area (FLA) in four environments. A total of 31 QTL were detected in four environments. Two QTL for FLL on chromosomes 3B and 4A (QFll-3B and QFll-4A) and one for FLW on chromosome 2A (QFlw-2A) were major stable QTL. Ten QTL clusters (C1–C10) simultaneously controlling FLRTs and yield-related traits (YRTs) were identified. To investigate the genetic relationship between FLRTs and YRTs, correlation analysis was conducted. FLRTs were found to be positively correlated with YRTs especially with kernel weight per spike and kernel number per spike in all the three RIL populations and negatively correlated with spike number per plant. Appropriate flag leaf size could benefit the formation of high yield potential. This study laid a genetic foundation for improving yield potential in wheat molecular breeding programs.
Weather extremes have widespread harmful impacts on ecosystems and human communities with more deaths and economic losses from flash floods than any other severe weather-related hazards. Flash floods attributed to storm runoff extremes are projected to become more frequent and damaging globally due to a warming climate and anthropogenic changes, but previous studies have not examined the response of these storm runoff extremes to naturally and anthropogenically driven changes in surface temperature and atmospheric moisture content. Here we show that storm runoff extremes increase in most regions at rates higher than suggested by Clausius-Clapeyron scaling, which are systematically close to or exceed those of precipitation extremes over most regions of the globe, accompanied by large spatial and decadal variability. These results suggest that current projected response of storm runoff extremes to climate and anthropogenic changes may be underestimated, posing large threats for ecosystem and community resilience under future warming conditions.
Plant productivity is impacted by drought stress, which adversely affects their morphological and physiological processes. In response, the plant activates its defense mechanisms, but severe drought impairs these responses. In this review, the morphological aspects of water deficit on plants were examined, including reduced germination, rooting, shoot development, and leaf growth, which ultimately lead to quantitative and qualitative yield losses. In addition, physiological aspects of drought were studied, including photosynthesis, chlorophyll content, respiration rate, stomata closure, water, and nutrients relations, and their efficiency. We also presented various agronomic and non-agronomic strategies to combat this global problem as part of the management approach. Breeding using modern methods such as marker-assisted selection, genomic selection, and targeted gene editing was proposed as a promising tool to develop more tolerant crop varieties. In addition, different agronomic methods (plant density, sowing date, crop rotation, conservation tillage, and use of biochar) were discussed. Furthermore, various strategies for improving drought tolerance of crops using nutrient management (salicylic acid, sulfate zinc, chemical fertilizers, and humic acid) were outlined. Mycorrhizae and growth-promoting bacteria were also discussed as effective approaches to achieving drought tolerance in crops. Overall, we concluded that developing drought-tolerant crops requires the use of multiple approaches, including agronomic and non-agronomic techniques and advanced breeding tools.
The plant cuticle, which covers all aerial parts of plants in their primary developmental stage, is the major barrier against water loss from leaves. Accumulation of cutin and waxes has often been linked to drought tolerance. Here we investigated whether cutin and waxes play a role in the drought adaption of barley mimicked by osmotic stress acting on roots. We compared the cuticle properties of cultivated barley (Hordeum vulgare spp. vulgare) with wild barley (Hordeum vulgare spp. spontaneum), and tested whether wax and cutin composition or amount and cuticular transpiration could be future breeding targets for more drought‐tolerant barley lines. In response to osmotic stress, accumulation of wax crystals was observed. This coincides with an increased wax and cutin gene expression and a total increase of wax and cutin amounts in leaves, which seems to be a general response triggered through root shoot signalling. Stomatal conductance decreased fast and significantly, whereas cuticular conductance remained unaffected in both wild and cultivated barley. The often‐made conclusion that higher amounts of wax and cutin necessarily reduce cuticular transpiration and thus enhance drought tolerance is not always straightforward. To prevent water loss, stomatal regulation under water stress is much more important than regulation or adaptation of cuticular transpiration in response to drought. This article is protected by copyright. All rights reserved.
The growth of grapevine [Vitis vinifera L.] is commonly limited by drought stress. The mechanisms by which grapevine copes with drought stress have not yet been extensively clarified. In this study, the drought and abscisic acid (ABA)-induced gene VvWRKY18 was demonstrated to decreased drought tolerance of Arabidopsis thaliana overexpression (VvWRKY18-OE) lines. Compared to wild-type plants, VvWRKY18-OE lines showed increased levels of malonaldehyde (MDA) and the reactive oxygen species (ROS) H2O2 and O2⁻ decreased levels of proline, weakened activity of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and decreased sensitivity to ABA with respect to stomatal closure.VvWRKY18-OE lines also showed an increase in stomatal density and a higher water loss rate. Negative regulators of stomatal development including SDD1, YDA, TMM, and MPK6, were downregulated in VvWRKY18-OE lines. Transcript levels of the stress-related genes DREB1A and CBF2 were significantly reduced in VvWRKY18-OE lines under drought stress. Taken together, these findings demonstrate that VvWRKY18 reduced drought tolerance in Arabidopsis. Our results contribute to understanding of the roles that WRKY genes play in drought stress and stomatal development.
Although mining is essential for human economic development, is amongst the most polluting anthropogenic sources that influence seriously in water resources. Thus, understanding the presence and concentration of heavy metals in water and sediment in the vicinity of mines is important for the sustainability of the ecosystem. In this work, a multidisciplinary approach was developed to characterize the contamination level, source apportionment, co-existence, and degree of ecological and human health risks of HMs on water resources in the Vatukoula Goldmine region (VGR), Fiji. The outcomes suggested significant contamination by Cd (range: 0.01–0.95 g/L), Pb (range: 0.03–0.53 g/L), and Mn (range: 0.01–3.66 g/L) in water samples surpassed the level set by Fiji and international laws, whereas higher concentration of Cd (range: 2.60–23.16 mg/kg), Pb (range: 28.50–200.90 mg/kg) and Zn (range: 36.50–196.66 mg/kg) were detected in sediment samples. Lead demonstrated a strong significant co-existence network with other metals (e.g., Mn, Ni). Source apportionment recognized four source patterns (Cd, Pb, Ni, and Mn) for water and (Cr, Cd–Pb, Mn, and Zn) for sediment which was further confirmed by principal component analysis. The mine inputs source mainly contributed to Cd (66.07%) for water, while mineral processing mostly contributed to Zn (76.10%) for sediment. High non-carcinogenic (>1) and carcinogenic (>10⁻⁴) health risks, particularly in children, are related to the elevated Cd, Pb and Cr contents from the VGR. Uncertainty analysis demonstrates that the 90th quantile of Cd led to higher carcinogenic risk. Pollution indices disclosed a moderate to extremely contamination status mainly along the Toko dam which poses high ecological risks identified by index calculation. However, sediment quality indicators based on probable effect levels showed that there was a 75% of likelihood that the concentrations of Cd and Pb adjacent to the VGR have a severe toxic impact on aquatic lives.
Understanding the mechanisms of drought resistance in crop species is crucial for the selection and breeding of tolerant rapeseed (Brassica napus L.) varieties. The present study aimed to assess the physiological and anatomical responses of two rapeseed genotypes, P287 (drought-tolerant) and T88 (drought-sensitive) under three intensities of drought stress. All physiological and anatomical parameters related to drought acclimation were significantly altered in both genotypes under stress conditions. At the fourth-leaf stage, the relative water content, chlorophyll content, protein content, malondialdehyde content, and the activities of peroxidase and catalase in P287 were significantly higher than those in T88, particularly under severe drought conditions. After rehydration, all physiological indexes recovered rapidly, especially in P287. In addition, under drought stress, compared with T88, P287 had thicker palisade tissue, thinner spongy tissue, higher ratio of chloroplast length to chloroplast width, higher stomatal density and stomatal closure rate. Overall, the interaction between physiological and anatomical features improved the drought tolerance of P287 under drought stress conditions.
A thorough understanding of the plant drought response mechanism and the relationships between plant functional traits and drought will help to improve the key biophysical process parameterization scheme in ecological and crop growth models. In this study, a drought level evaluation indicator, named water stress degree (Dws), was established by synthetically considering soil water content (WC), evapotranspiration, and drought duration to obtain a quantitative description of drought level. The maize physiological and functional traits responses to drought and subsequent rewatering were also investigated. Drought-rewatering field experiments with no water addition for 40 days during the vegetative period (VP) and reproductive period (RP) were respectively conducted at Jinzhou Agrometerological Experimental Station, northeast China in 2014 and 2016. The Dws values indicated that there were significant differences between growth stages and between years because the environmental conditions in 2014 and 2016 were different during the maize growth periods. Furthermore, Dws was larger in 2016 than in 2014 during the VP and RP. Leaf photosynthesis had a certain adaptability to drought, and the transpiration rate (E) drought response (DR) was quicker than the photosynthetic rate (Pn) response, and Pn recovery was greater than E recovery when the plants were rewatered during the VP. However, leaf photosynthesis is more sensitive to drought and less available to recover as normal in subsequent rewatering during the RP than the VP, which was intensified as Dws rose between 2014 and 2016. In addition, the leaf WC drought response was faster than the photosynthetic DR during the VP and RP, and leaf and stalk WCs responded more rapidly to drought during the VP than the RP. The decrease in ear WC during the earlier grouting period was larger in the VP than in the RP treatment. However, the drought-induced decrease in daily sap flow rate (DSF) during the RP was larger than during the VP, while the differences in DSF drought response and DSF recovery during rewatering were attributed to the inter-annual variation in Dws. Furthermore, the drought-caused reductions in leaf, stalk, and plant total dry matters and in leaf and stalk WCs had positively exponential or linear relationships with Dws. The results can help to understand the disaster-causing mechanism of drought-stricken maize.
To understand the growth response to drought, we performed a proteomics study in the leaf growth zone of maize (Zea mays L.) seedlings and functionally characterized the role of starch biosynthesis in the regulation of growth, photosynthesis and antioxidant capacity, using the shrunken‐2 mutant (sh2 ), defective in ADP‐glucose pyrophosphorylase.
Drought altered the abundance of 284 proteins overrepresented for photosynthesis, amino acid, sugar and starch metabolism, and redox‐regulation. Changes in protein levels correlated with enzyme activities (increased ATP synthase, cysteine synthase, starch synthase, RuBisCo, peroxiredoxin, glutaredoxin, thioredoxin and decreased triosephosphate isomerase, ferredoxin, cellulose synthase activities, respectively) and metabolite concentrations (increased ATP, cysteine, glycine, serine, starch, proline and decreased cellulose levels).
The sh2 mutant showed a reduced increase of starch levels under drought conditions, leading to soluble sugar starvation at the end of the night and correlating with an inhibition of leaf growth rates. Increased RuBisCo activity and pigment concentrations observed in WT in response to drought were lacking in the mutant, which suffered more oxidative damage and recovered more slowly after re‐watering.
These results demonstrate that starch biosynthesis contributes to maintaining leaf growth under drought stress and facilitates enhanced carbon acquisition upon recovery.
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Summary
Plant growth and productivity are adversely affected by environmental stresses. Heavy metal contamination owing to rapid industrialization and agricultural practices, drought, cold stress, high temperature and UV‐B radiation are generating agricultural crises in many areas worldwide and causing environmental imbalance. Plants exposed to environmental stresses endure morphological, physiological, and biochemical alteration as well as anatomical changes. These changes help the plants to cope with stress conditions and protect their systems against disturbance. Plants have evolved a range of anatomical changes at organ and organization level. Variations in root, xylem, and leaf anatomy, etc., have been observed in response to environmental stresses. Morphological changes in response to various stresses may appear in the form of reduced growth of internodes, leaf size, leaf surface area, branching pattern, shoot and root growth, etc. Alteration at the anatomical level is mainly due to decreased cell elongation, restricted stimulation of cell division and changes in differentiation conditions of cells, which result in varied anatomical characteristics of plant organs like roots, vascular tissues and leaves. Stresses cause the production of reactive oxygen species, which cause oxidative stress, thereby inducing growth retardation, disturbed photosynthetic apparatus and alteration in the ultrastructure of plant tissues, permeability of plasma membrane, stomatal behavior, etc. In this chapter, we highlight the impact of environmental conditions on the morphology and anatomy of plants.
The alleviation effects of exogenous putrescine treatment on the ultrastructure of and calcium ion flow rate in lettuce (Lactuca sativa L.) leaf cells under drought stress were studied. Lettuce seedlings were treated with foliar sprays of 0.1 mM putrescine for 8 days, after which drought stress was simulated by using 10% polyethylene glycol 6000. The morphological characteristics of the seedlings and the calcium ion flow rate across stomatal guard cells were subsequently determined, and the leaf cell ultrastructure was observed via transmission electron microscopy. Under drought stress, the morphological characteristics of the seedlings decreased, and calcium ion influx was predominant in the guard cells. In addition, compared to that under control conditions, the stomatal density under drought stress conditions increased significantly, the open/closed stoma ratio was lower, and the degree of stomatal opening was smaller. Exogenous putrescine sprays effectively reduced the stomatal density, increased the degree of stomatal opening, and increased the proportion of open stomata. In addition, the chloroplasts became round in shape, the thylakoid structure became blurry in appearance, the number of starch grains decreased, many osmium granules were produced, and plasmolysis occurred in the mesophyll cells. However, the chloroplasts were elongated, the thylakoid structure was clear, the starch grains were abundant, few osmium granules were produced, and plasmolysis did not occur. The above results show that, by altering the leaf cell ultrastructure as well as the flow rate and direction of calcium ions in guard cells, exogenous putrescine effectively improves the drought tolerance of lettuce.
Drought stress is one of serious threats of mankind particularly in arid and semiarid regions, it is the most serious threat to world food security, there are various negative effects on plant growth and total yield occurs under drought conditions, therefore, plants have different responses for adaptation and survive with drought conditions such as morphological, biochemical, physiological responses, and a molecular mechanism. Plants acclimatize with drought stress by use various strategies includes drought escape, drought avoidance and drought tolerance. Plant breeding using biotechnology and classical breeding techniques for improving plant drought tolerance, also, use of Exogenous plant growth regulators improving plant tolerant for drought stress.