Drought-induced Damage Research Articles

Critical water contents at leaf, stem and root level leading to irreversible drought-induced damage in two woody and one herbaceous species.

Plant water content is a simple and promising parameter for monitoring drought-driven plant mortality risk. However, critical water content thresholds leading to cell damage and plant failure are still unknown. Moreover, it is unclear whether whole-plant or a specific organ water content is the most reliable indicator of mortality risk. We assessed differences in dehydration thresholds in leaf, stem and root samples, hampering the organ-specific rehydration capacity and increasing the mortality risk. We also tested eventual differences between a fast experimental dehydration of uprooted plants, compared to long-term water stress induced by withholding irrigation in potted plants. We investigated three species with different growth forms and leaf habits i.e., Helianthus annuus (herbaceous), Populus nigra (deciduous tree) and Quercus ilex (evergreen tree). Results obtained by the two dehydration treatments largely overlapped, thus validating bench dehydration as a fast but reliable method to assess species-specific critical water content thresholds. Regardless of the organ considered, a relative water content value of 60% induced significant cell membrane damage and loss of rehydration capacity, thus leading to irreversible plant failure and death.

Natural diversity uncovers P5CS1 regulation and its role in drought stress tolerance and yield sustainability in barley.

Proline accumulation is one of the major responses of plants to many abiotic stresses. However, the significance of proline accumulation for drought stress tolerance remains enigmatic in crop plants. First, we examined the natural variation of the pyrolline-5-carboxylate synthase (P5CS1) among 49 barley genotypes. Allele mining identified a previously unknown allelic series that showed polymorphisms at 42 cis-elements across the P5CS1 promoter. Selected haplotypes had quantitative variation in P5CS1 gene expression and proline accumulation, putatively influenced by both abscisic acid-dependent and independent pathways under drought stress. Next, we introgressed the P5CS1 allele from a high proline accumulating wild barley accession ISR42-8 into cultivar Scarlett developing a near-isogenic line (NIL-143). NIL-143 accumulated higher proline concentrations than Scarlett under drought stress at seedling and reproductive stages. Under drought stress, NIL-143 showed less pigment damage, sustained photosynthetic health, and higher drought stress recovery compared to Scarlett. Further, the drought-induced damage to yield-related traits, mainly thousand-grain weight, was lower in NIL-143 compared with Scarlett in field conditions. Our data uncovered new variants of the P5CS1 promoter and the significance of the increased proline accumulation regulated by the P5CS1 allele of ISR42-8 in drought stress tolerance and yield stability in barley.

Abiotic stress tolerance in wheat with emphasis on drought

Environmental change presents a significant hazard to most tropical and subtropical crops across the world. Drought stress is among the negative repercussions of environmental modification that affects agricultural development and output. It has a significant influence on the vegetative and propagative phases of plants. Considering the current and prospective nutrition demands of a growing populace, it is critical to target crop production in drought-prone rainfed areas. Crops respond to drought stress in various manners, including structural, physio-chemical, and molecular responses. Drought tolerance encompasses processes that operate at several geographical and temporal dimensions, ranging from immediate stomatal closure to crop production management. There are multiple genes in wheat that are responsible for drought resistance and generate various enzymes and proteins under drought conditions. This review focusses the current advances in wheat physio-chemical, and molecular adaptation to drought tolerance. The experimental data revealed that drought stress negatively impacts multiple physiological processes that occur in wheat plants during their various growth phases, including germination, vegetative growth, reproductive development, and maturity. Therefore, studying the drought-induced damage in wheat plants, as well as strategies for boosting drought tolerance, is critical for increasing wheat output. Furthermore, molecular genetics and breeding strategies for developing drought tolerance in wheat to boost yield and quality are discussed

Detection of acoustic events in lavender for measuring xylem vulnerability to embolism and cellular damage.

Acoustic emission analysis is promising to investigate the physiological events leading to drought-induced injury and mortality. However, their nature and source are not fully understood, making this technique difficult to use as a direct measure of the loss of xylem hydraulic conductance. Acoustic emissions were recorded during severe dehydration in lavender plants (Lavandula angustifolia) and compared with the dynamics of embolism development and cell damage. The timing and characteristics of acoustic signals from two independent recording systems were compared by principal component analysis (PCA). Changes in water potential, branch diameter, loss of hydraulic conductance, and cellular damage were also measured to quantify drought-induced damages. Two distinct phases of acoustic emissions were observed during dehydration: the first one associated with a rapid loss of diameter and a significant increase in loss of xylem conductance (90%), and the second with slower changes in diameter and a significant increase in cellular damage. Based on PCA, a developed algorithm discriminated hydraulic-related acoustic signals from other sources, proposing a reconstruction of hydraulic vulnerability curves. Cellular damage preceded by hydraulic failure seems to lead to a lack of recovery. The second acoustic phase would allow detection of plant mortality.

Trehalose induced drought tolerance in plants: physiological and molecular responses

Drought stress is significant abiotic stress that limits crop growth and productivity across the globe. The intensity of drought stress continuously rises due to rapid climate change. Drought-induced alterations in physiological and bio-chemical processes by generating membrane dis-stability, oxidative stress, nutritional imbalance and leading to substantial reduction in growth and productivity. Plants accumulate various osmolytes that protect themselves from abiotic stresses' harmful effects. Trehalose (Tre) is a non-reducing sugar found in multiple microbes ranging from bacteria to yeast and in plants and it possesses an excellent ability to improve drought tolerance. Trehalose appreciably enhanced the plant growth, and counter the drought induced damages by maintaining cellular membranes, plant water relations, stomatal regulation, photosynthetic activities, nutrient uptake, osmolyte accumulation, activating stress proteins and detoxifying the reactive oxygen species (ROS) by strengthening the anti-oxidant system. Therefore, it is essential to understand the mechanism of exogenous and endogenous Tre in mitigating the drought-induced damages and to identify the potential research questions that must be answered in the future. Therefore, to better appraise the potential benefits of Tre in drought tolerance in this review, we discussed the diverse physiological and molecular mechanisms regulated by Tre under drought stress. We have a complete and updated picture on this topic to orientate future research directions on this topic.

Canopy damage during a natural drought depends on species identity, physiology and stand composition.

Vulnerability to xylem cavitation is a strong predictor of drought-induced damage in forest communities. However, biotic features of the community itself can influence water availability at the individual tree-level, thereby modifying patterns of drought damage. Using an experimental forest in Tasmania, Australia, we determined the vulnerability to cavitation (leaf P50 ) of four tree species and assessed the drought-induced canopy damage of 2944 6-yr-old trees after an extreme natural drought episode. We examined how individual damage was related to their size and the density and species identity of neighbouring trees. The two co-occurring dominant tree species, Eucalyptus delegatensis and Eucalyptus regnans, were the most vulnerable to drought-induced xylem cavitation and both species suffered significantly greater damage than neighbouring, subdominant species Pomaderris apetala and Acacia dealbata. While the two eucalypts had similar leaf P50 values, E. delegatensis suffered significantly greater damage, which was strongly related to the density of neighbouring P. apetala. Damage in E. regnans was less impacted by neighbouring plants and smaller trees of both eucalypts sustained significantly more damage than larger trees. Our findings demonstrate that natural drought damage is influenced by individual plant physiology as well as the composition, physiology and density of the surrounding stand.

Melatonin Enhances Drought Tolerance by Regulating Leaf Stomatal Behavior, Carbon and Nitrogen Metabolism, and Related Gene Expression in Maize Plants

It is commonly known that exogenously applied melatonin can alleviate the impact of drought stress, but the mechanism used by melatonin to regulate stomatal behavior and carbon (C) and nitrogen (N) metabolism to increase drought resistance remains elusive. Herein, our aim was to investigate the influence of exogenous melatonin on the regulation of C and N metabolism in maize plants under water deficit. In this study, we analyzed stomatal behavior, the key components of C and N metabolism, and the gene expression and activity of enzymes involved in the C and N metabolism in maize plants. The results showed that the application of melatonin (100 μM) significantly increased maize growth and sustained the opening of stomata, and secondarily increased the photosynthetic capacity in maize. Under drought stress, foliar application of melatonin induced the gene transcription and activities of sucrose phosphate synthetase, ADP-glucose pyrophosphorylase, phosphoenolpyruvate carboxylase, and citrate synthase, resulting in the enhancement of sucrose and starch synthesis and the tricarboxylic acid (TCA) cycle. This enhancement in sugar biosynthesis and the TCA cycle might lead to stronger N assimilation. As anticipated, NO3– reduction and NH4+ assimilation were also strengthened after melatonin treatment under drought stress. An increase was observed in some key enzymatic activities and transcription involved in nitrogen metabolism, such as that of nitrate reductase, nitrite reductase, glutamate synthase, and glutamine synthetase, in melatonin-treated, drought-stressed maize. Moreover, melatonin attenuated the drought-induced damage by reducing protein degradation and increasing the level of proline. Conclusively, our results indicate that exogenous melatonin enhances drought tolerance in maize via promoting stomatal opening and regulating C and N metabolism and related gene expression.

Exogenously applied Spd and Spm enhance drought tolerance in tea plants by increasing fatty acid desaturation and plasma membrane H+-ATPase activity

Polyamines, due to their positive charges, bind to ROS Reactive oxygen species (ROS) thereby stabilizing the plasma membrane (PM). Drought is one of the main limiting factors affecting tea plant yield and quality. However, the effect of Spermidine (Spd) or Spermine (Spm) on membrane stability and fluidity in tea plants under drought stress is poorly understood. In this investigation, an exogenous supply of 1 mM Spd or Spm did not mitigate drought stress-induced damage, however, an exogenous supply of 0.2 mM Spd or Spm application significantly alleviated drought-induced damage in tea plants. To further illustrate the role of 0.2 mM Spd or Spm in maintaining membrane integrity and fluidity, the fatty acid percentage and PM H+-ATPase activity were analyzed. Spd and Spm application significantly increased PM H+-ATPase activity by 43.79% compared with that without the addition of polyamine under drought stress. In addition, exogenous application of Spd and Spm also significantly increased C18:3 by approximately 10%, hence alleviating drought-reduced fatty acid unsaturation. In contrast, Spd and Spm metabolic inhibitors dicyclohexylamine (DCHA) further impaired PM H+-ATPase activity and fatty acid desaturation under the drought + DCHA treatment compared with the drought treatment, respectively. Taken together, 0.2 mM Spd and Spm application significantly enhanced drought tolerance by increasing fatty acid unsaturation and maintaining PM H+-ATPase activity in tea plants. Therefore, foliar application of 0.2 mM Spd or Spm can be a potential foliar-spraying substances for improving tea drought tolerance.

Exogenous melatonin protects alfalfa (Medicago sativa L.) seedlings from drought-induced damage by modulating reactive oxygen species metabolism, mineral balance and photosynthetic efficiency

• Data on melatonin-mediated drought tolerance in alfalfa was provided. • Drought is a constraint on the growth and establishment of seedlings. • The results accurately characterize the risk of abiotic stress in the environment. • These findings help to find sustainable strategy-enabled successful cultivation of alfalfa. Drought stress is a severe global environmental concern for the growth and development of alfalfa ( Medicago sativa L.), which is crucial for agricultural sustainability owing to its high feed value and economic prospects. Melatonin (MT) has emerged as a multifaceted biomolecule that plays a fundamental role in regulating plants' multiple environmental stresses. However, the significant effect of exogenous MT on drought stress tolerance in the alfalfa forage crops remains inexpressible. We investigated the effects of foliar-sprayed melatonin at different doses (50, 100, 200 μM) on alfalfa seedlings' growth and physiological responses under drought stress. Our results showed that drought stress reduced morphological growth attributes (by 12 to 54%), gas exchange parameters (by 37 to 88%), photosynthetic pigments (Chl a, and Chl b contents by 29%, and 40%), mineral contents, and increased lipid peroxidation (by 69%) and accumulation of reactive oxygen species (ROS) in alfalfa plants. In contrast, exogenous foliar application of MT significantly revived growth characteristics, boosted antioxidant enzyme activities, improved photosynthetic performance, decreased ROS-induced oxidative damage by increasing plant mineral elements, and lowered lipid peroxidation in plants under drought stress. In addition, MT also stimulated the accumulation of total soluble sugar and proline content by 48% and by 75% respectively, which were positively associated with improved leaf water status in drought-stressed plants. Meanwhile, our findings revealed that the highest efficiency was achieved at 100 μM melatonin. In conclusion, these findings bring a new perspective on melatonin-mediated drought stress tolerance and provide a foundational understanding of alfalfa's future cultivation in drought-prone regions globally.

In vivo monitoring of drought-induced embolism in Callitris rhomboidea trees reveals wide variation in branchlet vulnerability and high resistance to tissue death.

Damage to the plant water transport system through xylem cavitation is known to be a driver of plant death in drought conditions. However, a lack of techniques to continuously monitor xylem embolism in whole plants invivo has hampered our ability to investigate both how this damage propagates and the possible mechanistic link between xylem damage and tissue death. Using optical and fluorescence sensors, we monitored drought-induced xylem embolism accumulation and photosynthetic damage invivo throughout the canopy of a drought-resistant conifer, Callitris rhomboidea, during drought treatments of c. 1 month duration. We show that drought-induced damage to the xylem can be monitored invivo in whole trees during extended periods of water stress. Under these conditions, vulnerability of the xylem to cavitation varied widely among branchlets, with photosynthetic damage only recorded once > 90% of the xylem was cavitated. The variation in branchlet vulnerability has important implications for understanding how trees like C. rhomboidea survive drought, and the high resistance of branchlets to tissue damage points to runaway cavitation as a likely driver of tissue death in C. rhomboidea branch tips.

Short-term forest resilience after drought-induced die-off in Southwestern European forests

Drought-induced die-off in forests is becoming a widespread phenomenon across biomes, but the factors determining potential shifts in taxonomic and structural characteristics following mortality are largely unknown. We report on short-term patterns of resilience after drought-induced episodes of tree mortality across 48 monospecific forests from Morocco to Slovenia. Field surveys recorded plants growing beneath a canopy of dead, defoliated and healthy trees. Site-level structural characteristics and management legacy were also recorded. Resilience was assessed with reference to forest composition (self-replacement), structure, and changes in the climatic suitability of the replacing community relative to the climatic suitability of the dominant pre-drought species. Species climatic suitability was estimated from species distribution models calculated for the baseline 1970–2000 period.Short-term resilience decreased under higher levels of drought-induced damage to the dominant species and with evidences of management legacy. Greater resilience of structural features (fewer gaps, greater canopy height) was observed overall in forests with a larger basal area. Less gaps were also associated with greater woody species richness after drought. Overall, Fagaceae-dominated forests exhibited greater structural resilience than conifer-dominated ones. On those sites that were more climatically suited to the dominant pre-drought species, replacing communities tended to exhibit lower climatic suitability than pre-drought dominant species. There was a greater loss of climatic suitability under a legacy of management and drought intensity, but less so in the replacing communities with higher woody species richness.Our study reveals that short-term forest resilience is determined by pre-drought stand characteristics, often reflecting previous management legacies, and by the impact of drought on both the dominant pre-drought species and post-drought replacing species in terms of their climatic suitability.

Comparative Effects of Individual and Consortia Plant Growth Promoting Bacteria on Physiological and Enzymatic Mechanisms to Confer Drought Tolerance in Maize (Zea mays L.)

Mitigation strategies based on plant–microbe interactions to increase the performance of plants under water-deficit conditions are well documented. However, little is known about a suitable consortium of bacterial inoculants and underlying physiological and enzymatic events to improve drought tolerance in maize. We performed laboratory and pot experiments to understand the synergistic interactions among plant growth-promoting bacteria to alleviate the drought-induced damages in maize. Initially, ten bacterial strains were evaluated for their osmotic stress tolerance capacity by growing them in a media containing 0, 10, 20, and 30% polyethylene glycol (PEG-6000). Also, the seeds of a drought tolerant (NK-6654) and sensitive (SD-626) maize cultivar were inoculated with these bacterial strains in the first pot experiment to determine their effects on the growth and physiological processes. Later, in the second pot experiment, the best performing inoculants were selected to study the individual and synergistic effects of bacterial inoculation to confer drought tolerance in maize. Our findings showed that the inoculation with tolerant strains resulted in higher photosynthetic activity (25–39%), maintenance of leaf water status (14–18%) and pigments (27–32%), and stimulation of antioxidant machinery (28–38%) than no inoculation in water-stressed maize seedlings. Moreover, the treatment with bacteria consortia further stimulated the drought protective mechanisms and resulted in higher efficiency of photosynthetic (47–61%) and antioxidant systems (42–62%) than the individual inoculants under water-deficit conditions. We conclude that the inoculation with microbial consortia regulates water uptake, photosynthetic performance, and stress metabolites to minimize drought-induced damages in maize.

Exogenous Ca2+ Associated with Melatonin Alleviates Drought-Induced Damage in the Woody Tree Dalbergia odorifera

Exogenous Ca2+ Associated with Melatonin Alleviates Drought-Induced Damage in the Woody Tree Dalbergia odorifera

Effects of Throughfall Exclusion on Photosynthetic Traits in Mature Japanese Cedar (Cryptomeria japonica (L. f.) D. Don.)

As climate change progresses, it is becoming more crucial to understand how timber species respond to increased drought frequency and severity. Photosynthetic traits in a 40-year-old clonal Japanese cedar (Cryptomeria japonica) plantation were assessed under artificial drought stress using a roof to exclude rainfall and a control with no exclusion. C. japonica is a commercial tree that is native to Japan and has high growth on mesic sites. The maximum carboxylation rate (Vcmax), maximum electron transfer rate (Jmax), and dark respiration rate (Rd) in current-year shoots in the upper canopy were determined from spring to autumn over two growing seasons. In addition, the photosynthetic rate at light saturation (Pmax), stomatal conductance (gs), and intrinsic water use efficiency (WUEi) were measured in the morning and afternoon during the same period. Leaf mass per unit area (LMA) and nitrogen concentration (N) were also measured. The values of Vcmax, Jmax, Rd, N, and LMA did not differ between the two plots. By contrast, significantly lower Pmax and gs and higher WUEi were found in the drought plot, and the reduction in Pmax was accompanied by low gs values. Midday depressions in Pmax and gs were more pronounced in the drought plot relative to the control and were related to higher WUEi. Under drought conditions, mature Japanese cedar experienced little change in photosynthetic capacity, foliar N, or LMA, but they did tend to close the stomata to regulate transpiration, thus avoiding drought-induced damage to the photosynthetic machinery and improving WUEi.

Foliar Spray of Silicon Confers Drought Tolerance in Wheat (Triticum aestivum L.) by Enhancing Morpho-Physiological and Antioxidant Potential

Drought stress is one of the most severe environmental stresses and is a significant contributor to yield reductions in agricultural crops. Several agronomic approaches are recommended by the researchers and later followed by the farmers to minimize the drastic effects of drought. However, the exogenous application of plant growth regulators in combination with mineral nutrients is a recent, innovative strategy to overcome the damaging effects of drought. Here, we report a study aimed at investigating the protective effects of exogenously applied silicon (using potassium silicate or K2Si2O5 as a source) to improve drought tolerance in wheat (Triticum aestivum L.) grown under field conditions. The present study was carried out at Agronomic Research Farm area, Faculty of Agriculture and Environmental Sciences, The Islamia University of Bahawalpur. The experimental field was laid out in a randomized complete block design with split plot arrangements (RCBD-Split), and four repeats. The treatments included: T0 (control, water spray), and T1, T2, T3 i.e. foliar application of K2Si2O5 solutions at the rate of 1, 2 and 3%, respectively. The results showed that drought stress significantly affected the wheat yield by decreasing chlorophyll-a (1.07), chlorophyll-b (0.49), total chlorophyll contents (1.62), flag leaf area (38.33 cm2), plant height (100.17 cm), number of nodes per plant (3.91), tiller height (92.42), number of tillers m−2 (191.17), spike length (7.58 cm), number of spikes per plant (10.25), number of grains per spike (25.08), 1000-grain weight (36.66 g), total dry weight per plant (309.75 g), biological yield (23,424 kg/ha), and grain yield (4564.2 kg/ha). On the contrary, the foliar application of 2% K2Si2O5 considerably reduced the drought-induced damages by enhancing the chlorophyll-a (1.21), chlorophyll-b (0.64), total chlorophyll contents (1.92), flag leaf area (45.25 cm2), plant height (123.50 cm), number of nodes per plant (5.25), tiller height (99.42), number of tillers m−2 (276.26), spike length (12.92 cm), number of spikes per plant (14.25), number of grains per spike (38.33), 1000-grain weight (44.33 g), total dry weight per plant (385.00 g), biological yield (24,000 kg/ha), and grain yield (5074.8 kg/ha). These findings suggest that the exogenous application of K2Si2O5 could be utilized as a rapid, easy and effective approach to reduce drought-induced damages on wheat yield.

Physiological and transcriptome analyses for assessing the effects of exogenous uniconazole on drought tolerance in hemp (Cannabis sativa L.)

Uniconazole (S-(+)-uniconazole), a plant growth retardant, exerts key roles in modulating growth and development and increasing abiotic stress tolerance in plants. However, the underlying mechanisms by which uniconazole regulates drought response remain largely unknown. Here, the effects of exogenous uniconazole on drought tolerance in hemp were studied via physiological and transcriptome analyses of the drought-sensitive industrial hemp cultivar Hanma No. 2 grown under drought stress. Exogenous uniconazole treatment increased hemp tolerance to drought-induced damage by enhancing chlorophyll content and photosynthesis capacity, regulating activities of enzymes involved in carbon and nitrogen metabolism, and altering endogenous hormone levels. Expression of genes associated with porphyrin and chlorophyll metabolism, photosynthesis-antenna proteins, photosynthesis, starch and sucrose metabolism, nitrogen metabolism, and plant hormone signal transduction were significantly regulated by uniconazole compared with that by control (distilled water) under drought stress. Numerous genes were differentially expressed to increase chlorophyll content, enhance photosynthesis, regulate carbon–nitrogen metabolism-related enzyme activities, and alter endogenous hormone levels. Thus, uniconazole regulated physiological and molecular characteristics of photosynthesis, carbon–nitrogen metabolism, and plant hormone signal transduction to enhance drought resistance in industrial hemp.

Combined Proteomic and Physiological Analysis of Chloroplasts Reveals Drought and Recovery Response Mechanisms in Nicotiana benthamiana.

Chloroplasts play essential roles in plant metabolic processes and stress responses by functioning as environmental sensors. Understanding chloroplast responses to drought stress and subsequent recovery will help the ability to improve stress tolerance in plants. Here, a combined proteomic and physiological approach was used to investigate the response mechanisms of Nicotiana benthamiana chloroplasts to drought stress and subsequent recovery. Early in the stress response, changes in stomatal movement were accompanied by immediate changes in protein synthesis to sustain the photosynthetic process. Thereafter, increasing drought stress seriously affected photosynthetic efficiency and led to altered expression of photosynthesis- and carbon-fixation-related proteins to protect the plants against photo-oxidative damage. Additional repair mechanisms were activated at the early stage of recovery to restore physiological functions and repair drought-induced damages, even while the negative effects of drought stress were still ongoing. Prolonging the re-watering period led to the gradual recovery of photosynthesis at both physiological and protein levels, indicating that a long repair process is required to restore plant function. Our findings provide a precise view of drought and recovery response mechanisms in N. benthamiana and serve as a reference for further investigation into the physiological and molecular mechanisms underlying plant drought tolerance.

Enhancement of drought tolerance in Triticum aestivum L. seedlings using Azospirillum brasilense NO40 and Stenotrophomonas maltophilia B11

BackgroundThe effectiveness of two PGPB; Azospirillum brasilense NO40 and Stenotrophomonas maltophilia B11 was investigated in enhancing the drought tolerance of wheat (Triticum aestivum L.) seedlings cultivar Gemiza9. The inoculated or uninoculated grains were sown in unsterilized sandy soil and watered normally untill the 8th day. Drought stress was initiated by completely withholding water for 7 days (until wilting). Samples were collected after 15 days from sowing to evaluate some growth criteria, damage and defense indicators and to analyze the roots’ protein pattern.ResultsThe results showed that inoculating wheat seedlings with these strains significantly diminished the inhibitory effects of drought stress on the relative water content of roots, shoots and leaves; area of leaves; contents of pigments (chlorophyll a and b) and ascorbic acid; and on the protein patterns of roots. Moreover, the bacterial inoculation notably reduced the drought-induced damage indicated by lower leakage of electrolytes and less accumulation of Malondialdehyde and hydrogen peroxide, surprisingly with less enhanced production of proline and activities of catalase and peroxidase than their uninoculated counterparts. Under normal conditions, inoculating wheat plants with these PGPB resulted in significantly promoted growth and elevated contents of pigments and altered protein patterns of roots.ConclusionOverall, we can say that both Azospirillum brasilense NO40 and Stenotrophomonas maltophilia B11 were able to deactivate the growth inhibition in wheat seedlings to some extent, while maintaining a certain level of efficient protection against damage under drought stress.

Exogenous Gibberellic Acid or Dilute Bee Honey Boosts Drought Stress Tolerance in Vicia faba by Rebalancing Osmoprotectants, Antioxidants, Nutrients, and Phytohormones.

The use of growth regulators such as gibberellic acid (GA3) and biostimulants, including diluted bee honey (Db-H) can improve drought tolerance in many crops, including the faba bean (Vicia faba L.). Db-H contains high values of osmoprotectants, mineral nutrients, vitamins, and many antioxidants making it an effective growth regulator against environmental stress effects. Therefore, the present study was planned to investigate the potential improvement in the faba bean plant performance (growth and productivity) under full watering (100% of crop evapotranspiration (ETc)) and drought stress (60% of ETc) by foliar application of GA3 (20 mg L−1) or Db-H (20 g L−1). The ameliorative impacts of these growth regulators on growth, productivity, physio-biochemical attributes, nutrient status, antioxidant defense system, and phytohormones were evaluated. GA3 or Db-H attenuated the negative influences of drought stress on cell membrane stability, ion leakage, relative water content, nutrient status, leaf pigments related to photosynthesis (chlorophylls and carotenoids), and efficiency of the photosystem II (PSII in terms of Fv/Fm and performance index), thus improving faba bean growth, green pod yield, and water use efficiency. Drought stress caused an abnormal state of nutrients and photosynthetic machinery due to increased indicators of oxidative stress (malondialdehyde (MDA), hydrogen peroxide (H2O2) and superoxide (O2•−)), associated with increased osmoprotectants (proline, glycine betaine, soluble sugars, and soluble protein), non-enzymatic antioxidants (ascorbic acid, glutathione, and α-tocopherol), and enzymatic antioxidant activities (superoxide dismutase, catalase, glutathione reductase, and ascorbate peroxidase). However, foliar-applied GA3 or Db-H mediated further increases in osmoprotectants, antioxidant capacity, GA3, indole-3-acetic acid, and cytokinins, along with decreased levels of MDA and abscisic acid. These results suggest the use of GA3 or Db-H at the tested concentrations to mitigate drought-induced damage in bean plants to obtain satisfactory growth and productivity under a water deficit of up to 40%.

Priming with a Seaweed Extract Strongly Improves Drought Tolerance in Arabidopsis.

Drought represents a major threat to plants in natural ecosystems and agricultural settings. The biostimulant Super Fifty (SF), produced from the brown alga Ascophyllum nodosum, enables ecologically friendly stress mitigation. We investigated the physiological and whole-genome transcriptome responses of Arabidopsis thaliana to drought stress after a treatment with SF. SF strongly decreased drought-induced damage. Accumulation of reactive oxygen species (ROS), which typically stifle plant growth during drought, was reduced in SF-primed plants. Relative water content remained high in SF-treated plants, whilst ion leakage, a measure of cell damage, was reduced compared to controls. Plant growth requires a functional shoot apical meristem (SAM). Expression of a stress-responsive negative growth regulator, RESPONSIVE TO DESICCATION 26 (RD26), was repressed by SF treatment at the SAM, consistent with the model that SF priming maintains the function of the SAM during drought stress. Accordingly, expression of the cell cycle marker gene HISTONE H4 (HIS4) was maintained at the SAMs of SF-primed plants, revealing active cell cycle progression after SF priming during drought. In accordance with this, CYCP2;1, which promotes meristem cell division, was repressed by drought but enhanced by SF. SF also positively affected stomatal behavior to support the tolerance to drought stress. Collectively, our data show that SF priming mitigates multiple cellular processes that otherwise impair plant growth under drought stress, thereby providing a knowledge basis for future research on crops.