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Drought, the major limiting factor for plant growth and crop productivity, affecting several physiological and biochemical processes, is expected to increase in duration, intensity, and frequency as a consequence of climate change. Plants have developed several approaches to either avoid or tolerate water deficit. Plants as a response to drought stress (DS), close stomata, reducing carbon dioxide (CO2) entry in the leaf, thus decreasing photosynthesis which results in reduced synthesis of essential organic molecules that sustain the life on earth. The reduced CO2 fixation, decreases electron transport rate (ETR), while the absorbed light energy overdoes what can be used for photochemistry resulting in excess reactive oxygen species (ROS) and oxidative stress. Current imaging techniques allow non-destructive monitoring of changes in the physiological state of plants under DS. Thermographic visualization, near-infrared imaging, and chlorophyll a fluorescence imaging are the most common verified imaging techniques for detecting stress-related changes in the display of light emission from plant leaves. Chlorophyll a fluorescence analysis, by use of the pulse amplitude modulation (PAM) method, can principally calculate the amount of absorbed light energy that is directed for photochemistry in photosystem II (PSII) (ΦPSII), dissipated as heat (ΦNPQ), or dissipated by the non-radiative fluorescence processes (ΦNO). The method of chlorophyll a fluorescence imaging analysis by providing colour pictures of the whole leaf PSII photochemistry, can successfully identify the early drought stress warning signals. Its implementation allowed visualization of the leaf spatial photosynthetic heterogeneity and discrimination between mild drought stress (MiDS), moderate drought stress (MoDS), and severe drought stress (SDS). The fraction of open reaction centers of PSII (qp) is suggested as the most sensitive and suitable indicator of an early drought stress warning and also for selecting drought tolerant cultivars.

Salicylic acid (SA) and proline exhibit protective effects against a wide range of stresses. However, the combined impact of SA and proline on rice under drought stress is still unknown. Therefore, we investigated the protective roles of SA and/or proline in conferring drought tolerance in rice. There were eight treatments comprising the control (T1; 95–100% FC), 1.5 mM SA (T2), 2 mM proline (T3), 0.75 mM SA + 1 mM proline (T4), 45–50% FC (T5, drought stress), T5 + 1.5 mM SA (T6), T5 + 2 mM proline (T7), and T5 + 0.75 mM SA + 1 mM proline (T8), and two rice varieties: BRRI dhan66 and BRRI dhan75. Drought stress significantly decreased the plant growth, biomass, yield attributes, photosynthetic rate (Pn), stomatal conductance (gs), transpiration rate (Tr), photosynthetic pigments (chlorophyll and carotenoids content), relative water content (RWC), membrane stability index (MSI), soluble sugar and starch content, and uptake of N, P and K+ in roots and shoots. Drought-induced oxidative stress in the form of increased hydrogen peroxide (H2O2) production and lipid peroxidation (MDA) was observed. The combined application of SA (0.75 mM) + proline (1 mM) was found to be more effective than the single application of either for drought stress mitigation in rice. A combined dose of SA + proline alleviated oxidative stress through boosting antioxidant enzymatic activity in contrast to their separate application. The application of SA + proline also enhanced proline, soluble sugar and starch content, which resulted in the amelioration of osmotic stress. Consequently, the combined application of SA and proline significantly increased the gas exchange characteristics, photosynthetic pigments, RWC, MSI, nutrient uptake, plant growth, biomass and yield of rice. Therefore, the combined application of SA and proline alleviated the detrimental impacts of drought stress more pronouncedly than their separate application did by increasing osmoprotectants, improving nutrient transport, up-regulating antioxidant enzyme activity and inhibiting oxidative stress.

We investigated flavonoid accumulation and lipid peroxidation in young leaves (YL) and mature leaves (ML) of Arabidopsis thaliana plants, whose watering stopped 24 h before sampling, characterized as onset of drought stress (OnDS), six days before sampling, characterized as mild drought stress (MiDS), and ten days before sampling, characterized as moderate drought stress (MoDS). The response to drought stress (DS) of photosystem II (PSII) photochemistry, in both leaf types, was evaluated by estimating the allocation of absorbed light to photochemistry (ΦPSII), to heat dissipation by regulated non-photochemical energy loss (ΦNPQ) and to non-regulated energy dissipated in PSII (ΦNO). Young leaves were better protected at MoDS than ML leaves, by having higher concentration of flavonoids that promote acclimation of YL PSII photochemistry to MoDS, showing lower lipid peroxidation and excitation pressure (1 − qp). Young leaves at MoDS possessed lower 1 − qp values and lower excess excitation energy (EXC), not only compared to MoDS ML, but even to MiDS YL. They also possessed a higher capacity to maintain low ΦNO, suggesting a lower singlet oxygen (1O2) generation. Our results highlight that leaves of different developmental stage may display different responses to DS, due to differential accumulation of metabolites, and imply that PSII photochemistry in Arabidopsis thaliana may not show a dose dependent DS response.

Background Drought stress is a predominant abiotic factor contributing to reduced crop yields globally. Therefore, exploring the molecular mechanism of drought control is of great significance to improve drought resistance and ultimately achieve crop yield increase. As a plant endogenous hormone, melatonin plays a key role in the regulation of abiotic stress, but the key genes and metabolic pathways of melatonin mediated drought resistance regulation in alfalfa have not been fully revealed. Based on transcriptomics and physiological index detection, this study aimed to explore the regulatory mechanism of melatonin in alleviating drought stress during alfalfa germination. Results The findings revealed that alfalfa seedlings treated with melatonin exhibited higher germination rates, increased shoot length, and greater fresh weight compared to those exposed solely to drought stress. Additionally, there was a reduction in the levels of malondialdehyde (MDA) and superoxide anion (O 2 − ), while the activity and concentration of superoxide dismutase (SOD), peroxidase (POD), and glutathione (GSH) were enhanced to varying extents. To investigate the molecular mechanism underlying melatonin-mediated drought resistance in alfalfa, we performed a transcriptomic analysis on the seedlings. In the drought treatment group, we identified a total of 1,991 differentially expressed genes (DEGs), comprising 778 up-regulated and 1,213 down-regulated genes. Conversely, in the melatonin-treated group, we discovered 2,336 DEGs, including 882 up-regulated and 1,454 down-regulated genes. Conclusions Through the application of GO functional annotation and KEGG pathway enrichment analysis, we discovered that DEGs were predominantly enriched in pathways related to flavonoid and isoflavone biosynthesis, plant hormone biosynthesis and signal transduction, glutathione metabolism, and MAPK signaling, and the ABC transporter signaling. Notably, the DEGs added to the MT group showed greater enrichment in these pathways. This suggests that MT mitigates drought stress by modulating the expression of genes associated with energy supply and antioxidant capacity. These findings hold significant reference value for breeding drought-tolerant alfalfa and other crops.

Background Sucrose non-fermenting-1-related protein kinases (SnRKs) have been implicated in plant growth and stress responses. Although SnRK3.23 is known to be involved in drought stress, the underlying mechanism of resistance differs between Arabidopsis and rice, and little is known about its function in wheat. Results In the current work, TaSnRK3.23B was detected on the cell membrane and in the nucleus. TaSnRK3.23B overexpression in Arabidopsis promoted reactive oxygen species (ROS) scavenging via the accumulation of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) and then conferred significant tolerance to drought. The prediction analysis, yeast two-hybrid, and bimolecular fluorescence complementation (BiFC) assays revealed that TaSnRK3.23B interacted with TaCBL2B and TaCBL6B, which are calcineurin B-like (CBL) proteins. The predicted model demonstrated that TaSnRK3 subfamily proteins participate in Ca 2+ signaling mediated by TaCBL2B/TaCBL6B and subsequently provide drought stress tolerance by promoting ROS scavenging in wheat. Conclusions Altogether, the obtained findings contribute to a better understanding of the functions of SnRK3.23 in wheat and offer genetic suggestions for improving drought resistance of wheat.

Background Drought stress is a major constraint on seed germination and crop productivity, particularly for drought-sensitive crops like common buckwheat ( Fagopyrum esculentum ). Exogenous melatonin has emerged as a promising strategy to mitigate drought stress by enhancing plant physiological and biochemical responses. However, its specific roles in regulating antioxidant defenses, osmotic adjustment, and plant compounds biosynthesis during buckwheat seed germination under drought stress remain poorly understood. Results This study investigated the effects of 200 µM exogenous melatonin on common buckwheat germination under polyethylene glycol (PEG-6000)-induced drought stress. Melatonin significantly improved germination rates and radicle growth, reduced membrane damage, and enhanced osmotic regulation by increasing proline, soluble sugars, and proteins. Antioxidant enzyme activities (catalase, peroxidase, and superoxide dismutase) and associated gene expression ( FeCAT , FePOD , FeSOD ) were markedly upregulated. Molecular docking and dynamics simulations revealed a stable interaction between rutin, a secondary metabolite, and catalase, suggesting enhanced enzyme stabilization. Additionally, melatonin increased rutin and methyl jasmonate synthesis, which contributed to antioxidant defenses and reduced oxidative damage. The coordinated effects of melatonin improved drought tolerance in buckwheat seeds by optimizing osmotic balance, strengthening antioxidant capacity, and stabilizing cellular structures. Conclusions Exogenous melatonin enhances drought tolerance in common buckwheat seeds through the coordinated regulation of antioxidant defenses, osmotic adjustment, and plant compounds production, including methyl jasmonate and rutin, during germination. These findings offer valuable insights for developing practical strategies to improve drought resilience and crop establishment in sensitive agricultural species under water-limited conditions.

Background Drought resistance is an increasingly important trait for many plants—including St. Augustinegrass, a major warm-season turfgrass—as more municipalities impose restrictions on frequency and amount of irrigation. Breeding efforts have focused on breeding for drought resistance, and several drought-related quantitative trait loci (QTL) have been identified for St. Augustinegrass in previous studies. However, the molecular basis of this trait remains poorly understood, posing a significant roadblock to the genetic improvement of the species. Results This study sought to validate those QTL regions in an independent biparental population developed from two sibling lines, XSA10098 and XSA10127. The drought evaluation in two greenhouse trials showed significant genotype variation for drought stress traits including leaf wilting, percent green cover, relative water content, percent recovery, and the area under the leaf wilting-, percent green cover-, and percent recovery- curves. A linkage map was constructed using 12,269 SNPs, representing the densest St. Augustinegrass linkage map to date. A multiple QTL mapping approach identified 24 QTL including overlapping regions on linkage groups 3, 4, 6, and 9 between this study and previous St. Augustinegrass drought resistance studies. At the transcriptome level, 1965 and 1005 differentially expressed genes were identified in the drought sensitive and tolerant genotypes, respectively. Gene Ontology and KEGG analysis found different mechanisms adopted by the two genotypes in response to drought stress. Integrating QTL and transcriptomics analyses revealed several candidate genes which are involved in processes including cell wall organization, photorespiration, zinc ion transport, regulation of reactive oxygen species, channel activity, and regulation in response to abiotic stress. Conclusions By innovatively integrating QTL and transcriptomics, our study advances the understanding of the genetic control of water stress response in St. Augustinegrass, providing a foundation for targeted drought resistance breeding.

Background The frequency and severity of abiotic stress events, especially drought, are increasing due to climate change. The plant root is the most important organ for water uptake and the first to be affected by water limitation. It is therefore becoming increasingly important to include root traits in studies on drought stress tolerance. However, phenotyping under field conditions remains a challenging task. In this study, plants were grown in a hydroponic system with polyethylene glycol as an osmotic stressor and in sand pots to examine the root system of eleven spring barley genotypes. The root anatomy of two genotypes with different response to drought was investigated microscopically. Results Root diameter increased significantly ( p  < 0.05) under polyethylene glycol treatment by 54% but decreased significantly ( p  < 0.05) by 12% under drought stress in sand pots. Polyethylene glycol treatment increased root tip diameter (51%) and reduced diameter of the elongation zone (14%) compared to the control. Under drought stress, shoot mass of plants grown in sand pots showed a higher correlation ( r  = 0.30) with the shoot mass under field condition than polyethylene glycol treated plants ( r = -0.22). Conclusion These results indicate that barley roots take up polyethylene glycol by the root tip and polyethylene glycol prevents further water uptake. Polyethylene glycol-triggered osmotic stress is therefore unsuitable for investigating root morphology traits in barley. Root architecture of roots grown in sand pots is more comparable to roots grown under field conditions.

Background Plants in arid environments can regulate the generation of specialized metabolites to enhance their adaptability. Roots serve as the first defense line, responding directly to drought situations; however, the knowledge regarding the molecular mechanisms of metabolite changes to drought in maize roots remain largely limited. Here, we employed RNA-seq and UPLC-MS/MS methods to examine changes in the root metabolome and transcriptome of maize seedlings subjected to moderate drought (MD) and severe drought (SD) conditions by controlling water supply. Results Compared to the untreated control group, 460 differentially accumulated metabolites were detected in roots under MD and SD conditions. Among these metabolites, lignin compounds emerged as the primary response to drought. Most lignin metabolites, including caffealdehyde, sinapyl alcohol, coniferaldehyde, p-coumaryl alcohol, and p-coumaric acid, showed a significant increase under MD but decreased under SD. Transcriptional profiling identified 903 and 5306 differential genes in roots treated with MD and SD, respectively. The majority of these genes were associated with lignin biosynthesis, hormone synthesis and signal transduction, and defense response processes. These metabolites and genes play crucial roles in lignin biosynthesis, antioxidant capacity, hormone balance, and root growth, particularly under MD conditions, which aligns with the results from morpho-physiological studies. Further, a conjoint omics analysis highlighted the significant regulatory roles of hormone-associated genes in lignin formation. Conclusion Our results suggest that the co-regulation of the lignin biosynthesis pathway and hormone signals significantly enhances root performance, helping maize maintain growth under MD conditions. This study leads to a better understanding of the regulatory mechanisms involved in maize root adaptation to drought environments.

Background Silicon has an important role in regulating water management in plants. It is deposited in cell walls and creates a mechanical barrier against external factors. The aim of this study was to determine the role of silicon supplementation in the synthesis and distribution of callose in oilseed rape roots and to characterize the modifications of cell wall structure of these organs after exposure to drought stress. Histological and ultrastructural analyses were performed to determine the changes in the distribution of arabinogalactan proteins, pectins, and extensin in roots of Brassica napus growing under drought and supplemented with silicon. Callose deposition and the accumulation of callose synthase protein were assessed, followed by transcriptional analysis of callose synthase genes. Results The results showed that silicon supplementation under drought conditions alter the direction of cortex cell differentiation, promoting fiber formation and proliferation of callose-depositing cells in the roots of the tested plants. This was reflected in an increase in the level of callose synthase and a decrease in the transcriptional activity of the gene encoding this enzyme, indicating regulation based on negative feedback under drought stress. The changes in abundance and distribution of investigated arabinogalactan proteins, pectins and extensin in roots of Si supplemented plants growing under drought stress were observed, indicating cell walls remodeling. Conclusion Silicon supplementation in oilseed rape roots induced significant changes in cell wall composition, including increased callose deposition and altered pectins and arabinogalactan proteins distribution. These modifications, along with the formation of fibres in the root cortex, likely contribute to enhanced cell wall strength providing a physical barrier against water loss and mechanical stress, as a probable defence mechanism induced during drought stress.