Enhanced Drought Stress Research Articles

Co-expression of stress-responsive regulatory genes, MuNAC4, MuWRKY3 and MuMYB96 associated with resistant-traits improves drought adaptation in transgenic groundnut (Arachis hypogaea l.) plants.

Groundnut, cultivated under rain-fed conditions is prone to yield losses due to intermittent drought stress. Drought tolerance is a complex phenomenon and multiple gene expression required to maintain the cellular tolerance. Transcription factors (TFs) regulate many functional genes involved in tolerance mechanisms. In this study, three stress-responsive regulatory TFs cloned from horse gram, (Macrotyloma uniflorum (Lam) Verdc.), MuMYB96, involved in cuticular wax biosynthesis; MuWRKY3, associated with anti-oxidant defense mechanism and MuNAC4, tangled with lateral root development were simultaneously expressed to enhance drought stress resistance in groundnut (Arachis hypogaea L.). The multigene transgenic groundnut lines showed reduced ROS production, membrane damage, and increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) enzyme activity, evidencing improved antioxidative defense mechanisms under drought stress. Multigene transgenic plants showed lower proline content, increased soluble sugars, epicuticular wax content and higher relative water content suggesting higher maintenance of tissue water status compared to wildype and mock plants. The scanning electron microscopy (SEM) analysis showed a substantial increase in deposition of cuticular waxes and variation in stomatal number in multigene transgenic lines compared to wild type and mock plants. The multigene transgenic plants showed increased growth of lateral roots, chlorophyll content, and stay-green nature in drought stress compared to wild type and mock plants. Expression analysis of transgenes, MuMYB96, MuWRKY3, and MuNAC4 and their downstream target genes, KCS6, KCR1, APX3, CSD1, LBD16 and DBP using qRT-PCR showed a two- to four-fold increase in transcript levels in multigene transgenic groundnut plants over wild type and mock plants under drought stress. Our study demonstrate that introducing multiple genes with simultaneous expression of genes is a viable option to improve stress tolerance and productivity under drought stress.

Novel Single-Nucleotide Variants for Morpho-Physiological Traits Involved in Enhancing Drought Stress Tolerance in Barley.

Barley (Hordeum vulgare L.) thrives in the arid and semi-arid regions of the world; nevertheless, it suffers large grain yield losses due to drought stress. A panel of 426 lines of barley was evaluated in Egypt under deficit (DI) and full irrigation (FI) during the 2019 and 2020 growing seasons. Observations were recorded on the number of days to flowering (NDF), total chlorophyll content (CH), canopy temperature (CAN), grain filling duration (GFD), plant height (PH), and grain yield (Yield) under DI and FI. The lines were genotyped using the 9K Infinium iSelect single nucleotide polymorphisms (SNP) genotyping platform, which resulted in 6913 high-quality SNPs. In conjunction with the SNP markers, the phenotypic data were subjected to a genome-wide association scan (GWAS) using Bayesian-information and Linkage-disequilibrium Iteratively Nested Keyway (BLINK). The GWAS results indicated that 36 SNPs were significantly associated with the studied traits under DI and FI. Furthermore, eight markers were significant and common across DI and FI water regimes, while 14 markers were uniquely associated with the studied traits under DI. Under DI and FI, three (11_10326, 11_20042, and 11_20170) and five (11_20099, 11_10326, 11_20840, 12_30298, and 11_20605) markers, respectively, had pleiotropic effect on at least two traits. Among the significant markers, 24 were annotated to known barley genes. Most of these genes were involved in plant responses to environmental stimuli such as drought. Overall, nine of the significant markers were previously reported, and 27 markers might be considered novel. Several markers identified in this study could enable the prediction of barley accessions with optimal agronomic performance under DI and FI.

Seed Endophyte bacteria enhance drought stress tolerance in Hordeum vulgare by regulating, physiological characteristics, antioxidants and minerals uptake.

Growth stimulating bacteria help remediate dry arid soil and plant stress. Here, Pseudomonas sp. and Pantoea sp. we used to study the stress ecology of Hordeum vulgare and the environmental impact of water deficit on soil characteristics, growth, photosynthesis apparatus, mineral acquisition and antioxidiant defense. Plants inoculated with Pseudomonas or Pantoea had significantly higher (about 2 folds) soil carbon flux (soil respiration), chlorophyll levels (18%), net photosynthetic rate (33% in Pantoea and 54% in Pseudomonas), (44%) stomatal conductance than uninoculated plants in stressed conditions. Both bacterial strains improved leaf growth (23-29%) and root development under well-watered conditions but reduced around (25%) root biomass under drought. Plants inoculated with Pseudomonas or Pantoea under drought also increased of about 27% leaf respiration and transpiration (48%) but decreased water use efficiency, photoinhibition (91%), and the risk of oxidative stress (ETR/A) (49%). Drought stress increased most of the studied antioxidant enzymatic activities in the plants inoculated with Pseudomonas or Pantoea, which reduce the membrane damage and protect plants form oxidative defenses. Drought stress increased K+ acquisition around 50% in both shoots inoculated with Pseudomonas or Pantoea relative to non-stressed plants. Plants inoculated with Pseudomonas or Pantoea increased shoot Na+ while root Na+ only increased in plants inoculated with Pseudomonas in stressed conditions. Drought stress increased shoot Mg2+ in plants inoculated with Pseudomonas or Pantoea but did not affect Ca2+ relative to non-stressed plants. Drought stress increased about 70% K+/Na+ ratio only in plants inoculated with Pseudomonas relative to non-stressed plants. Our results indicate that inoculating barley with the studied bacterial strains increases plant biomass and can therefore play a role in the environmental remediation of drylands for food production.

Long-Term Effects of Cold Atmospheric Plasma-Treated Water on the Antioxidative System of Hordeum vulgare

Facing climate change, the development of innovative agricultural technologies securing food production becomes increasingly important. Plasma-treated water (PTW) might be a promising tool to enhance drought stress tolerance in plants. Knowledge about the effects of PTW on the physiology of plants, especially on their antioxidative system on a long-term scale, is still scarce. In this work, PTW was applied to barley leaves (Hordeum vulgare cv. Kosmos) and various constituents of the plants’ antioxidative system were analyzed 30 days after treatment. An additional drought stress was performed after foliar PTW application followed by a recovery period to elucidate whether PTW treatment improved stress tolerance. Upon PTW treatment, the Total Antioxidant Capacity (TAC) in leaves and roots was lower in comparison to deionized water treated plants. In contrast, PTW treatment caused a higher content of chlorophyll, quantum yield and total ascorbate content in leaves compared to deionized water treated plants. After additional drought application and subsequent recovery period, an enhancement of values for TAC, contents of malondialdehyde, glutathione as well as activity of ascorbate peroxidase indicated a possible upregulation of antioxidative properties in roots. Hydrogen peroxide and nitric oxide might mediate abiotic stress tolerance and are considered as key components of PTW.

Enhancing drought stress tolerance in Camelina (Camelina sativa L.) through exogenous application of potassium.

The current study was performed under controlled conditions to study the effects of exogenous potassium application on carotenoid contents and drought tolerance in Camelina. Water deficit levels such as 100% FC (control) and 40% FC (drought stress) were imposed after germination of Camelina plants grown to maturity, and different treatments of exogenous K+ were applied at the vegetative stage. We have reported 17 traits of plant growth, physiology, antioxidant enzyme activity, focusing on carotenoids in Camelina to explore their potential yield and yield components. For this purpose, we used multivariate analysis techniques (descriptive statistics, correlation matrix, analysis of variance [ANOVA] and principal components analysis [PCA] to determine the best relation between potassium and studied traits). The results showed a large number of variations in the studied trait under control and water deficit condition. Plant fresh weight (g) was negatively correlated with shoot length and SOD insignificantly correlated with plant fresh weight (g) under water deficit conditions. Potassium loading predicted that foliar application (3 mM K2 SO4 ), foliar application (6 mM KNO3 ), foliar application (12 mM KNO3 ) and foliar application (12 mM K2 SO4 ) are the important doses that contribute the most to enhance the growth, physiological and biochemical activities and carotenoids to improve the Camelina yield under water deficit condition. These doses should be considered in the future to improve the Camelina yield under semi-arid conditions with increased genetic diversity (varietal selection).

Straw Incorporation in Contaminated Soil Enhances Drought Tolerance but Simultaneously Increases the Accumulation of Heavy Metals in Rice

Heavy metals (HMs) and drought stress are worldwide issues of concern because of their adverse effects on the growth and productivity of rice. Straw burning causes air pollution via greenhouse gas (GHG) emissions and it requires sustainable management. The introduction of HMs into the food chain poses a major health risk to humans. In this regard, straw incorporation into the soil could reduce air pollution and drought stress. However, its simultaneous impact on HMs’ uptake and drought stress tolerance in crops is unknown. Therefore, the present study aimed to investigate the impact of rice straw incorporation in soil on HMs (Cd, Cu, Pb, and Fe) availability, accumulation, and drought stress tolerance in rice (Oryza sativa L.) grown in pots under glasshouse conditions. The soil samples were collected from a non-contaminated agricultural field (control) and the contaminated field, irrigated with industrial effluent and treated with straw. Straw (1% w/w) was mixed in soils and control plants without straw application were grown under both contaminated and normal soil conditions. The results showed that straw incorporation in soils significantly enhanced the accumulation of HMs in rice grain and other vegetative parts of rice as compared to control. Moreover, straw application harmed chlorophyll and carotenoids. Straw application significantly increased proline in leaves (274.0 µg mL−1) as compared to the control (166.8 µg mL−1). Relative water contents were higher in straw-treated plants, thereby increasing drought stress tolerance. Straw application increased the accumulation of HMs and consequently reduced the biomass of the plant. In conclusion, straw incorporation enhanced drought stress tolerance but simultaneously elevated the accumulation of HMs under contaminated soil in Oryza sativa L.

Transcriptomics for Drought Stress Mediated by Biological Processes in-relation to Key Regulated Pathways in Gossypium darwinii.

Wild cotton Gossypium darwinii, an allotetraploid harbours important traits useful for tolerating abiotic stress, i.e., drought, salt and good genetic stability, hence these characteristics can be transferred to cultivated cotton for genetic improvement. In this study, we analyzed the RNA-seq transcriptomes from leaves of G. darwinii seedlings with and without drought stress. A total of 86.7 million valid reads with an average length of 95.79bp were generated from the two samples and 58,960 transcripts with a length of more than 500bp were assembled. We searched the known proteins on the strength of sequence similarity; these transcripts were annotated with COG, KEGG and GO functional categories. According to gene expression abundance RPKM value, we carried out RT-qPCR analysis to determine the expression pattern of the obtained transcription factors. A total of 58,960 genes was differentially expressed (DEG), with 32,693 and 25,919 genes found to be upregulated and downregulated, respectively. Through gene ontology and KEGG pathways, the upregulated genes were found to associate with all the GO terms, molecular functions (MF), biological process (BP) and cellular components (CC), which are highly linked to enhancing drought stress tolerance. The study provides an in-depth knowledge of regulation of pathways and genes involved in photosynthesis during drought stress in G. darwinii. These pathways and genes were found to be significantly downregulated and this information could be further utilized by cotton breeders in developing a more drought tolerant cotton germplasm.

CsbZIP50 binds to the G-box/ABRE motif in CsRD29A promoter to enhance drought tolerance in cucumber

Cucumber (Cucumis sativus L.) is a high water-demanding and drought-susceptible vegetable crop. Basic leucine zipper (bZIP) transcription factors (TFs) have been linked to drought stress response in plants. Here we characterized a G subfamily gene in cucumber, CsbZIP50, which was strongly induced by drought stress and an exogenous abscisic acid (ABA) treatment. Under drought stress, CsbZIP50-overexpressing plants exhibited enhanced drought tolerance compared with wild-type plants, as indicated by the higher antioxidant enzyme activities but lower reactive oxygen species (ROS) and malondialdehyde contents. In addition, overexpression of CsbZIP50 enhanced cucumber’s sensitivity to exogenously applied ABA, and up-regulated the expression of its stress-related genes. Moreover, we found that CsbZIP50 activated CsRD29 expression by directly binding to the G-box/ABRE cis-acting element in its promoter, both in vitro and in vivo. Yeast two-hybrid, luciferase complementation imaging, and pull-down assays showed that CsbZIP50 physically interacted with two IQ domain-containing proteins, CsIQD1 and CsIQD4, both of which promoted the ability of CsbZIP50 to activate the expression of CsRD29. Taken together, our results show that CsbZIP50 enhances drought stress tolerance in cucumber by regulating drought-responsive gene expression and ROS levels.

Comparative transcriptomics reveals new insights into melatonin-enhanced drought tolerance in naked oat seedlings.

The growth and development of naked oat (Avena nuda L.) seedlings, a grain recognized as nutritious and healthy, is limited by drought. Melatonin plays a positive role in plants under drought stress. However, its function is unclear in naked oats. This study demonstrated that melatonin enhances drought stress tolerance in oat seedlings. Melatonin application alleviated the declining growth parameters of two naked oat varieties, Huazao No.2 (H2) and Jizhangyou No.15 (J15), under drought stress by increasing the chlorophyll content and photosynthetic rate of leaves. Melatonin pretreatment induced differential gene expression in H2 and J15 under drought stress. Subsequently, the differential gene expression responses to melatonin in the two varieties were further analyzed. The key drought response transcription factors and the regulatory effect of melatonin on drought-related transcription factors were assessed, focusing on genes encoding proteins in the ABA signal transduction pathway, including PYL, PP2C, ABF, SNRK2, and IAA. Taken together, this study provides new insights into the effect and underlying mechanism of melatonin in alleviating drought stress in naked oat seedlings.

Genome-Wide Identification and Expression Analysis Elucidates the Potential Role of PFK Gene Family in Drought Stress Tolerance and Sugar Metabolism in Cotton.

Drought has been identified as a major threat for global crop production worldwide. Phosphofructokinase (PFK) is vital for sugar metabolism. During phosphorylation, plants have two enzymes: ATP-dependent phosphofructokinase (PFK) and pyrophosphate-dependent fructose-6-phosphate phosphotransferase (PFP). Genome-wide identification led to the identification of 80 PFK genes, 26 genes in G. hirsutum and G. barbadense, and 14 genes in G. arboreum and G. raimondii. Phylogenetic, gene structure, and motif analyses showed that PFK genes were grouped into two main categories, namely, PFK and PFP, with 18 and 8 genes in the allotetraploid species and 10 PFK and 4 PFP genes in the diploid species, respectively. Using the RNA-seq expressions of 26 genes from GhPFK, a co-expression network analysis was performed to identify the hub genes. GhPFK04, GhPFK05, GhPFK09, GhPFK11, GhPFK13, GhPFK14, and GhPFK17 in leaves and GhPFK02, GhPFK09, GhPFK11, GhPFK15, GhPFK16, and GhPFK17 in root tissues were found as hub genes. RT-qPCR analysis validated the expressions of identified hub genes. Interestingly, GhPFK11 and GhPFK17 were identified as common hub genes, and these might be the true candidate genes involved in the drought stress tolerance. In the KEGG enrichment analysis, amino acids such as L-valine, L-histidine, L-glutamine, L-serine, L-homoserine, L-methionine, L-cysteine, and gluconic acid were significantly upregulated, whereas sugars, mainly fructose-1-phosphate, D-mannitol, D-sorbitol, dulcitol, and lactose, were significantly downregulated during drought stress. Genome-wide analysis paves the way for a deeper understanding of the PFK genes and establishes the groundwork for future research into PFK’s role in enhancing drought stress tolerance and sugar metabolism in cotton.

The chrysanthemum DEAD-box RNA helicase CmRH56 regulates rhizome outgrowth in response to drought stress.

Plants have evolved complex mechanisms to reprogram growth in response to drought stress. In herbaceous perennial plant species, the rhizome, which is normally an organ for propagation and food storage, can also support plant growth in stressful environments, and allows the plant to perennate and survive stress damage. However, the mechanisms that regulate rhizome growth in perennial herbs during abiotic stresses are unknown. Here, we identified a chrysanthemum (Chrysanthemum morifolium) DEAD-box RNA helicase gene, CmRH56, that is specifically expressed in the rhizome shoot apex. Knock down of CmRH56 transcript levels decreased the number of rhizomes and enhanced drought stress tolerance. We determined that CmRH56 represses the expression of a putative gibberellin (GA) catabolic gene, GA2 oxidase6 (CmGA2ox6). Exogenous GA treatment and silencing of CmGA2ox6 resulted in more rhizomes. These results demonstrate that CmRH56 suppresses rhizome outgrowth under drought stress conditions by blocking GA biosynthesis.

Melatonin alleviates the adverse effects of water stress in adult olive cultivars (Olea europea cv. Sevillana & Roughani) in field condition

Olive trees are considered among the most resilient crops in Mediterranean basin. However, prolonged water stress may adversely affect plant productivity and quality of fruits and oil. Therefore, it is essential to design new agronomic strategies to improve plant water stress tolerance and secure yield and product stability of this important agricultural crop. Under water deficit, plants cope with serious threats, and melatonin (MEL), as a versatile signaling biomolecule, can play a crucial role in morphological and physiological modifications of plants able to enhance drought stress tolerance. In this view, the current research aimed at elucidating the potential beneficial role of exogenous foliar application of MEL (0 and 100 µM) to Sevillana and Roughani olive cultivars under different water stress levels (100%, 75%, and 50% ET). In particular, the morphological, physiological and biochemical changes occurring in leaves treated with or without MEL and the quality of fruits and oil were discussed. A decrease of electrolyte leakage (EL) and malondialdehyde (MDA) content as well as an increase of relative water content (RWC) in MEL-sprayed leaves of drought stress trees were observed. The application of MEL was also associated with higher K+ to Na+ ratio, Ca2+ content, phenolic and soluble carbohydrates contents and a lower decline chlorophyll (Chl) levels. MEL-treated leaves also showed higher catalase (CAT) and peroxidase (POD) activities, responsible for scavenging reactive oxygen species (ROS) generated during drought stress in a severity-dependent manner. MEL-foliar application enhanced the oil content and yield in the olive fruits in both cultivars compared to the untreated ones. Since MEL was also able to exert a beneficial effect on both Sevillana and Roughani cultivar trees by improving their crop water productivity (WPc) under water deficit, it can be considered an effective eco-friendly candidate to minimize the detrimental consequences of water stress.

Shade and microbes enhance drought stress tolerance in plants by inducing phytohormones at molecular levels: a review

Abstract Plants are frequently exposed to adverse environments during their life span. Among them drought stress is one of the major threats to agricultural productivity. In order to survive in such unstable environment, plants have developed mechanisms through which they recognize the severity of the stress based on the incoming environmental stimuli. To combat the detrimental effects of drought, the plants have evolved various strategies to modulate their physio-hormonal attributes. These strategies that can be modulated by shade and microbes contribute to enhancing tolerance to drought and reducing yield loss. Plant hormones, such as abscisic acid, auxin and ethylene have a major role in the shade- and microbe-associated improvement of drought tolerance through their effects on various metabolic pathways. In this process, the CLAVATA3/EMBRYOSURROUNDING REGION-RELATED 25 peptide has a major role due to its effect on ABA synthesis as shown in our regulatory model.

Sodium metasilicate solution enhances drought stress tolerance by improving physiological characteristics in apple stocks

Sodium metasilicate solution treatment contributes to improved plant tolerance to drought stress. In this study, pot experiments were conducted to compare the effect of sodium metasilicate solution on Malus halliana and Malus hupehensis seedlings under drought stress. Principal component analysis (PCA) was used to evaluate the effects of sodium metasilicate solutions on gas exchange, fluorescence, and physiological characteristics. Forty days after transplantation, the control (75% field capacity (FC)) and treatment 1 (50% FC) seedlings were sprayed with distilled water, and the other treatment (50% FC) seedlings were sprayed with a sodium metasilicate (Na2SiO3·9H2O) solution at different concentrations. The results showed that the growth of M. halliana and M. hupehensis was inhibited when exposed to drought stress. This adverse effect was reversed by applying sodium metasilicate solution, and there was a significant concentration effect. Compared to the control, sodium metasilicate solution increased the proline (Pro) content. At the same time, the decrease in the SPAD values, net photosynthetic rate (P n), stomatal conductance (G s), transpiration rate (T r), initial fluorescence (F 0), maximum fluorescence (F m), photochemical efficiency (F v/F m), electron transfer rate (ETR), and superoxide dismutase (SOD) activity were effectively controlled. The increase in intercellular CO2 concentration (C i) and malondialdehyde (MDA) content was also restricted. Additionally, the PCA showed that the first principal component of M. halliana accounted for 80.42% variance, contributed by P n, T r, G s, Pro, SOD, F v/F m, and ETR. The first principal component of M. hupehensis accounted for 69.72% and mainly contained P n, SPAD, and F v/F m index information. The PCA evaluation showed that the effect of sodium metasilicate solution on M. halliana and M. hupehensis seedlings under drought stress was most significant (p < 0.05) at concentrations of 2.5 and 3.75 mM·L−1, respectively.

Graphene Oxide, a Novel Nanomaterial as Soil Water Retention Agent, Dramatically Enhances Drought Stress Tolerance in Soybean Plants.

Drought is one of the most severe environmental stressors that place major constraints on the growth of soybeans (Glycine max L.). Graphene oxide (GO) is a nanomaterial that can promote plant growth without toxic effects. In this study, the physiological and molecular responses to drought stress with GO treatment were examined. We discovered that the relative water content (RWC) of stems and leaves treated with GO was 127 and 128% higher than that of the WT plants, respectively. The root parameters in GO-treated soybeans were increased by 33, 38, 34, and 35% than WT plants in total root length, root surface area, root diameter, and root volume, respectively. The activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) were also increased by 29, 57, 28, and 66%, respectively. However, the relative conductivity (REC), malondialdehyde (MDA), and hydrogen peroxide (H2O2) accumulation were remarkably decreased. Furthermore, the content of drought-related hormones JA, SA, and ABA in GO-treated soybeans increased by 32, 34, and 67% than WT plants, respectively. At the molecular level, the effects of GO treatment were manifested by relatively higher expression of four drought-related genes: GmP5CS, GmGOLS, GmDREB1, and GmNCED1. Taken together, our findings revealed that GO could directly increase plant defense enzymes, hormone content, and the expression of drought-related genes, thereby improving the soybean’s ability to resist drought. These findings could provide new opportunities for improving drought tolerance in soybeans through effective soil water retention agents.

Alleviation of the adverse effects of drought stress using a desert adapted endophytic fungus and glucose in tomato

Beneficial interaction of plants with fungi is one strategy for adapting to environmental stresses like drought. Serendipita indica, an endophytic root fungus, promotes plant growth and enhances tolerance to abiotic stresses. The present study aimed to investigate the amelioration of drought stress in tomato (Solanum lycopersicum L.) upon S. indica and glucose application through morpho-physiological analysis. A completely randomized design was applied with two types of fungal inoculation (non-inoculated and S. indica), two glucose concentrations (0 and 20 mM), and three levels of drought stress (0, 10%, and 20% polyethylene glycol) with three replications per treatment. The plants were collected to analyze various growth and physiological parameters 6 weeks after inoculation. The results showed that S. indica enhances root and shoot biomass and also root volume of inoculated plants in all treatments. An increase in carbohydrate (76%), proline (3.77-fold), potassium (21%), phosphorous (2.62-fold), antioxidant enzymes (peroxidase, ascorbate peroxidase, catalase and superoxide dismutase), total chlorophyll (33%), and carotenoid (16%) content were also observed with S. indica treated plants over untreated plants under drought stress. Additionally, the endophyte decreased hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL) by 20, 10 and 22%, respectively. The results showed that the level of carbohydrate (90%), proline (35%), potassium (7%), plant water status (3%), chlorophyll (11%) and carotenoid (6%), as well as the activities of antioxidant enzymes, were increased in glucose-treated plants. Moreover, glucose application decreases the levels of MDA, hydrogen peroxide (H2O2), and EL by 4, 7 and 13%, respectively. Overall, the interaction effect between fungal inoculation and glucose treatment with drought stress was significant in nearly all measured traits, which means both fungus and glucose promotes plant growth and can enhance drought stress tolerance. Hence, these indicate that S. indica and glucose co-application should be further investigated with field trials.

Exogenous application of spermidine mitigates the adverse effects of drought stress in faba bean (

In Tunisia, drought stress is a major environmental factor limiting crop production and causing relatively low and unstable faba bean yields. In the present study, we explored the putative role of spermidine (0.5, 1, 1.5 and 2mM) in ameliorating the effects of drought stress induced by polyethylene glycol (PEG-6000, -0.58MPa) in faba bean seedlings. Drought stress reduced photosynthetic performance, chlorophyll and relative water content in leaves of faba bean variety Badii. Moreover, drought increased proline, electrolyte leakage and malondialdehyde content by inducing reactive oxygen species (hydrogen peroxide) generation in leaves. However, applying spermidine increased the activities of catalase, superoxide dismutase, ascorbate peroxidase and guaiacol peroxidase. The results show that the application of spermidine especially at a rate of 1.5mM effectively reduces oxidative damage and alleviates negative effects caused by drought stress. In addition, exogenous spermidine increased the expression of polyamine biosynthetic enzymes' genes (VfADC , VfSAMDC and VfSPDS ), and reduced the expression of VfSPMS suggesting that exogenous spermidine can regulate polyamines' metabolic status under drought challenge, and consequently may enhance drought stress tolerance in faba bean. Real-time quantitative polymerase chain reaction analysis revealed that some drought responsive genes (VfNAC , VfHSP , VfNCED , VfLEA , VfCAT , VfAPX , VfRD22 , VfMYB , VfDHN , VfERF , VfSOD and VfWRKY ) from various metabolic pathways were differentially expressed under drought stress. Overall, these genes were more abundantly transcribed in the spermidine-treated plants compared to untreated suggesting an important role of spermidine in modulating faba bean drought stress response and tolerance.

A Vacuolar Invertase CsVI2 Regulates Sucrose Metabolism and Increases Drought Tolerance in Cucumis sativus L.

Vacuolar invertase (VI) can irreversibly degrade sucrose into glucose and fructose and involve in plants abiotic-stress-tolerance. Cucumber (Cucumis sativus L.) is susceptible to drought stress, especially during the seedling stage. To date, the involvement of VI in drought tolerance in cucumber seedlings is in urgent need of exploration. In the present study, a cucumber vacuolar invertase gene, CsVI2, was isolated and functionally characterized. The results showed that (1) CsVI2 showed vacuolar invertase activity both in vivo and in vitro; (2) the transcript level of CsVI2, along with VI activity, was significantly induced by drought stress. Moreover, the expression of sucrose synthase 3 (CsSUS3) was increased and that of sucrose phosphate synthase 1 (CsSPS1) was decreased after exposure to drought stress, which was followed by an increase in sucrose synthase activity and a decrease in sucrose phosphate synthase activity; (3) CsVI2-overexpressing transformed cucumber seedlings showed enhanced vacuolar invertase activity and drought tolerance and 4) protein–protein interaction modelling indicated that a cucumber invertase inhibitor, CsINVINH3, can interact with CsVI2. In summary, the results indicate that CsVI2 as an invertase can regulate sucrose metabolism and enhance drought stress in cucumber seedlings.

Maize PHYTOMELATONIN RECEPTOR1 functions in plant tolerance to osmotic and drought stress.

Phytomelatonin is a universal signal molecule that regulates plant growth and stress responses; however, only one receptor that can directly bind with and perceive melatonin signaling has been identified so far, namely AtPMTR1/CAND2 in Arabidopsis. Whether other plants contain a similar receptor and, if so, how it functions is still unknown. In this study, we identified a new phytomelatonin receptor in the monocot maize (Zea mays), and investigated its role in plant responses to osmotic and drought stress. Using homology searching, we identified a plasma membrane-localized protein, Zm00001eb214610/ZmPMTR1, with strong binding activity to melatonin as a potential phytomelatonin receptor in maize. Overexpressing ZmPMTR1 in Arabidopsis Col-0 promoted osmotic stress tolerance, and rescued osmotic stress sensitivity of the Arabidopsis cand2-1 mutant. Furthermore, ZmPMTR1 also largely rescued defects in melatonin-induced stomatal closure in the cand2-1 mutant, thereby reducing water loss rate and increasing tolerance to drought stress. In addition, we identified a maize mutant of ZmPMTR1, EMS4-06e2fl, with a point-mutation causing premature termination of protein translation, and found that this mutant had lower leaf temperatures, increased rate of water loss, and enhanced drought stress sensitivity. Thus, we present ZmPMTR1 as the first phytomelatonin receptor to be identified and examined in a monocot plant, and our results indicate that it plays an important function in the response of maize to drought stress.

Responses of Lowland Rice Genotypes under Terminal Water Stress and Identification of Drought Tolerance to Stabilize Rice Productivity in Southern Thailand.

Lowland rice is an important cereal crop that plays a key role in the food security and the economy of Thailand. Terminal water stress (TWS) in rainfed lowland areas poses threats to rice productivity due to stress occurrence at terminal crop stages and extreme sensitivity of rice to TWS. A two-year study was conducted to characterize the performance of yield and yield attributes of twelve Thai lowland rice genotypes under TWS, to identify stress-tolerant genotypes using stress response indices and to identify promising stress indices which are correlated with grain yield (GY) under well-watered (WW) and TWS conditions for their use as rapid identifiers in a rice crop breeding program for enhancing drought stress tolerance. Measurements were recorded under WW and TWS conditions. Highly significant variations were observed amongst assessed genotypes for their yield productivity responses. According to stress response indices, genotypes were categorized into stress-tolerant and stress susceptible genotypes. Genotypes Hom Pathum, Sang Yod, Dum Ja and Pathum Thani-1 were found highly stress tolerant and relatively high yielding; genotypes Look Pla and Lep Nok were stress tolerant, whereas genotypes Chor Lung, Hom Nang Kaew and Hom Chan were moderately tolerant genotypes. Hence, stress-tolerant genotypes could be potentially used for cultivation under rainfed and water-limited conditions, where TWS is predicted particularly in southern Thailand to stabilize rice productivity. Stress tolerance indices, including stress tolerance index (STI), geometric mean productivity (GMP), mean productivity index (MPRO) and harmonic mean index (MHAR), indicated strong and positive associations with GY under WW and TWS; thus, these indices could be used to indicate stress tolerance in rice crop breeding program aimed at a rapid screening of lowland rice genotypes for stress tolerance.