Polyethylene Glycol-induced Drought Research Articles

Enhancing growth and bioactive metabolites characteristics in Mentha pulegium L. via silicon nanoparticles during in vitro drought stress

The development and production of secondary metabolites from priceless medicinal plants are restricted by drought stress. Mentha pulegium L. belongs to the Lamiaceae family and is a significant plant grown in the Mediterranean region for its medicinal and aesthetic properties. This study investigated the effects of three polyethylene glycol (PEG) (0, 5, and 10%) as a drought stress inducer and four silicon nanoparticle (SiNP) (0, 25, 50, and 100 ppm) concentrations as an elicitor to overcome the adverse effect of drought stress, on the growth parameters and bioactive chemical composition of M. pulegium L. plants grown in vitro. The experiment was performed as a factorial experiment using a completely randomized design (CRD) consisting of 12 treatments with two factors (3 PEG × 4 SiNPs concentrations), 6 replicates were used for each treatment for a total of 72 experimental units.The percentage of shoot formation was inversely proportional to the PEG concentration; for the highest PEG concentration, the lowest percentage of shoot formation (70.26%) was achieved at 10% PEG. SiNPs at 50 ppm enhanced shoot formation, the number of shoots, shoot height, fresh and dry weight, rosmarinic acid, total phenols, and 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity. The methanol extract from M. pulegium revealed the presence of significant secondary metabolites using gas chromatography‒mass spectrometry (GC–MS). The principal constituents of the extract were limonene (2.51, 2.99%), linalool (3.84, 4.64%), geraniol (6.49, 8.77%), menthol (59.73, 65.43%), pulegone (3.76, 2.76%) and hexadecanoic acid methyl ester or methyl palmitate (3.2, 4.71%) for the 0 ppm SiNPs, PEG 0% and 50 ppm SiNPs, and PEG 10%, respectively. Most of the chemical components identified by GC‒MS in the methanol extract were greater in the 50 ppm SiNP and 10% PEG treatment groups than in the control group. SiNP improves drought tolerance by regulating biosynthesis and accumulating some osmolytes and lessens the negative effects of polyethylene glycol-induced drought stress.Based on the results, the best treatment for most of the parameters was 50 ppm SiNPs combined with 10% PEG, the morphological and chemical characteristics were inversely proportional to the PEG concentration, as the highest PEG concentration (10%) had the lowest results. Most parameters decreased at the highest SiNP concentration (100 ppm), except for the DPPH scavenging percentage, as there was no significant difference between the 50 and 100 ppm SiNPs.

The Identification of Drought Tolerance Candidate Genes in Oryza sativa L. ssp. Japonica Seedlings through Genome-Wide Association Study and Linkage Mapping

Drought stress poses a significant threat to rice production, necessitating the identification of genes associated with drought tolerance. This study employed a combination of genome-wide association study (GWAS) and linkage mapping to pinpoint seedling drought tolerance genes in Japonica rice. Using the leaf rolling scale (LRS) as the phenotypic index, we assessed rice drought tolerance under polyethylene glycol-induced drought during the seedling stage. A lead SNP C8_28933410 by GWAS was identified, which was located within qLRS-8-1 identified by linkage mapping on chromosome 8. Combing the LD block analyses and QTL interval, a 138.6 kb overlap interval was considered as the candidate region. Haplotype analysis, qRT-PCR, sequence analysis, and mutant phenotype verification led to the speculation that LOC_Os08g05520 is a candidate gene associated with drought tolerance. Our findings provide a valuable reference for breeders aiming to enhance rice drought tolerance.

Polyethylene glycol-induced drought stress screening of selected Philippine high-yielding sugarcane varieties

A greenhouse study was conducted to characterize the drought response of eight high-yielding sugarcane varieties at tillering stage using polyethylene glycol 6000 (PEG6000) induced drought conditions. Plant height, stalk diameter, dry matter accumulation, root characteristics, stomatal conductance, chlorophyll fluorescence, SPAD, normalized difference vegetation index (NDVI), and canopy temperature were evaluated at 2.5 months after planting after four weeks of induced drought conditions. The study aimed to determine whether 1.0% PEG treatment would be able to produce significant differences among test genotypes and use it as a basis to determine drought-tolerant and susceptible varieties. Significant differences were observed among genotypes in PEG stress treatments. PEG stress resulted in significant reductions relative to non-PEG treatment in plant height (32.1%), leaf dry matter (31.6%), and stalk dry matter (49.5%) while total root length (11.8%), root surface area (7.8%) and root volume (19.6%) have generally increased. Reduced plant height, stalk diameter, and dry matter accumulation were observed in susceptible genotypes, while potential tolerant lines maintained or exhibited less reduction in these traits. Moreover, principal component analysis suggests that stalk dry matter, stomatal conductance, chlorophyll fluorescence plant height, SPAD, canopy temperature, and NDVI, highly contributed to the overall variation in the data (41.5%). With this, vars. 2289, 1011, 2569, and 1899 were identified to be potential drought-tolerant varieties while vars. 1763 and 2155 were potential drought susceptible varieties. Screening for drought tolerance under controlled conditions using PEG-induced drought stress offers a promising approach for sugarcane breeding especially when focusing on specific drought responses during important formative stages such as tillering stage. Being able to select genotypes of interest as early as the tillering stage would significantly hasten breeding cycles and will highly benefit the efforts towards drought stress tolerance in sugarcane.

Water uptake, anatomical, and biochemical changes of sorghum genotypes subjected to polyethylene glycol-induced drought stress

Absract To investigate the water uptake, anatomical and biochemical changes of sorghum, three genotypes including grain sorghum [Sorghum bicolor (L.) Moench subsp. bicolor], Sudan grass [Sorghum bicolor (L.) Moench subsp. drummondii (Steud.) de Wet ex Davidse] and Johnson grass [Sorghum halepense (L.) Pers.] were subjected to polyethylene glycol (PEG 60000)-induced drought stress (PEG 60000) at 0, −0.15, and −0.3 MPa levels, hydroponically. In all genotypes, stele diameter decreased as osmotic potential of the medium decreased and the largest stele diameter (247 µm) was observed in Johnson grass at control and declined to 196 µm under −0.3 MPa PEG. Drought affected the diameter of peripheral metaxylem (PMX) and central metaxylem (CMX), negatively. The number of PMX and CMX in Johnson grass was 36 and 200% more than in grain sorghum under −0.3 MPa PEG, respectively. In all genotypes, chlorophyll a and b declined under drought, but in Johnson grass, it only decreased 25 and 29%, respectively. Johnson grass had the highest total chlorophyll content, while carotenoid content was stable under drought stress in this genotype. Drought stress increased catalase and peroxidase activities but decreased relative water content (RWC) and hydraulic conductivity (hc). Under drought, the higher seedling dry weight and root to shoot ratio in Johnson grass might be related to higher hc, total chlorophyll content, and RWC. Moreover, Johnson grass showed less water loss and more efficiency in water uptake under induced drought stress; and it could be attributed to the larger stele diameter, number, and diameter of PMX, substantiating their roles in drought adaptation.

Mechanistic Insights into Potassium-Conferred Drought Stress Tolerance in Cultivated and Tibetan Wild Barley: Differential Osmoregulation, Nutrient Retention, Secondary Metabolism and Antioxidative Defense Capacity.

Keeping the significance of potassium (K) nutrition in focus, this study explores the genotypic responses of two wild Tibetan barley genotypes (drought tolerant XZ5 and drought sensitive XZ54) and one drought tolerant barley cv. Tadmor, under the exposure of polyethylene glycol-induced drought stress. The results revealed that drought and K deprivation attenuated overall plant growth in all the tested genotypes; however, XZ5 was least affected due to its ability to retain K in its tissues which could be attributed to the smallest reductions of photosynthetic parameters, relative chlorophyll contents and the lowest Na+/K+ ratios in all treatments. Our results also indicate that higher H+/K+-ATPase activity (enhancement of 1.6 and 1.3-fold for shoot; 1.4 and 2.5-fold for root), higher shoot K+ (2 and 2.3-fold) and Ca2+ content (1.5 and 1.7-fold), better maintenance of turgor pressure by osmolyte accumulation and enhanced antioxidative performance to scavenge ROS, ultimately suppress lipid peroxidation (in shoots: 4% and 35%; in roots 4% and 20% less) and bestow higher tolerance to XZ5 against drought stress in comparison with Tadmor and XZ54, respectively. Conclusively, this study adds further evidence to support the concept that Tibetan wild barley genotypes that utilize K efficiently could serve as a valuable genetic resource for the provision of genes for improved K metabolism in addition to those for combating drought stress, thereby enabling the development of elite barley lines better tolerant of abiotic stresses.

Phosphate-Solubilizing Enterobacter ludwigii AFFR02 and Bacillus megaterium Mj1212 Rescues Alfalfa’s Growth under Post-Drought Stress

Drought stress is a prevalent environmental stress that adversely affects agricultural industries worldwide. In this study, bacterial isolates, AFFR02 and Mj1212, showed tolerance to polyethylene glycol-induced (PEG) drought stress (approximately 15%) and possess strong phosphate-solubilizing capacity. Moreover, we investigated the plant growth attributes, chlorophyll content, and ion uptake in alfalfa plants (Medicago sativa L) inoculated with isolates AFFR02 and Mj1212 under drought stress. We observed that drought stress drastically affects alfalfa’s growth attributes: shoot length: SL (24.88%), root length: RL (29.62%), shoot fresh weight: SFW (49.62%), root fresh weight: RFW (45.09%), stalk diameter: SD (52.84%), and chlorophyll content: CC (19.2%). However, in bacterial-inoculated alfalfa plants, the growth attributes significantly recovered were SL (12.42%), RL (21.30%), SFW (50.74%), RFW (46.42%), SD (76.72%), and CC (17.98%). In drought-stressed alfalfa plants, we observed a significant decrease in the relative water content (7.45%), whereas there was an increase in electrical conductivity (68.87%) and abscisic acid contents (164.42%). Antioxidant analysis showed a significant increase in total phenolic content (46.08%), DPPH-scavenging activity (39.66%), total flavonoid (13.68%), and superoxide dismutase (28.51%) in alfalfa treated with drought stress and bacterial isolates AFFR02 and Mj1212 simultaneously. Moreover, an increase in inductively coupled plasma (ICP) analysis of potassium (17.98%), phosphorous (11.14%), calcium (3.07%), and magnesium (6.71%) was recorded for bacteria-inoculated alfalfa plants under drought stress. In conclusion, bacterial isolates AFFR02 and Mj1212 enhance alfalfa growth under drought stress. Therefore, the isolates could be used as potential candidates in smart-climate agricultural practices in drought-stricken areas worldwide.

Exogenous abscisic acid and jasmonic acid restrain polyethylene glycol-induced drought by improving the growth and antioxidative enzyme activities in pearl millet.

Drought stress is one of the most immense and permanent constraints in agriculture, which leads to a massive loss of crop productivity. However, little is known about the mitigation role of exogenously applied abscisic acid (ABA) and jasmonic acid (JA) in pearl millet (Pennisetum glaucum L.) under PEG-induced drought stress. Therefore, the current study investigated the putative role of exogenous ABA and JA in improving drought stress tolerance in pearl millet. Thirteen-day-old seedlings were exposed to six different treatments as follow; control (ck), PEG-600 (20%), JA (100 μM), ABA (100 μM), PEG+JA, and PEG+ABA, and data were collected at 7 and 14 days after treatment (DAT). Results showed that PEG decreased plant growth while the oxidative damage increased due to over production of H2 O2 and MDA content as a result of decreased activities of the antioxidative enzymes including APX, CAT, and SOD in the leaves. However, exogenous ABA and JA positively enhanced the growth profile of seedlings by improving chlorophyll and relative water content under PEG treatment. A significant improvement was observed in the plant defense system resulting from increased activities of antioxidative enzymes due to exogenous ABA and JA under PEG. Overall, the performance of JA was found better than ABA under PEG-induced drought stress, and future investigations are needed to explore the potential effects of these phytohormones on the long-term crop management and productivity under drought stress.

Physiological and Transcriptome Profiling Analyses Reveal Important Roles of Coronatine in Improving Drought Tolerance of Tobacco

Coronatine (COR) is a phytotoxin produced by Pseudomonas syringae and is a functional analogue of the bioactive hormone JA-Ile, which is widely involved in plant defence responses. In this study, we explored the effects of exogenous applications of COR on tobacco plants under polyethylene glycol-induced drought stress. Compared with control (CK), COR-treated tobacco plants exhibited higher leaf relative water content and better photosynthetic performance under drought exposure. Ultrastructural examination revealed that drought led to stomatal closure and disorganization of granum stacking in the chloroplasts (with obvious accumulation of plastoglobuli), and mitochondria in the CK samples presented injured cristae. In the leaf tissue of the COR-treated plants, regularly stacked granum thylakoids, few plastoglobuli and intact mitochondrial membranes and cristae were observed. Totals of 1803 and 6207 differentially expressed genes (DEGs) were identified between the samples from the COR-treated and CK plants under well-watered and drought conditions. Functional annotation analysis revealed that these DEGs were involved mainly in plant hormone signal transduction, cellular carbohydrate metabolic processes and photosynthesis processes. Six hundred forty transcription factor genes were also identified among the DEGs. This study provides a global view of COR-induced drought stress tolerance in tobacco from both physiological and transcriptional aspects.

Genome-wide characterization of drought stress responsive long non-coding RNAs in Tibetan wild barley

Drought is the most common and frequently occurring abiotic stress limiting crop yield and quality. Long non-coding RNAs (lncRNA) play crucial roles in regulating expression of genes in plants under various abiotic stress. The participation of lncRNAs in plant drought tolerance in barley is largely unknown. Here, we compared the lncRNA transcriptome in roots of two Tibetan wild barley genotypes XZ5 (drought-tolerant) and XZ54 (drought-sensitive), and one drought tolerant cv. Tadmor in response to polyethylene glycol-induced drought stress. In total, 23,651 novel lncRNAs were identified, among which 535 were characterized as drought responsive according to their different expression profile among XZ5, and XZ54 and Tadmor in response to drought stress. LncRNA target prediction revealed 1279 potential lncRNA-messenger RNA (mRNA) pairs, among which 503 pairs function in cis-acting mode and 776 in trans. Functional enrichment analysis showed that the targets were significantly enriched in molecular functions related to plant hormone signal transduction, diterpenoid biosynthesis, and ascorbate/aldarate metabolism. Multiple promising targets of drought-responsive lncRNAs were discovered, including the SPL3, BRI1 gene. Further analysis of genotypic difference in transcriptome we identified 10 drought-tolerance associated lncRNAs in XZ5, being exclusively induced by drought stress in XZ5 among the three genotypes, and sequencing data were confirmed by RT-qPCR. The lncRNA-mRNA interaction-based functional role showed these lncRNAs mediated the regulation of kinase mediated signal transduction, a serine/threonine-protein kinase SMG1 is likely responsible for drought tolerance in XZ5. These findings extend our knowledge of lncRNAs as important regulators in drought tolerance.

The effect of polyethylene glycol-induced drought stress on photosynthesis, carbohydrates and cell membrane in Stevia rebaudiana grown in greenhouse

Drought stress is one of the major environmental stresses that limit crop production in arid regions. A greenhouse culture experiment was conducted to evaluate the response of an agronomically and economically important sweet medical herb (Stevia rebaudiana) to polyethylene glycol (PEG 6000)-induced drought stress (5, 10, and 15% (w/v) PEG, equivalent to leaf water potentials of − 0.49, − 1.40 and − 2.93 MPa, respectively) for 1 month. Plant mass, a major determinant of Stevia yield, showed a reduction after PEG treatments. PEG-reduced photosynthesis traits included the maximal quantum yield of photosystem II (Fv/Fm), efficiency of photosystems I and II (PIabs), intercellular CO2, net photosynthesis, chlorophylls, carotenoids and water use efficiency, followed by the reduction of carbohydrates. Under PEG treatment, the reactive oxygen species (ROS) accumulation occurred and plants exhibited an increase in H2O2 generation. Consequently, an increase in malondialdehyde and electrolyte leakage was evident in PEG treatment, indicating membrane lipid peroxidation. In PEG-treated plants, the ROS accumulation was accompanied by an increase in activity of some enzymatic and non-enzymatic antioxidants. Leaf extracts of PEG-treated plants showed lower superoxide anion, hydroxyl and nitric oxide radical scavenging activity than control plants. Drought stress also caused the accumulation of the compatible solutes proline and glycine betaine. Collectively, the results demonstrated that PEG-induced oxidative stress, due to insufficient antioxidant mechanisms, provoked damages to cell membrane and photosynthetic apparatus, with consequently reduced carbohydrates and plant growth. These results are of basic importance as vegetative growth is the major determining criterion for Stevia crops and adequate irrigation is crucial for obtaining higher yield.

Differences in Seedling Growth of 23 Creeping Bentgrass Cultivars under Polyethylene Glycol-induced Drought Conditions

Drought is the most important abiotic stress in crop production including turfgrass management. Using drought tolerant plants can help minimize stress damage. In this study, 23 commercially available cultivars of creeping bentgrass (Agrostis stolonifera) were evaluated for their responses to drought stress that was induced by polyethylene glycol (PEG) 6000 in a hydroponic system during the seed germination and seedling growth stage. In such a system, water potential was adjusted to 0.0 (the control), −0.3, and −0.6 MPa to mimic the drought condition. The absolute water content (AWC), shoot dry weight (SDW), root dry weight (RDW), longest root length (LRL), specific root length (SRL), and root-to-shoot dry weight ratio (RSR) in the plants grown for 4 weeks in the treatment were determined. Results showed that SDW and LRL were unaffected by drought; however, RDW and RSR increased, whereas SRL and AWC were reduced under drought. Among the 23 creeping bentgrass cultivars evaluated, Independence and Crystal Bluelinks had a higher turfgrass performance index (TPI), which represented the number of times a cultivar ranked in the top statistical group across all parameters. The results suggest that ‘Independence’ and ‘Crystal Bluelinks’ may be more adapted to drought than the other cultivars at the seedling stage.

Identification of quantitative trait loci associated with drought tolerance traits in rice (Oryza sativa L.) under PEG and field drought stress

Two recombinant inbred line F10 rice populations (IAPAR-9/Akihikari and IAPAR-9/Liaoyan241) were used to identify quantitative trait loci (QTLs) for ten drought tolerance traits at the budding and early seedling stage under polyethylene glycol-induced drought stress, and two traits of leaf rolling index (LRI) and leaf withering degree (LWD) under field drought stress. The results showed that the drought-tolerance capacity of IAPAR-9 was stronger than that of Akihikari and Liaoyan241. Thirty-four QTLs for 12 drought tolerance traits were detected, and among them, in the IAPAR-9/Akihikari population, qLRI9-1 and qLRI10-1 for LRI were repeatedly detected in RM3600-RM553 on chromosome 9 and in RM6100-RM3773 on chromosome 10, respectively, at two times points of July 31 and August 13 in 2014. The two QTLs are stable against the environmental impact, and qLRI9-1 and qLRI10-1 explained 6.77–13.66% and 5.01–8.32% of the phenotypic variance, respectively, at the two times points. qLWD9-2 for LWD in the IAPAR-9/Liaoyan241 population contributed 8.73% of variation was detected in the same marker interval with the qLRI9-1, and qLRI1-1 for LRI and qLWD1-1 for LWD were located in the same marker interval RM11054-RM5646 on chromosome 1, which contributed 18.82 and 5.78% of phenotype variation respectively. qGV3 for germination vigor and qRGV3 for relative germination vigor at the budding stage were detected in the same marker interval RM426-RM570 on chromosome 3, which explained 14.98 and 16.30% of the observed phenotypic variation respectively, representing major QTLs. The above-mentioned stable or major QTLs regions could be useful for molecular marker assisted selection breeding, fine mapping, and cloning.

Potential toxicity of nano-graphene oxide on callus cell of Plantago major L. under polyethylene glycol-induced dehydration

Graphene-based nanomaterials have shown a great potential towards improving plant performance in various contexts. However, their increased application over the last few years has raised concerns about their potential biological and environmental risks, warranting optimization and safety assessment considerations. The current study was performed to explore the potential impacts of nano-garphene oxide (NGO) at various concentrations (100–800µgmL−1) on morphological, physiological and biochemical responses of Plantago major L. calli cultures under normal and polyethylene glycol-induced drought stress conditions. Leaf-derived calli on the ½ MS-treated medium with polyethylene glycol showed a decrease in relative growth rate (78.5%), osmotic potential value (48.2%) and an increase in dry matter (35.1%) and H2O2 (54.2%) contents at the highest employed NGO concentration compared with control (p < 0.05). The engineered NGO affected secondary metabolites and amino acid contents under normal water availability as well: at 800µgmL−1, NGO significantly increased total phenolic (40.9%) and flavonoid (35.3%) contents, but significantly reduced proline (26.9%) content compared to the respective control. The integrated biological marker (IBR/n) index for antioxidant enzymes (SOD, CAT, POD, and APX) activities was differentially influenced by the experimental treatments. Overall, the results demonstrated that NGO can positively affect the performance of P. major L. calli cells when applied at specific concentrations, and provide useful inputs into the further studies on phytotoxicity assessment of NGO.

Genome-wide in silico identification, characterization and transcriptional analysis of the family of growth-regulating factors in common bean (Phaseolus vulgaris L.) subjected to polyethylene glycol-induced drought stress

According to most recent findings, growth regulating factors (GRFs) are plant-specific transcription factors (TFs) that play important roles in many processes, including abiotic and biotic stress response mechanisms. Completion of the common bean (Phaseolus vulgaris) genome project has provided researchers with the opportunity to identify all GRF genes in this species. With this aim, a genome-wide in silico study was performed and 10 GRF proteins (called PhvGRFs) were identified in the common bean genome. Conserved and mandatory motifs (QLQ and WRC) were confirmed in all identified PhvGRFs and two segmental duplication events were determined. Most of the PhvGRFs were found to be more similar to Arabidopsis thaliana GRFs than to Zea mays GRFs in a phylogenetic tree. According to the expression analysis of 10 PhvGRFs, inversely related expression patterns were observed in the roots of Yakutiye and Zulbiye cultivars based on their capacity to adopt to drought stress. After drought treatment of the Zulbiye cultivar, a drought-sensitive common bean cultivar, PhvGRF1, PhvGRF2, PhvGRF3, PhvGRF5, PhvGRF6, PhvGRF9 and PhvGRF10 genes were upregulated 2- to 4-fold in root tissues, as compared to the untreated control. The trend of PhvGRF1, PhvGRF2, PhvGRF3, PhvGRF5, PhvGRF6, PhvGRF7, PhvGRF9 and PhvGRF10 genes showed a consistent decline of 2- to 6-fold in root tissues of the drought-tolerant Yakutiye cultivar subjected to 24 h of drought stress. We demonstrated that the expression patterns of the identified PhvGRFs correlated with the drought-stress response in a cultivar-specific manner in the common bean. We suggest that members of the GRF family can also be used for genetic engineering applications in the common bean.

Impact of osmotic stress on seedling growth observations, membrane characteristics and antioxidant defense system of different wheat genotypes

The objective of the present study was to find out a straightforward technique for screening the tolerance of ten wheat genotypes to two levels of osmotic stress at early seedling stage. Data revealed that polyethylene glycol-induced drought had general negative effect on seedling morphological characters indicated by plumule and radicle length, number of adventitious roots as well as seedling biomass and water content. Water deficit could also suppress membrane integrity by stimulating lipid peroxidation with marked increase in membrane leakage and subsequent decrease in its stability index. For all the addressed germination parameters and seedling membrane features, the impact of severe drought was more pronounced than that of moderate drought. Simultaneously, moderate stress could activate peroxidase, polyphenol oxidase and ascorbic peroxidase of the studied genotypes; but these enzymes were inhibited by severe stress. The activity of catalase, superoxide dismutase and glutathione reductase was conversely retarded by drought whether at moderate or severe level. More interestingly, a novel function “Stress Impact Index; SII” was introduced to rank the estimated morpho-physiological traits (SIItrait) as well as the considered genotypes (SIIgenotype) according to their sensitivity to stress. Values of SIItrait implied that germination parameters were generally affected by drought more intensively than membrane characteristics and finally came the antioxidant enzymes with the least degree of suppression when applying stress. Based on the magnitudes of SIIgenotype, Sids 13 seemed to be the most drought-tolerant wheat cultivar while Shandawel 1 could be the most sensitive one at their juvenile growth stage.

Pseudomonas putida attunes morphophysiological, biochemical and molecular responses in Cicer arietinum L. during drought stress and recovery

Drought is one of the most important abiotic stresses that adversely affect plant growth and yield potential. However, some drought resistant rhizosphere competent bacteria are known to improve plant health and promote growth during abiotic stresses. Present study showed the role of Pseudomonas putida MTCC5279 (RA) in ameliorating drought stress on cv. BG-362 (desi) and cv. BG-1003 (kabuli) chickpea cultivars under in vitro and green house conditions. Polyethylene glycol-induced drought stress severely affected seed germination in both cultivars which was considerably improved on RA-inoculation. Drought stress significantly affected various growth parameters, water status, membrane integrity, osmolyte accumulation, ROS scavenging ability and stress-responsive gene expressions, which were positively modulated upon application of RA in both chickpea cultivars. Quantitative real-time (qRT)-PCR analysis showed differential expression of genes involved in transcription activation (DREB1A and NAC1), stress response (LEA and DHN), ROS scavenging (CAT, APX, GST), ethylene biosynthesis (ACO and ACS), salicylic acid (PR1) and jasmonate (MYC2) signalling in both chickpea cultivars exposed to drought stress and recovery in the presence or absence of RA. The observations imply that RA confers drought tolerance in chickpea by altering various physical, physiological and biochemical parameters, as well as by modulating differential expression of at least 11 stress-responsive genes. To the best of our knowledge, this is the first report on detailed analysis of plant growth promotion and stress alleviation in one month old desi and kabuli chickpea subjected to drought stress for 0, 1, 3 and 7 days and recovery in the presence of a PGPR.

The enhanced drought tolerance of rice plants under ammonium is related to aquaporin (AQP)

Previously, we demonstrated that drought resistance in rice seedlings was increased by ammonium (NH4+) treatment, but not by nitrate (NO3−) treatment, and that the change was associated with root development. To study the effects of different forms of nitrogen on water uptake and root growth under drought conditions, we subjected two rice cultivars (cv. ‘Shanyou 63’ hybrid indica and cv. ‘Yangdao 6’ indica, China) to polyethylene glycol-induced drought stress in a glasshouse using hydroponic culture. Under drought conditions, NH4+ significantly stimulated root growth compared to NO3−, as indicated by the root length, surface area, volume, and numbers of lateral roots and root tips. Drought stress decreased the root elongation rate in both cultivars when they were supplied with NO3−, while the rate was unaffected in the presence of NH4+. Drought stress significantly increased root protoplast water permeability, root hydraulic conductivity, and the expression of root aquaporin (AQP) plasma intrinsic protein (PIP) genes in rice plants supplied with NH4+; these changes were not observed in plants supplied with NO3−. Additionally, ethylene, which is involved in the regulation of root growth, accumulated in rice roots supplied with NO3− under conditions of drought stress. We conclude that the increase in AQP expression and/or activity enhanced the root water uptake ability and the drought tolerance of rice plants supplied with NH4+.

Expression Analysis of the ADH Genes in Arabidopsis Plants Exposed to PEG-induced Water Stress

In plants, ethanolic fermentation occurs during limited oxygen condition and under certain environmental stresses. Many of the observations reported on the ADH1 gene during environmental stress conditions were obtained from studies that used single isoforms of the gene ADH1 even though many isoforms of the genes are known to be operational in plants based the complete genome sequence of more than 20 different plant species. Here, the Arabidopsis plants were exposed to polyethylene glycol-induced drought stress and the whole set of ADH (EC.1.1.1.1) genes as well as the enzyme activity of ADH in response to PEG-induced water stress condition was presented and discussed. At enzyme levels, both the root and leaf NADH-ADH activities were increased 5.9 and 4.4 folds when treated with 5% (w/v) PEG-20,000. At gene level, the majority of the ADH1 gene AT1G77120 and two of the ADH-like genes (AT1G64710 and AT5G24760) were up-regulated in the leaf and root. The result suggests that ADH1 together with other two more ADH-likes genes were responsive in the leaf and root operating along side during the PEG-induced water stress and these evidences support the conclusion that the capacity of ethanolic fermentation was enhanced in response to drought.

Morphological changes in response to drought stress in cultivated and wild almond species.

This study was undertaken to identify morphological changes in young seedlings of 5 Iranian almond species (Prunus dulcis, P. eburnea, P. eleagnifolia, P. haussknechti, and P. scoparia) under polyethylene glycol-induced drought stress. Drought stress caused a significant reduction in plant growth parameters such as fresh and dry weights of plant organs, leaf number, total leaf area, and leaf relative water content in all almond species. Specific leaf weight also increased significantly in drought-treated plants compared to control. No significant changes in shoot length, individual leaf area, leaf dimension (length and width), or stomatal size and frequency were observed in response to drought treatments. P. eburnea had the highest relative water content among the species and showed the smallest decrease in fresh and dry weights of organs and greatest decrease in leaf number and total leaf area (the most reduction in transpiration area) as an adaptive mechanism to drought stress.

Comprehensive transcriptomic study on horse gram (Macrotyloma uniflorum): De novo assembly, functional characterization and comparative analysis in relation to drought stress

BackgroundDrought tolerance is an attribute maintained in plants by cross-talk between multiple and cascading metabolic pathways. Without a sequenced genome available for horse gram, it is difficult to comprehend such complex networks and intercalated genes associated with drought tolerance of horse gram (Macrotyloma uniflorum). Therefore, de novo transcriptome discovery and associated analyses was done for this highly drought tolerant yet under exploited legume to decipher its genetic makeup.ResultsEight samples comprising of shoot and root tissues of two horse gram genotypes (drought-sensitive; M-191 and drought-tolerant; M-249) were used for comparison under control and polyethylene glycol-induced drought stress conditions. Using Illumina sequencing technology, a total of 229,297,896 paired end read pairs were generated and utilized for de novo assembly of horse gram. Significant BLAST hits were obtained for 26,045 transcripts while, 3,558 transcripts had no hits but contained important conserved domains. A total of 21,887 unigenes were identified. SSRs containing sequences covered 16.25% of the transcriptome with predominant tri- and mono-nucleotides (43%). The total GC content of the transcriptome was found to be 43.44%. Under Gene Ontology response to stimulus, DNA binding and catalytic activity was highly expressed during drought stress conditions. Serine/threonine protein kinase was found to dominate in Enzyme Classification while pathways belonging to ribosome metabolism followed by plant pathogen interaction and plant hormone signal transduction were predominant in Kyoto Encyclopedia of Genes and Genomes analysis. Independent search on plant metabolic network pathways suggested valine degradation, gluconeogenesis and purine nucleotide degradation to be highly influenced under drought stress in horse gram. Transcription factors belonging to NAC, MYB-related, and WRKY families were found highly represented under drought stress. qRT-PCR validated the expression profile for 9 out of 10 genes analyzed in response to drought stress.ConclusionsDe novo transcriptome discovery and analysis has generated enormous information over horse gram genomics. The genes and pathways identified suggest efficient regulation leading to active adaptation as a basal defense response against drought stress by horse gram. The knowledge generated can be further utilized for exploring other underexploited plants for stress responsive genes and improving plant tolerance.