PEG-induced Drought Stress Research Articles

Effects of Drought Stress on Hybrids of Vigna radiata at Germination Stage

Drought is one the critical abiotic factors that reduces the germination, growth and yield of crops. Therefore the present project was designed with the objective to screen the best drought tolerant hybrid of Vigna radiata. Genetic variations for drought tolerance among these hybrids were assessed by simple and efficient technique. Seven hybrids of V. radiata (9801, 7002, 9706, 08003, 07007, 97012 and 08007) were used for screening against three levels of drought stress (zero, control), 5% (-0.05 MPa) and 10% (-0.1 MPa) induced by Polyethyleneglycol (PEG6000). A. higher proline content was observed in 07007 (6.10 μg/g fresh weight) as compared to all other hybrids. Treated seedlings of each hybrid were com-pared with their respective control to evaluate the differences in their growth under drought. Different parameters such as percentage of germination, germination stress tolerance index (GSI), shoot and root weights (bath fresh and dry) and lengths, root length stress index (RLSI), dry matter stress index (DMSI) and plant height stress index (PHSI) showed considerable variations. Germination percentage, shoot weights, PHSI and DMSI decreased in all hybrids along with the increase of PEG induced drought stress (5% and 10% PEG). In contrary, root weights and RLSI were increased under drought. Overall 07007 showed a better performance, and can therefore be classified as a drought tolerant hybrid.

The Panax ginseng PgTIP1 gene confers enhanced salt and drought tolerance to transgenic soybean plants by maintaining homeostasis of water, salt ions and ROS

The Panax ginseng PgTIP1 gene has been demonstrated to have high water channel activity by its heterologous expression in Xenopus laevis oocytes and in yeast, and it also plays significant roles in enhancing the salt/drought tolerance of PgTIP1-transgenic Arabidopsis plants and salt adaptation of PgTIP1-transformed Glycine max. In this work, PgTIP1 gene was transformed into the hybrid soybean strain 4076 (F5), which was selected for salt tolerance generation by generation from the cross assembly of G. max N23674 cultivar × G. soja BB52 accession. The PgTIP1-transgenic soybean plants mediated by the pollen tube pathway, represented by lines L19 and L29, were simultaneously analyzed at physiological and molecular levels for enhanced salt and drought tolerance. The results showed that the salt-stressed PgTIP1-transgenic lines L19 and L29 acquired better leaf stomatal movement and water-gas exchange capacity; less absorption, transport and accumulation of Na+, Cl−; a lower Na+/K+ ratio; and enhanced antioxidase activities of SOD, POD, CAT, and APX than WT in the roots and leaves. Under PEG-induced drought stress, the PgTIP1-transgenic plants showed greater leaf water-retention capacity and reduced cell membrane damage in roots and leaves. Therefore, the PgTIP1-transgenic soybean lines showed both salt and drought tolerance, which are related not only to the primary functions of the PgTIP1 gene in terms of water status regulation but also to its secondary roles in up-regulating the expression of stress-related genes (GmNHX1, GmSOS1, GmCLC1, GmCAT1, GmAPX1, GmNCED1 and GmP5CS1), which are involved in homeostasis of Na+, K+, and Cl−; ROS scavenging; and synthesis of ABA, proline, etc.

Ammonium uptake increases in response to PEG-induced drought stress in Malus hupehensis Rehd.

It is unclear how plants optimize their preference for different forms of inorganic nitrogen to enhance their survival and fitness in challenging environments. Using a hydroponics culture system, we monitored morphological, physiological, and molecular changes in Malus hupehensis seedlings when drought conditions (induced by 5% polyethylene glycol, or PEG) were combined with a low or normal supply of N (0.05 mM or 1 mM NH4NO3, respectively). We found here that PEG-induced drought stress negatively inhibited the growth of Malus hupehensis seedlings and resulted in higher NH4+/NO3− ratios in their roots and leaves. The net ammonium influx at the surface of fine roots rose dramatically under drought treatment, while that of nitrate was less changed. This was confirmed by higher absorption of stable 15NH4+ isotope than of 15NO3− under drought conditions. Consistently, two ammonium transporter genes closely related to ammonium uptake (AMT4;2 and AMT4;3) were notably up-regulated in response to drought stress, while transcript levels of most genes related to nitrate uptake/reduction and nitrogen assimilation decreased. Therefore, in acclimating to drought, Malus hupehensis plants exhibited relatively increased uptake of NH4+ compared to NO3−. In addition, reducing N supply may alleviate the adverse affect of drought stress on the growth of Malus hupehensis.

Physiological and biochemical changes in different drought-tolerant alfalfa (Medicago sativa L.) varieties under PEG-induced drought stress

Medicago sativa L. cv. Longzhong is a nutritious forage plant in dryland regions of the Loess Plateau with strong drought tolerance and broad adaptability. To understand the adaptation mechanism of alfalfa (M. sativa L. cv. Longzhong) to drought stress, growth, and physiological parameters including levels of chlorophyll content, osmotic adjustment, reactive oxygen species (ROS), and antioxidant enzymes and antioxidants were measured under simulated levels of drought (− 0.40, − 0.80, − 1.20, − 1.60, and − 2.00 MPa). The changes in M. sativa L. cv. Longzhong were compared with those of plants of M. sativa L. cv. Longdong control (Variety I) suited to moderate rainfall areas and M. sativa L. cv. Gannong No. 3 (Variety II) suited to irrigated areas. The results showed that root–shoot ratio, the chlorophyll (a + b) and osmolytes contents, the degree of lipid peroxidation and ROS production, and the levels of antioxidative enzymes and antioxidants increased significantly with increasing drought stress, whereas plant height, aboveground biomass, chlorophyll a/b ratio, leaf water potential (Ψ1), and relative water content (RWC) decreased in response to drought. The Longzhong variety responded early to beginning drought stress (between 0 and − 0.4 MPa) compared with the controls. Under drought stress (between − 0.4 and − 2.0 MPa), the Longzhong variety had significantly higher belowground biomass, root–shoot ratio, Ψ1, RWC, catalase (CAT) activity and reduced glutathione content than those of Varieties I and II, but hydrogen peroxide and hydroxyl free radical (OH·) contents were significantly lower. Step regression analysis showed that OH·, CAT, malondialdehyde, superoxide anion-free radical (O 2 ·− ), and superoxide dismutase of Longzhong had the most marked response to drought stress. In conclusion, the stronger drought tolerance of the Longzhong variety might be due to its higher water-holding capacity, root–shoot ratio, and ability to coordinate enzymatic and non-enzymatic antioxidant systems, which coordinate the peroxidation and oxidative systems.

Aktivnost antioksidativnih enzima u ponicima grahorica u uslovima suše

Drought greatly affects normal plant growth, endangering physiological and biochemical processes in plants. Under the influence of unfavorable environmental conditions, antioxidant protection systems in plant cell can be activated regardless of the stage of growth and development of plants. The experiment was conducted on three vetches species (V. sativa, V. villosa and V. pannonica) under PEG-induced drought stress. Activity of antioxidant enzymes: superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APx, EC 1.11.1.1) and catalase (CAT, EC 1. 11. 1. 6), was determined in shoots and roots of 10-day-old seedlings. Lack of water during germination period activated all the examined antioxidant enzymes in both organs of all tested Vicia species. The activity of SOD and APx generally increased at higher stress levels, while the enzyme CAT showed different patterns of action in all tested species. The results of this study suggest that drought stress causes the production of oxygen radicals that lead to oxidative stress in plants.

Exogenous Application of GABA Improves PEG-Induced Drought Tolerance Positively Associated with GABA-Shunt, Polyamines, and Proline Metabolism in White Clover.

In order to investigate the physiological effects of exogenous γ-aminobutyric acid (GABA) on drought tolerance in white clover (Trifolium repens), GABA shunt, polyamines (PAs), and proline (Pro) metabolism were examined after plants pretreated with or without GABA (8 mM) and then exposed to water or 15% PEG-induced drought stress in growth chamber. In this study, exogenous application of GABA effectively alleviated drought-induced damage in leaves, as reflected by significantly higher relative water content, lower electrolyte leakage, lipid peroxidation, and leaf wilt. Exogenous GABA further promoted drought-induced increases in GABA transaminase and alpha ketone glutarate dehydrogenase activities, but inhibited glutamate decarboxylase activity under both control and drought conditions, resulting in an increase in endogenous glutamate (Glu) and GABA content. Besides, exogenous GABA could well accelerated PAs synthesis and suppressed PAs catabolism, which lead to the extremely enhanced different types of PAs content (free Put and Spd, insoluble bound Spd and Spm, soluble conjugated Spd and Spm, and total Put, Spd and Spm) under drought stress. In addition, exogenous GABA application further activated drought-induced Δ1-pyrroline-5-carboxylate synthetase and proline dehydrogenase activities, but suppressed drought-facilitated ornithine -δ-amino transferase activities, leading to a higher Pro accumulation and metabolism in GABA-pretreated plants in the middle and last period of drought. The results suggested that increased endogenous GABA by exogenous GABA treatment could improve drought tolerance of white clover associated with a positive regulation in the GABA-shunt, PAs and Pro metabolism.

Drought Stress Enhances Up-Regulation of Anthocyanin Biosynthesis in Grapevine leafroll-associated virus 3-Infected in vitro Grapevine (Vitis vinifera) Leaves.

Reddish-purple coloration on the leaf blades and downward rolling of leaf margins are typical symptoms of grapevine leafroll disease (GLD) in red-fruited grapevine cultivars. These typical symptoms are attributed to the expression of genes encoding enzymes for anthocyanins synthesis, and the accumulation of flavonoids in diseased leaves. Drought has been proven to accelerate development of GLD symptoms in virus-infected leaves of grapevine. However, it is not known how drought affects GLD expression nor how anthocyanin biosynthesis in virus-infected leaves is altered. The present study used HPLC to determine the types and levels of anthocyanins, and applied reverse transcription quantitative polymerase chain reaction (RT-qPCR) to analyze the expression of genes encoding enzymes for anthocyanin synthesis. Plantlets of Grapevine leafroll-associated virus 3 (GLRaV-3)-infected Vitis vinifera 'Cabernet Sauvignon' were grown in vitro under PEG-induced drought stress. HPLC found no anthocyanin-related peaks in the healthy plantlets with or without PEG-induced stress, while 11 peaks were detected in the infected plantlets with or without PEG-induced drought stress, but the peaks were significantly higher in infected drought-stressed plantlets. Increased accumulation of total anthocyanin compounds was related to the development of GLD symptoms in the infected plantlets under PEG stress. The highest level of up-regulated gene expression was found in GLRaV-3-infected leaves with PEG-induced drought stress. Analyses of variance and correlation of anthocyanin accumulation with related gene expression levels found that GLRaV-3-infection was the key factor in increased anthocyanin accumulation. This accumulation involved the up-regulation of two key genes, MYBA1 and UFGT, and their expression levels were further enhanced by drought stress.

Antioxidant system and photosynthetic characteristics responses to short-term PEG-induced drought stress in cucumber seedling leaves

The effect of short-term drought stress on the water content, antioxidant system and photosynthetic characteristics was investigated using cucumber (Cucumis sativus L.) seedlings. The results indicated that polyethylene glycol induced water stress reduced water content in shoots of cucumber seedling after treatment of 36 hours, and caused obvious reductions in net photosynthetic rate, stomatal conductance, intercellular CO2 concentration and transpiration of leaves. In addition, water stress significantly reduced the photosynthetic pigment content and inhibited photochemical activity, including actual photochemical efficiency, maximal quantum yield of photosystem II photochemistry and coefficient for photochemical quenching. Meanwhile non-photochemical quenching increased. As responses to drought stress, significant increases in electrolyte leakage, malondialdehyde, superoxide anion and hydrogen peroxide levels were detected in leaves. The superoxide dismutases, catalase, glutathione reductase and dehydroascorbate reductase activities, protein, ascorbate and glutathione content, all decreased and peroxidases activity increased, while ascorbate peroxidase and monodehydroascorbate reductase activities exhibited different trend under different degree of water stress. Therefore, it can be concluded that water stress strongly disrupted the normal metabolism of leaves and restrained water absorption.

Exogenously applied polyamines ameliorate osmotic stress-induced damages and delay leaf rolling by improving the antioxidant system in maize genotypes

Leaf rolling (LR), particularly in crops, is a dehydration avoidance mechanism that results from water loss in plants under drought conditions. Two maize cultivars (Zea mays L.) differing in their tolerance to drought (cultivar Side was selected as stress-tolerant and cultivar Karacay was selected as stress-sensitive) under PEG-induced drought stress were used in this study to understand the effects of polyamines (PAs) on LR response and the role of the antioxidant system in the delayed LR process. Aerial parts of the seedlings were excised prior to the experiment and then submerged in a Hoagland nutrient solution with or without 0.1 mM Putrescine and 0.1 mM Spermine for 17 h, after which they were submitted to osmotic stress treatments (5% PEG) for 24 h. LR was physically prevented in order to clarify the relationship between PAs and antioxidant systems in LR response. Plants were evaluated by measuring the accumulation of hydrogen peroxide (H2O2), lipid peroxidation, antioxidant enzyme activities, and nonenzymatic antioxidant levels. Exogenous applications of PAs prevented water loss and delayed LR in comparison with the control (seedlings treated only with PEG). PAs almost totally prevented increases in lipid peroxidation. Antioxidant enzyme activities in rolled leaves were induced in response to osmotic stress in both maize seedlings via PA application. Ascorbate, glutathione, and endogenous PA levels increased as a result of PA applications. H2O2 content was lower in PA-pretreated plants than in the control in both cultivars. The activity/effectiveness of antioxidant system components of the physical prevention of leaf rolling (PLR) group of plants were lower than those of the group of plants with rolled leaves, especially in sensitive Karacay, whereas more induced H2O2 content and lipid peroxidation were determined in the PLR group. In addition, exogenous applications of PAs further increased the components of Side's antioxidant system in comparison with Karacay. When considered together, the data suggest that exogenous PAs may have a H2O2-mediated regulatory role in the LR process through the induction of antioxidant machinery. A stimulated antioxidant system decreases oxidative stress damage from excess accumulation of H2O2, thus delaying LR. In summary, exogenous PAs could help plants invert the adverse effects of osmotic stress and might play a key role in providing tolerance in plants through modulating the antioxidant system and decreasing H2O2 levels and water loss in plants via LR, as an alternative drought-protection mechanism. In addition, maize cultivars with late LR by PA applications may be provided as an opportunity for improving yield potential in drought-prone areas.

Effects of PEG-induced drought stress on regulation of indole alkaloid biosynthesis in Catharanthus roseus

ABSTRACTCatharanthus roseus (C. roseus) plants were used to investigate the terpenoid indole alkaloids (TIAs) accumulation under the condition of PEG-induced drought stress. Multivariate analysis showed that 35% PEG6000 could induce more obvious and stable accumulation on proline (PRO) content and the relative water content (RWC). The results indicated that there were gradual increase and then decrease (p < .05) in the contents of vindoline (VIN) and catharanthine (CAT) under 35% PEG6000 stress, but the content of vinblastine (VBL) increased gradually. In addition, the expression levels of tryptophan decarboxylase (TDC), strictosidine synthase (STR) and deacetylvindoline-4-O-acetyltransferase (DAT) were upregulated in plants under 35% PEG6000 stress. Further correlation analysis indicated that CAT accumulation was significantly correlated with TDC gene expression, and VBL accumulation was significantly correlated with peroxidase (p < .05). Our results suggest that the cultivation of C. roseus in drought stress would serve as effective treatment for accumulating TIAs.

Mechanisms underlying toxicity and stimulatory role of single-walled carbon nanotubes in Hyoscyamus niger during drought stress simulated by polyethylene glycol

In this study, seeds of Hyoscyamus niger were exposed to different concentrations (50–800μgmL−1) of single-walled carbon nanotubes (SWCNTs) under different levels of drought stress (0.5–1.5MPa) for 14days. Germinated seeds were subsequently allowed to grow in the same culture media for 7 more days to test the further response of the seedlings in terms of biochemical changes to the employed treatments. Seeds subjected to drought showed reduction in germination percentage, vigor and lengths of roots and shoots. However, inclusion of SWCNTs at the two lowest concentrations significantly alleviated the drought stress (up to moderate levels only)-induced reduction in germination and growth attributes. This happened due to increased water uptake, up-regulation of mechanisms involved in starch hydrolysis, and reduction in oxidative injury indices including H2O2, malondialdehyde contents and electrolyte leakage. The improved plant performance under PEG-induced drought stress was a consequence of changes in the expression of various antioxidant enzymes including SOD, POD, CAT, and APX, and also biosynthesis of proteins, phenolics, and specific metabolites such as proline. Results demonstrate that treatment by low concentrations of SWCNTs can induce tolerance in seedlings against low to moderate levels of drought through enhancing water uptake and activating plant defense system.

Five novel transcription factors as potential regulators of OsNHX1 gene expression in a salt tolerant rice genotype.

This manuscript reports the identification and characterization of five transcription factors binding to the promoter of OsNHX1 in a salt stress tolerant rice genotype (Hasawi). Although NHX1 encoding genes are known to be highly regulated at the transcription level by different abiotic stresses, namely salt and drought stress, until now only onetranscription factor (TF) binding to its promoter has been reported. In order to unveil the TFs regulating NHX1 gene expression, which is known to be highly induced under salt stress, we have used a Y1H system to screen a salt induced rice cDNA expression library from Hasawi. This approach allowed us to identify five TFs belonging to three distinct TF families: one TCP (OsPCF2), one CPP (OsCPP5) and three NIN-like (OsNIN-like2, OsNIN-like3 and OsNIN-like4) binding to the OsNHX1 gene promoter. We have also shown that these TFs act either as transcriptional activators (OsPCF2, OsNIN-like4) or repressors (OsCPP5, OsNIN-like2) and their encoding genes are differentially regulated by salt and PEG-induced drought stress in two rice genotypes, Nipponbare (salt-sensitive) and Hasawi (salt-tolerant). The transactivation activity of OsNIN-like3 was not possible to determine. Increased soil salinity has a direct impact on the reduction of plant growth and crop yield and it is therefore fundamental to understand the molecular mechanisms underlying gene expression regulation under adverse environmental conditions. OsNHX1 is the most abundant K+-Na+/H+ antiporter localized in the tonoplast and its gene expression is induced by salt, drought and ABA. To investigate how OsNHX1 is transcriptionally regulated in response to salt stress in a salt-tolerant rice genotype (Hasawi), a salt-stress-induced cDNA expression library was constructed and subsequently screened using the yeast one-hybrid system and the OsNHX1 promoter as bait. Five transcription factors (TFs) belonging to three distinct TF families: one TCP (OsPCF2), one CPP (OsCPP5) and three NIN-like (OsNIN-like2, OsNIN-like3 and OsNIN-like4) were identified as binding to OsNHX1 promoter. Transactivation activity assays performed in Arabidopsis and rice protoplasts showed that OsPCF2 and OsNIN-like4 are activators of the OsNHX1 gene expression, while OsCPP5 and OsNIN-like2 act as repressors. The transactivation activity of OsNIN-like3 needs to be further investigated. Gene expression studies showed that OsNHX1 transcript level is highly induced by salt and PEG-induced drought stress in both shoots and roots in both Nipponbare and Hasawi rice genotypes. Nevertheless, OsNHX1 seems to play a particular role in shoots in response to drought. Most of the TFs binding to OsNHX1 promoter showed a modest transcriptional regulation under stress conditions, however, in response to most of the conditions studied, the OsPCF2 was induced earlier than OsNHX1, indicating that OsPCF2 may activate OsNHX1 gene expression. In addition, although the OsNHX1 response to salt and PEG-induced drought stress in either shoots or roots was quite similar in both rice genotypes, the expression of OsPCF2 in roots under salt stress and the OsNIN-like4 in roots subjected to PEG was mainly up-regulated in Hasawi, indicating that these TFs may be associated with the salt and drought stress tolerance observed for this genotype.

Elucidation of Complex Nature of PEG Induced Drought-Stress Response in Rice Root Using Comparative Proteomics Approach.

Along with many adaptive strategies, dynamic changes in protein abundance seem to be the common strategy to cope up with abiotic stresses which can be best explored through proteomics. Understanding of drought response is the key to decipher regulatory mechanism of better adaptation. Rice (Oryza sativa L.) proteome represents a phenomenal source of proteins that govern traits of agronomic importance, such as drought tolerance. In this study, a comparison of root cytoplasmic proteome was done for a drought tolerant rice (Heena) cultivar in PEG induced drought conditions. A total of 510 protein spots were observed by PDQuest analysis and 125 differentially regulated spots were subjected for MALDI-TOF MS-MS analysis out of which 102 protein spots identified which further led to identification of 78 proteins with a significant score. These 78 differentially expressed proteins appeared to be involved in different biological pathways. The largest percentage of identified proteins was involved in bioenergy and metabolism (29%) and mainly consists of malate dehydrogenase, succinyl-CoA, putative acetyl-CoA synthetase, and pyruvate dehydrogenase etc. This was followed by proteins related to cell defense and rescue (22%) such as monodehydroascorbate reductase and stress-induced protein sti1, then by protein biogenesis and storage class (21%) e.g. putative thiamine biosynthesis protein, putative beta-alanine synthase, and cysteine synthase. Further, cell signaling (9%) proteins like actin and prolyl endopeptidase, and proteins with miscellaneous function (19%) like Sgt1 and some hypothetical proteins were also represented a large contribution toward drought regulatory mechanism in rice. We propose that protein biogenesis, cell defense, and superior homeostasis may render better drought-adaptation. These findings might expedite the functional determination of the drought-responsive proteins and their prioritization as potential molecular targets for perfect adaptation.

Responses of In vitro-Grown Plantlets (Vitis vinifera) to Grapevine leafroll-Associated Virus-3 and PEG-Induced Drought Stress.

Stresses caused by viral diseases and drought have long threatened sustainable production of grapevine. These two stresses frequently occur simultaneously in many of grapevine growing regions of the world. We studied responses of in vitro-grown plantlets (Vitis vinifera) to Grapevine leafroll associated virus-3 (GLRaV-3) and PEG-induced drought stress. Results showed that stress induced by either virus infection or drought had negative effects on vegetative growth, caused significant decreases and increases in total soluble protein and free proline, respectively, induced obvious cell membrane damage and cell death, and markedly increased accumulations of and H2O2. Co-stress by virus and drought had much severer effects than single stress on the said parameters. Virus infection alone did not cause significant alternations in activities of POD, ROS, and SOD, and contents of MDA, which, however, markedly increased in the plantlets when grown under single drought stress and co-stress by the virus and drought. Levels of ABA increased, while those of IAA decreased in the plantlets stressed by virus infection or drought. Simultaneous stresses by the virus and drought had co-effects on the levels of ABA and IAA. Up-regulation of expressions of ABA biosynthesis genes and down-regulation of expressions of IAA biosynthesis genes were responsible for the alternations of ABA and IAA levels induced by either the virus infection or drought stress and co-stress by them. Experimental strategies established in the present study using in vitro system facilitate investigations on ‘pure’ biotic and abiotic stress on plants. The results obtained here provide new insights into adverse effects of stress induced by virus and drought, in single and particularly their combination, on plants, and allow us to re-orientate agricultural managements toward sustainable development of the agriculture.

English

English

Sulfur Use Efficiency Is a Significant Determinant of Drought Stress Tolerance in Relation to Photosynthetic Activity in Brassica napus Cultivars.

To investigate the varietal difference in sulfur use efficiency (SUE) and drought stress tolerance, Brassica napus ‘Mosa’ and ‘Saturnin’ were exposed to polyethylene glycol (PEG)-induced drought stress for 72 h. Direct quantification of S uptake, de novo synthesis of amino acids and proteins was performed by tracing 34S. The responses of photosynthetic activity in relation to SUE were also examined. The total amount of newly absorbed S decreased with drought stress in both cultivars but the decrease rate was significantly higher in Mosa (-64%) than in Saturnin (-41%). Drought stress also decreased the amount of S assimilated into amino acids (34S-amino acids) and proteins (34S-proteins). The total amount of S incorporated into amino acids and proteins was generally higher in Saturnin (663.7 μg S per plant) than in Mosa (337.3 μg S per plant). The estimation of SUE based on S uptake (SUpE) and S assimilation (SUaE) showed that SUE was much higher in Saturnin than in Mosa. The inhibition of photosynthetic activity including Rubisco protein degradation caused by drought stress was much lower in the cultivar with higher SUE (Saturnin). The present study clearly indicates that the genotype with higher SUE is more tolerant to PEG-induced drought stress.

Physiological and molecular analysis on root growth associated with the tolerance to aluminum and drought individual and combined in Tibetan wild and cultivated barley.

The drought-stimulated gene expression of NCED, SUS, and KS - DHN and ABA signal cross-talk with other phytohormones maintains barley root growth under drought stress at pH 4.0 plus polyethylene glycol plus aluminum. Aluminum (Al) toxicity and drought are two major factors that limit barley production. In this work, the individual and combined effects of Al/acid and polyethylene glycol (PEG 6000) induced drought stress that suppressed root growth and caused oxidative damage as characterized by increased H2O2 and O2(.-) accumulation. The wild-barley genotypes, XZ5 and XZ29, exhibited a higher tolerance than the two cultivars Dayton (Al tolerant) and Tadmor (drought tolerant) under combined stress (pH 4.0 + PEG + Al). The oxidative damage induced by PEG was more severe at pH 4.0 than at pH 6.0. In XZ29, the highest root secretion of malate and citrate was recorded, and the least Al uptake in the four genotypes. In XZ5, a peak accumulation of ABA and minor synthesis of zeatin riboside and ethylene were found being essential in maintaining primary root elongation and root hair development. PEG-induced drought stress repressed Al uptake in root tips, with a lower increase in callose formation and HvMATE (Hordeum vulgare multidrug and toxic compound exudation) expression compared to Al-induced callose production. Stress by pH 4.0 + PEG + Al up-regulated 9-cis-epoxycarotenoid dioxygenase (NCED) which is involved in ABA biosynthesis. Such treatment stimulated the regulation of ABA-dependent genes sucrose synthase (SUS) and KS-type dehydrin (KS-DHN) in root tips. Our results suggest that the tolerance ranking to pH 4.0 + PEG + Al stress in Tibetan wild barley by gene expression is closely correlated to physiological indices. The results show that acclimatisation to pH 4.0 + PEG + Al stress involves specific responses in XZ5 and XZ29. The present study provides insights into the effects of Al/acid and drought combined stress on the abundance of physiological indices in the roots of barley varieties.

Nitrogen uptake and metabolism of Populus simonii in response to PEG-induced drought stress

In the present study, changes in nitrogen uptake, assimilation and the transcript abundance of associated genes were investigated in Populus simonii seedlings treated with 5% polyethylene glycol (PEG)-induced drought stress under hydroponic culture conditions with low and normal nitrogen levels (0.01mM NH4NO3 and 1mM NH4NO3, respectively). Drought stress negatively affected plant growth at both low and normal nitrogen levels. NH4+ and NO3− concentrations were significantly decreased in the roots and leaves of PEG-treated P. simonii seedlings; however, the ratio of NH4+ and NO3− was increased in these plants. Drought stress also decreased NR and GOGAT activity in roots and leaves, irrespective of the nitrogen levels. However, the NH4+ concentrations and NR activity in roots and leaves were increased in response to 1mM NH4NO3 under drought stress. PEG-treated plants also showed better growth at normal nitrogen level (1mM NH4NO3), with increased biomass, total fine root length and larger root surface area. Most genes related to nitrate uptake, reduction and N metabolism were down-regulated; however, two ammonium transporter genes closely related to NH4+ uptake (AMT1;2 and AMT1;6) were up-regulated in response to drought stress. These results suggested that increased N nutrition may have contributed to drought tolerance in P. simonii by increasing NH4+ uptake and decreasing nitrogen metabolism.

Germination of tomatoes under PEG-induced drought stress

Summary: The aims of this study were: to assess the effects of drought stress on germination percentage, germination energy and number of days to complete germination in fifteen tomato populations; to distinguish the treatment that is the most suitable for classifying the tomatoes for their response to early-imposed drought; as well as to distinguish populations which could be used for breeding tolerant varieties. The experiment included control germination assay (distilled water) and the increasing (4, 8, and 12%, w/v) polyethylene glycol (PEG) treatments. Both germination percentage and energy considerably decreased with the increasing PEG treatments, while the observed average increase in the number of days required to complete germination remained statistically insignificant. The differences in germination among the populations were most pronounced in 12% PEG treatment, which is therefore recommended for further research. Several populations are indicated as tolerant; however, tomato drought tolerance exhibited as early as at the germination stage does not necessarily indicate the tolerance in later phases of plant development. The population 105 is recommended for breeding drought tolerant varieties.

Molecular and biochemical mechanisms associated with differential responses to drought tolerance in wheat (Triticum aestivum L.)

Drought stress is a common abiotic stress in wheat. In this study, PEG-induced drought stress caused significant decline in morpho-physiological characteristics in Bijoy but not in BG-25, suggesting that drought tolerance mechanisms exist in BG-25. Semi-quantitative RT-PCR (reverse transcriptase) revealed the upregulation of TaCRT1 (calreticulin Ca2+-binding protein) and DREB1A (dehydration responsive transcription factor) transcripts in drought-stressed roots of BG-25 and Bijoy, albeit to a lesser extent. These imply that increased TaCRT1 expression may be associated with the survival of the wheat plants under drought conditions. In addition, DREB1A suggests its involvement in gene regulation associated with drought tolerance. Higher antioxidant enzyme capacity (catalase, peroxidase and glutathione reductase) along with less MDA content in roots of BG-25 suggests that wheat tolerance to drought stress could be associated with higher oxidative scavenging ability. Finally, elevated S-metabolites (glutathione, methionine and cysteine) and proline in BG-25 indicates that strong antioxidant defense play a vital role in drought tolerance in wheat.