Differentially expressed proteins associated with drought tolerance in bananas (<Emphasis Type="Italic">Musa</Emphasis> spp.)

Bananas are one of the most important fruits in tropical and subtropical regions worldwide. Each year, banana plantations expand, but the areas available are mostly dry lands. The establishment of strategies for obtaining drought tolerant cultivars depends on understanding of biological responses at genetic, molecular and biochemical levels. Proteomics is a powerful tool for functional characterization of the response of plants to abiotic stress and little is known about drought tolerance in Musa spp. Therefore, the aim of this study was to identify proteins related to drought tolerance in two contrasting banana genotypes, Prata Anã and BRS Tropical, susceptible and tolerant to drought, respectively. Proteins were extracted from rhizomes of bananas grown under greenhouse conditions with control, irrigated and water deficit regimes. The differential protein expression pattern was established by two-dimensional (2-D) electrophoresis and spots analyzed in nano Q-Tof Micro UPLC. Twenty-three differentially expressed proteins were found in the tolerant genotype (BRS Tropical) under water deficit, with proteins involved in metabolism, defense and transport. Proteins were classified according to known function and biosynthetic pathways. Signaling proteins in response to water stress, especially for the biological function of growth and development of plants cells, were also encountered, whereas heat shock proteins played a significant role. This is the first report of proteomic analysis for drought tolerance in ‘Pome’ and ‘Silk-type’ bananas containing the ‘B’ genome. Our work provides insights into Musa spp. response to drought and data for further studies regarding molecular mechanisms, which determine how Musa spp. cells better overcome environmental perturbations.     

Improving water use efficiency by changing hydraulic and stomatal characteristics in soybean exposed to drought: the involvement of nitric oxide

A variety of cellular responses is needed to ensure the plants survival during drought, but little is known about the signaling mechanisms involved in this process. Soybean cultivars (EMBRAPA 48 and BR 16, tolerant and sensitive to drought, respectively) were exposed to the following treatments: control conditions (plants in field capacity), drought (20% of available water in the soil), sodium nitroprusside (SNP) treatment (plants irrigated and treated with 100-µM SNP [SNP–nitric oxide (NO) donor molecule], and Drought + SNP (plants subjected to drought and SNP treatment). Plants remained in these conditions until the reproductive stage and were evaluated for physiological (photosynthetic pigments, chlorophyll a fluorescence and gas exchange rates), hydraulic (water potential, osmotic potential and leaf hydraulic conductivity) and morpho-anatomical traits (biomass, venation density and stomatal characterization). Exposure to water deficit considerably reduced water potential in both cultivars and resulted in decrease in photosynthesis and biomass accumulation. The addition of the NO donor attenuated these damaging effects of water deficit and increased the tolerance index of both cultivars. The results showed that NO was able to reduce plant's water loss, while maintaining their biomass production through alteration in stomatal characteristics, hydraulic conductivity and the biomass distribution pattern. These hydraulic and morpho-anatomical alterations allowed the plants to obtain, transport and lose less water to the atmosphere, even in water deficit conditions.     

Drought tolerance in two oil palm hybrids as related to adjustments in carbon metabolism and vegetative growth

Drought tolerance was examined in two oil palm hybrids (BRS Manicoré and BRS C 2501) grown in large pots and subjected to long-term drought (57 days) and rehydration. Regardless of hybrids, predawn water potential (Ψ _pd), net photosynthesis rates, and stomatal conductance decreased similarly upon drought imposition, but the absolute values of these variables were lower in BRS C 2501 than in BRS Manicoré. Overall, drought-induced decreases in activities of key enzymes associated with carbon metabolism, including Rubisco, ADP-glucose pyrophosphorylase, and sucrose-phosphate synthase, were stronger in BRS C 2501 than in BRS Manicoré. Our data suggest that synthesis of starch (and possibly sucrose) was fundamentally limited by a lower substrate availability rather than by enzymatic constraints, particularly until day 34 after suspending watering. Drought stress provoked similar decreases in biomass accumulation in either hybrid; however, BRS Manicoré plants displayed higher total leaf area and root length coupled with greater relative decreases in dry matter of above-ground parts than of roots as compared to BRS C 2501, thereby leading to an increased root-to-above ground ratio in the former. Upon resuming irrigation, the slow recovery of Ψ _pd preceded the recovery of stomatal conductance and photosynthesis irrespective of hybrid. BRS Manicoré was better able to recover enzyme activities and carbohydrate status than BRS C 2501. In conclusion, both hybrids could tolerate (or survive) the severe drought conditions, but, overall, BRS Manicoré plants were better able to adjust its physiological, morphological, and biochemical traits to cope with drought than did BRS C 2501.     

甘薯品种抗旱适应性综合评价的方法研究

在对水分胁迫下甘薯形态、生长势、生理生化和产量性状等指标与品种抗旱性进行相关分析的基础上,采用抗旱系数法、聚类分析法、隶属函数法对品种抗旱适应性予以综合评价.综合评价的结果,将15个供试甘薯品种按抗旱水平由弱到强划分为不抗（农大红、漳薯1号、8908-383）、低抗（宿芋1号、9318-58、渝苏303、89-1、95-411-153、西蒙1号）、中抗（92-111-107、渝薯34、南薯88、92-103-30）和高抗（Y3、潮薯1号）四级.上述几种关于甘薯品种抗旱适应性综合评价的方法具有较好的一致性.     

Quantitative trait loci for rooting pattern traits of common beans grown under drought stress versus non-stress conditions

Drought is the major abiotic constraint contributing to yield reduction in common bean (Phaseolus vulgaris L.) worldwide. An increasing scarcity of water in the future will make improving adaptation to drought stress a major objective of most crop breeding efforts. Drought avoidance by increased extraction of soil moisture from greater depth under drought conditions is an adaptive mechanism of common bean. A recombinant inbred line population of DOR364?×?BAT477 was evaluated for rooting pattern traits in soil cylinder tubes under soil drying (progressive water stress) and non-stress (well-watered with 80% of field capacity) treatments in a greenhouse. One of the parents, BAT 477, is a deep-rooting genotype while the other parent, DOR 364, is a commercial cultivar in Central America. The recombinant inbred line population expressed quantitative variation and transgressive segregation for ten rooting pattern traits as well as five shoot traits of 48-day-old plants. A mixed model quantitative trait locus (QTL) mapping analysis was carried out using a genetic map constructed with 165 genetic markers that covered 11 linkage groups of the common bean genome. Genotype estimates were calculated from best design and spatial effects model for each trait. A total of 15 putative QTL were identified for seven rooting pattern traits and four shoot traits. The QTL detected were scattered over five of the 11 linkage groups. The QTL detected for all the root traits except total root length and fine root length were main effect QTL and did not interact with the level of water supply. The total root length and fine root length QTL with significant QTL?×?environment interaction only differed in magnitude of effect, and interaction was of a non-crossover type. Other QTL for total root length, fine roots, thick roots, root volume and root biomass were co-localized and also explained relatively more genetic variance. This suggests that the QTL affecting root traits in common beans are based on constitutive expression of genes and that drought avoidance based on deep rooting, longer root length, thicker roots, increasing root length distribution with depth, root volume and root biomass can be used in molecular breeding. The positive alleles for most of the QTL detected in this study were derived from the paternal parent BAT477. The results from the present analyses highlighted the feasibility of marker-aided selection as an alternative to conventional labor-intensive, phenotypic screening of drought avoidance root traits.     

Water deficit induces variation in expression of stress-responsive genes in two peanut (Arachis hypogaea L.) cultivars with different tolerance to drought.

Peanut (Arachis hypogaea L.) is an important subsistence and cash crop in the semi-arid tropics where it often suffers from drought stress. Although its ecophysiological responses are studied, little is known about the molecular events involved in its adaptive responses to drought. The aim of this study was to investigate the involvement of membrane phospholipid and protein degrading enzymes as well as protective proteins such as "late embryogenesis-abundant" (LEA) protein in peanut adaptive responses to drought. Partial cDNAs encoding putative phospholipase D alpha, cysteine protease, serine protease and a full-length cDNA encoding a LEA protein were cloned. Their expression in response to progressive water deficit and rehydration was compared between cultivars differing in their tolerance to drought. Differential gene expression pattern according to either water deficit intensity and cultivar's tolerance to drought were observed. A good correspondence between the molecular responses of the studied cultivars and their physiological responses previously defined in greenhouse and field experiments was found. Molecular characters, as they were detectable at an early stage, could therefore be efficiently integrated in groundnut breeding programmes for drought adaptation. Thus, the relevance of the target genes as drought tolerance indicators is discussed.     

Morpho-physiological and molecular characterization of drought tolerance traits in Gossypium hirsutum genotypes under drought stress

Drought stress is one of the major abiotic stresses affecting lint yield and fibre quality in cotton. With increase in population, degrading natural resources and frequent drought occurrences, development of high yielding, drought tolerant cotton cultivars is critical for sustainable cotton production across countries. Six Gossypium hirsutum genotypes identified for drought tolerance, wider adaptability and better fibre quality traits were characterized for various morpho-physiological and biochemical characters and their molecular basis was investigated under drought stress. Under drought conditions, genotypes revealed statistically significant differences for all the morpho-physiological and biochemical traits. The interaction (genotype × treatment) effects were highly significant for root length, excised leaf water loss and cell membrane thermostability indicating differential interaction of genotypes under control and stress conditions. Correlation studies revealed that under drought stress, relative water content had significant positive correlation with root length and root-to-shoot ratio while it had significant negative correlation with excised leaf water loss, epicuticular wax, proline, potassium and total soluble sugar content. Analysis of expression of fourteen drought stress related genes under water stress indicated that both ABA dependent and ABA independent mechanisms of drought tolerance might be operating differentially in the studied genotypes. IC325280 and LRA5166 exhibited ABA mediated expression of stress responsive genes and traits. Molecular basis of drought tolerance in IC357406, Suraj, IC259637 and CNH 28I genotypes could be attributed to ABA independent pathway. Based on physiological phenotyping, the genotypes IC325280 and IC357406 were identified to possess better root traits and LRA5166 was found to have enhanced cellular level tolerance. Variety Suraj exhibited good osmotic adjustment and better root traits to withstand water stress. The identified drought component trait(s) in specific genotypes would pave way for their pyramiding through marker assisted cotton breeding.Electronic supplementary materialThe online version of this article (10.1007/s12298-020-00890-3) contains supplementary material, which is available to authorized users.     

Sorghum (Sorghum bicolor) varieties adopt strongly contrasting strategies in response to drought

Sorghum is one of the most drought tolerant crops but surprisingly, little is known about the mechanisms achieving this. We have compared physiological and biochemical responses to drought in two sorghum cultivars with contrasting drought tolerance. These closely related cultivars have starkly contrasting responses to water deficit. In the less tolerant Samsorg 40, drought induced progressive loss of photosynthesis. The more drought tolerant Samsorg 17 maintained photosynthesis, transpiration and chlorophyll content until the most extreme conditions. In Samsorg 40, there was a highly specific down‐regulation of selected proteins, with loss of PSII and Rubisco but maintenance of PSI and cytochrome b₆f, allowing plants to maintain ATP synthesis. The nitrogen released allows for accumulation of glycine betaine and proline. To the best of our knowledge, this is the first example of specific reengineering of the photosynthetic apparatus in response to drought. In contrast, in Samsorg 17 we detected no substantial change in the photosynthetic apparatus. Rather, plants showed constitutively high soluble sugar concentration, enabling them to maintain transpiration and photosynthesis, even in extremely dry conditions. The implications for these strikingly contrasted strategies are discussed in relation to agricultural and natural systems.     

Genetic variation in physiological responses of mungbeans (<Emphasis Type="Italic">Vigna radiata</Emphasis> (L.) Wilczek) to drought

Mungbean is a relatively drought tolerant leguminous crop with a short life cycle. Using leaf water loss (LWL) as a screen for drought tolerance, two mungbean genotypes exhibiting more than two–fold variation in leaf water loss were explored for the genetic variation in their physiological and molecular responses to drought. Efficient stomatal regulation together with better photosynthetic capacity constituted an important trait combination for drought adaptation in water saving low LWL genotype. The stomatal closure under drought was accompanied with a concomitant down-regulation of farnesyl transferase gene. However, cooler canopy temperature, a well branched root system coupled with a relatively higher proline accumulation in water spending high LWL genotype constituted another set of adaptive traits operating when exposed to deficit soil moisture conditions. We report drought induced down-regulation of proline dehydrogenase and the presence of 118 base pair intron in this gene. The high seed yield of low LWL genotype despite a hotter canopy might be attributed to higher net assimilation and quantum yield recorded under drought in this genotype. Thus, these interlinked features contribute to adaptive mechanisms of mungbeans which is widely grown in harsh environments exposed to drought and high temperatures.     

Alterations in photosynthetic pigments, protein and osmotic components in cotton genotypes subjected to short-term drought stress followed by recovery

In order to assess drought tolerance mechanism in cotton, short-term drought-induced biochemical responses were monitored in two cotton (Gossypium hirsutum L.) genotypes contrasting their tolerance to water deficit. The seeds of two genotypes, namely GM 090304 (moderately drought tolerant) and Ca/H 631 (drought sensitive), were sown in pots containing soil, sand and peat in the ratio of 1:1:1, and irrigated every alternate day up to 45 days after sowing when each genotype was subjected to a cycle of water stress by withholding irrigation for 7 days. The stress cycle was terminated by re-watering the stressed plants for 7 days. The leaf of the drought tolerant genotype (GM 090304) maintained higher relative water content under water stress than that of the drought sensitive genotype (Ca/H 631). The levels of biochemical components, such as chlorophylls, carotenoids, total protein, free proline, total free amino acids, sugars, starch and polyphenols, were measured during the stress as well as the recovery periods. The chlorophylls, carotenoids, protein and starch contents decreased in drought stressed plants as compared to control and tended to increase when the plants were recovered from stress. The degree of decrease in chlorophylls, carotenoids and protein contents under drought was higher in the sensitive genotype (Ca/H 631) as compared to the moderately tolerant genotype (GM 090304). However, proline, total free amino acids, total sugars, reducing sugars and polyphenol contents were increased in drought stressed plants and tended to decrease during the period of recovery. Drought-induced increases in total free amino acids, proline, sugars and polyphenols were significantly higher in the moderately tolerant genotype (GM 090304) than in the sensitive genotype (Ca/H 631). These results suggest that proline, sugars and polyphenols act as main compatible solutes in cotton in order to maintain osmotic balance, to protect cellular macromolecules, to detoxify the cells, and to scavenge free radicals under water stress condition.     

Challenges in pea breeding for tolerance to drought: Status and prospects

Drought is increasingly frequent in the context of climate change and is considered a major constraint for crop yield. Water scarcity can impair growth, disturb plant water relations and reduce water use efficiency. Pea (Pisum sativum) is a temperate grain legume rich in protein, fibre, micronutrients and bioactive compounds that can benefit human health. In reducing pea yield because of drought, the intensity and duration of stress are critical. This review describes several drought resistance mechanisms in pea based on morphology, physiology and biochemical changes during/after the water deficit period. Drought tolerance of pea can be managed by adopting strategies such as screening, breeding and marker-assisted selection. Therefore, various biotechnological approaches have led to the development of drought-tolerant pea cultivars. Finally, the main objective of the current research is to point out some useful traits for drought tolerance in peas and also, mention the methods that can be useful for future studies and breeding programmes.     

Drought Tolerance in Mung Bean is Associated with the Genotypic Divergence,Regulation of Proline,Photosynthetic Pigment and Water Relation

Drought is one of the critical conditions for the growth and productivity of many crops including mung bean (Vigna radiata L. Wilczek). Screening of genotypes for variations is one of the suitable strategies for evaluating crop adaptability and global food security. In this context, the study investigated the physiological and biochemical responses of four drought tolerant (BARI Mung-8, BMX-08010-2, BMX-010015, BMX-08009-7), and four drought sensitive (BARI Mung-1, BARI Mung-3, BU Mung-4, BMX-05001) mung bean genotypes under wellwatered (WW) and water deficit (WD) conditions. The WW treatment maintained sufficient soil moisture (22% ± 0.5%, i.e., 30% deficit of available water) by regularly supplying water. Whereas, the WD treatment was maintained throughout the growing period, and water was applied when the wilting symptom appeared. The drought tolerant (DT) genotypes BARI Mung-8, BMX-08010-2, BMX-010015, BMX-08009-7 showed a high level of proline accumulation (2.52–5.99 mg g⁻¹ FW), photosynthetic pigment (total chlorophyll 2.96–3.27 mg g⁻¹ FW at flowering stage, and 1.62–2.38 mg g⁻¹ FW at pod developing stage), plant water relation attributes including relative water content (RWC) (82%–84%), water retention capacity (WRC) (12–14) as well as lower water saturation deficit (WSD) (19%–23%), and water uptake capacity (WUC) (2.58–2.89) under WD condition, which provided consequently higher relative seed yield. These indicate that the tolerant genotypes gained better physiobiochemical attributes and adaptability in response to drought conditions. Furthermore, the genotype BMX- 08010-2 showed superiority in terms of those physio-biochemical traits, susceptibility index (SSI) and stress tolerance index (STI) to other genotypes. Based on the physiological and biochemical responses, the BMX-08010-2 was found to be a suitable genotype for sustaining yield under drought stress, and subsequently, it could be recommended for crop improvement through hybridization programs. In addition, the identified traits can be used as markers to identify tolerant genotypes for drought-prone areas.     

Models and tools for studying drought stress responses in peas

The pea (Pisum sativum L.) is an important pulse crop but the growing area is limited because of its relatively low yield stability. In many parts of the world the most important abiotic factor limiting the survival and yield of plants is the restricted water supply, and the crop productivity can only be increased by improving drought tolerance. Development of pea cultivars well adapted to dry conditions has been one of the major tasks in breeding programs. Conventional breeding of new cultivars for dry conditions required extensive selection and testing for yield performance over diverse environments using various biometrical approaches. Several morphological and biochemical traits have been proven to be related to drought resistance, and methods based on physiological attributes can also be used in development of better varieties. Osmoregulation plays a role in the maintenance of turgor pressure under water stress conditions, and information on the behaviour of genotypes under osmotic stress can help selection for drought resistance. Biotechnological approaches including in vitro test, genetic transformation, and the use of molecular markers and mutants could be useful tools in breeding of pea. In this minireview we summarized the present status of different approaches related to drought stress improvement in the pea.     

Analysis of early responses to drought associated with field drought adaptation in four Sahelian groundnut (Arachis hypogaea L.) cultivars

Groundnut (Arachis hypogaea L.) is the most important oil and cash crop in the sub-Sahelian tropics. Plant adaptation to drought, i.e. cultivars (cvs) that can maintain yield when water is limited, is a complex phenomenon which is not yet fully understood. This study aimed to identify traits expressed at the early stages of the cycle that could reveal cv differences in drought adaptation in the field. The field productivity of four Sahelian groundnut cvs was assessed during three crop seasons in Bambey (Senegal). The same cvs grown in rhizotrons were subjected to early drought stress and to a desiccation test to assess cell membrane tolerance. Between-cv differences were found with respect to pod yield, biomass production, water use efficiency (WUE), stomatal regulation and cell membrane tolerance. Two strategies to cope with water deficit were identified. The first behaviour was characterised by high rapid water loss, late stomatal closure and low cell membrane damage during drought. These traits are all found in the semi-late Virginia cv 57-422 and, into a lesser extent, in the early Spanish cv Fleur 11. For both cvs, biomass production was boosted under favourable conditions in rhizotrons but the semi-late cv had poor pod yield under end-of-season water deficit conditions. The second strategy involved opposite characters, leading to the maintenance of a higher water status, resulting in lower photosynthesis and yield. This characterised the early Spanish cv 73-30, and also, to some extent, the early Spanish cv 55-437. Earliness associated with high WUE, stomatal conductance and cell membrane tolerance, were the main traits of Fleur 11, a cv derived from a Virginia × Spanish cross, which was able to maintain acceptable yield under varying drought patterns in the field. These traits, as they were detectable at an early stage, could therefore be efficiently integrated in groundnut breeding programmes for drought adaptation.     

Photosynthetic parameters and leaf water potential of five common bean genotypes under mild water deficit

The leaf water potential, gas exchange and chlorophyll fluorescence were evaluated in five common bean (Phaseolus vulgaris) genotypes A222, A320, BAT477, Carioca and Ouro Negro subjected to moderate water deficit. At the maximum water deficit (10 d of water withholding), the leaf water potential of genotypes A320 and A222 was higher (−0.35 and −0.50 MPa) when compared to the other genotypes (−0.67 to −0.77 MPa). The stomatal conductance and net photosynthetic rate were significantly reduced in all genotypes due to the water deficit. The greater reduction in stomatal conductance of A320 under drought resulted in high intrinsic water use efficiency. Mild water deficit affected the photochemical apparatus in bean genotypes probably by down-regulation since plants did not show photoinhibition. The photochemical apparatus of A222 and A320 genotypes was more sensitive to drought stress, showing reduced apparent electron transport even after the recovery of plant water status. On the other hand, even after 10 d of water withholding, the maximum efficiency of photosystem 2 was not affected, what suggest efficiency of the photoprotection mechanisms.     

Expression profiling of rice cultivars differing in their tolerance to long-term drought stress

Understanding the molecular basis of plant performance under water-limiting conditions will help to breed crop plants with a lower water demand. We investigated the physiological and gene expression response of drought-tolerant (IR57311 and LC-93-4) and drought-sensitive (Nipponbare and Taipei 309) rice (Oryza sativa L.) cultivars to 18 days of drought stress in climate chamber experiments. Drought stressed plants grew significantly slower than the controls. Gene expression profiles were measured in leaf samples with the 20 K NSF oligonucleotide microarray. A linear model was fitted to the data to identify genes that were significantly regulated under drought stress. In all drought stressed cultivars, 245 genes were significantly repressed and 413 genes induced. Genes differing in their expression pattern under drought stress between tolerant and sensitive cultivars were identified by the genotype x environment (G x E) interaction term. More genes were significantly drought regulated in the sensitive than in the tolerant cultivars. Localizing all expressed genes on the rice genome map, we checked which genes with a significant G x E interaction co-localized with published quantitative trait loci regions for drought tolerance. These genes are more likely to be important for drought tolerance in an agricultural environment. To identify the metabolic processes with a significant G x E effect, we adapted the analysis software MapMan for rice. We found a drought stress induced shift toward senescence related degradation processes that was more pronounced in the sensitive than in the tolerant cultivars. In spite of higher growth rates and water use, more photosynthesis related genes were down-regulated in the tolerant than in the sensitive cultivars.     

Physiological responses of wheat to drought stress and its mitigation approaches

Drought is a polygenically controlled stress and a major agricultural risk that reduces crop productivity and limits the successful insight of land potential throughout the world. This review article has been divided into two parts, i.e., effect of drought stress on physiology of wheat and potential drought mitigation approaches. In the first part, physiological responses of wheat to stress were discussed. Cell membrane stability, relative water content, early maturity, decreased leaf area, small plant size, increased dry weight and root–shoot ratio, and the whole-plant transpiration rate response to enhanced atmospheric vapor pressure deficit are physiological traits associated with drought tolerance in wheat. Reduction of relative water content closes stomata and thereby reduces stomatal conductance. Osmotic adjustment improves drought tolerance by allowing cell enlargement, plant growth, and stomata to stay partially open and by maintaining CO₂ fixation under severe water deficit. The wheat plant accumulates several organic and inorganic solutes in its cytosol to lessen its osmotic potential for maintenance of cell turgor. Drought affects photosynthesis negatively by changing the inner structure of chloroplasts, mitochondria, and chlorophyll content and minerals. Destruction of the photosystem II (PSII) oxygen releasing complex and reaction center can disturb production and use of electrons, causing lipid peroxidation of cell membrane through the production of reactive oxygen species. In the second part, drought mitigation approaches were discussed. Seed, drought, bacterial, and hormonal priming are common approaches used to lessen the effects of water deficit. Physiological trait-based breeding, molecular breeding, marker-assisted backcrossing, aerial phenotyping, water budgeting, and resource allocation are modern approaches used to develop drought tolerant wheat cultivars. Wheat genotypes produced as a result of a combination of all these methodologies will increase food security regarding the currently changing climate.     

Responses of pomegranate cultivars to severe water stress and recovery: changes on antioxidant enzyme activities,gene expression patterns and water stress responsive metabolites

The biochemical and molecular responses of five commercially well-known pomegranate cultivars to severe water stress were studied. The cultivars were subjected to 14-day water stress by withholding irrigation, followed by re-watering for 7 days. Results showed clear differences in metabolites contents and activities of antioxidant enzymes among various pomegranate cultivars during severe water stress and recovery. According to our results, increased accumulation of proline in pomegranate was not related to osmotic adjustment during severe water stress. Except for ‘Ghojagh’, leaves grown under severe water stress conditions showed symptoms of oxidative stress such as reduced chlorophyll concentration. The improved performance of ‘Ghojagh’ under drought stress may be associated with an efficient osmotic adjustment. The up- or down regulated expression of cytosolic glutathione reductase (cytosolic GR) and glutathione peroxidase were observed under drought conditions. Moreover, the suppressed expression of cytosolic GR was also noted. Comparatively, ‘Rabab’ exhibited higher antioxidant capacity and an efficient ROS-scavenging mechanism under drought stress. Lower levels of membrane lipid peroxidation in ‘Ghojagh’ and ‘Rabab’ under drought stress and the marked reduction of malondialdehyde concentration after re-watering represents that these cultivars have a good tolerance to drought stress. As a first step towards the study of the biochemical and molecular responses of pomegranate plants to water stress, this research provides new information into the mechanisms of drought tolerance in the plants.