Effect of drought on chlorophyll content and antioxidant enzyme activities in leaves of three wheat cultivars varying in productivity

Seedlings of three wheat varieties (Triticum aestivum L.)—highly productive cv. Ballada, moderately productive cv. Belchanka, and low productive cv. Beltskaya—were exposed to progressive soil drought (cessation of watering for 3, 5, and 7 days) and then analyzed for chlorophyll content and activities of ferredoxin-NADP⁺ oxidoreductase (FNR) and antioxidant enzymes, namely, glutathione reductase (GR) and ascorbate peroxidase (AscP). In addition, the proline content, and the extent of lipid peroxidation were examined. In the first period of water limitation, the water loss from leaves was slight for all wheat cultivars, which is characteristic of drought-resistant varieties. After 7-day drought the leaf water content decreased by 5.2–6.8%. The total chlorophyll content expressed per unit dry weight increased insignificantly during the first two periods of drought but decreased by 13–15% later on. This decrease was not accompanied by changes in chlorophyll a/b ratio. The plant dehydration did not induce significant changes in FNR activity. Activities of GR and AscP in leaves of wheat cultivars Ballada and Belchanka increased on the 3rd and 5th days of drought. Owing to the coordinated increase in GR and AscP activities, the lipid peroxidation rate remained at nearly the control level observed in water-sufficient plants. When the dehydration period was prolonged to 7 days, activities of GR and AscP in wheat cultivars reduced in parallel with the increase in malonic dialdehyde (MDA) content, indicating that the antioxidant enzyme defense system was weakened and lipid peroxidation enhanced. Unlike Ballada and Belchanka, the wheat cv. Beltskaya did not exhibit the increase in GR and AscP activities during progressive soil drought. The increase in MDA content by 16% in this cultivar was only observed after a 7-day drought period. The proline content in leaves of all wheat cultivars increased substantially during drought treatment. Thus, in wheat cultivars examined, different responses of the defense systems were mobilized to implement plant protection against water stress. The activities of antioxidant enzyme defense system depended on wheat cultivar, duration of drought, and the stage of leaf development.     

The responses of the enzymes related with ascorbate–glutathione cycle during drought stress in apple leaves

To explore the significance of the ascorbate–glutathione cycle under drought stress, the leaves of 2-year-old potted apple (Malus domestica Borkh.) plants were used to investigate the changes of each component of the ascorbate–glutathione cycle as well as the gene expression of dehydroascorbate reductase (DHAR, EC 1.8.5.1), ascorbate peroxidase (APX, EC 1.11.1.11) and glutathione reductase (GR, EC 1.6.4.2) under drought stress. The results showed that the malondialdehyde (MDA) and H₂O₂ concentrations in apple leaves increased during drought stress and began to decrease after re-watering. The contents of total ascorbate, reduced ascorbic acid (AsA), total glutathione and glutathione (GSH) were obviously upregulated in apple leaves when the soil water content was 40–45%. With further increase of the drought level, the contents of the antioxidants and especially redox state of AsA and GSH declined. However, levels of them increased again after re-watering. Moreover, drought stress induced significant increase of the activities of enzymes such as APX, scavenging H₂O₂, and also of monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), DHAR and GR used to regenerate AsA and GSH, especially when the soil water content was above 40–45%. During severe drought stress, activities of the enzymes were decreased and after re-watering increased again. Gene expression of cytoplasmic DHAR, cytoplasmic APX and cytoplasmic GR showed similar changes as the enzyme activities, respectively. The results suggest that the ascorbate–glutathione cycle is up-regulated in response to drought stress, but cannot be regulated at severe drought stress conditions.     

Antitranspirant functions of stem periderms and their influence on corticular photosynthesis under drought stress

Transpiration and photosynthesis of current-year stems and adult leaves of different deciduous tree species were investigated to estimate their probable influence on carbon balance. Peridermal transpiration of young stems was found to be rather small as compared to the transpiration of leaves (stem/leaf like 1/5–1/20). A characteristic that was mainly attributable to the lower peridermal conductance to water and CO₂, which made up only 8–28% of stomatal conductance. Water vapour conductance was significantly lower in stems, but also non-responsive to PAR, which led to a comparatively higher water use efficiency (WUE, ratio assimilation/transpiration). Thus, although corticular photosynthesis reached only 11–37% of leaf photosynthesis, it may be a means of improving the carbon balance of stems under limited water availability. The influence of drought stress on primary photosynthetic reactions was also studied. Under simulated drought conditions the drying time needed to provoke a 50% reduction (t ₅₀) in dark- and light-adapted PSII efficiency (Fv/Fm, ΔF/Fm′) was up to ten times higher in stems than in leaves. Nevertheless, up to a relative water deficit (RWD) of around 40–50% dark-adapted PSII efficiency of leaves and stems was rather insensitive to dehydration, showing that the efficiency of open PS II reaction centres is not impaired. Thus, it may be concluded that in stems as well as in leaves the primary site of drought damage is at the level of dark enzyme reactions and not within PSII. However, enduring severe drought caused photoinhibitory damage to the photosynthetic apparatus of leaves and stems; thereby RWD₅₀ values (= RWD needed to provoke a 50% reduction in Fv/Fm ad ΔF/Fm′) were comparably lower in stems as compared to leaves, indicating a possibly higher drought sensitivity of the cortex chlorenchyma.     

Transgene flow to hybrid rice and its male-sterile lines

Gene flow from genetically modified (GM) crops to the same species or wild relatives is a major concern in risk assessment. Transgenic rice with insect and/or disease resistance, herbicide, salt and/or drought tolerance and improved quality has been successfully developed. However, data on rice gene flow from environmental risk assessment studies are currently insufficient for the large-scale commercialization of GM rice. We have provided data on the gene flow frequency at 17 distances between a GM japonica line containing the bar gene as a pollen donor and two indica hybrid rice varieties and four male-sterile (ms) lines. The GM line was planted in a 640m² in an isolated experimental plot (2.4 ha), which simulates actual conditions of rice production with pollen competition. Results showed that: (1) under parallel plantation at the 0-m zone, the transgene flow frequency to the ms lines ranged from 3.145 to 36.116% and was significantly higher than that to hybrid rice cultivars (0.037–0.045%). (2) Gene flow frequency decreased as the distance increased, with a sharp cutoff point at about 1–2 m; (3) The maximum distance of transgene flow was 30–40 m to rice cultivars and 40–150 m to ms lines. We believe that these data will be useful for the risk assessment and management of transgenic rice lines, especially in Asia where 90% of world's rice is produced and hybrid rice varieties are extensively used. Shirong Jia, Feng Wang and Lei Shi contributed equally to this investigation.     

Effect of drought stress on leaf optical properties in drought-resistant and drought-sensitive maize and triticale genotypes

The effect of a short (7 d), prolonged (14 d) soil drought (D) and (7 d) recovery (DR) on the leaf optical properties — reflectance (R), transmittance (T) and absorptance (A) in photosynthetically active radiation (PAR) and near infrared radiation (NIR) range of irradiation (750–1100 nm) was studied for maize and triticale genotypes differing in drought tolerance. The drought stress caused the changes in leaf optical properties parameters in comparison with non-drought plants. The observed harmful influence of drought was more visible for maize than triticale.     

Physiology of rice tungro virus disease: Proline accumulation due to infection

Tungro virus infection stimulates proline accumulation in leaves of rice ( Oryza sativa L.), especially in a sensitive cultivar, Taichung Native 1. Disease-induced proline accumulation increases with the severity of the disease. Proline also accumulates in senescing, detached healthy rice leaves. The magnitude of proline accumulation in these leaves was further accentuated by ABA and retarded by kinetin. In the absence of drought stress, virus infection induces severe symptoms (stunting) in a drought tolerant cultivar (Lalnakanda 41) when compared to cultivars with intermediate (MW 10) and high sensitivity (Cauvery) to drought. Thus tungro virus mimics water stress in inducing proline accumulation in rice leaves. In both cases a common factor, ABA, may mediate proline accumulation. In drought stress, proline accumulation is associated with tolerance, while in virus stress, proline accumulation is connected with sensitivity. It is, therefore, clear that proline cannot always act to relieve physiological stress.     

Microbial Availability and Size Fractionation of Dissolved Organic Carbon After Drought in an Intermittent Stream: Biogeochemical Link Across the Stream–Riparian Interface

The evolution of dissolved organic carbon (DOC) molecular-weight fractions, DOC biodegradability (BDOC), DOC origin [fluorescence index (FI)], and enzyme activities between the stream waters (main and ephemeral channel) and ground waters (riparian and hillslope) were analyzed during the transition from drought to precipitation in a forested Mediterranean stream. After the first rains, DOC content in stream water reached its maximum value (10–18 mg L⁻¹), being explained by the leaching of deciduous leaves accumulated on the stream bed during drought. During this period, the largest molecules (>10 kDa), were the most biodegradable, as indicated by high BDOC values measured during storm events and high enzymatic activities (especially for leucine-aminopeptidase). DOC >100 kDa was strongly immobilized (78%) at the stream–riparian interface, whereas the smallest molecules (<1 kDa) were highly mobile and accumulated in ground waters, indicating their greater recalcitrance. Differential enzymatic patterns between compartments showed a fast utilization of polysaccharides in the flowing water but a major protein utilization in the ground water. The results of the FI indicated a more terrestrial origin of the larger molecules in the flowing water, also suggesting that transformation of material occurs through the stream–riparian interface. Microbial immobilization and fast utilization of the most biodegradable fraction at the stream–riparian interface is suggested as a relevant DOC retention mechanism just after initial recharging of the ground water compartment. Large and rapid DOC inputs entering the intermittent river system during the transition from drought to precipitation provide available N and C sources for the heterotrophs. Heterotrophs efficiently utilize these resources that were in limited supply during the period of drought. Such changes in C cycling may highlight possible changes in organic matter dynamics under the prediction of extended drying periods in aquatic ecosystems.     

In vitro screening of rice genotypes for drought tolerance using polyethylene glycol

The aim of the present investigation was to study in vitro somatic embryogenesis and to screen calli for drought tolerance using mature embryos as explants. Mature embryos of three aromatic (Pusa Basmati 1, Pant Sugandh Dhan 17, Taraori Basmati) and one non-aromatic (Narendra 359) indica rice (Oryza sativa L.) varieties were used for developing callus on Murashige and Skoog medium supplemented with 2, 4-dichlorophenoxy acetic acid (2, 4-D) (2.0 mg l⁻¹ for Narendra 359 and 2.5 mg l⁻¹ for Pusa Basmati 1, Taraori Basmati and Pant Sugandh Dhan 17). Screening of calli was done by sub-culturing calli for 15 days on Murashige and Skoog (MS) basal medium supplemented with different concentrations of polyethylene glycol (PEG)-6000 as chemical drought inducer. Callus volume decreased and total proline content was found to be increased significantly with increase in PEG concentration. Narendra 359 showed best response in terms of callus growth at 70 g l⁻¹ of PEG. The highest percentage somatic embryogenesis among selected calli was observed in Pusa Basmati 1 and the lowest in Pant Sugandh Dhan 17. Excellent shooting and rooting (94%) was observed in MS + 0.1 mg l⁻¹ naphthalene acetic acid (NAA) and MS + 2.0 mg l⁻¹ 2, 4-D. Regenerated plants were successfully acclimatized with 98% efficiency in greenhouse and grown under pot conditions up to maturity. It was observed that PEG treated somaclones accumulated more proline, chlorophyll content and developed more tiller and height than normal somaclones. Ten random amplified polymorphic DNA (RAPD) primers were used to amplify genomic DNA of somaclones of different varieties. Level of genetic polymorphism existing among these somaclones indicates that these markers can be used in breeding program for improving varieties through in vitro techniques.     

Water relations, activities of antioxidants, ethylene evolution and membrane integrity of pigeonpea roots as affected by soil moisture

The plants of pigeonpea (Cajanus cajan L.) cv. H77-216 were subjected to moderate [soil moisture content (SMC) = 7.3 ± 0.5 %] and severe (SMC = 4.3 ± 0.5 %) drought by withholding the irrigation at vegetative stage (45 d after sowing). The control plants were maintained at SMC of 11.0 ± 0.5 %. Half of the stressed plants were re-irrigated and their recovery was studied after 2 d. Leaf water potential, osmotic potential, and relative water content of leaf and root decreased significantly while a sharp rise in proline and total soluble sugars contents were noticed. Drought induced a significant increase in 1-aminocyclopropane 1-carboxylic acid (ACC) content and ACC oxidase activity which caused a considerable increase in ethylene evolution. Malondialdehyde content and relative stress injury were increased under drought whereas reverse was true for ascorbic acid content. The membrane integrity of roots decreased during stress and recovered on rehydration. The specific activity of total superoxide dismutase, ascorbate peroxidase, glutathione reductase, and glutathione transferase decreased to 37 – 78 %, 17 – 62 %, 29 – 36 % and 57 – 79 % at moderate and severe drought, respectively. The increase in activity of catalase and peroxidase could not overcome the accumulation of H₂O₂ content in the roots.     

QTLs linked to leaf epicuticular wax,physio-morphological and plant production traits under drought stress in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Drought stress is the major constraint to rice (Oryza sativa L.) production and yield stability in rainfed ecosystems. Identifying genomic regions contributing to drought resistance will help to develop rice cultivars suitable for rainfed regions through marker-assisted breeding. Quantitative trait loci (QTLs) linked to leaf epicuticular wax, physio-morphological and plant production traits under water stress and irrigated conditions were mapped in a doubled haploid (DH) line population from the cross CT9993-5-10-1-M/IR62266-42-6-2. The DH lines were subjected to water stress during anthesis. The DH lines showed significant variation for epicuticular wax (EW), physio-morphological and plant production traits under stress and irrigated conditions. A total of 19 QTLs were identified for the various traits under drought stress and irrigated conditions in the field, which individually explained 9.6%–65.6% of the phenotypic variation. A region EM15_10-ME8_4-R1394A-G2132 on chromosome 8 was identified for leaf EW and rate of water loss i.e., time taken to reach 70% RWC from excised leaves in rice lines subjected to drought stress. A large effect QTL (65.6%) was detected on chromosome 2 for harvest index under stress. QTLs identified for EW, rate of water loss from excised leaves and harvest index under stress in this study co-located with QTLs linked to shoot and root-related drought resistance traits in these rice lines and might be useful for rainfed rice improvement.     

Isolation of Plant Gene Space-Related Sequence Elements by High C+G Patch (HCGP) Filtration: Model Study on Rice

For the isolation of gene space representative sequence elements, a new methodology—high C+G patch (HCGP) filtration—has been developed using rice as a model. The method is based on the fragmentation of the genomic DNA by methylation-sensitive HpaII and MspI restriction endonucleases having exclusively G/C base pair-containing recognition sites. These enzymes fragment the genome at high C+G content and hypomethylated regions. Cloning fragments spanning such regions in close vicinity (200–2,000 bp) revealed that about 60% of the clones represented gene space sequences resulting in twofold enrichment of these sequences, which is close to the theoretical maximum in rice. The sequence information of clones used in the present study was deposited in the NCBI database under the accession numbers EI 365676–EI 366364.     

The decline in ascorbic acid content is associated with cadmium toxicity of rice seedlings

Cadmium (Cd) toxicity of rice (Oryza sativa L. cv. Taichung Native 1) seedlings was evaluated by the decrease in chlorophyll content and the increase in malondialdehyde (MDA) in the second leaves of rice seedlings. CdCl₂ (5 μM) treatment was accompanied by a decrease in the contents of ascorbic acid (AsA) and AsA + dehydroascorbate (DHA) and in the ratios of AsA/DHA in leaves. However, CdCl₂ treatment resulted in an increase in DHA content in leaves. Moreover, the decrease in AsA content was prior to the occurrence of chlorosis and associated with the increase in MDA content in the leaves of seedlings treated with Cd. Pretreatment with 0.5 mM AsA or l-galactono-1,4-lactone (GalL), the biosynthetic precursor of AsA, for 6 h resulted in an increase in the contents of AsA and reduced glutathione (GSH), the ratios of AsA/DHA and GSH/oxidized glutathione, and the activities of ascorbate peroxidase (APX) and glutathione reductase (GR) in the leaves of rice seedlings. Quantitative RT-PCR was applied to quantify the mRNA levels for OsAPX and OsGR genes from rice leaves to examine the effect of AsA or GalL pretreatment on the expression of OsAPX and OsGR genes in rice leaves. The expression of OsAPX2, OsAPX3, OsAPX4, OsAPX5, OsAPX6, OsAPX7, and OsGR1 was increased by AsA or GalL pretreatment. Rice seedlings pretreated with AsA or GalL were observed to reduce the subsequent Cd-induced toxicity. Our results suggest that AsA content may play a role in regulating Cd toxicity of rice seedlings.     

Bioassay as a tool for assessing susceptible and resistant plant species for field contaminated with industrial effluent

A bioassay technique was used to select plant species that were able to germinate and grow in a site contaminated with flash torch and battery manufacturing industrial effluents. Three varieties each of rice, namely Surya-52, Jaya-14 and Pant-10; three varieties of pulses [Gram (Bahar), Mung (K-851) and Lens (T-9)] and three varieties of oilseeds (Mustard-RS-30, Mustard-B-9 and Mustard T-69) were used for the determination of phytotoxicity by bioassay technique. The average % phytotoxicity for rice was 18.03% (14.34–22.7%), for pulses was 15.76% (8.75–26.64%) and for oil seed was 11.09% (6.42–15.24%). Accumulation of metals (Cu, Fe, Mn, Cd, Cr and Pb) was estimated in the root, shoot and edible parts of different crop varieties grown in pot culture up to maturity and treated with industrial effluent. The concentration of different metal ions in root, shoot and edible parts were in the range of Cu: 9.25–45.25, 7.25–42.35 and 5.65–35.26; Fe: 60.66–212.25, 45.24–155.62; Mn: 7.12–38.30, 6.25–27.27.23 and 4.25–24.45; Cd: 0.80–2.45, 0.75–2.12 and 0.45–1.95, Cr: 6.54–28.25, 5.36–24.45 and 4.35–16.32; and Pb: 0.95–3.75, 0.78–2.25 μg/g d.w. respectively. A higher concentration of Cd was found in Surya-52 rice variety and in Gram (Bahar) pulse variety and of Pb was detected in Surya-52 rice variety. Cd and Pb are non-essential metal ions and highly toxic to plants. Accumulation of toxic metal ions like Pb and Cd in the edible parts of oil a seed variety may not exceed the recommended daily intake limits. Percentage phytotoxicity and inhibition of root and shoot length was also less in the oil seed variety. Thus these plant varieties can be considered for cultivation in fields contaminated by waste from the flash-torch and battery-manufacturing industry.     

Functional analysis of six drought-inducible promoters in transgenic rice plants throughout all stages of plant growth

There are few efficient promoters for use with stress-inducible gene expression in plants, and in particular for monocotyledonous crops. Here, we report the identification of six genes, Rab21, Wsi18, Lea3, Uge1, Dip1, and R1G1B that were induced by drought stress in rice microarray experiments. Gene promoters were linked to the gfp reporter and their activities were analyzed in transgenic rice plants throughout all stages of plant growth, from dry seeds to vegetative tissues to flowers, both before and after drought treatments. In fold induction levels, Rab21 and Wsi18 promoters ranged from 65- and 36-fold in leaves to 1,355- and 492-fold in flowers, respectively, whereas Lea3 and Uge1 were higher in leaves, but lower in roots and flowers, as compared with Rab21 and Wsi18. Dip1 and R1G1B promoters had higher basal levels of activity under normal growth conditions in all tissues, resulting in smaller fold-induction levels than those of the others. In drought treatment time course, activities of Dip1 and R1G1B promoters rapidly increased, peaked at 2 h, and remained constant until 8 h, while that of Lea3 slowly yet steadily increased until 8 h. Interestingly, Rab21 activity increased rapidly and steadily in response to drought stress until expression peaked at 8 h. Thus, we have isolated and characterized six rice promoters that are all distinct in fold induction, tissue specificity, and induction kinetics under drought conditions, providing a variety of drought-inducible promoters for crop biotechnology.     

Influence of Azolla management on the growth,yield of rice and soil fertility

A field experiment conducted at Central Rice Research Institute, Cuttack, during three successive seasons showed that with the 120-day-duration variety Ratna two dual crops ofAzolla pinnata R. Brown (Bangkok isolate) could be achieved 25 and 50 days after transplanting (DAT) by inoculating 2.0 t ha⁻¹ of fresh Azolla 10 and 30 DAT respectively. One basal crop of Azolla could also be grown using the same inoculum 20 days before transplanting (DBT) in fallow rice fields. The three crops of Azolla grown—once before transplanting and twice after transplanting—gave an average total biomass of 38–63 and 43–64 t ha⁻¹ fresh Azolla containing 64–90 and 76–94 kg N ha⁻¹ respectively in the square and rectangular spacings. Two crops of Azolla grown only as a dual crop, on the other hand, gave 26–39 and 29–41 t ha⁻¹ fresh Azolla which contained 44–61 and 43–59 kg N ha⁻¹ respectively. Growth and yield of rice were significantly higher in Azolla basal plus Azolla dual twice incorporated treatments than in the Azolla dual twice incorporation, Azolla basal plus 30 kg N ha⁻¹ urea and 60 kg N ha⁻¹ urea treatments. Azolla basal plus 30 kg N ha⁻¹ urea and 60 kg N ha⁻¹ urea showed similar yields but Azolla dual twice incorporation was significantly lower than those. The different spacing with same plant populations did not affect growth and yield significantly, whereas Azolla growth during dual cropping was 8.3 and 64% more in the rectangular spacing than in the square spacing in Azolla basal plus Azolla dual twice incorporation and Azolla dual twice incorporation treatments.     

High Frequency Plant Regeneration from Callus Culture of Pleione formosana Hayata

High frequency plant regeneration was induced from protocorm-derived callus cultured on half-strength of Murashige—Skoog medium with 2,4-dichlorophenoxyacetic acid (2,4-D, 0–5 mg l⁻¹) and 1-phenyl-3-(1,2,3-thiadiazol-5-yl, 0–1 mg l⁻¹) urea (TDZ) in the dark. Twelve totipotent callus lines were selected within 76 callus lines regenerated on half-strength of Murashige—Skoog (MS) medium with 0.5 mg l⁻¹ TDZ. The proliferation rate was 4–5-fold in fresh weight after 30 days of culture on half-strength MS medium containing 5 mg l⁻¹ 2,4-D and 0.5 mg l⁻¹ TDZ in the dark. The maximum number of shoot buds generated by 0.01 g callus explant was 134 after 4 months of culture. These calli were regenerated to plantlets via protocorm-like bodies (PLBs) after 75–150 days of culture. The shoots, with two true leaves, were transferred to hormone-free medium, rooting and eventually formed plantlets. Totipotent callus lines of Pleione formosana Hayata have been successfully established in this study.     

Drought-induced changes in photosynthetic membranes of two wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) cultivars

Two wheat (Triticum aestivum L.) cultivars contrasting in architectonics and differing in drought resistance, Azamatli-95 (short stature, vertically oriented small leaves, drought-tolerant) and Giymatli-2/17 (short stature, broad and drooping leaves, drought-sensitive), were studied. It was found that the content of CP I (115 kDa) and 63-kDa apoprotein P700 and also LHC II polypeptides increases slightly in the drought-resistant cv. Azamatli-95 under extreme water supply limitation, while their content decreases in drought-sensitive cv. Giymatli-2/17. The intensity of synthesis of α- and β-subunits of CF₁ (55 and 53.5 kDa) and 33–30.5 kDa proteins also decreases in the sensitive genotype. The intensity of short wavelength peaks at 687 and 695 nm sharply increases in the fluorescence spectra (77K) of chloroplasts from Giymatli-2/17 under water deficiency, and there is a stimulation of the ratio of fluorescence band intensity F687/F740. After exposure to drought, cv. Giymatli-2/17 shows a larger reduction in the actual PS II photochemical efficiency of chloroplasts than cv. Azamatli-95. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 8, pp. 1109–1116.     

In vitro screening for increased drought tolerance in rice

Summary In vitro screening at the cellular level was performed with mature seed-derived callus from five rice varieties, viz. IR 18351-229-3, IR 3185-6-3-3-2, SR 26-B, Nona Bokra, and C 14-8 of diverse geographical origin and with differential drought resistance at the in planta level. Callus was induced from mature seeds on Murashige and Skoog medium supplemented with 2.0 mgl⁻¹ (9 μM) of 2,4-dichlorophenoxyacetic acid (2,4-D) and 5.0, 10.0, and 15.0 gl⁻¹ of high molecular weight polyethylene glycol (PEG, 6000) as stressing agent to create chemical drought. Simultaneous efforts were also made to assess the effects of chemical drought in altering morphogenetic response in different varieties under in vitro culture. Seed germination was almost unaffected in SR 26-B and C 14-8, unlike in other varieties where germination was seriously affected. In general, seed germination was found to be decreased in three genotypes, viz. IR 18351-229-3, IR 3185-6-3-3-2, and Nona Bokra, with increased PEG concentrations. All genotypes displayed callus induction percentage in decreasing order with increased PEG concentrations supplemented in the callus induction medium (CIM), except SR 26-B and Nona Bokra. Callus induction was found to be more on CIM fortified with 5.0 gl⁻¹ PEG. In general, embryogenic callus induction and plantlet regeneration was found to be indirectly proportional to increased PEG concentrations used in CIM. Considering all characters, C 14-8 was found to be most appropriate in developing drought-tolerant lines under in vitro culture conditions followed by SR 26-B and Nona Bokra. A number of putative drought-tolerant plants were developed in C 14-8, SR 26-B, Nona Bokra, and IR 18351-29-3, and forwarded for field evaluation. In the majority of the progenies, a monogenic inheritance pattern for the drought tolerance character was observed.