BIOCHEMICAL AND MOLECULAR CHANGES IN PEARL MILLET (Pennisetum Glaucum L.) GENOTYPES SUBJECTED TO SHORT TERM WATER STRESS AND ITS REVIVAL
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JAU,JUNAGADH
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Key words: drought stress, rewatering, antioxidants, proteomics, gene expression
Pearl millet (Pennisetum Glaucum L.) grows on marginal soils that could be frequently subjected to water-deficit conditions. Drought is considered as one of the environmental stress, which decreases crop productivity greatly compared with other environmental stress in India. Mechanisms of pearl millet plants in response to drought stress and rewatering remain largely unknown. The experiment was conducted mainly in two parts. In the first experiment, by using PEG-6000 induced drought stress, ten different pearl millet genotypes was screened for their drought tolerance at the seedling stage. In second part of the experiment was conducted, short-term drought-induced biochemical and molecular responses were monitored in two pearl millet (Pennisetum Glaucum L.) genotypes contrasting in their tolerance to water deficit stress. The seeds of two genotypes selected from first experiment, namely J-2454 (drought tolerant) and J-2549 (drought sensitive), were sown in pots containing soil and sand. The pots are irrigated every alternate day up to 30 (tillering) and 55 (flowering) days after germination when each genotype was subjected to a cycle of water stress by withholding irrigation for consecutive 8 days. The stress cycle was terminated by re-watering the stressed plants for 8 days. The pearl millet genotypes showed decrease in RWC, MSI and CSI but the extent of reduction varied with genotypes and developmental stage of the crop. At the initial stage, the impact of water deficit stress was lower, but with the advancement of crop growth stage a more pronounced effect was observed. The production of various ROS and lipid peroxidation also supports this conclusion, showing a greater degree of oxidative stress when water deficit stress is imposed at flowering stage than at tillering stage. Higher activities of SOD, CAT, APX and GR, as a whole, contributed to less oxidative stress in tolerant J-2454 genotype, establishing the role of antioxidant defense system in pearl millet to tolerate water deficit stress. Phytohormones, osmolytes and polyamines levels reported genotypic and stage specific and are induced more in tolerant J-2454 compared to susceptible J-2549 genotype. The proteomic study using two dimensional gel electrophoresis indicated changes in protein expression as a response to drought stress in pearl millet plants. Differential gene expression analysis showed that maintenance of higher transcripts levels of SOD, APX and DREB in tolerant (J-2454) compared to the susceptible (J-2549) genotype suggests that they could be involved in scavenging oxidative stress-induced reactive oxygen and removing hydrogen peroxide in pearl millet through changes in the level of gene expression. These results suggest that osmolyte accumulation and antioxidant enzymes, phytohormones and differential gene expression could contribute to a better drought tolerance of J-2454 genotype than J-2549 genotype at both plant growth stages.
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BIOCHEMISTRY