Browsing by Author "Virendra Pal Singh"
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ThesisItem Open Access ROLE OF ASCORBIC ACID IN DROUGHT TOLERANCE OF WHEAT(DIVISION OF PLANT PHYSIOLOGY INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI –, 2018) SUMAN ROY; Virendra Pal SinghWheat crop is severely affected by drought stress especially at reproductive stages. The antioxidant mediated mechanisms play a pivotal role in combating drought stress. Among them, ascorbic acid is an important non enzymatic antioxidant which helps in scavenging the reactive oxygen species under drought. Reports show that there are beneficial effects of exogenous application of ascorbate under abiotic stresses.However, there is limited knowledge about the role of endogenous content in ameliorating water deficit stress. Hence, in this study, the association of endogenous reduced ascorbate with drought stress tolerance at reproductive stage has been investigated in wheat. Endogenous reduced ascorbate content of twenty nine wheat genotypes under irrigated and drought condition showed a wide genotypic variability and a decreasing trend under drought. Present study showed that endogenous reduced ascorbate content under irrigated condition is responsible for drought stress tolerance. Genotypes with higher level of reduced ascorbate under irrigated condition also showed higher level of membrane stability, chlorophyll content under drought condition as compared to the genotypes having low reduced ascorbate. The genotypes with higher reduced ascorbate under irrigated condition also had a low drought susceptibility index compared to the genotypes having low endogenous reduced ascorbate. Our results further showed that hydrogen peroxide production is more under drought stress and the degree increases with the susceptibility of the genotypes compared to the tolerant ones. The tolerant genotypes C 306 showed better PS II yield and photosynthetic rate as compared to HW 5206. The antioxidant enzyme activity (SOD, catalase, GR, APX) is also higher in C 306 compared to HW 5206. The real time PCR results showed higher expression of ascorbate peroxidase gene expression in tolerant genotypes C306 and PBW 142 compared to susceptible genotypes HW 2032 and HW 5206. Again, the gene responsible for regeneration of ascorbate from oxidised to redox state i.e., dehydroascorbate reductase (DHAR) also showed a similar pattern. DHAR is the key gene responsible for the regeneration of ascorbate. Hence full length DHAR cDNA was cloned from wheat genotype DBW14. Overexpression cassette made with 35S promoter and T-Nos terminator was overexpressed in wild type Arabidopsis thalianac.v Columbia. Transgenics were confirmed by polymerase chain reaction (PCR). Artificial drought was imposed on both the wild type and transgenic plants with PEG 6000 and assessed at 4 weeks after sowing.When plants are four weeks old, the DHAR overexpressed plants showed better phenotype under drought stress compared to the wild 125 types. The H2O2 content is less in transgenic compared to the wild type. This result further confirmed that more reduced ascorbate produced, as a result of higher expression of TaDHAR, detoxified more reactive oxygen species in transgenic compared to the wild type Arabidopsis plants.