Influence of drought stress on cellular ultrastructure and antioxidant system in tea cultivars with different drought sensitivities.

Drought is the major yield-limiting abiotic factor of tea cultivation. In the present study, influence of drought stress on cellular ultrastructure and antioxidants was studied drought-tolerant (TV-23) and -sensitive (S.3/A3) tea cultivars by imposing drought stress for 21 days. Drought stress led to considerable structural alterations in mitochondria, chloroplast and vacuole. Lesser membrane integrity and higher structural damage was observed in S.3/A3. Chlorophyll a, chl-b and carotenoids content in leaves decreased in each cultivar; however, the decrement was more brisk in S.3/A3. Proline, total soluble sugar, ascorbic acid and abscisic acid were elevated in TV-23 whereas hydrogen peroxide, superoxide anion, lipid peroxidation and electrolyte leakage increased rapidly in S.3/A3. Starch content decreased both in leaves and roots of each cultivar and was more pronounced in roots of TV-23. Under drought, enhanced activities of ascorbate peroxidase, catalase, peroxidase and superoxide dismutase were recorded in both roots and leaves of each cultivar, but the rate of enhancement was more in TV-23. This indicated that tolerant cultivar exhibited higher antioxidant capacity and a stronger protective mechanism such that their ultrastructural integrity was better maintained during exposure to drought stress.