OXIDATIVE DAMAGE AND CHANGES IN ACTIVITIES OF ANTIOXIDANT ENZYMES IN WHEAT SEEDLINGS EXPOSED TO ULTRAVIOLET-B RADIATION

The effect of supplementary UV-B exposure (1 mW per cm(2)) on damage t o photosynthetic membranes, and enzymatic and nonenzymatic processes m etabolizing active oxygen species were studied in young wheat seedling s (Triticum aestivum L. cv DWR162), Supplementary UV-B radiation cause d changes in thylakoid protein profile. Thylakoid protein of 47 and 43 kDa molecular mass decreased significantly. Pigment-protein complexes were also affected. Chlorophyll-protein complexes CP1a, CP1, CPa and light harvesting complexes LHCP2 and LHCP3 showed decreases while LHCP 1 increased due to the treatment. Exposure to UV-B caused oxidation of thylakoid proteins and lipids, The activities of superoxide dismutase (EC 1.15.1.1) and peroxidase (EC 1.11.1.7) increased with increasing duration of exposure. While the activity of the peroxidase enzyme incr eased continuously, activity of superoxide dismutase decreased after 1 0 days of UV-B exposure, Catalase (EC 1.11.1.6) activity increased ini tially, but was followed by a decrease. The supplementary UV-B treatme nt also induced two isoenzymes of peroxidase, and the total amount of peroxidase was also increased, Ascorbate and dehydroascorbate pools in creased initially, followed by a decrease, The study suggests that exp osure to supplementary UV-B radiation results in oxidative damage of p rotein including light harvesting complexes and lipids in thylakoid me mbranes, and changes in the activities of enzymes involved in the meta bolism of oxygen radicals.