Abstract:
The effect of supplementary UV-B exposure (1 mW per cm(2)) on damage to photosynthetic membranes, and enzymatic and nonenzymatic processes metabolizing active oxygen species were studied in young wheat seedlings (Triticum aestivum L. cv DWR162), Supplementary UV-B radiation caused 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 LHCP1 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 increased continuously, activity of superoxide dismutase decreased after 10 days of UV-B exposure, Catalase (EC 1.11.1.6) activity increased initially, but was followed by a decrease. The supplementary UV-B treatment also induced two isoenzymes of peroxidase, and the total amount of peroxidase was also increased, Ascorbate and dehydroascorbate pools increased initially, followed by a decrease, The study suggests that exposure to supplementary UV-B radiation results in oxidative damage of protein including light harvesting complexes and lipids in thylakoid membranes, and changes in the activities of enzymes involved in the metabolism of oxygen radicals.
