Effect of elevated UV-B radiation on the antioxidant system of two rice landraces in paddy fields on Yuanyang Terrace

This study was performed to determine the effect of elevated UV-B radiation on physiological properties of rice plants under paddy field conditions. UV-B at different intensity levels (0, 2.5, 5.0 and 7.5 kJ/m2) were applied to two local rice cultivars, Baijiaolaojing at 1600 m and Yuelianggu at 1800 m, growing in paddy fields on Yuanyang Terrace. Contents of H2O2 and nlalondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activity and total antioxidant capacity (T-AOC) in leaves were assayed. Results showed that after UV-B radiation treatments of Baijiaolaojing and Yuelianggu, plants at booting stage showed an increase of 52.3 small tide 79.3% and 86.0 small tide 195.4% in leaf H2O2 content, and 46.5 small tide 96.8% and 75.9 small tide 95.9% in leaf MDA content; At heading stage, plants had an increase of 35.2 small tide 66.0% and 77.2 small tide 121.3% in leaf H2O2 content, and 47.3 small tide 90.0% and 54.2 small tide 87.4% in leaf MDA content, respectively. UV-B radiation induced stronger enzymatic activity of leaf SOD, CAT and POD. The amount of SOD activity increased up to 86.0% or 73.5%; CAT activity up to 58.4% or 42.3% and POD up to 36.1% or 59.1% in Baijiaolaojing or Yuelianggu after the UV-B treatments. UV-B radiation led to higher leaf T-AOC, reaching the maximum of 45.3% and 32.2% in Baijiaolaojing and Yuelianggu, respectively. A highly significant correlation was found between leaf H2O2 and MDA contents and activity of SOD, CAT and POD and T-AOC in the two cultivars. These results indicated the accumulation of H2O2 and MDA would induce to the increased activity of antioxidant enzyme and the enzymatic activities would contribute to enhancing plants UV-B radiation tolerance.