Protective Effects Of NaHSO₃ On Physiological And Biochemical Processes In Red Kidney Bean Leaves Under Enhanced Ultraviolet-B Radiation

The destruction of the ozone layer leads to an increase of UV-B radiation reaching the earth surface. UV-B has a intense effect on organism and ecosystem, as well as quality and composition of atmosphere. The great influences of enhanced UV-B on the growth and yield of crop have become hot topic in current research. But the studies about how to improve plant resistance to enhanced UV-B have almost not reported. In this paper, the protective actions of NaHSO₃ in physiological and biochemical processes of red kidney bean leaves under enhanced UV-B radiation were investigated. The results showed that the brown spots on leaf surface and curly leaf increased with prolonging of enhanced UV-B radiation. During UV-B radiation,for 48 to 60h, the leaves begin to wilt. The effects of enhanced UV-B radiation on the red kidney bean leaves included the increases of membrane permeability and reactive oxygen species (ROS) content as well the products of membrane lipid peroxidation, the decrease of antioxidant enzymes activities and chlorophyll content, and the increase of flavonoids content etc. These data suggested that the leaves of red kidney bean were markedly damaged under enhanced UV-B radiation stress.The damages in red kidney bean leaves induced by enhanced UV-B radiation could be reduced by 0.5mmol/L NaHSO₃. They included that the decrease of brown spots on leaf surface and leaf wilt degree, the reduce of chlorophyll degradation, the increase of flavonoids level. And the decreases of hydroxyrpyruvate reducase activity and glycolate oxidase activity, two key enzymes in photorespiration pathway, in the leaves under UV-B radiation stress were observed in the present of NaHSO₃. These results indicated that NaHSO₃ could inhibit photorespiration. In the present of NaHSO₃, the contents of H₂O₂ and MDA in red kidney bean leaves were significant lower than that of the control (UV-B radiation), and the activities of antioxidant enzymes (POD and AP) were higher than that of the control. The results demonstrated that the treatment with NaHSO₃ could reduce the contents of ROS in red kidney bean leaves under enhanced UV-B radiation and lightened the leaf damages in oxidant stress induced by UV-B stress. The results about chlorophyll fluorescence parameters, including Fv/Fm, qP, qN, ETR, determination indicated that NaHSO₃ could cause the increase of electron transport in PS â…¡, the reduce of maximum efficiency of PS â…¡ photochemistry decrease, alter the balance of proton gradient across thylakoid membrane, the stimulation of electron flow cycle and couple phosphorylation in PS â… , the increase solar energy using, and the decrease of ROS product in chloroplasts. SDS—PAGE analysis of thylakoid under UV-B showed that several proteins of thylakoid were change .To sum up, the results suggest that NaHSO₃ can effectively increase the tolerance of plant to UV-B stress by enhance antioxidant enzymes activities (POD and AP), reduce the produce of ROS, improvement of chlorophyll fluorescence parameters, and decrease the photorespiration etc.