Physiological And Biochemical Responses To Supplementary UV-B Radiation In Spirodela Polyhiza

With the depletion of ozone layer in stratosphere, solar UV-B radiation on the earth surface is increasing. Plants use sunlight for photosynthesis, and it is inevitable that they are affected by enhabced UV-B radiation in the sunlight. Duckweeds (Spirodela polyhiza) were used as my experiment material in the present thesis to study physiological and biochemistryresponses to suoolementary UV-B radition.Duckweeds were irradiated with supplementary UV-B with the intensity of 2.8W/m2 for 8 h from 8: 00-16: 00 per day. Plants grown in the natural light conditions without supplementary UV-B radiation were used as control. The results were as follows:(1) Supplementary UV-B radiation increased superoxide dismutase (SOD) and AP activity within 2 day- treatment. With the increase of exposure time, the antioxidative ability of Spirodela polyhiza dereased, SOD and AP activities were induced, and ASA content of treated plants were always lower than those of control plants, but the proline (Pro) contents in treated plants increased. These factors would break the balance of the metabolism of ROS and the active oxygen accumulation in leafy thallus of Spirodela polyhiza could be the result, the membrane lipid peroxidation was accelerated (MDA content increased), ultra-microstructure of chloroplast was damaged, photosynthetic capacity dereased, biomass (dry weight) reduced.(2) Under UV-B radiation, the nitrogenous metabolism in leafy thallus of Spirodela polyhiza was in disorder. The activities of NR increased fistly and then decreased after UV-B treatment. The GDH activities of treated plants were lower than those of control plants during the whole experiment. Enhanced UV-B radiation reduced the contents of NO3--N in Spirodela polyhiza. The present results indicated that enhanced UV-B radiation affected the absorption of nitrate, assimilation of nitrogen and synthesis ofamino acids.(3) UV-B radiation increased the phenylalanina ammonia-lyase (PAL) activity in leafy thallus of duckweeds, and as a consequence, flavonoids were accumulated. Flavonoids synthesis induced by supplementary UV-B is an adaptive response of duckweeks under enhanced UV-B radition.