Abstract:Nitric oxide (NO) plays an important role in the regulation of plant growth and response to stress. To further study the response mechanism of nitric oxide gas signal to enhanced UV-B in Chinese cabbage, we studied the changes of biomass,leaf number,leaf length,content of chlorophyll, photosynthetic rate, chlorophyⅡ fluorescence characteristics,content of Rubisco activase (RCA) and its activase, its coding gene expression on 20-day age of Chinese cabbage seedling under exogenouns NO, enhanced UV-B(10.8 kJ·m-2·d-1) radiation and combined process. The results showed that, compared with control, after enhanced UV-B radiation, biomass, leaf number, leaf length, content of chlorophyll, photosynthetic rate, and chlorophyⅡ fluorescence characteristics, rubisco activase content and its coding gene expression quantity decreased in Chinese cabbage seedling.But exogenous NO can alleviate the damage which caused by enhanced UV-B radiation on Chinese cabbage seedling. Such as, biomass,leaf number,leaf length,chlorophyⅡ fluorescence characteristics and rubisco activase content and its gene expression increased. In conclusion, NO could reduce the damage and protect the cabbage seedlings under enhanced UV-B radiation stress by means of raising the photosynthesis rate and increasing the biomass and chlorophyll content. This study provide a theoretical basis for further study on the role of nitric oxide gas in the physiological process of plant resistance.