Study On Photosynthetic And Antioxiant Properties In Leaf Rice Photo-oxidation Mutant 813HS

This study compared the differences in photosynthetic and antioxidant characteristics between the rice photo-oxidation mutant 812HS and its wild type 812S. The results were as following:1. Photosynthetic pigment contents in 812HS and 812S were at the same level just in the end of rain season, and there were no phenotypic differences between them. After long-term light irradiation in field, total chlorophyll content of 812HS and 812S was decreased by 68% and 12% respectively, meanwhile the ratio of Chla/b and 812HS increased to a level that was significantly higher than 812S. In addition, carotenoid content of 812HS was decreased by 63% which was 5.7 times for 812S. The absorption spectra of thylakoid membrane reflected the results as the above.2. The fluorescence emission spectra thylakoid membrane exhibited that the peak of fluorescence emission in 812HS was significant lower than its wild type and had a displacement. This may results from that light harvesting pigments of 812HS cannot capture and pass light to PS Ⅱ center effectively. The chlorophyll fluorescence kinetics parameters demonstrated that the light harvesting ability of 812HS and 812S had no difference while the ability of light energy conversion and transfer differed between both. The φpEo and φpPo in 812HS were decreased by 74.16% and 19.89% respectively, indicating that φEo had higher sensitive for strong light than φpPo. Furthermore, net photosynthetic efficiency and PS II oxygen evolution rate of mutant 812HS were dramatically decreased to the level that was significantly lower than 812S.3. During the whole experiment, the contents of O2·- and H2O2 in 812HS and 812S exhibited an increasing trend and 812HS had a higher increase than 812S. With the increase of the active oxygen content,812HS also showed a higher antioxidant enzymes (SOD, POD, CAT, APX) activity and antioxidant (AsA, GSH) content than its wild type. Despite of its higher antioxidant activity, the result of MDA content indicated that 812HS suffered more severe photo-damage. The cracked chloroplast membrane and the increasing number and volume of osmiophilic droplets also proved that 812HS suffered severe injury.In summary, light sensitivity characteristic of 812HS may be caused by the instability of PS Ⅱ activity and photosynthetic disability. This characteristic makes it easy to concentrate a lot of reactive oxygen species under high light condition, which causes damage to the chloroplast mechanism and photosynthetic membrane, thus showing bleaching phenomenon.