Physiological Effects Of Drought Stress On Transfer C4 Genes (PEPC & PPDK) Rice Leaf Photosynthesis And Antioxidant Properties

The present study aimed at investigating the effects of water stress on photosynthesis and antioxidant system of C4transgenic (PEPC&PPDK) rice R2P. The main conclusions were listed as follows:1.20%PEG6000was used to simulate the serious drought during the seeding stage. Under this condition, the chlorophyll content and net photosynthesis rate of R2P were decreased and lower than those of R299. Regarding the chlorophyll fluorescence parameters, the degree of the increase in Fo and the decrease in Fv/Fm and Plabs of R2P were both less than those of R299. Moreover, the electron transport chain activity and the photophosphorylation rate of R2P were reduced less than those of R299. As for the antioxidation, drought induced higher increases in the SOD activity and proline content of R2P than those of R299while the O2-and MDA contents were enhanced to a lower extent than those in R299. The TEM observations indicated that after drought treatment for4days, the chloroplast structure of R2P was significantly changed. The chloroplast membrane and the thylakoid membrane were partially damaged. On the other hand, the chloroplast lamellae was no longer closely associated, although the overall structure of chloroplast remained fairly intact. However, in the case of R299, the chloroplast membrane was seriouly damaged. The granular and stroma thylakoid boundaries were vague and they arranged unparallelly to the long axis of chloroplasts. Furthermore, the dissolution of stroma lamellae resulted in transparent cavity in stroma.2. During the reproductive growth period, drought simulation experiments in the field were conducted. As soon as the flag leaves were fully expanded, the plants were exposed to water stress treatment and the soil water potential was controlled by-10kPa (light drought). After20days, the changing tendencies of R2P in chlorophyll content, net photosynthesis rate and photophosphorylation level were similar to those in R299, characterized by a decrease followed by an increase. These parameters were lower as compared with those in the respective control groups and the decreases in the R2P group were less than those in the R299group. After drought treatment for10days and20days, the PEPC activity of R2P were respectively raised by176%and60%, higher than that of R299(35.6%and42.8%). The decrease in Initial RuBisCO activity of R2P was lower than that of R299. In relation to the antioxidation, the improvement in SOD activity of R2P induced buy drought was higher than that of R299while the enhancements in O2-and MDA of R2P were lower.In conclusion, during the seeding stage and the reproductive growth stage, the decreases in the photosynthetic rates of R2P were lower than those of R299. This might be attributable to the higher efficient antioxidant system of R2P, which stabilized the cellular structure and ensured the ongoing of photosynthesis.