Different tolerance of photosynthetic apparatus to Cd stress in two rice cultivars with the same leaf Cd accumulation

In plants, cadmium (Cd) is regarded as one of the most toxic metals and affects many physiological and biochemical processes. To investigate the effects of Cd on photosynthesis and antioxidant system of japonica and indica rice cultivars, Wuyu 21 (WY21) and IIyou 808 (IIY808) seedlings were exposed to different concentrations of Cd for 7 days. Our results indicated that Cd treatments resulted in the significant decrease in photosynthetic capacity and the obvious oxidative damage in WY21 and IIY808. Although Cd contents in the leaves and stem had no obvious difference between WY21 and IIY808 under Cd stress, japonica cultivar WY21 showed higher Cd contents of roots and photosynthetic efficiency compared with indica cultivar IIY808 under Cd stress. In contrast, the lower generation of reactive oxygen species (ROS) and cell death were observed in WY21 relative to IIY808. However, almost all antioxidant enzymes activities and the concentrations of four antioxidants showed no significant differences between WY21 and IIY808. Furthermore, the severe oxidative damage in IIY808 was accompanied by the marked decline in the levels of two photosystem II (PSII) proteins (D2 and D1) under high concentration of Cd. In conclusion, we concluded that high Cd resistance in japonica cultivar WY21 is probably attributed to the high photosynthesis under Cd stress.