THE EFFECTS OF CD2+ STRESS ON PHOTOSYSTEM II FUNCTIONING OF RICE (ORYZA SATIVA L.) LEAVES UNDER ELEVATED CO2 LEVEL

The effects of elevated levels of CO2 (EC) and cadmium (Cd2+) on the photosystem II of rice leaves were studied using fast chlorophyll fluorescence technique. Rice seedlings (two-leaves-stage) were treated under atmospheric CO2 (AC, 400 mu mol/mol) and elevated CO2 (EC, 800 mu mol/mol), while applied 0, 50, 150, 250 and 500 mu mol/L Cd2+ concentrations respectively. Chlorophyll fluorescence parameters were measured after six days treatments. The results showed that: (1) Under Cd2+, F-V/F-0, phi Po, Psi o, phi Eo and PIABS decreased significantly, while V-K, V-J, W-K, M-0, phi Do, ABS/RC, TR0/RC, DI0/RC increased significantly compared to AC. Additional effects were found on the donor side, reaction centers and acceptor side under Cd2+, which caused a lower energy connectivity, reduction of PS. activity and electron transfer efficiency as well as an increase of heat dissipation. (2) EC significantly increased F-V/F-0, phi Po, Psi o, phi Eo and PIABS, while significantly decreased V-J and phi Do compared to AC. EC increased the photo-energy conversion efficiency of PS Pi. (3) Under EC and Cd2+ treatments, the adverse effects of Cd2+ were slightly alleviated by EC in EC 50 (EC + 50 mu mol/L Cd2+, the following abbreviations are consistent with this), but the negative influence on photosystem. was still the most significant.