EFFECTS OF CADMIUM STRESS ON PHOTOSYNTHETIC APPARATUS OF TOBACCO

The effects of cadmium (Cd) stress on the photosynthetic apparatus of the tobacco to Cd stress were analyzed. The results showed that the chlorophyll content in the tobacco leaves declined as the Cd concentration increased. In Cd-challenged tobacco leaves, the performance index on absorption basis (PIABS), which is based on light absorption, could better reflect Cd-induced toxicity to PSII reaction centers than the maximum photochemical efficiency of PSII (Fv/Fm). As the concentration of Cd increased, the relative variable fluorescence at the J step (VJ) was significantly increased in the tobacco leaves, and a VJ of 50 mu mol center dot L-1 Cd was significantly different from that of the control (CK). As Cd concentration increased, the quantum yield for electron transport (phi Eo) was significantly reduced in the tobacco leaves, while maximum quantum yield for non-photochemical quenching (phi Do) was markedly increased. Moreover, absorption flux per reaction center (ABS/RC) significantly increased when Cd concentration reached 100 mol center dot L-1. The above results suggest that the tobacco leaves adapt to Cd stress by lowering the electron transmission rate and the activity of PSII reaction centers and increasing thermal dissipation.