Abstract: In order to reveal the effect mechanism of Cs on plant photosynthesis, different concentrations of CsCl were used to treat spinach seedlings which were cultured in quartz sand. The chlorophyll fluorescence induction kinetic analysis method were used to explore damaged position, damaged degree and photosynthetic electron transfer of spinach leaf PSII after Cs stress. The results showed that the OEC on the donor side of the PSII reaction center of spinach suffered slight damage when the CsCl concentration is 1~5 mmol/L. In order to adapt to the change of external environment, the opening degree of active reaction centers in spinach were increased under low concentration treatment, which promotes the increase of PSII photosynthetic activity were reflected by the rised parameters of φ_Po,φ_Eo,Ψ_o. Photosynthetic electron transport were blocked because of the damage on the PSII donor side OEC of spinach leaves, reaction center and receptor side of PSII when the concentrations of CsCl reach 10 mmol/L.

Key words: cesium, spinach, photosynthetic machinery, fast chlorophyll fluorescence induction kinetics, JIP-test