Abstract:

【Objective】 For discovering the mechanism of Cd damage on leaves of Malus hupehensis Rehd., the activity of photosystemⅡ (PSⅡ), net photosynthetic rate (Pn) and their correlation in leaves treated with CdCl2 were studied. 【Method】 After 30 days of treatment by CdCl2 in 1/2 Hoagland solution, the Pn, stomatal conductance (Gs), intercellular CO2 concentration (Ci) and chlorophyll fluorescence parameters in leaves of Malus hupehensis Rehd. were measured, and the relationship between these parameters under CdCl2 treatment were analyzed. 【Result】 Under the treatment of CdCl2, the Pn and Gs reduced, the Ci and the fluorescence intensity Fk at 300 μs increased, and the maximum photochemistry efficiency of PSⅡ(Fv/Fm, φPo), the quantum yield for electron transport (φEo) , the performance index on absorption basis (PIABS) and the density of active reaction center (RC/CS) all decreased significantly. Furthermore, the range of variation of these parameters increased with the increasing of CdCl2 concentration. The direct effect of the relatively variable fluorescence intensity VK and the ratio of variable fluorescence Fv on the amplitude Fj-Fo (WK) at 300 μs for Pn were higher than that of others through the path analysis. 【Conclusion】 CdCl2 damaged the sides of acceptor and donor and the reaction centers of PSⅡ of leaves of Malus hupehensis Rehd. The activity of PSⅡand Pn decreased, and the direct effects of VK and WK on the important fluorescence parameters for Pn were larger than other parameters under CdCl2 treatment.

Key words: Malus hupehensis Rehd., CdCl2, photosynthetic rate, photosystemⅡ, chlorophyll fluorescence