Abstract: With “Nongpu” No.12 bean seedling leaves(Phaseolus vulgaris L.), we used the AOX inhibitor salicylhydroxamic acid(1 mmol·L^-1; SHAM) to inhibit AOX activity in vivo, and studied the protective effects of alternative respiratory pathway on the photosystem Ⅱ under the CuCl₂ stress. The treatment with CuCl₂ caused a significant decrease in the ratio of F_v/F_m(the potential maximal photochemical efficiency of PSⅡ), F_v'/F_m'(the maximum quantum efficiency of PSⅡ photochemistry at illumination), Y(Ⅱ)(effective photochemical quantum yield of PSⅡ photosynthetic), qP(photochemical quenching coefficient), and the chlorophyll content, but the levels of NPQ(non-photochemical quenching) and the capacity of the alternative respiratory pathway were significantly increased. Compared with the bean seedling under CuCl₂ stress, the CuCl₂-stressed bean seedling pretreated with inhibitor of alternative respiratory(salicylhydroxamic acid) had lower levels of F_v/F_m, F_v'/F_m', Y(Ⅱ), qP and chlorophyll content, and higher levels of NPQ. These observations suggest that under the CuCl₂ stress, the alternative respiratory pathway can protect the photosystem Ⅱ of the bean leaves from CuCl₂ stress by alleviating the decrease of the photochemical efficiency of PSⅡ, maintaining the proportion of open PSⅡ centres, reducing the heat dissipation of the antenna pigment and chlorophyll content disruption.

Key words: alternative respiratory pathway, CuCl₂ stress, Phaseolus vulgaris L., chlorophyll fluorescence