Effects of Cyclic Electron Flow Inhibitor （Antimycin A） on Photosystem Photoinhibition of Sweet Pepper Leaves upon Exposure to Chilling Stress Under Low Irradiance

In chloroplast, there were two pathways involved in the cyclic electron flow around photosystem 1 （PS 1）. One was the NADH dehydrogenase （NDH）-dependent flow and the other was the ferredoxin quinone reductase-dependent flow. It was proposed that the NDH-dependent cyclic electron flow around PSI was related to the xanthophyll cycle-dependent non-photochemical quenching （NPQ） at chilling temperature under low irradiance （CL）. The function of the chloroplastic cyclic electron flow around PS 1 was examined by comparing sweet pepper （Capsicum annuum L.） control with its antimycin A （AA）-fed leaves upon exposure to CL stress. During CL stress, the maximum photochemical efficiency of PS2 （Fv/Fm） decreased markedly in both controls and AA-fed leaves, and P700＋ was also lower in AA-fed leaves than in controls. These results implied that cyclic electron flow around PS 1 functioned to protect the photosynthetic apparatus from CL stress. Under such stress, NPQ and PS2-driven electron transport rate were different between AA-fed leaves and controls. The lower NPQ in AA-fed leaves might be related to an inefficient proton gradient across thylakoid membranes （ApH） because of inhibiting cyclic electron flow around PS 1 under CL stress.