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 (PS1). One was theNADH dehydrogenase (NDH)-dependent flow and the other was the ferredoxin quinone reductase-dependent flow. Itwas proposed that the NDH-dependent cyclic electron flow around PS1 was related to the xanthophyll cycle-dependentnon-photochemical quenching (NPQ) at chilling temperature under low irradiance (CL). The function of the chloroplasticcyclic electron flow around PS1 was examined by comparing sweet pepper (Capsicum annuum L.) control with its antimycinA (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 PS1 functioned to protect the photosynthetic apparatus from CLstress. Under such stress, NPQ and PS2-driven electron transport rate were different between AA-fed leaves andcontrols. The lower NPQ in AA-fed leaves might be related to an inefficient proton gradient across thylakoid membranes(?pH) because of inhibiting cyclic electron flow around PS1 under CL stress.