PHOTOSYSTEM I-DEPENDENT CYCLIC ELECTRON FLOW IN INTACT SPINACH-CHLOROPLASTS - OCCURRENCE, DEPENDENCE ON REDOX CONDITIONS AND ELECTRON-ACCEPTORS AND INHIBITION BY ANTIMYCIN-A

Photosystem I-dependent cyclic electron transport is shown to operate in intact spinach chloroplasts with oxaloacetate, but not with nitrite or methylviologen as electron accepters. It is regulated by the redox state of the chloroplast NADP system. Inhibition of cyclic electron t ransport by antimycin A occurs immediately on addition of this antibio tic in the light. It is unrelated to a different function of antimycin A, inhibition of nonphotochemical quenching of chlorophyll fluorescen ce, which requires prior dissipation of the transthylakoid proton grad ient before antimycin A can become effective.