Ferredoxin-dependent and antimycin A-sensitive reduction of cytochrome b-559 by far-red light in maize thylakoids; participation of a menadiol-reducible cytochrome b-559 in cyclic electron flow
1995
Miyake, C. | Schreiber, U. | Asada, K.
Thylakoids from mesophyll cells of maize showed a high rate of the ferredoxin (Fd)-dependent and antimycin A (AntiA)-sensitive cyclic electron flow as determined by the quenching of 9-aminoacridine fluorescence which indicates the formation of delta pH across the membranes. Spectrophotometric survey of the thylakoids showed the reduction of a Cyt having an a-peak at 559 nm [Cyt b-559(Fd)] by far-red light, which depended on Fd and was sensitive to AntiA. Dose dependencies of Fd and AntiA on the photoreduction of Cyt b-559(Fd) were the same as those of the formation of delta pH. Cyt b-559(Fd) occurred in an oxidized form even in the presence of ascorbate and was reduced by far-red light. In darkness, it was reduced only by menadiol (Em,7 = -10 mV). Thus, Cyt b-559(Fd) was distinguished from Cyt b-559 in the PSII complex by its low redox potential. The present results indicate that Cyt b-559(Fd) mediates electron transfer from Fd to plastoquinone during Fd-dependent cyclic electron flow around PSI.
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