Photoreactions of cytochrome b563 and f554 in intact spinach chloroplasts: regulation of cyclic electron flow.

In intact spinach chloroplasts cytochrome b563 and cytochrome f show an antagonistic redox behaviour in the extent and kinetics of light/dark-induced absorbance changes. The extent of cytochrome b563 photoreduction appears to be influenced by the redox state of plastoquinone suggesting a regulation of cyclic electron flow at this level. Far-red illumination induces a membrane state with altered redox reactions of both cytochromes at a more oxidized level.