[Effect of ferricyanide, dark adaptation and aging on the properties of the EPR I signal of chloroplasts].

Ferricyanide (10-3 M) is shown to oxidize from 25 to 50% of the total P700 pool in the dark. The ferri-ferrocyanide mixture thus obtained, acting as redox buffer, accelerates the P700+ dark reduction after continuous far red illumination is turned off or after a saturating flash. The oxidized P700 yield on the flash increase in the presence of ferricyanide as a result oxidation of species in the neighborhood of P700 centers. During aging (24 h at 2--3 degrees in the dark) the yield of flash-induced P700 oxidation also increases thus indicating the loss of cyclic electron flow in aged chloroplasts.