Oxygen-Evolving System of Inactive Photosystem II Complexes in Chlorella

Abstract

Incubation of green alga Chlorella pyrenoidosa Chick in darkness at 37–38°C for 10–30 h resulted in inactivation of the oxygen-evolving complex (OEC): the maximum yield of oxygen evolution during a series of short light flashes shifted from the third to the fifth flash; the transition of S2- and S3-states of OEC to a stable S1-state was markedly accelerated. This inactivation of OEC was accompanied by the accumulation of inactive complexes of photosystem II (PSII), in which the reduction of primary quinone acceptor and the conversion into the closed state occurred with a low efficiency, even in the presence of 5 μM DCMU. The treatment of light-grown algal cells with hydroxylamine impaired OEC functioning, in similarity to the effect of dark incubation, but caused no accumulation of inactive PSII complexes. We conclude that the inactivation of OEC is not the cause of the inactivation of PSII complex. The decline in the efficiency of electron-transport reactions, both on the donor and acceptor sides of PSII may be related to modification of major proteins in the PS II reaction center.