Weak Light-Induced Oxygen Consumption Observed during Photoreactivation Is Coupled to the Recovery of Oxygen Evolving Activity

Abstract

During photoreactivation of the O2-evolving center in Tris-inactivated/Mn-depleted thylakoids, a slow (^-consumption occurred. This O2-consumption became detectable when the O2-evolving activity of thylakoids was inactivated by Tris-treatment and decreased as photoreactivation proceeded. The O2-consumption and photoreactivation similarly required Mn2+ at fiM levels in addition to PSII electron donors and shared several common characteristics. Stimulation of 02-consumption and photoreactivation by these cofactors were always accompanied by enhancement in chlorophyll fluorescence induction, suggesting the involvement of a Mehler-type reaction in photoreactiva tion. Although the electron transport due to this 02-consumption was rapid enough to oxidize 4 Mn2+ ions to reconstitute the tetranuclear Mn-cluster in each O2-evolving center in a few seconds, actual recovery of O 2-evolving activity occurred more slowly in a few minutes. It was inferred that photoreactivation in Tris-inactivated thylakoids is not a simple photooxidation of Mn 2+ but involves more complicated processes which are coupled to the Mehlertype electron transport from PSII to oxygen via PSI.