Photoinactivation of the reactivation capacity of photosystem II in pea subchloroplast particles after a complete removal of manganese.

After a complete removal of Mn from pea subchloroplast photosystem-II (PS II) preparations the electron phototransfer and oxygen evolution are restored upon addition of Mn(2+) and Ca(2+). Pre-illumination of the sample in the absence of Mn(2+) leads to photoinhibition (PI) - irreversible loss of the capability of PS II to be reactivated by Mn(2+). The effect of PI is considerably decreased in the presence of Mn(2+) (∼4 Mn atoms per reaction center of PS II) and it is increased in the presence of ferricyanide or p-benzoquinone revealing the oxidative nature of the photoeffect. PI results in suppression of oxygen evolution, variable fluorescence, photoreduction of 2,6-dichlorophenol indophenol from either water or diphenylcarbazide. However, photooxidation of chlorophyll P680, the primary electron donor of PS II as well as dark and photoinduced EPR signal II (ascribed to secondary electron donors D 1 and Z) are preserved. PI is accompanied by photooxidation of 2-3 carotenoid molecules per PS II reaction center (RC) that is accelerated in the presence of ferricyanide and is inhibited upon addition of Mn(2+) or diuron. The conclusion is made that PI in the absence of Mn leads to irreversible oxidative inactivation of electron transfer from water to RC of PS II which remains photochemically active. A loss of functional interaction of RC with the electron transport chain as a common feature for different types of PS II photoinhibition is discussed.