Photosynthesis Research 23: 59-65, 1990. © 1990 Kluwer Academic Publishers. Printedin the Netherlands. Regular paper Photoinactivation of the reactivation capacity of photosystem II in pea subchloroplast particles after a complete removal of manganese V.V. Klimov, M.A. Shafiev & S.I. Allakhverdiev Institute of Soil Science and Photosynthesis USSR Academy of Sciences, 142292 Pushchino, Moscow Region, USSR Received 8 August 1988; accepted in revised form January 1989 Key words: Photoinactivation, photosystem II, manganese, reaction center Abstract 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, pho- tooxidation 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~ and Z) are preserved. PI is accompanied by photooxida- tion 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. Abbreviations; AA- photoinduced absorbance changes, DPC- diphenylcarbazide, DPIP- 2,6-dich- lorophenol indophenol, Fo -- constant fluorescence of chlorophyll, AF-- photoinduced changes of Chl fluorescence yield, Mn -- manganese; P680 -- the primary electron donor in PS II, PI -- photoinhibition, PS II -- photosystem II, Q -- the primary (quinone) electron acceptor in PS II, RC -- reaction center Introduction Illumination of photosynthetizing organisms leads, besides the physiological light reactions of electron transfer, to destructive changes in photosynthetic apparatus. They can originate from the short-lived (but possesing high reactivity) excited states of the pigments as well as from the long-lived products of the primary photoreactions of charge separation. The life-time of the changed redox-states of the electron carriers and, consequently, the probability of destructive processes are considerably increased upon blocking the electron transport chain by means of removing its individual components or adding specific inhibitors. Photosystem lI (PSII) of plants and algae is characterized by high sensitivity to photoinhibition which is considered to result in bloking the electron transfer in the acceptor side of this photosystem (Powles 1984). The rate of photoinhibition is in- creased upon creation of anaerobic or, especially, reductive conditions (Karapetyan and Klimov 1973, Krause et al. 1985, Arntz and Trebst 1986, Allakhverdiev et al. 1987). On the other hand, upon