Production of reactive oxygen species in chloride- and calcium-depleted photosystem II and their involvement in photoinhibition

Mixed photosystem II (PSII) samples consisting of Cl--depleted and active, or Ca2+-depleted and active PSII enriched membrane fragments, respectively, were investigated with respect to their susceptibility to light. In the presence of Cl--depleted PSII, active centers were damaged more severely, most likely caused by a higher amount of reactive oxygen species formed in the nonfunctional centers. Cl- depletion led to an increased H2O2 production, which seemed to be responsible for the stimulation of PSII activity loss. To distinguish between direct H2O2 formation by partial water oxidation and indirect H2O2 formation by oxygen reduction involving the prior formation of O-2(-.), the production of reactive oxygen species was followed by spin trapping EPR spectroscopy. All samples investigated, i.e. PSII with a functional water splitting complex, Ca2+- and Cl--depleted PSII, produced upon illumination O-2(-.) and OH. radicals on the acceptor side, while Cl-depleted PSII produced additionally OH. radicals originating from H2O2 formed on the donor side of PSII. (C) 2004 Elsevier B.V. All rights reserved.