Oxygenic photosynthesis produces various radicals and active oxygen species with harmful effects on photosystem II (PSII). Such photodamage occurs at all light intensities. Damaged PSII centres, however, do not usually accumulate in the thylakoid membrane due to a rapid and efficient repair mechanism. The excellent design of PSII gives protection to most of the protein components and the damage is most often targeted only to the reaction centre D1 protein. Repair of PSII via turnover of the damaged protein subunits is a complex process involving (i) highly regulated reversible phosphorylation of several PSII core subunits, (ii) monomerization and migration of the PSII core from the grana to the stroma lamellae, (iii) partial disassembly of the PSII core monomer, (iv) highly specific proteolysis of the damaged proteins, and finally (v) a multi-step replacement of the damaged proteins with de novo synthesized copies followed by (vi) the reassembly, dimerization, and photoactivation of the PSII complexes. These processes will shortly be reviewed paying particular attention to the damage, turnover, and assembly of the PSII complex in grana and stroma thylakoids during the photoinhibition-repair cycle of PSII. Moreover, a two-dimensional Blue-native gel map of thylakoid membrane protein complexes, and their modification in the grana and stroma lamellae during a high-light treatment, is presented.
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