INVOLVEMENT OF PROTEIN-PHOSPHORYLATION IN THE SENSITIVITY OF PHOTOSYSTEM-II TO STRONG ILLUMINATION

Four types of differently phosphorylated-thylakoids isolated from fiel d grown spinach (Spincia oleracea L.) were tested for the sensitivity of photosystem II (PSII) to photoinactivation. Phosphorylation of ligh t-harvesting II complexes (LHCII) protected PSII electron transfer fro m photoinhibitory damage, while the phosphorylation of the PSII core p olypeptides slightly accelerated the decline of electron transfer duri ng high irradiance treatment. Dephosphorylation of the CP43 apoprotein and PsbH protein by an alkaline phosphatase resulted in an extreme se nsitivity of the thylakoids to strong illumination. The PSII photoinac tivation of thylakoids with the impaired oxygen-evolving complex was f ound to be independent of phosphorylation. The thylakoids of the therm ophilic cyanobacterium Synechococcus elongatus were used in order to c ompare the plants with an organism where LHCII complexes are missing a nd the PSII core proteins are not phosphorylated.