Deactivation processes in PsbA1-Photosystem II and PsbA3-Photosystem II under photoinhibitory conditions in the cyanobacterium Thermosynechococcus elongatus

The sensitivity to high light conditions of Photosystem II with either PsbA1 (WT*1) or PsbA3 (WT*3) as the D1 protein was studied in whole cells of the thermophilic cyanobacterium Thermosynechococcus elongatus. When the cells are cultivated under high light conditions the following results were found: (i) The O2 evolution activity decreases faster in WT*1 cells than in WT*3 cells both in the absence and in the presence of lincomycin, a protein synthesis inhibitor; (ii) In WT*1 cells, the rate constant for the decrease of the O2 evolution activity is comparable in the presence and in the absence of lincomycin; (iii) The D1 content revealed by western blot analysis decays similarly in both WT*1 and WT*3 cells and much slowly than O2 evolution; (iv) The faster decrease in O2 evolution in WT*1 than in WT*3 cells correlates with a much faster inhibition of the S2-state formation; (v) The shape of the WT*1 cells is altered. All these results are in agreement with a photo-inhibition process resulting in the loss of the O2 activity much faster than the D1 turnover in PsbA1-PSII and likely to a greater production of reactive oxygen species under high light conditions in WT*1 than in WT*3. This latter result is discussed in view of the known effects of the PsbA1 to PsbA3 substitution on the redox properties of the Photosystem II cofactors. The observation that under low light conditions WT*3 cells are able to express the psbA3 gene, whereas under similar conditions wild type cells are expressing mainly the psbA1 gene is also discussed. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.

► We studied sensitivity to high light conditions of PSII with either PsbA1 or PsbA3.
► The loss of the O2 evolution was mush faster in WT*1 cells than in WT*3 cells.
► Degradation pattern of D1 protein in WT*1 was similar to that in WT*3.
► Deactivation of the Mn-cluster in WT*1 was faster than that in WT*3 by high light.