Comparison of D1´- and D1-containing PS II reaction centre complexes under different environmental conditions in...

In oxygenic photosynthesis, the D1 protein of Photosystem II is the primary target of photodamage and environmental stress can accelerate this process. The cyanobacterial response to stress includes transcriptional regulation of genes encoding D1, including low-oxygen-induction of psbA1 encoding the D1´ protein in Synechocystis sp. PCC 6803. The psbA1 gene is also transiently up-regulated in high light, and its deletion has been reported to increase ammonium-induced photoinhibition. Therefore we investigated the role of D1´-containing PS II centres under different environmental conditions. A strain containing only D1´-PS II centres under aerobic conditions exhibited increased sensitivity to ammonium chloride and high light compared to a D1-containing strain. Additionally a D1´-PS II strain was outperformed by a D1-PS II strain under normal conditions; however, a strain containing low-oxygen-induced D1´-PS II centres was more resilient under high light than an equivalent D1 strain. These D1´-containing centres had chlorophyll a fluorescence characteristics indicative of altered forward electron transport and back charge recombination with the donor side of PS II. Our results indicate D1´-PS II centres are important in the reconfiguration of thylakoid electron transport in response to high light and low oxygen.