Transient effects of salt shock on the photosynthetic machinery in synechocystis sp. PCC 6803

The transient effects of NaCl on chlorophyll (Chl) fluorescence in Synechocystis sp. PCC 6803 cells were examined. In dark-adapted cells, salt shock induced a transition from state 2 to state 1, and the artificial quinones, phenyl-1,4-benzoquinone (PBQ) and 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone (DBMIB), quenched the Chl fluorescence markedly after addition of 0.8 mol/L NaCl. In light-adapted cells, the addition of NaCl caused a significant increase in the stationary fluorescence yield, which resulted in a decrease in the quantum yield of photosystem II (PSII). The results indicate that salt shock can induce a change in the affinity between the photosystems and the phycobilisomes (PBS) and can perturb the orientation of the Chl molecules in PSII.