Effect of exogenous glucose on the expression and activity of NADPH dehydrogenase complexes in the cyanobacterium Synechocystis sp. strain PCC 6803.

Active NADPH dehydrogenase super- and medium-complexes were newly identified in cyanobacteria and are essential to cyclic photosystem I (PSI) activity and respiration and to CO(2) uptake, respectively. Synechocystis sp. strain PCC 6803 cells were treated with exogenous glucose (Glc) for different times. Active staining of NADPH-nitroblue tetrazolium oxidoreductase and western blot were conducted, and the initial rate of P700(+) dark reduction was measured. The expression and enzyme activity of the NADPH dehydrogenase super-complex were gradually inhibited and were found to be closely associated with the decrease in cyclic PSI activity, as reflected by the initial rate of P700(+) dark reduction. By contrast, those of the NADPH dehydrogenase medium-complex and the activity of CO(2) uptake reflected by the expression levels of NdhD3 and NdhF3 were not significantly affected by the addition of exogenous Glc to the cultures; however, the expression and enzyme activity of this medium-complex were found to be significantly influenced by the changes in CO(2) concentration. These results indicated that (1) the responses of the 2 cyanobacterial NADPH dehydrogenase complexes to exogenous Glc in terms of their expression and activity differed and that (2) these responses were closely associated with their respective physiological roles.