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 CO₂ 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 CO₂ 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 CO₂ 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.