Expression and activity of type 1 NAD(P)H dehydrogenase at different growth phases of the cyanobacterium, Synechocystis PCC 6803

The expression and activity of type 1 NAD(P)H dehydrogenase (NDH-1) were investigated in Synechocystis PCC 6803 cells during different growth phases (i.e. lag, logarithmic, stationary and decline phases). The relative amount of NDH-1, estimated by Western blot analysis using antibodies against NdhH, NdhI and NdhK, increased more than two-fold during growth from the lag to the logarithmic phase and then decreased after the logarithmic phase to reach lowest levels after 15 days (decline phase). The activity of light-dependent NADPH oxidation and cyclic electron flow around photosystem I (PSI) changed nearly in parallel with the amount of NdhH, NdhI and NdhK in cells across the growth phases. In contrast, the activity of photosynthetic O-2 evolution and respiratory O-2 uptake was not significantly different across phases of growth; the fluctuation of the activity at different phases was within 40%. These results suggested that the activity of light-dependent NADPH oxidation and PSI-cyclic electron flow are restricted by the amount of NDH-1 and that other factor(s) are limiting the rates of photosynthesis and respiration.