A new type of adaptation of the cyanobacterium Spirulina platensis to illumination conditions

Incubation of cells of the cyanobacterium Spiralina platensis under conditions of exposure to low-intensity (2-3 muE m(-2) s(-1)) red light, which was predominantly absorbed by photosystem I (PS I), caused atypical adaptation changes. Invariable pigment composition and stoichiometry of the photosystems was observed in the cells incubated under these conditions against the background of a decrease in the rate of photosynthetic fixation of CO2 (by one-half) and a 1.5-fold increase in the rate of dark respiration relative to cells incubated under conditions of exposure to green light. Comparison of these data with a high rate of dark relaxation of PAW in the presence of diuron suggests, that deficiency of reduced equivalents on the donor side of PS I in Spirulina cells exposed to red light is compensated by electron supply from the respiratory chain NAD(P)H dehydrogenase complex.