EFFECT OF CARBON AND NITROGEN ASSIMILATION ON CHLOROPHYLL FLUORESCENCE EMISSION BY THE CYANOBACTERIUM ANACYSTIS-NIDULANS

O2 evolution and chlorophyll a fluorescence emission have been monitored in intact cells of the cyanobacterium Anacystis nidulans 1402-1 to study the influence of carbon and nitrogen assimilation on the operation of the photosynthetic apparatus. The pattern of fluorescence induction in dark-adapted cyanobacterial cells was different from that of higher plants. Cyanobacteria undergo large, rapid state transitions upon illumination, which lead to marked changes in the fluorescence yield, complicating the estimation of quenching coefficients. The Kautsky effect was not evident, although it could be masked by a state II-state I transition, upon illumination with actinic light. The use of inhibitors of carbon assimilation such as D,L-glyceraldehyde or iodoacetamide allowed us to relate changes in variable fluorescence to active CO2 fixation. Ammonium, but not nitrate, induced non-photochemical fluorescence quenching, in agreement with a previous report on green algae, indicative of an ammonium-induced state I transition.