Photoinhibition and Reactivation of Photosynthesis in the Cyanobacterium Anacystis nidulans.

The susceptibility of photosynthesis to photoinhibition and its recovery were studied on cultures of the cyanobacterium Anacystis nidulans. Oxygen evolution and low temperature fluorescence kinetics were measured. Upon exposure to high light A. nidulans showed a rapid decrease in oxygen evolution followed by a quasi steady state rate of photosynthesis. This quasi steady state rate decreased with increasing photon flux density of the photoinhibitory light. Reactivation of photosynthesis in dim light after the photoinhibitory treatment was rapid: 85 to 95% recovery occurred within 2 hours. In the presence of the translation inhibitor, streptomycin (250 micrograms per milliliter), no reactivation occurred. We also found that the damage increased dramatically if the high light treatment was done with streptomycin added. A transcription inhibitor, rifampicin, did not inhibit the reactivation process. Based on these data we conclude that the photoinhibitory damage observed is the net result of a balance between the photoinhibitory process and the operation of the repairing mechanism(s).