Photoinhibition and its recovery in two strains of the cyanobacterium spirulina platensis

Two strains of Spirulina platensis, marked Sp-G and Sp-RB, were studied for their response to high photon flux densities (PFD). Sp-RB, a gas vacuolated strain, appeared more sensitive to the high PFD treatment as compared with Sp-G, a non-vacuolated strain. The loss of the photosynthetic activity due to the photoinhibitory treatment was obtained at the level of whole cells as well as the membrane level. Sp-RB was more sensitive than Sp-G at both levels. Experiments using chloramphenicol during the photoinhibition process, and others in which the fate of radio-active labeled thylakoid proteins was followed, indicated that the difference between the strains lies in the rate of loss of the Dl polypeptide with an electrophoretic mobility of 32-34 kDa. Both strains recovered from the photoinhibition when placed under low PFD. The recovery process started immediately after PFD was reduced, without any observed lag period, and was sensitive to chloramphenicol. Light was required for full recovery of activity. The rate of recovery of the two strains studied was very similar.