INFLUENCE OF LIGHT AND TEMPERATURE ON PHOTOINHIBITION OF PHOTOSYNTHESIS IN SPIRULINA-PLATENSIS

Photoinhibition of photosynthesis and its recovery in the cyanobacterium Spirulina platensis was studied to find how photosynthetic rates were influenced by light and temperature. By exposing cell samples from a turbidostat culture to combinations of light and temperature, a connection between light, temperature and photoinhibition was found. The experiments showed that a 10 degree increase from 20 degrees C to 30 degrees C considerably reduced the photoinhibition. At 25 degrees C a photon flux density of 1720 mu mol m(-2) s(-1) reduced the photosynthetic rate by 50% in 1 h, but a similarly high photon flux density had nearly no negative effect at 35 degrees C. Reactivation in low light from 50% photoinhibition was fast and complete in 60 min at 30 degrees C, while at 20 degrees C only about 1/6 of the full capacity was regained in the same time. Addition of the protein synthesis inhibitor streptomycin to cultures undergoing photoinhibition and regeneration indicated the presence also in this organism of a repair mechanism based on protein synthesis.