ULTRAVIOLET-B EFFECTS ON SPIRULINA-PLATENSIS CELLS - MODIFICATION OF CHROMOPHORE-PROTEIN INTERACTION AND ENERGY-TRANSFER CHARACTERISTICS OFPHYCOBILISOMES

Exposure of ultraviolet-B (280-320 nm, 1.9 mW m(-2) s(-1)) radiation o f intact Spirulina platensis for 9 h caused specific loss of the 85.5 KDa anchor protein of phycobilisomes, the major light-harvesting anten na complex of photosystem II. Associated with the loss of 85.5 KDa pro tein, the UV-B irradiation also caused photobleaching of phycobilins a nd alteration in the chromophore protein interactions, as evidenced fi om the visible circular dichroic measurements, and it also affected t he energy transfer process within the phycobilisomes, as inferred from the low-temperature, 77 K, fluorescence spectral analysis. Our result s, thus, clearly demonstrate for the first time that the phycobilisome s effectively act as targets for UV-B induced damage of photosynthetic apparatus in cyanobacteria. (C) 1998 Academic Press.