Disintegration of phycobilisomes in a rice field cyanobacterium Nostoc sp. following UV irradiation.

The effects of ultraviolet-B (UV-B, 280-315 nm) irradiation on survival, growth and phycobilisome assembly have been studied in the N2-fixing cyanobacterium Nostoc sp. Survival and growth were virtually arrested after 120 min of UV irradiation. The phycobiliprotein fractions showed a decrease in absorption and fluorescence as well as a shift towards shorter wavelengths indicating the impairment of energy transfer from phycobiliproteins to the photosynthetic reaction centers. This was further supported by SDS-PAGE analysis of the fractions which revealed a loss in high molecular mass rod-core and core-membrane linker polypeptides. Also the low molecular mass phycobilin (alpha beta) monomers decreased, showing that the supra-molecular organization of the phycobilisomes disintegrated during UV irradiation.