UV effects on photosynthesis and phycobiliprotein composition in the flagellate Cyanophora paradoxa

Abstract

The effects of solar and artificial ultraviolet radiation on photosynthetic oxygen production and phycobiliprotein composition were investigated in the freshwater flagellate, Cyanophora paradoxa. The phycobiliproteins of the cell acting as photosynthetic accessory pigments were found to be readily affected by even short exposure to ultraviolet radiation, while the membrane-bound chlorophyll protein complexes were hardly impaired as demonstrated by SDS polyacrylamide gel electrophoresis, isoelectric focussing and fast protein liquid chromatography (FPLC). The phycobilisomes are dissembled from the outside inwards and go from higher molecular weight components to hexamers ( αβ) 6, trimers ( αβ) 3 and finally monomers (αβ). Fluorescence spectra indicated that the energy transfer from accessory pigments to the photosystems was impaired by ultraviolet radiation. Photosynthetic oxygen production was affected on a much faster timescale than changes in the absorption spectra or at the protein level.