Ultraviolet-B Effects onSpirulina platensisCells: Modification of Chromophore–Protein Interaction and Energy Transfer Characteristics of Phycobilisomes

Abstract

Exposure of ultraviolet-B (280–320 nm, 1.9 mW m ^-2s ^-1) radiation of intactSpirulina platensisfor 9 h caused specific loss of the 85.5 KDa anchor protein of phycobilisomes, the major light-harvesting antenna complex of photosystem II. Associated with the loss of 85.5 KDa protein, the UV-B irradiation also caused photobleaching of phycobilins and alteration in the chromophore protein interactions, as evidenced from the visible circular dichroic measurements, and it also affected the energy transfer process within the phycobilisomes, as inferred from the low-temperature, 77 K, fluorescence spectral analysis. Our results, thus, clearly demonstrate for the first time that the phycobilisomes effectively act as targets for UV-B induced damage of photosynthetic apparatus in cyanobacteria.