Damages of photosynthetic apparatus in Anacystis nidulans by ultraviolet-B radiation

Abstract

Changes in photosystem (PS) 2 activity were measured in Anacystis nidulans cells exposed to UV-B irradiation. The decrease in PS 2 activity was biphasic in cells exposed at the surface (0 cm) and at 2 cm depth in the water column, while gradual in those exposed at 10 and 30 cm depth. Addition of supplemental "white light" reduced the extent of UV-B damage. Decrease in photosynthetic activity was primarily due to the loss of energy transfer from phycobilisome to chlorophyll as the former in cyanobacteria acts as the primary light-harvesting complex. This was supported by the absorption and fluorescence excitation and emission spectral studies. All these changes were proportionally reduced by the thickness of the water column that reduced UV-B irradiance.