Damages of photosynthetic apparatus inAnacystis 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.

The long-term effects of UV exclusion on the microbial composition and photosynthetic competence of bacteria in hot-spring microbial mats

“…It is known that UVR exposure causes the disassembly of phycobiliproteins [37] which were in extremely low concentrations in these mats. This results in a loss of energy transfer to PS II and thus may be bene¢cial under photoinhibitory light intensities [38]. Carotenoids are well known to protect against high-light and high-UV damage in cyanobacteria, not so much through screening, but through their ability to intercept the triplet chlorophyll state, thus preventing the formation of singlet oxygen and other reactive oxygen species that are produced by UV and high visible irradiance, as well as by quenching singlet oxygen directly (see [6,36]).…”

The long-term effects of UV exclusion on the microbial composition and photosynthetic competence of bacteria in hot-spring microbial mats

“…It is known that UVR exposure causes the disassembly of phycobiliproteins [37] which were in extremely low concentrations in these mats. This results in a loss of energy transfer to PS II and thus may be beneficial under photoinhibitory light intensities [38]. Carotenoids are well known to protect against high‐light and high‐UV damage in cyanobacteria, not so much through screening, but through their ability to intercept the triplet chlorophyll state, thus preventing the formation of singlet oxygen and other reactive oxygen species that are produced by UV and high visible irradiance, as well as by quenching singlet oxygen directly (see [6,36]).…”