Role of white light in reversing UV-B-mediated effects in the N-2-fixing cyanobacterium Anabaena BT2
The effects of various irradiances of artificial UV-B (280-315 nm) in the presence or absence of visible light (photosynthetically active radiation) on growth, survival, (CO2)-C-14 uptake and ribulose 1,5-bisphosphate carboxylase (RuBISCO) activity were studied in the N-2-fixing cyanobacterium Anabaena BT2. We tested the hypothesis whether or not visible radiation offers any protection against UV-B-induced deleterious effects on growth and photosynthesis in Anabaena BT2. Attempts were also made to determine the irradiances of U-V-B where inhibitory effects could be mitigated by simultaneous irradiation with visible light. Exposure of cultures to 0.2 W m(-2) or higher irradiance of UV-B caused inhibition of growth and survival and growth ceased above 1.0 W m(-2). (CO2)-C-14 uptake and RuBISCO activity were found to be more sensitive to UV-B and around 60% reduction in (CO2)-C-14 uptake and RuBISCO activity occurred after exposure of cultures to 0.4 W m(-2) for 1 h. However, growth, (CO2)-C-14 uptake and RuBISCO activity were nearly normal when UV-B (0.4 W m(-2)) and visible light (14.4 W m(-2)) were given simultaneously. Blue radiation (450 nm) was found to be the most effective in photoreactivation against UV-B, better than UV-A or any other light wavelength band. Our results demonstrate that the studied cyanobacterium possesses active photoreactivation mechanism(s) against UV-B-mediated damage which in turn probably allow survival under natural conditions in spite of being continuously exposed to the UV-B component present in the solar radiation. Continued growth of many algae and cyanobacteria in the presence of intense solar UV-B radiation under natural conditions seems to be due to the active role of photoreactivation. (C) 2003 Elsevier B.V. All rights reserved.
Journal Of Photochemistry And Photobiology B-Biology