Role of white light in reversing UV-B-mediated effects in the N-2-fixing cyanobacterium Anabaena BT2



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.


Ashok Kumar, Madhu B. Tyagi, Nilima Singh, Rashmi Tyagi, Prabhat N. Jha, Rajeshwar P. Sinha, Donat-P. Häder



Journal Of Photochemistry And Photobiology B-Biology