title: Differential effect of ultraviolet-B radiation on certain metabolic processes in a chromatically adapting Nostoc.
abstract: The impact of UV-B radiation on growth, pigmentation and certain physiological processes has been studied in a N2-fixing chromatically adapting cyanobacterium, Nostoc spongiaeforme. A brownish form (phycoerythrin rich) was found to be more tolerant to UV-B than the blue-green (phycocyanin rich) form of N. spongiaeforme. Continuous exposure to UV-B (5.5 W m-2) for 90 min caused complete killing of the blue-green strain whereas the brown strain showed complete loss of survival after 180 min. Pigment content was more strongly inhibited in the blue-green strain than in the brown. Nitrogenase activity was completely abolished in both strains within 35 min of UV-B treatment. Restoration of nitrogenase occurred upon transfer to fluorescent or incandescent light after a lag of 5-6 h, suggesting fresh synthesis of nitrogenase. Unlike the above processes, in vivo nitrate reductase activity was stimulated by UV-B treatment, the degree of enhancement being significantly higher in the blue-green strain. Like the effect of UV-B on nitrogenase, 14CO2 uptake was also completely abolished by UV-B treatment in both strains. Our findings suggest that UV-B may produce a deleterious effect on several metabolic activities of cyanobacteria, especially in cells lacking phycoerythrin. Strains containing phycoerythrin appear to be more tolerant to UV-B, probably because of their inherent property of adapting to a variety of light qualities.
authors.affiliation: Centre of Advanced Study in Botany and Biotechnology Programme, Banaras Hindu University, Varanasi, India.
authors.forename: R
authors.initials: R
authors.lastname: Tyagi
authors.forename: G
authors.initials: G
authors.lastname: Srinivas
authors.forename: D
authors.initials: D
authors.lastname: Vyas
authors.forename: A
authors.initials: A
authors.lastname: Kumar
authors.forename: H D
authors.initials: HD
authors.lastname: Kumar
mesh_terms: D000222:Adaptation, Physiological; D002245:Carbon Dioxide / Q000378:metabolism; D000458:Cyanobacteria / Q000254:growth & development / Q000378:metabolism / Q000528:radiation effects*; D008027:Light; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism / Q000528:radiation effects; D009591:Nitrogenase / Q000378:metabolism / Q000528:radiation effects; D010858:Pigmentation / Q000187:drug effects; D014466:Ultraviolet Rays
chemical_list: D002245:Carbon Dioxide; D009591:Nitrogenase; D009565:Nitrate Reductases; D050901:Nitrate Reductase