ACTA PROTOZOOLOGICA Acta Protozoologica (1995) 34: 187 - 180 Effects of UV-B Irradiation on Growth, Survival, Pigmentation and Nitrogen Metabolism Enzymes in Cyanobacteria Rajeshwar P. SINHA 13 , Har D. KUMAR 2 , Ashok KUMAR 3 and Donat-P. HADER 1 ^nstitut fur Botanik und Pharmazeutische Biologie, Friedrich-Alexander-Universitat, Erlangen, Germany; 2 Department of Botany, Banaras Hindu University, Varanasi, India; 3 School of Biotechnology, Banaras Hindu University, Varanasi, India Summary. The effects of artificial UV-B irradiation on growth, survival, pigmentation, nitrate reductase (NR), glutamine synthetase (GS) and total protein profile have been studied in a number of Infixing cyanobacterial strains isolated from rice (paddy) fields in India. Different organisms show different effects in terms of growth and survival. Complete killing of Anabaena sp. and Nostoc carmium occurs after 120 min of UV-B exposure, whereas the same occurs only after 150 min of exposure in the case of Nostoc commune and Scytonema sp. Growth patterns of the cells treated with UV-B revealed that Nostoc commune and Scytonema sp. are comparatively more tolerant than Anabaena sp. and Nostoc carmium. Pigment content, particularly phycocyanin, was severely decreased following UV-B irradiation in all strains tested so far. In vivo NR activity was found to increase, while in vivo GS activity was decreased following exposure to UV-B for different durations in all test organisms; although complete inhibition of GS activity did not occur even after 120 min of UV-B exposure. SDS PAGE analysis of the total protein profile of the cells treated with UV-B shows a linear decrease in the protein content with increase in UV-B exposure time. Complete elimination of most of the protein bands occurs after 90 and 120 min of UV-B exposure in Nostoc carmium and Anabaena sp. whereas the same occurs only after 150 min of UV-B treatment in Nostoc commune and Scytonema sp. Key words. Anabaena, cyanobacteria, glutamine synthetase, nitrate reductase, Nostoc, Scytonema, ultraviolet radiation. INTRODUCTION Cyanobacteria are phylogenetically the oldest group of oxygen evolving photosynthetic prokaryotes, which occupy an important place in both aquatic and terrestrial ecosystems (Newton et al. 1979, Dohler et al. 1986). The members of cyanobacteria are also unique in their cos- Address for correspondence: D.-P. Hader, Institut für Botanik und Pharmazeutische Biologie, Friedrich-Alexander-Universität, Staudtstr. 5, D-91058 Erlangen, Germany; Fax: 49 9131 858215; E-mail: haeder@botanik 1 -pc.biologie.uni-erlangen.de mopolitan distribution ranging from hot springs to arctic regions, and are therefore expected to face different levels of UV-B (Stanier and Cohen-Bazire 1977). Due to their capacity to utilize atmospheric nitrogen, they occupy a central position in the nutrient cycling. These nitrogen fixing organisms use the enzyme nitrogenase to convert N 2 directly into ammonium (NH 4 ), a form through which nitrogen enters the food chain. It has been estimated that cyanobacteria fix over 35 million tons of nitrogen annually (Hader et al. 1989) which is thus available for use by higher plants. The role of nitrogen fixing cyanobacteria as a natural biofertilizer, increasing http://rcin.org.pl