Calcium and Phosphate Regulation of Nitrogen Metabolism in the Cyanobacterium Spirulina platensis Under the High Light Stress |
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Authors: | DP Singh Namita Singh |
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Institution: | (1) School of Environmental Sciences, B.B.Ambedkar University, Lucknow-226025, India, IN;(2) Institute of Microbiology and Biotechnology, Barkatullah University, Bhopal-462026, India, IN |
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Abstract: | High light stress (40 W/m2)-induced alterations in the nitrogen assimilatory enzymes in Spirulina platensis were studied under the Ca2+ and phosphate (Pi)-supplemented as well as starved conditions. Results revealed that activities of nitrate reductase (NR),
amino acid transferases (AST/GOT and ALT/GPT), and protease enzymes in the high-light-incubated cells were relatively higher
under the Ca2+- and Pi-starved conditions. On the contrary, relative rates of glutamine synthetase (GS) and ATPase activities were lower
in the Ca2+- and Pi-starved cells. But the Spirulina cells under the Ca2+- and Pi-added conditions showed enhanced activity of both GS and ATPase enzymes. During the high-light stress, a decline
in the GS activity, particularly under the Ca2+- and Pi-starved conditions, was indicative of a nitrogen starvation-like condition. This could be one of the reasons for
induction of the NR and protease enzymes. A higher rate of GS activity was recorded under both the Ca2+- and Pi-supplemented conditions, perhaps owing to the enhanced rate of ATPase activity in such conditions. But a declining
pattern of both NR and protease activities in the presence of Ca2+ and Pi, despite the higher rate of ATPase activity, might involve some other mechanism like the protein-kinase system.
Received: 11 May 2000 / Accepted: 13 June 2000 |
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