Calcium and phosphate regulation of nitrogen metabolism in the cyanobacterium Spirulina platensis under the high light stress.
High light stress (40 W/m(2))-induced alterations in the nitrogen assimilatory enzymes in Spirulina platensis were studied under the Ca(2+) 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 Ca(2+)- and Pi-starved conditions. On the contrary, relative rates of glutamine synthetase (GS) and ATPase activities were lower in the Ca(2+)- and Pi-starved cells. But the Spirulina cells under the Ca(2+)- 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 Ca(2+)- 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 Ca(2+)- 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 Ca(2+) and Pi, despite the higher rate of ATPase activity, might involve some other mechanism like the protein-kinase system.
Singh
D P
DP
School of Environmental Sciences, B.B.Ambedkar University, Lucknow-226025, India.
Singh
N
N
D000251:Adenosine Triphosphatases / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000458:Cyanobacteria / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects*; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D010710:Phosphates / Q000378:metabolism*; D014166:Transferases / Q000378:metabolism
D010710:Phosphates; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D014166:Transferases; D000251:Adenosine Triphosphatases; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen; D002118:Calcium