title: Effects of UV-B and heavy metals on nitrogen and phosphorus metabolism in three cyanobacteria.
abstract: Cyanobacteria sp. (diazotrophic and planktonic) hold a major position in ecosystem, former one due to their intrinsic capability of N2-fixation and later because of mineralization of organic matter. Unfortunately, their exposure to variety of abiotic stresses is unavoidable. Comparative analysis of interactive effect of UV-B and heavy metals (Cd/Zn) on nitrogen and phosphorus metabolism of three cyanobacteria (Anabaena, Microcystis, Nostoc) revealed additive inhibition (χ(2) significant p < 0.05) of NH4(+) and PO4(3-) uptake whereas increase in nitrate uptake upon UV-B + heavy metal exposure. Glutamine synthetase and Alkaline phosphatase activity was reduced after all treatments whereas Nitrate reductase activity showed slight stimulation in UV-B and UV-B + heavy metals treatment. Combination of UV-B and metals seems more detrimental to the NH4(+), PO4(3-) uptake, GS and APA activity. A significant stimulation in NO3(-) uptake and NR activity following exposure to UV-B in all the three cyanobacteria suggests UV-B-induced structural change(s) in the enzyme/carriers. Metals seem to compete for the binding sites of the enzymes and carriers; as noticed for Anabaena and Microcystis showing change in Km while no change in the Km value of Nostoc suggests non-competitive nutrient uptake. Higher accumulation and more adverse effect on Na(+) and K(+) efflux proposes Cd as more toxic compared to Zn.
authors.affiliation: Molecular Biology Section, Center of Advanced Study in Botany, Banaras Hindu University, Varanasi, India.
authors.forename: Shivam
authors.initials: S
authors.lastname: Yadav
authors.affiliation: MMV, Banaras Hindu University, Varanasi, India.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Prajapati
authors.affiliation: MMV, Banaras Hindu University, Varanasi, India.
authors.forename: Neelam
authors.initials: N
authors.lastname: Atri
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D002857:Chromium / Q000378:metabolism; D000458:Cyanobacteria / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000528:radiation effects; D057075:Enzyme Assays; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism; D019216:Metals, Heavy / Q000494:pharmacology*; D050901:Nitrate Reductase / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D009586:Nitrogen Fixation / Q000187:drug effects / Q000528:radiation effects; D010758:Phosphorus / Q000378:metabolism*; D014466:Ultraviolet Rays
chemical_list: D019216:Metals, Heavy; D009566:Nitrates; D002857:Chromium; D010758:Phosphorus; D050901:Nitrate Reductase; D000469:Alkaline Phosphatase; D005974:Glutamate-Ammonia Ligase; D009584:Nitrogen
keywords: Alkaline phosphatase (APA); Anabaena; Glutamine synthetase (GS); Microcystis; Nitrate reductase (NR); Nostoc