title: Effect of nickel on certain physiological and biochemical behaviors of an acid tolerant Chlorella vulgaris.
abstract: This study concerns the inhibitory effects of acid pH and nickel on growth, nutrient (NO3- and NH4+) uptake, carbon fixation, O2 evolution, electron transport chain and enzyme (nitrate reductase and ATPase) activities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with decreasing pH, the tolerant strain was found to be metabolically more active than the wild-type. A reduced cation (NH4+, Na+, K+ and Ca2+) uptake, coupled with a facilitated influx of anions (NH4+, PO4(3-) and HCO3-), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase activity at decreasing pH revealed the involvement of superactive ATPase in exporting H+ ions and keeping the internal pH neutral. A difference in Na+ and K+ efflux of the two strains at decreasing pH suggests there is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought about by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane potential and permeability not only offers protection against acidity, but also co-tolerance to metals.
authors.affiliation: Laboratory of Algal Biology, Banaras Hindu University, Varanasi, India.
authors.forename: P K
authors.initials: PK
authors.lastname: Rai
authors.forename: N
authors.initials: N
authors.lastname: Mallick
authors.forename: L C
authors.initials: LC
authors.lastname: Rai
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000838:Anions / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D002414:Cations, Monovalent / Q000378:metabolism; D002708:Chlorella / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development; D006863:Hydrogen-Ion Concentration; D009532:Nickel / Q000378:metabolism / Q000494:pharmacology*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism; D010788:Photosynthesis
chemical_list: D000838:Anions; D002413:Cations, Divalent; D002414:Cations, Monovalent; D009532:Nickel; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D000251:Adenosine Triphosphatases