title: Recovery of uptake and assimilation of nitrate in Scenedesmus sp. previously exposed to elevated levels of Cu2+ and Zn2+.
abstract: A study of the effects of elevated levels of Cu2+ and Zn2+ on NO3- uptake and nitrate reductase (NR) activity in Scenedesmus sp. was carried out. The two metals inhibited NR and NO3- uptake in a concentration-dependent manner, with the latter process being inhibited more strongly than the former. After withdrawal of metal stress, NR activity and NO3- uptake recovered in a metal ion concentration-dependent manner. Dark pretreatment of the alga enhanced the toxic effects of the metal ions on NR activity and NO3- uptake. The recovery from metal stress was slower in the dark-pretreated cells in comparison to the light-pretreated cells. No recovery of NR and NO3- uptake occurred in the presence of the photosynthetic inhibitor, 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), suggesting that photosynthesis was required for the recovery from metal stress. Cycloheximide blocked the recovery of NR activity in metal-treated alga, suggesting that new enzyme synthesis was required for the recovery from metal stress.
authors.affiliation: Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi 221 005, India.
authors.forename: Bhumi Nath
authors.initials: BN
authors.lastname: Tripathi
authors.forename: Surya Kant
authors.initials: SK
authors.lastname: Mehta
authors.forename: Jai Prakash
authors.initials: JP
authors.lastname: Gaur
mesh_terms: D003300:Copper / Q000494:pharmacology*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism*; D044444:Scenedesmus / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D013997:Time Factors; D015032:Zinc / Q000494:pharmacology*
chemical_list: D009566:Nitrates; D003300:Copper; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D015032:Zinc