Recovery of uptake and assimilation of nitrate in Scenedesmus sp. previously exposed to elevated levels of Cu2+ and Zn2+.
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.
Tripathi
Bhumi Nath
BN
Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi 221 005, India.
Mehta
Surya Kant
SK
Gaur
Jai Prakash
JP
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*
D009566:Nitrates; D003300:Copper; D009565:Nitrate Reductases; D050901:Nitrate Reductase; D015032:Zinc