title: Oxidative stress in Scenedesmus sp. during short- and long-term exposure to Cu2+ and Zn2+.
abstract: Algae are exposed to elevated levels of heavy metals in water bodies generally for a long-term, and occasionally for a short-term duration. The present study deals with oxidative stress in Scenedesmus sp., commonly found in nutrient-rich freshwaters, during short- (6h) and long-term (7d) exposure to Cu(2+) and Zn(2+). The cells accumulated almost 2- and 4-times more Cu(2+) and Zn(2+) inside the cells during long-term than during short-term exposure to these metals. But the data on photosynthetic O(2) evolution and cell viability suggest that Scenedesmus sp. experienced lesser metal stress in long-term than in short-term experiment. Although malondialdehyde content was slightly higher in the long-term experiment, the amount produced by one unit intracellular metal was significantly lower than that in the short-term experiment. Superoxide dismutase activity of Scenedesmus sp. was >30% higher during long-term than during short-term exposure to Cu(2+) and Zn(2+). But, catalase and ascorbate peroxidase activities increased only at 2.5 microM Cu(2+) and 25 microM Zn(2+) when oxidative stress was mild, but were inhibited at 10 microM Cu(2+) under intense oxidative stress. Cu(2+) and Zn(2+) reduced glutathione reductase activity and total SH content of Scenedesmus sp. in both the experiments, with greater reduction occurring in the long-term experiment. The depletion of total thiol was positively related with the intracellular level of metals. Thiols might have helped Scenedesmus sp. in overcoming metal-induced oxidative stress, but depletion of thiol pool is known to make cells vulnerable to oxidative stress. The study suggests that antioxidant enzymes play a role only under mild oxidative stress. An increased accumulation of proline seems to be an important strategy for alleviating metal-induced oxidative stress in Scenedesmus sp. The study shows that Scenedesmus sp. could acclimatize during long-term exposure to toxic concentrations of the test metals.
authors.affiliation: Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi 221 005, India.
authors.forename: B N
authors.initials: BN
authors.lastname: Tripathi
authors.forename: S K
authors.initials: SK
authors.lastname: Mehta
authors.forename: Anshu
authors.initials: A
authors.lastname: Amar
authors.forename: J P
authors.initials: JP
authors.lastname: Gaur
mesh_terms: D003300:Copper / Q000032:analysis / Q000633:toxicity*; D015227:Lipid Peroxidation / Q000187:drug effects; D018384:Oxidative Stress; D010088:Oxidoreductases / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D011392:Proline / Q000378:metabolism; D044444:Scenedesmus / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000633:toxicity*; D015032:Zinc / Q000032:analysis / Q000633:toxicity*
chemical_list: D014874:Water Pollutants, Chemical; D003300:Copper; D011392:Proline; D010088:Oxidoreductases; D015032:Zinc; D010100:Oxygen