摘要 : 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 nutrie... 展开 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- (6 h) and long-term (7d) exposure to Cu2+ and Zn2+. The cells accumulated almost 2- and 4times more Cu2+ and Zn2+ inside the cells during long-term than during short-term exposure to these metals. But the data on photosynthetic 02 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 Scenedestnus sp. was > 30% higher during long-term than during short-term exposure to Cu2+ and Zn2+. But, catalase and ascorbate peroxidase activities increased only at 2.5 mu M Cu2+ and 25 mu M Zn2+ when oxidative stress was mild, but were inhibited at 10 mu M Cu2+ under intense oxidative stress. Cu2+ and Zn2+ reduced glutathione reductase activity and total SH content of Scenedesinus 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 antioxiclant 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 Scenedesinus sp. The study shows that Scenedesinus sp. could acclimatize during long-term exposure to toxic concentrations of the test metals. (c) 2005 Elsevier Ltd. All rights reserved. 收起