Tripathi B N, Mehta S K, Amar Anshu, Gaur J P
Laboratory of Algal Biology, Department of Botany, Banaras Hindu University, Varanasi 221 005, India.
Chemosphere. 2006 Jan;62(4):538-44. doi: 10.1016/j.chemosphere.2005.06.031. Epub 2005 Aug 9.
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.
藻类通常长期暴露于水体中高水平的重金属，偶尔也会短期暴露。本研究探讨了在富营养淡水中常见的栅藻属在短期（6小时）和长期（7天）暴露于铜离子（Cu(2+)）和锌离子（Zn(2+)）期间的氧化应激情况。与短期暴露于这些金属相比，长期暴露时细胞内积累的铜离子和锌离子几乎多2倍和4倍。但关于光合放氧和细胞活力的数据表明，栅藻属在长期实验中经历的金属应激比短期实验中要小。虽然长期实验中丙二醛含量略高，但每单位细胞内金属产生的丙二醛量明显低于短期实验。栅藻属的超氧化物歧化酶活性在长期暴露于铜离子和锌离子时比短期暴露时高30%以上。但是，过氧化氢酶和抗坏血酸过氧化物酶活性仅在氧化应激较轻的2.5微摩尔铜离子和25微摩尔锌离子时增加，而在强烈氧化应激下的10微摩尔铜离子时受到抑制。在两个实验中，铜离子和锌离子均降低了栅藻属的谷胱甘肽还原酶活性和总巯基含量，长期实验中的降低幅度更大。总巯基的消耗与细胞内金属水平呈正相关。巯基可能有助于栅藻属克服金属诱导的氧化应激，但已知巯基库的消耗会使细胞易受氧化应激影响。该研究表明抗氧化酶仅在轻度氧化应激下起作用。脯氨酸积累增加似乎是减轻栅藻属中金属诱导的氧化应激的重要策略。该研究表明栅藻属在长期暴露于测试金属的有毒浓度时能够适应。
