title: Chronic toxicity and responses of several important enzymes in Daphnia magna on exposure to sublethal microcystin-LR.
abstract: In the current study, the toxicological mechanisms of microcystin-LR and its disadvantageous effects on Daphnia magna were examined. Survival rate, number of newborn, activity of several important enzymes [glutathione S-transferase (GST), lactate dehydrogenase (LDH), phosphatases, and glutathione], accumulated microcystins, and ultrastructural changes in different organs of Daphnia were monitored over the course of 21-day chronic tests. The results indicated that low concentrations of dissolved microcystin had no harmful effect on Daphnia. On the contrary, stimulatory effects were detected. In the presence of toxin at high dosage and for long-term exposure, GST and glutathione levels decreased significantly. The decreased enzyme activity in the antioxidant system probably was caused by detoxification reactions with toxins. And these processes of detoxification at the beginning of chronic tests may enable phosphatases in Daphnia magna to withstand inhibition by the toxins. At the same time, we also found that the LDH activity in test animals increased with exposure to microcystin-LR, indicating that adverse effects occurred in Daphnia. With microcystin given at a higher dosage or for a longer exposure, the effect on Daphnia magna was fatal. In the meantime, microcystin began to accumulate in Daphnia magna, and phosphatase activity started to be inhibited. From the ultrastructure results of cells in D. magna, we obtained new information: the alimentary canal may be the target organ affected by exposure of microcystins to D. magna. The results of the current study also suggested that the oxidative damage and PPI (protein phosphatase inhibition) mechanisms of vertebrates also are adapted to Daphnia.
authors.affiliation: State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei 430072, People's Republic of China.
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Lirong
authors.initials: L
authors.lastname: Song
authors.forename: Danyun
authors.initials: D
authors.lastname: Ou
authors.forename: Nanqin
authors.initials: N
authors.lastname: Gan
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D003621:Daphnia / Q000201:enzymology*; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000633:toxicity*; D041981:Gastrointestinal Tract / Q000201:enzymology; D005978:Glutathione / Q000032:analysis; D005982:Glutathione Transferase / Q000032:analysis; D008387:Marine Toxins; D052998:Microcystins; D018384:Oxidative Stress; D010456:Peptides, Cyclic / Q000493:pharmacokinetics / Q000494:pharmacology* / Q000633:toxicity*; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism; D013534:Survival
chemical_list: D004791:Enzyme Inhibitors; D008387:Marine Toxins; D052998:Microcystins; D010456:Peptides, Cyclic; D005982:Glutathione Transferase; D010749:Phosphoprotein Phosphatases; C057862:cyanoginosin LR; D005978:Glutathione