| In experimental condition, antioxidant defense system, lipid peroxidation and DNA damage in the digestive gland and gill of the oyster Ostrea cucullata were measured after the oyster were exposed to water soluble fraction of 0# diesel oil at concentrations of 0.5, 2, 5 mg/L. Samples were collected in exposure time of 1, 4, 7, 11 and 15 days. A field investigation was explored in Xiamen island and coastal area nearby, the oysters were collected from four stations: Lundu port> Xinlin bay -. Tong'an bay and Huangcuo, to research the relation between the petroleum hydrocarbon level and the antioxidant defense system. The measured parameters of antioxidant defense system included antioxidant enzymes, superoxidant dismutase (SOD), catalase (CAT), selenium dependent glutathione peroxidase (Se-GPx) and glutathione S-transferase (GST); water-solubility antioxidant, glutathione (GSH). DNA single strand break was analyzed as index of DNA damage. The results showed:1. Antioxidant defense system distribution was different in the digestive gland and gill. In digestive gland, SOD, CAT activity and GSH content were higher than gill, but Se-GPx and GST activity were reversed, hi normal condition, DNA damage and lipid peroxidation also occured hi the digestive gland and gill, there was no significant difference of DNA damage degree between the digestive gland and gill, but the lipid peroxidation hi digestive gland was more serious than gill.2. There was little change in the oyster exposed to low concentration WSF, only the induction of GST and the depletion of GSH were observed in the terminal exposure time. In medium and high concentration WSF group, GSH was the most sensitive response to petroleum hydrocarbon pollution, Se-GPx, GST, CAT activity also had significant changes, but the change of SOD activity was only found in the oyster gill exposed to high level WSF group in the terminal exposure time. After the oyster were deprived of pollution for 6 days, all the biochemical parameters recovered to the control level, except GSH content. The results indicated that the GSH and GSH-dependent enzymes had the most important role in againsting the oxidative stress caused by petroleum hydrocarbon pollution. The dose-effect and tune-effect relations were between the biochemical response and petroleum hydrocarbon pollution. Different biochemical response showed different dose-effect pattern, and dependented on the exposure time. The time-effect pattern of antioxidant defense system was increase first then decrease, the increase was an adaptive reponse to petroleum hydrocarbon pollution, and the decrease showed the toxicity of pollution. The exposures caused a time-dependent enhancement in DNA single strand break and lipid peroxidation degree, and there was relativity between lipid peroxidation and GSH content and DNA single strand break.3. The variety of antioxidant defense system caused by petroleum hydrocarbonpollution was a kind of time-dependent ordinal change. The first change was happened in GSH content, and then GST, Se-GPx, CAT, in turn, SOD activity was induced in 11 days. The biochemical response first altered could reflect the initial site on which the pollutant effect organism and the first defense mechanism of organism, the subsequent change could imply how the toxicity of pollutant spread and deepen, and the arrangement of defense mechanism. The inductivity of antioxidant defense system exposed to petroleum hydrocarbon pollutant was different in the digestive gland and gill, but it was hard to say which tissue is more sensitive.4. The content of petroleum hydrocarbon in oyster collected from four stations (Lundu port, Xinlin bay, Tong'an bay, Huangcuo) were 380.68. 112.34. 27.3 K 20.37 v g/g wet, respectively. The antioxidant defense system improved with the increase of petroleum hydrocarbon level in oyster, the biggest amplification was found in GST activity and the smallest was GSH content. All the antioxidant enzymes measured had a good positive relative with the petroleum hydrocarbon level, ex...
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