Abstract
Abstract Background In this study, we investigated transcription and enzyme level responses of mussels Mytilus galloprovincialis exposed to hypoxic conditions. Genes for catalase (CAT), cytochrome P450, glutathione S-transferase (GST), metallothionein, superoxide dismutase (SOD), cytochrome c oxidase subunit 1 (COX-1), and NADH dehydrogenase subunit 2 were selected for study. Transcriptional changes were investigated in mussels exposed to hypoxia for 24 and 48 h and were compared to changes in control mussels maintained at normal oxygen levels. Activities of CAT, GST, and SOD enzymes, and lipid peroxidation (LPO) were also investigated in mussels following exposure to hypoxia for 24, 48, and 72 h. Results Relative to the control group, the CAT activity decreased in all hypoxia treatments, while the activity of GST significantly increased in mussels exposed to hypoxia for 24 and 48 h, but decreased in those exposed for 72 h. The LPO levels were significantly higher in mussels in the 24- and 48-h hypoxia treatments than those in the control mussels, but there was no significant change in the SOD activities among all hypoxia treatments. Messenger RNA levels for the CAT, cytochrome P450, GST, metallothionein, and SOD genes were not significantly affected by hypoxic conditions for 48 h, but the expressions of the COX-1 and NADH dehydrogenase subunit 2 genes were significantly repressed in mussels in both the 24- and 48-h exposure treatments. Conclusions These results demonstrate the transcriptional stability and changes among several genes related to oxidative stress under oxygen-depletion conditions in M. galloprovincialis and provide useful information about the modulation of antioxidant enzyme activities induced by hypoxia in a marine animal.
Highlights
In this study, we investigated transcription and enzyme level responses of mussels Mytilus galloprovincialis exposed to hypoxic conditions
Twelve mussels were exposed to 2 mg/L of dissolved oxygen (DO) for 10 days in a water tank, while a control group of mussels was maintained in natural seawater
60% of the mussels in the 2 mg/L DO treatment had died after 7 days, and a further 33% had died after 10 days (Figure 2)
Summary
We investigated transcription and enzyme level responses of mussels Mytilus galloprovincialis exposed to hypoxic conditions. Hypoxia is often caused by excessive anthropogenic inputs of nutrients and Hypoxia and anoxia generally occur in near-bottom waters of coastal zones and estuaries, and are often associated with eutrophication, microbial respiration, and oxygen depletion (Diaz and Rosenberg 2008). In severe cases, such oxygen depletion may lead to ‘dead zones’ where mass mortalities of benthic organisms occur. Nutrient runoff into aquatic environments can stimulate plant growth and lead to algal blooms (Justic et al 1993). The algae eventually die and are subject to oxidative decay by microorganisms, which results in the depletion of DO, which in turn can lead to hypoxia or dead zones in aquatic environments
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