Oxidative Modification Of Metallothionein In Earthworm Under Cadmium Stress

With the development of the industry and application of agricultural chemicals, heavy metal pollution of soil becomes increasingly serious in China. Cadmium(Cd) is one of the most toxic heavy metals, which seriously threatens the propagation growth and the human health. Earthworm is an important invertebrate in soil. MT in earthworms plays a role in detoxication, for it can bind abundant heavy metals. However, studies have shown that sulfhydryl (-SH) in metalothionein can be oxidized into disulfide bonds (S-S) with the release of heavy metal ions under physiological conditions and oxidative stress. So far little research has been conducted in oxidative modification of protein caused by soil pollution. So to strengthen research in this area has significance in developing new biomakers and providing early warning of soil pollution, which can also provide a theoretical basis for prevention and restoration of soil pollution. Therefore, we studied the impact of Cd on the oxidative modification of earthworm MT, through chronic toxicity test of soil. The major results showed as follows.1Impact of Cd on the content of MT in earthwormResults showed that the content of MT increased significantly with the increase of Cd concentration and exposure time in total. Cd concentration played the most important role among Cd concentration, exposure time and dosage. The content of MT remained unchanged during the first7days in all earthworms exposed to different concentrations of Cd, however, after14and21days the contents of MT changed significantly. This would suggest that there is a lag time between Cd exposure and induction. The content of MT in earthworms of control group remained unchanged with a certain background content of MT, while groups exposed to100and300mg·kg-1changed significantly. This concluded that the inducement of MT is a physiological responses to Cd stress.2Impact of Cd on oxidative modification of MT in earthwormResults showed that a part amounts of-SH had been oxidized into S-S before Cd was added into the soil. This may be related to the soil containing0.92mg·kg-1Cd, and it also indicated that there was a dynamic balance between-SH and S-S in earthworm. The contents of-SH and S-S increased with the Cd additions, however, the proportion of S-S in the total-SH decreased, suggesting that with the the extent of MT oxidative modification didn’t increase but preventing Cd toxicity.