Oxidative stress in Arabidopsis thaliana exposed to cadmium is due to hydrogen peroxide accumulation

We have developed a Cd-resistant type (RT) from a Cd-sensitive wild-type (WT) of Arabidopsis thalaiana, and seedlings were grown on MS medium containing up to 500 μM of CdCl2 to study the relationship between Cd-induced phytoxicity and oxidative stress. Compared to WT, RT showed a higher level of survival, and lower hydrogen peroxide and lipid peroxidation levels expressed as thiobarbituric acid reacting substances (TBARS) production. These results indicate that RT seedlings experienced lower oxidative stress from Cd exposure. Furthermore, compared to WT, RT had significantly higher activities of superoxide dismutase (SOD and enzymes related to hydrogen peroxide removal such as guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR). The differential between the responses of WT and RT seedlings to Cd suggests that Cd-induced phytotoxicity can be induced by hydrogen peroxide accumulation and subsequent oxidative stress. The results also imply that a lower hydrogen peroxide accumulation confers Cd-tolerance in seedlings.