Effect of Sulfur Dioxide on ROS Production, Gene Expression and Antioxidant Enzyme Activity in Arabidopsis Plants

Sulfur dioxide (SO(2)) is one of the most common and harmful air pollutants. To analyze antioxidant response of plants to SO(2) stress, we investigated the reactive oxygen species (ROS) levels, transcript alterations and antioxidant enzyme activities in Arabidopsis thaliana (Col-0) exposed to 0, 2.5, 10 and 30 mg m(-3) of SO(2). The results showed that both superoxide radical (O(2)(-⋅)) generation rate and hydrogen peroxide (H(2)O(2)) content increased in SO(2)-treated Arabidopsis shoots. GeneChip and RT-PCR analysis revealed that transcript levels of peroxidase (POD), glutathione peroxidase (GPX) and superoxide dismutase (SOD) genes enhanced after exposure to 30 mg m(-3) SO(2) for 72 h. The content of glutathione and activities of SOD, POD and GPX increased significantly during 72 h of SO(2) exposure. However, catalases (CAT) activity changed slightly under SO(2) stress. Furthermore, the results of in-gel enzyme assays indicated that SOD (FeSOD and Cu/ZnSOD) and POD isoforms increased after exposure to SO(2) for 72 h, whereas two CAT isoforms (CAT2 and CAT3) declined. Malondialdehyde content kept at a low level within 72 h of SO(2) exposure, but increased significantly after exposure to 30 mg m(-3) SO(2) for 120 h along with decrease in the level of ROS and activities of SOD and GPX. Our results indicated that increased ROS may act as a signal to induce defense response to SO(2) stress. Antioxidant status plays an important role in plant protection against SO(2)-caused oxidative stress, though the defense capacity cannot sufficiently alleviate oxidative damage occurring under prolonged exposure to higher concentrations of SO(2).