Abstract:Sulfur dioxide (SO2 ) is one of the most common and harmful air pollutants. It results primarily from the combustion of sulfur containing fossil fuels, metallurgical processes involving sulfide ores, the production of sulfuric acid and volcanic activity. Exposure to high concentration of SO2 can induce leaf necrosis, plant growth inhibition and DNA damage in leaves and roots. However, plants adapt to environmental stresses by developing a number of mechanisms for regulation of defense response. Expression of stress responsive gene increases under rapidly changing environmental conditions, which may play important roles in regulating responses to abiotic stresses. To further understanding the adaptive mechanisms of higher plants, effects of SO2 exposure on generation of reactive oxygen species (ROS), mRNA level, isoenzymes characteristics and activities of defense enzymes were investigated in Arabidopsis thaliana (L.). By using oligoneucleotide arrays, a genomic-wide gene expression was investigated in shoots of A. thaliana Col-0. Our experiments found that 494 genes showed more than one fold difference in mRNA levels between SO2 fumigation and the control, and many defense-related genes including antioxidant defense enzymes, glutathione s-transferase (GST) and thioredoxins genes showed enhanced expression after exposure to 30 mg?m-3 SO2 for 72 h. Exposure to SO2 (2.5, 10 and 30 mg?m-3, respectively) increased O-?2 production rate and H2O2 content. Both O-?2 production and H2O2 content rised up with increasing SO2 concentration and prolonged period, demonstrating an accumulation of ROS in A. thaliana leaves. Analysis of differential protein expression carried out by detecting difference in anti-oxidative enzymes activities and the characteristics of superoxide dismutase (SOD) and catalase (CAT) isoenzymes banding patterns between SO2 fumigation and the control. Results of the present study showed that exposure to SO2 (2.5, 10 and 30 mg?m-3, respectively) induced significant increases in activities of SOD, peroxidase (POD), glutathione peroxidase (GPX) and glutathione S-transferase (GST), but decreases in activities of SOD and CAT in A. thaliana leaves exposed to 30 mg?m-3 SO2 for 72 h. Meanwhile both FeSOD and CuZnSOD isoforms increased, along with CAT2 and CAT3 isoforms decreased. Changes in both activities of anti-oxidative enzymes and characteristics of SOD and CAT isoenzyme (bands) demonstrated the differential expression levels of defense proteins in A. thaliana leaves. These results showed that SO2 caused changes in mRNA and protein expression levels of anti-oxidative defense enzymes. In addition, contents of reduced glutathione (GSH) increased significantly in A. thaliana leaves during SO2 fumigation. Our results suggest that defense response genes may have a particular function in plant adaptation to environmental change. Antioxidant therapy may play a major role in preventing SO2 damage in plant cells.