DIFFERENTIAL RESPONSE OF CU,ZN SUPEROXIDE DISMUTASES IN 2 PEA CULTIVARS DURING A SHORT-TERM EXPOSURE TO SULFUR-DIOXIDE

Pea cultivars Progress and Nugget have been shown previously to be dif ferentially sensitive with respect to apparent photosynthesis in a sho rt-term exposure to 0.8 mu l/l SO2. One possible contributing factor t o the relative insensitivity of apparent photosynthesis of Progress to SO2 is an increase in superoxide dismutase (SOD) activities. We show here that both chloroplastic and cytoplastic Cu,Zn-SOD proteins increa sed in Progress on exposure to sulfur dioxide whereas both proteins de creased in Nugget. The increase in cytosolic Cu,Zn-SOD protein was gre ater than that of chloroplastic Cu,Zn-SOD protein. Using a gene-specif ic probe for the plastid SOD, northern blot analysis revealed an initi al decrease in transcript abundance of the chloroplastic Cu,Zn-SOD gen e in Progress on exposure to SO, with an eventual recovery to pre-expo sure levels. The transcript levels of the chloroplastic Cu,Zn-SOD decr eased in Nugget over the time period of the exposure. These results su ggest that a combination of translational and post-translational mecha nisms may be involved in SO2-induced changes in cytosolic and plastidi c Cu,Zn-SODs in pea.