Synthesis of Isozymes of Superoxide Dismutase in Maize Leaves in Response to O3, SO2and Elevated O2

Matters, G. L. and Scandalios, J. G. 1987. Synthesis of isozymes of superoxide dismutase in maize leaves in response to O3 SO2 and elevated O2.—J. exp. Bot 38: 842–852. The activities of the enzymes superoxide dismutase (SOD) and catalase were determined in maize leaves treated with O3or SO2for 8 h, or with elevated levels of oxygen for up to 96 h. Neither O3nor SO2significantly increased the levels of superoxide dismutase or catalase activity. However, after 72 h in an atmosphere containing 90% oxygen, superoxide dismutase activity was increased, but not the activities of catalase, ascorbate pcroxidase, and malate dehydrogenase. Immunological analysis showed that amounts of the cytosolic superoxide dismutase isozymes, SOD-2 and SOD-4, were increased by the elevated oxygen but not the chroloplast (SOD-1) or mitochondrial (SOD-3) isozymes. Immunoprecipitation of translation products of leaf polysomes indicated that the higher levels of SOD-2 and SOD-4 were due to increased amounts of polysome-bound mRNA coding for these proteins. The specific response of SOD-2 and SOD-4 to 90% oxygen treatments contrasts with the increase in all SOD isozymes in maize leaves treated with the herbicide paraquat.