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

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Abstract
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.