Localization of superoxide dismutase in leaves of C3 and C4 plants

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Abstract
Chloroplasts, mitochondria and cytoplasm, isolated from pea, wheat, maize and sorghum mesophyll protoplasts, contain distinct forms of superoxide dismutase (SOD). In all species evaluated, chloroplasts exhibited a single cyanide-sensitive SOD. This chloroplastic enzyme was the most anionic SOD observed in whole leaf and protoplast extracts and constitutes 50–80% of the total soluble SOD. Pea and wheat protoplasts had only one cytoplasmic SOD, a cyanide-sensitive form of intermediate mobility; maize and sorghum had two such cytoplasmic enzymes. A single cyanide-insensitive SOD was present in extracts from both C3 and C4 tissues and was associated with mitochondria. Although bundle sheath cells of sorghum and maize are known to be deficient in Photosystem II, there was no apparent difference in SOD between mesophyll and bundle sheath cells. Mesophyll protoplasts and bundle sheath strands from these C4 plants contained the same forms of SOD. Levels of soluble SOD were similar, on a chlorophyll basis, in the two cell types as was distribution of activity among the various forms of the enzyme.