The nature and localization of superoxide dismutase in fronds of Lemna gibba L. and the effect of copper and zinc deficiency on its activity

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Abstract
Superoxide dismutase (SOD) is present in the fronds of Lemna gibba L. Differential centrifugation showed that ca. 90% of the enzyme is present in the 140,000 g soluble cell fraction. Lemna SOD is sensitive to cyanide and is probably a Cu‐Zn metallo‐protein. Gel filtration showed the SOD to have a mass of 31,000 daltons. In Zn‐defizient culture media, the activity of Lemna SOD was less than in fronds grown in complete nutrient media whereas in Cu‐deficient media little change was found in the enzyme activity. The SOD activity in Zn‐deficient plants could be partly restored to the level of Zn‐sufficient fronds by adding Zn2+ to the enzyme assay solution.