One of the sources of hydrogen peroxide in plant tissues is the oxidation of glycolate. During the processes of photosynthesis glycolate is synthesized in chloroplasts and oxidized by glycolate oxidase after being transported into peroxisomes. Since photosynthesis provides substrates of glycolate oxidation, green leaves get more hydrogen peroxide than etiolated leaves. Therefore, it is reasonable to find more catalase present in peroxisomes of green leaves than in etiolated leaves.
The highly inbred maize strain W64A was used in these experiments to determine the subcellular distribution of catalase during the development of seedlings. The leaves of 5-day or 6-day-old green and etiolated seedlings were used to prepare homogenates separately for sucrose density gradient centrifugation. Catalase activity was found in peroxisomal and soluble fractions as expected, but in addition it was also found in the mitochondrial fractions. Green leaves have higher catalase activity in the peroxisomal fraction than the etiolated leaves (Table 1). The ratio of catalase activity in green leaves to that of etiolated leaves indicates that the effect of light is greater on the peroxisomes than on the mitochondrial and soluble fractions (Table 2). These results suggest that peroxisome development in light is one of the factors which elevate catalase activity in corn leaves, although there may be some other mechanisms involved. The genetic control and physiological function of the compartmentalized catalases is being investigated.
D. Y. Chang and John G. Scandalios
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