In the highly inbred maize strain W64A, catalase isozyme Ct₁ is present in the developing kernels and in the dry seed stage; the Ct₂ isozyme dominates in the scutellum during germination (Scandalios, Isozymes III, p. 213-238, 1975). One catalase isozyme, observed both in meso- and epicotyls of etiolated seedlings, has a distinctive mobility on starch gel electrophoresis (Figure 1).

In our studies on the intracellular distribution of catalase isozymes in the scutellum, we found catalase to be associated with the glyoxysomes and the soluble fraction (Scandalios, J. Hered. 65:28, 1974). More recently we found, upon fractionating cells from the epicotyl, that there exists a fraction of catalase clearly associated with the mitochondria (using cytochrome oxidase as the marker enzyme)--see Figure 1. No detectable microbody marker enzymes (i.e., isocitratase) could be measured either in the crude homogenate or from the gradient. Catalase activity in the young etiolated epicotyl is only found in the mitochondrial and soluble fractions. This mitochondrial-associated catalase cannot be washed out either by buffer or by high salts. These results indicate that the intracellular distribution of catalase is dependent on the cellular metabolic environment, which is obviously different in the etiolated epicotyl and the scutellum; the mitochondrial associated catalase may be involved in functioning in the alternative oxidase pathway of mitochondria.

Figure 1.

W. F. Tong and J. G. Scandalios

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