Abstract

The catalase molecule in germinating pumpkin cotyledons is synthesized as a precursor (59-kDa) form, whose relative molecular mass is larger than the mature enzyme (55-kDa). Although both types of molecules are localized in the microbodies, the 59-kDa species has been shown to be present predominantly in the leaf peroxisomes isolated from green cotyledons, while the 55-kDa species is predominantly in the glyoxysomes from etiolated cotyledons [Yamaguchi et al. (1984) Proc. Natl. Acad. Sci. USA, 81: 4809]. We examined the distribution of the 59- and 55-kDa catalase molecules in dark- and light-grown tissues of pumpkin seedlings as well as in other plant species, using the immunoblotting technique. The ratios of the 59- and 55-kDa catalase species differed in the pumpkin tissues examined. Light interferes with the conversion of the 59-kDa precursor to the 55-kDa form, especially in the cotyledons. The effect of light was less pronounced in the roots and hypocotyls, indicating that the light regulation of the conversion is tissue-specific. Dark- and light-grown cotyledons from cucumber and watermelon seedlings showed a similar light regulation, suggesting that cucurbitaceous plants possess similar light-regulatory mechanism. From the analysis of catalase protein from various plant tissues, a limited correlation between molecular forms of catalase and different microbody populations was observed.

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