CATALASE AND SUPEROXIDE-DISMUTASE GENE-EXPRESSION AND DISTRIBUTION DURING STEM DEVELOPMENT IN MAIZE

The temporal and spatial patterns of expression of the Cat and Sod genes encoding the multiple catalases and superoxide dismutases in maize have been examined throughout stem development. Three stages of stem development have been defined based upon catalase activity profiles and stem internode elongation. At stage 1, catalase activity is low and internodes remain short; at stage 2, catalase activity dramatically increases and internodes rapidly elongate; and at stage 3, catalase activity decreases to levels intermediate to stage 1 and 2, and internode elongation ceases. Zymogram analysis and immunoassays show that only the CAT-3 catalase isozyme is present in the stem, even though both Cat1 and Cat3 mRNAs accumulate throughout stem development. Cat2 mRNA is not detectable in the developing stem. In full-grown stems catalase is localized primarily in the sclerenchyma beneath the epidermis and around the vascular bundles and may possibly play a role in lignification. Unlike catalase, all the superoxide dismutase (SOD) isozymes and transcripts are present in the developing stem. Thus, these two major antioxidant gene-enzyme systems show differential patterns of expression during stem development in maize.