Cytochemical localization of peroxidase activity in root cells

The distribution of peroxidase in the apical 3 mm of pea roots has been investigated using the histochemical method employing 3,3-diaminobenzidine as a substrate. At the tissue level the enzyme is localized predominately in the root cap, epidermis, inner cortical cells, endodermis, phloem and maturing xylem. At the subcellular level peroxidase is found mainly in the intercellular regions of the cortex cell walls and in the cytoplasm and vacuoles of the steler cells. Root microbodies, unlike those of leaves, do not appear to be able to oxidize this substrate. The significance of these observations is discussed in relation to the validity of the technique and the proposed roles of the enzyme in cellular metabolism.