The Cytochemical Localization of Peroxidase in Tomato Fruit Cells

The localization of peroxidase activity a t the ultrastructural level in tomato fruit (Lycopersicon esculentum Mill cv. Walters) has been accomplished using the diaminobenzidine histochemical reaction. In immature tomato fruit the peroxidase activity was most prominent at the inner surface of the tonoplast, although some cell wall activity was observed. However, in mature tomato fruit most of the peroxidase activity was localized in the cell wall. No activity was found in organelles or in the cytoplasm of either immature or mature fruit. The significance of these observations is discussed in relation to the physiological role of the enzyme in fruit ripening.