Ultrastructural localization of polyphenoloxidase and peroxidase in roots and hypocotyls of cotton seedlings

Abstract

Polyphenoloxidase and peroxidase were localized and differentiated from each other in the roots and hypocotyls of cotton when these tissues were treated with dihydroxyphenylalanine (DOPA) and diaminobenizidine (DAB), respectively. The DOPA reaction occurred in the thylakoids of plastids from the endodermis of the root and in plastids from several tissues of the hypocotyl. The reaction was inhibited by diethyldithiocarbamate (DIECA), but catalase had no effect. An intense DAB reaction occurred in the epidermal, subepidermal, and endodermal cell walls of both roots and hypocotyls with a lesser reaction in the cortex and stele. DAB also caused a reaction in the microbodies in cells of all tissues, but a reaction could not be detected in other organelles. Aminotriazole (AT) inhibited the reaction in the microbodies but not in the cell walls, whereas the reaction was prevented entirely if H₂O₂ was eliminated from the medium. These results indicate that the two enzyme systems are localized in different and discrete areas in the cotton tissue and that the plastids are intimately involved in phenolic metabolism.