Localization of polyphenol oxidase activity in the lamellae and membrane-bound inclusions of etiolated soybean hypocotyl chloroplasts

Abstract

Localization for polyphenol oxidase was carried out on 6-day-old etiolated soybean (Glycine max (L.) Merr.) tissue. Light and electron microscope observations of tissues exposed to the substrate L-dihydroxyphenylalanine after chemical fixation revealed that polyphenol oxidase activity was present in the lamellae and membrane-bound inclusions of chloroplasts. Inhibitors of polyphenol oxidase, diethyldithiocarbamate and phenylhydrazine, prevented formation of the reaction product. Only plastids in epidermal and associated cortex collenchyma cell layers contained inclusions and enzyme activity. Most guard cells and all cortex parenchyma cells were devoid of both. Homogenates of epidermal strips were shown to contain 95–99% of the total polyphenol oxidase activity present in hypocotyls.