Polarity of Production of Polyphenols and Development of Various Enzyme Activities in Cut-injured Sweet Potato Root Tissue

Investigation of polyphenol production in cut-injured sweet potato (Ipomoea batatas Lam. cv. Kokei 14) roots by histochemical and quantitative methods showed that polyphenols were produced in striking amounts in the proximal side of the tissue pieces (2 cm thick), but only in small amounts in cells of the distal side. In response to cut injury, formation of the enzymes related to polyphenol biosynthesis, phenylalanine ammonia-lyase and trans-cinnamic acid 4-hydroxylase, was also pronounced in the proximal side of the tissue pieces and slight in the distal side. The similar polarity was observed in the development of activities of various enzymes, such as NADPH-cytochrome c oxidoreductase, acid invertase, peroxidase, o-diphenol oxidase, and cytochrome c-O(2) oxidoreductase. Acropetal development of polyphenol contents and of various enzyme activities may be related to the acropetal movement of indoleacetic acid (IAA) in roots of various plants. Treatment of the distal surface of tissue pieces with IAA or 2,4-dichlorophenoxyacetic acid caused polyphenol production but treatment with gibberellic acid, abscisic acid, kinetin, or ethylene had little effect. The results suggest that IAA may play a role in the metabolic response to cut injury.