PHENOL METABOLISM IN RELATION TO DISEASE RESISTANCE OF POTATO TUBER I. ACTIVTIES OF PHENOL OXIDASE AND SOME ENZYMES RELATED TO GLYCOLYSIS AS AFFECTED BY CHLOROGENIC ACID TREATMENT

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Disks of potato tubers, 0.5 mm in thickness, were treated with a mixture of chlorogenic and ascorbic acids. When they were not washed with water after the treatment,they became brown. Activities of phenol oxidase and glutathione reductase and o-diphenol content increased more rapidly in these disks than in untreated control. Activity of the pentose phosphate pathway was increased by the treatment, while that of EMDEN-MEYERHOF-PARNAS pathway was greatly inhibited. In washed unbrowned disks, the changes in those activities were negligible or smaller than those in the browned disks, although chlorogenic acid which had permeated remained in the tissue after washing. Oxidized products of chlorogenic acid and possibly of ascorbic acid may be a trigger in this alteration in metabolism. Malonate and streptomycin also induced similar effects on the phenol metabolism in the tuber disks. Increases in o-diphenol contents and in phenol oxidase activity were caused probably by preferential inhibition of EMDEN-MEYERHOF-PARNAS pathway and tricarboxylic acid cycle. These results are discussed in relation to the mechanism of disease resistance of potato tuber.