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Physiology and Biochemistry

Induction of Rishitin-Metabolizing Activity in Potato Tuber Tissue Disks by Wounding and Identification of Rishitin Metabolites. Y. Ishiguri, Plant Pathology Laboratory, Faculty of Agriculture, Nagoya University, Japan; K. Tomiyama(2), N. Doke(3), A. Murai(4), N. Katsui(5), F. Yagihashi(6) and T. Masamune(7). (2)(3)Plant Pathology Laboratory, Faculty of Agriculture, Nagoya University, Japan; (4)(5)(6)(7)Department of Chemistry, Faculty of Science, Hokkaido University, Japan. Phytopathology 68:720-725. Accepted for publication 13 October 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-720.

Rishitin, the phytoalexin of potato, was metabolized by fresh and aged potato-tuber disks. In aged disks, radioactivity of rishitin-14C began to decrease almost simultaneously after incubation with rishitin-14C and continued to decrease at the rate of 3.6 μg rishitin/g fresh wt/hr. The decrease in radioactivity of rishitin-14C was accompanied by an increase in radioactivity in the ether-soluble fraction (minus rishitin) and then followed by that in the water-soluble fraction. In fresh disks, on the contrary, there was a lag of a few hours before the initiation of decrease in radioactivity of rishitin-14C. These results suggest that intact potato tissue has little activity to metabolize rishitin, but that the activity was induced by wounding. Two 14C-labeled compounds were isolated from the ether-soluble metabolites of rishitin in tuber tissue treated with 14C-rishitin. They were identified as rishitin-M-1 and rishitin-M-2 on the basis of R1 values after thin-layer chromatography (TLC), autoradiography, and color reactions after two-dimensional TLC.

Additional keywords: potato late blight.