Induction of Rishitin-Metabolizing Activity in Potato Tuber Tissue Disks by Wounding and Identification of Rishitin Metabolites

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Abstract
Rishitin, the phytoalexin of potato, was metabolized by fresh and aged tuber disks [of potato resistant to Phytophthora infestans]. In aged disks, radioactivity to rishitin-14C began to decrease almost simultaneously after incubation with rishitin-14C and continued to decrease at the rate of 3.6 .mu.g rishitin/g fresh wt per h. The decrease in radioactivity of rishitin-14C was accompanied by an increase in radioactivity in the ether-soluble fraction (minus rishitin), then followed by that in the water-soluble fraction. In fresh disks 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 based on the Rf values after TLC, autoradiography and color reactions after 2-dimensional TLC.

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