Biological activities of rishitin, an antifungal compound isolated from diseased potato tubers, and its derivatives

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Rishitin, a norsesquiterpene alcohol, found in infected, resistant potato-tuber tissue completely inhibited zoospore germination and germtube elongation of Phytophthora infestans (MONT) DE BARY at 10^<-3>M. There was little difference in sensitivity to rishitin among races of Phytophthora infestans. IAA-induced elongation of Avena coleoptile sections and GA_3-induced elongation of wheat leaf sections were also inhibited by rishitin. The inhibition of IAA-induced elongation of Avena coleoptiles was relieved to some extent by increasing IAA concentration. However, little relief of the inhibition of GA_3-induced elongation of wheat leaf sections was obtained by increasing GA_3 concentration. No plant injury was observed ~t this concentration of rishitin (10^<-3>M). Examination of a series of rishitin derivatives indicated that the hydroxyl group at C-3 is indispensable for antifungal activity. This activity was intensified by saturating the double bond between the rings of rishitin and/or that of the isopropenyl group at C-7, though activity decreased when oxygenated functional groups were introduced into the side chain. Aromatization of the A ring did not lower biological activities. The anti-fungal activities of most rishitin derivatives almost paralleled their activities as plant growth retardants. However, some compounds without antifungal activity were active as growth retardants.
日本植物生理学会の論文