Sakuranetin, a flavanone phytoalexin from ultraviolet-irradiated rice leaves

A new rice phytoalexin, sakuranetin (5,4′-dihydroxy-7-methoxyflavanone) was isolated from ultraviolet-irradiated rice leaves. The ED50 value of sakuranetin against spore germination of Pyricularia oryzae was approximately 15 ppm. A marked incorporation of [14C]phenylalanine into sakuranetin was observed in ultraviolet-irradiated rice leaves. Sakuranetin has also been observed in blast-infected rice leaves and the content in a resistant cultivar after infection with P. oryzae was much higher than in a susceptible cultivar.