The occurrence of lipid hydroperoxide-decomposing activities in rice [Oryza sativa] and the relationship of such activities to the formation of antifungal substances

Two fractions that decomposed lipid hydroperoxide (lipid hydroperoxide-decomposing activities), were isolated from rice seeds by ion-exchange chromatography on DEAE-Toyopearl. Thin-layer chromatography showed that both fractions generated two products (I and II) when 9-linoleate hydroperoxide (9-LOOH) was used as a substrate. Structural analysis by gas chromatography/mass spectrometry showed that products I and II were 9-hydroxyoctadecadienoic acid and 9,12,13-trihydroxyoctadec-lO-enoic acid, respectively, which have been isolated from rice leaves as antifungal substances that are active against rice blast fungus. The antifungal activity of 9-LOOH was examined against the blast fungus and compared with that of product I. Both compounds strongly inhibited conidial germination, growth of germ tubes and formation of appressoria at 50ppm. Product I was more active in this assay than 9-LOOH.