1978 Volume 44 Issue 4 Pages 478-484
The occurrence in oat leaves of non-antifungal steroids, avenacosides (Avd) A and B, was confirmed by chemical and physical analysis for primary leaves of oat cultivar Shokan 1. Enzymatic conversion of Avds A and B into antifungal steroids 26-desglucoavenacosides (26-DGA) A and B, respectively, was also demonstrated. The enzyme was active to β-glucoside linkage at C-26 of Avds and was inactive to that of sugar moiety at C-3 of Avds and 26-DGAs. No split of glycoside linkage of flavonoids present in oat leaves as well as p-nitro-β-d-glucoside was detected. The activity was maximum at pH 6.0, heat labile and inhibited by p-chloromercuric benzoate but not by gluconolactone. In leaves injured by cutting, conversion of Avds into 26-DGAs occurred within 5min and the degree of conversion was correlated with the increased antifungal activity of steroid fraction from hot methanol extracts of leaves, as measured by the growth of uredospores of Puccinia coronata avenae. It was suggested that the activation system of Avds to antifungal forms in association with the activation of a specific β-glucosidase was involved in the injured response of oat leaves.