Treatment of the first leaves of barley seedlings with the
oxylipin colneleic acid, or the two trihydroxy
oxylipins 9,12,13-trihydroxy-11(E)-octadecenoic
acid and 9,12,13-trihydroxy-10(E)-octadecenoic
acid, reduced
infection of that leaf by the powdery mildew fungus Blumeria graminis Speer f sp hordei Marchal. When applied to first leaves,
etheroleic acid and
colneleic acid, as well as the trihydroxy
oxylipin 9,12,13-trihydroxy-10(E),15(Z)-octadecadienoic
acid, also reduced mildew
infection in second leaves. In all cases where local and systemic effects against mildew were observed, activity of the defence-related
enzyme phenylalanine ammonia lyase (PAL) was increased, but only following challenge inoculation with powdery mildew.
Peroxidase activity was not affected by
oxylipin treatment or mildew inoculation. Whether the effects observed were due to the
oxylipins or to breakdown products is not known, since no information is available on the stability of these particular
oxylipins on leaf surfaces. Nevertheless, these data represent the first report of systemic effects against pathogen
infection following pre-treatment with
oxylipins.