Volatile-mediated signaling induces resistance of barley against infection with the biotrophic fungus Blumeria graminis f.sp. hordei

Abstract

Plants have evolved a vast variety of secondary metabolites to counteract biotic stress. Volatile organic compounds (VOCs) are carbon-based molecules induced by herbivore attack or pathogen infection. A mixture of plant VOCs is released for direct or indirect plant defense, plant-plant or plant-insect communication. Recent studies suggest that VOCs can also induce biotic stress resistance in distant organs and neighboring plants. Among other VOCs, green leaf volatiles (GLVs) are quickly released by plant tissue after the onset of herbivory or wounding.

We analysed VOCs emitted by 13-day old barley plants (Hordeum vulgare L.) after mechanical wounding using passive absorbers and TD-GC/MS detection. We investigated the influence of pure (Z)-3-hexenyl acetate (Z3HAC) as well as complex VOCs from wounded barley plants on the barley - powdery mildew interaction by pre-exposure in a static and a dynamic headspace connected to a powdery mildew susceptibility assay.

GLVs dominated the volatile profile of wounded barley plants with Z3HAC as the most prominent compound. Pre-exposure with Z3HAC resulted in induced resistance of barley against fungal infection. Barley complex volatiles emitted after mechanical wounding, similarly, enhanced resistance in receiver plants.

We found volatile-induced modification of the interaction towards an enhanced resistance against fungal infection. In addition, Z3HAC triggered a modulation of the alcohol dehydrogenase isoenzyme activity in receiver plants, a physiological response that possibly contributes to induced resistance. Plant-originated volatile metabolites could be a useful supplementation for future agronomic or horticultural practices.