Thionin in cell walls and papillae of barley in compatible and incompatible interactions with Erysiphe graminis f. sp. hordei

The thionin content of the cell walls and papillae of barley cvs Amsel and Emir, inoculated with Erysiphe graminis races C17A and C10E, was determined by immunocytochemistry using the protein A/gold technique. The distribution and concentration of this protein were similar in both cultivars in regions of the epidermal cell wall which had no contact with fungal structures and so thionin content was not determined by the same genetic system which controlled race-specific resistance in the two cultivars. However, in compatible combinations (cv. Amsel/race C17A or cv. Emir/race C10E) thionin concentration was decreased in epidermal cell walls at penetration sites directly beneath appressoria. In contrast, in incompatible combinations between cv Amsel and race C10E there was no change and between cv and Emir race C17A the epidermal cell walls directly beneath appressoria contained slightly more thionin than the walls away from the infection site. Labelling also appeared to be higher in papillae of incompatible combinations. Thus, high levels of thionin were correlated with incompatibility. A novel fingerprint method was used to qualitatively analyse changes in thionin mRNA populations in the two barley cultivars. Three major subgroups of thionin-specific transcripts were distinguished each of which encodes several different but closely related thionin variants. However the relative concentrations of these fractions did not change in the different host pathogen combinations.