NEW APPROACHES TOWARDS BIOCHEMICAL-MECHANISMS OF RESISTANCE SUSCEPTIBILITY OF GRAMINEAE TO POWDERY MILDEW (ERYSIPHE-GRAMINIS)

Investigations on biochemical mechanisms of gramineae resistance/susce ptibility to powdery mildew were differentiated in experiments for non -specific (I), race-specific (II) and induced (III) resistance/suscept ibility. I. Chosen geni from the Gramineae family differ significantly in respect to their qualitative pattern and quantitative amounts of e pidermal beta-cyanoglucosides. Different cultivars from the genus Hord eum show different amounts of epidermal beta-cyanoglucosides. Total am ounts of beta-cyanoglucosides of epidermal tissue from second leaves a re less than those from first leaves. Increased NO3-nutrition of Horde um vulgare decrease the amounts of beta-cyanoglucosides but increase t he amounts of amino acids in the epidermal tissue of first leaves. Thi s is especially true for the epidermal specific amino acid alpha-Aaa. II. Solubilized macro-molecules from the epidermal plasma membrane of Hordeum vulgare bind to germinated conidiospores of virulent races wit h a higher affinity than the ungerminated conidiospores of avirulent r aces of powdery mildew, respectively. The race-cultivar specific bindi ng may depend on a membrane borne glycoprotein with an apparental mole cular mass of 10 KD under denaturing conditions (SDS, mercaptoethanol) or 120 KD under native conditions, respectively. This glycoprotein sh ows Ca++ stimulated beta-glycosidase activity. III. Changes in the phy siological metabolism of mildew infected epidermal tissue of Hordeum v ulgare depend on the compatibility of the host-pathogen-interaction. I ncompatible interactions of powdery mildews and Hordeum on the host's first leaves lead to significant changes of carbohydrate, amino acid a nd protein metabolism of the developing healthy second leaves. We supp ose that these metabolic changes are correlated to an altered structur al sensitivity of this tissue to post-inoculations with the pathogen.