ACCUMULATION OF A PUTATIVE GUANIDINE COMPOUND IN RELATION TO OTHER EARLY DEFENSE REACTIONS IN EPIDERMAL-CELLS OF BARLEY AND WHEAT EXHIBITING RESISTANCE TO ERYSIPHE-GRAMINIS F SP HORDEI

The infection process was compared in interactions between Erysiphe gr aminis f.sp. hordei isolate A6 and two near-isogenic barley lines (the susceptible line P-01 and the resistant line P-02), and the non-host wheat. A low frequency of successful infections, measured as the perce ntage of germinated conidia forming primary haustoria, was detected in both susceptible (7.5 %), and resistant (7.3 %) barley isolines and w heat plants (22.3 %). In all three types of planes, papilla formation around the sites of attempted penetration seems to be a general resist ance factor and thus not the determining step for distinguishing betwe en race-specific and non-host resistance. In wheat plants, further res istance was manifested early after penetration and characterized by hy persensitively reacting (HR) single cells, no or limited growth of elo ngating secondary hyphae and no visible sign of infection. The race-sp ecific resistance of barley isoline P-02 occurred later after penetrat ion, and was characterized by plant tissue necrosis and no or weak fun gal sporulation. In the susceptible barley isoline P-01, successful in fections resulted in heavily sporulating powdery mildew colonies. Puta tive guanidine compounds, indicated by the Sakaguchi test, occurred in papillae 4-5 h after inoculation and subsequently in HR cells too, an d are apparently associated with the very early resistance responses i n barley and wheat. The highly basic guanidine compounds, not identifi ed previously in plant defence responses, were found io be bound to th e cell wall, and referred to as ''basic staining material''. Accumulat ion of polyphenolic substances and callose were demonstrated in papill ae and HR cells of both barley and wheat. Lignification occurred in wh eat, but did not occur or did so only minimally in barley.