Eine vorlaufige Bewertung der Rolle reaktiver Sauerstoffspezies bei Abwehrreaktionen von Getreide gegenuber pilzlichen Pathogenen

During the development of the powdery mildew fungus (Blumeria [syn. Erysiphe] graminis f. sp. hordei) on near-isogenic barley lines superoxide radical anions (O₂(·^-)) accumulate depending on the function of specific genes for powdery mildew resistance (Huckelhoven and Kogel 1998), but not after treatment with the plant activator 2,6-Dichloroisonicotinic acid in Chemically Induced Resistance (CIR) (Kogel and Huckelhoven, in press). In the present work we studied histochemically the accumulation of H₂O₂ in chemically induced powdery mildew infected barley, cv Pallas, compared to H₂O₂ accumulation in constitutive resistant lines. Additionally, pathogenesis-specific O₂(·^-) and H₂O₂ generation was examined in the interaction of Pyricularia oryzae with rice (Oryza sativa L.). The typical CIR phenotype was characterized by penetration resistance. Fungal growth was arrested prior to haustorial formation in localized cell wall appositions (effective papillae), followed by cell death of the attacked epidermal cell (HR). In contrast to O₂(·^-), accumulation of H₂O₂ was detected very frequently at interaction sites on chemically induced plants. In rice, cells undergoing cell death in response to fungal attack accumulated H₂O₂. However, O₂(·^-) accumulation was not detected after infection neither in a compatible nor in an incompatible interaction of the rice plants with Pyricularia oryzae. Histochemical determination of reactive oxygen species demonstrates that H₂O₂ takes part in mechanisms of CIR and race-cultivar-specific resistance and confirm the hypothesis that the phenotype of CIR in barley is a phenocopy of a resistance mechanism conferred by specific genes for powdery mildew resistance (Kogel et al. 1994).