HEAT-INDUCED RESISTANCE IN BARLEY TO POWDERY MILDEW (BLUMERIA-GRAMINIS F-SP HORDEI) IS ASSOCIATED WITH A BURST OF ACTIVE OXYGEN SPECIES

A 50 degrees C heat pulse was applied to leaves of barley (Hordeum vul gare cv. Golden Promise) for 60 s to induce resistance against the pat hogen Blumeria graminis f.sp. hordei (syn. Erysiphe graminis f.sp. hor dei). The heat treatment resulted in the production of both superoxide anions and hydrogen peroxide, indicating that the treated plants unde rwent an oxidative burst. Heat-induced resistance was phenotypically s imilar to resistance induced with hydrogen peroxide and was characteri zed by the absence of papilla formation and an arrest of fungal growth after appressorium formation. Heat-induced resistance was also associ ated with an increase in total glutathione levels. Changes were detect ed in soluble proteins in the intercellular wash fluid, most prominent ly, two proteins of 22 KDa and 23 kDa were drastically reduced in abun dance after heat as well as hydrogen peroxide treatment, suggesting in solubilization. The decline of the 22 kDa and 23 kDa proteins in the I WF and the accumulation of a 35 kDa protein in the fraction of covalen tly bound cell wall. proteins is consistent with the suggestion that h eat-induced resistance might be based on reinforcement of the cell wal l against fungal invaders. (C) 1998 Academic Press.