Possible Involvement of Lipoxygenase in the Mechanism of Resistance of Oats to Puccinia coronat avenae

Possible participation of the peroxidation system in the cultivar‐race specificity was studied for the oat‐crown rust system. The levels of lipid peroxidation and total lipoxygenase (LOX) activity were extensively increased in leaves of cv. Shokan l responding with resistance to race 226. One anionic and one cationic LOX isozyme was detected in the extract of Shokan 1 leaves inoculated with race 226. In addition, three anionic and one cationic isozymes were consistently found in the extract of uninoculated and compatible race 203‐inoculated leaves. The blockage experiments with race 226‐inoculated leaves using RNA and protein synthesis inhibitors indicated that the two LOX isozymes characteristic of the incompatible combination are de novo synthesized and their activity is causally linked to the resistance expression. Production of the two isozymes was also demonstrated in the five resistant Pc oat lines, but not in the two susceptible Pc lines.