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Peroxidase is considered one of several plant defense related enzymt;1S involved in disease resistance mechanism of host plants following inoculation
with pathogenic agents. In this study, peroxidase specific activity as well ItS total soluble protein were measured spectrophotometrically in resistant
(Roho/Mazurka line) and susceptible cv. Yazd-5 (Afzal) barley seedlings following incoculation with Erysiphe graminis f.sp. hordei isolate K400, the
causal agent of powdery mildew disease. The results revealed that total soluble protein content increased in Rohol Mazurka resistant line at 12 hr post-inoculation. reached a maximum level at 72 hr and was significantly
greater tnan that of the non-inoculated controL Peroxidase specific activity increased in the resistant line 48 hr after the inoculation and reached a
maximum rate at 72 hr. This was not observed in the susceptible Afzal-cultivar. Non-denaturing polyacrylamide gel electrophoresis (native-PAGE) stained
specilically for peroxidase activity showed the presence of a new acidic isozymic band with Rm value of OAO as well as thicker activity bands in the resistant leaf tissue at 72 and 120 hr post-inoculation times. However, this was absent in the susceptible leaf tissue. It can be concluded that peroxidase
activation may playa defensive role in the biochemical resistance of barley seedlings following an inoculation with the powdery mildew fungus.