Changes in peroxidase and polyphenol oxidase activities in susceptible and resistant wheat heads inoculated with Fusarium graminearum and induced resistance

Guaiacol-peroxidase (POX) and polyphenol oxidase (PPO) activities were measured spectrophotometrically in resistant (cvs. Sumai # 3 and Wang shui-bai) and susceptible (cvs. Falat and Golestan) wheat heads at flowering, milk, dough and ripening stages following the inoculation with Fusarium graminearum at anthesis. POX specific activity in resistant and susceptible wheat cultivars showed a significant increase during the milk stage as compared with the non-inoculated control plants. POX activity reached the highest level in heads of Wang shui-bui followed by those of Falat, Sumai # 3 and Golestan cultivars at milk stage. The optimal pH for POX activity was 5.4. POX was inhibited by KCN. Native polyacrylamide gel revealed the presence of upto three basic (cationic) and six acidic (anionic) isozymes in wheat heads after a specific activity stain. PPO specific activity in wheat heads reached a maximum level during the milk stage and subsequently declined. This activity was three times higher in the resistant cultivars than the non-inoculated control plants. In Falat and Golestan cultivars, PPO activity level was half of those in resistant cultivars. The optimal pH for PPO was 6.4. PPO-catalyzed reaction was inhibited by ascorbic acid. Activity stain in non-denaturing polyacrylamide get revealed the presence of one basic and six acidic isozymes in wheat heads. The susceptible Falat heads pre-treated with an autoclaved mycelial wall preparation showed induced resistance against FHB and increased activities of POX and PPO. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.