ACTIVITIES OF HYDROGEN PEROXIDE-SCAVENGING ENZYMES IN GERMINATING WHEAT SEEDS

During imbibition and germination of wheat (Triticum aestivum) in the dark over 72 h, activities of the enzymes of the ascorbate (AsA)-dependent H2O2-Scavenging pathway, AsA peroxidase, monodehydroascorbate (MDAsA) reductase, dehydroascorbate (DHAsA) reductase and glutathione (GSSG) reductase as well as superoxide dismutase (SOD), catalase and guaiacol peroxidase were determined both in whole grains and in isolated embryos and endosperm. With the exception of DHAsA reductase, activities of the other enzymes assayed increased in germinating seeds, especially during radicle emergence (between 24-48 h of imbibition). These increases, particularly for AsA peroxidase, were much higher in the embryo than in the endosperm. Within 72 h of imbibition, activities per seed increased 116-fold for AsA peroxidase, 19-fold for guaiacol peroxidase, 5-fold for catalase and only 1.4-fold for SOD. In contrast to the decreases in DHAsA reductase, the other AsA recycling enzyme, MDAsA reductase, increased 5-fold within 72 h. The results indicate that, in wheat seeds, imbibition and germination is associated with enhanced cellular capacity to detoxify H2O2. For this detoxification the operation of AsA peroxidase together with the AsA-regenerating enzymes appears to be of particular importance.