Hydrolase and oxido-reductase activities in Diuraphis noxia and Rhopalosiphum padi (Hemiptera : Aphididae)

Four hydrolases and five oxido-reductases were examined using native stacki ng polyacrylamide gel electrophoresis. Homogenate of Russian wheat aphid, D iuraphis noxia (Mordvilko), bird cherry-oat aphid, Rhopalosiphum padi (L.), 'Arapahoe' (aphid-susceptible) and 'Halt' (aphid-resistant) wheat, Triticu m aestivum L., and powdery mildew-infected Erysiphe graminis DC. ex Merat f . sp. tritici Em. Marchal, Arapahoe wheat leaves were assayed for enzyme ac tivities. Pectinesterase, polygalacturonase (or pectinase), cellulase, and amylase activities were examined in the hydrolase group. Catalase, peroxida se, catechol oxidase, superoxide dismutase, and ascorbate oxidase activitie s were examined in the group of oxido-reductases. The two aphid species had the same hydrolases but different oxido-reductases. Although pectinesteras e and cellulase enzymes were present in D. noxia and R. padi, the banding p atterns were different. Polygalacturonase and S-amylase were not detected f i om either aphid species. In the oxido-reductase group, catalase was detec ted from D. noxia, wheras peroxidase was detected from R. padi. Superoxide dismutase and ascorbate oxidase activities also were detected from both aph ids. Enzyme assays using aphid head tissue that included salivary glands bu t excluded aphid foregut supported the enzyme assays using whole aphids. Pe roxidase activity was detected from the salivary tissue of R. padi, but not D. noxia, and catalase activity was detected from D. noxia salivary tissue , but not R. padi. We suggest that the salivary enzyme difference between t he 2 aphid species (i.e., catalase and peroxidase) is important in the type of damage symptom formation on susceptible wheat plants.