Ethylene production and peroxidase activity in aphid-infested barley

The purpose of this work was to investigate whether ethylene is involved in the oxidative and defensive responses of barley to the aphids Schizaphis g raminum (biotype C) and Rhopalophum padi. The effect of aphid infestation o n ethylene production was measured in two barley cultivars (Frontera and Ar amir) that differ in their susceptibility to aphids. Ethylene evolution was higher in plants infested for 16 hr than in plants infested for 4 hr in bo th cultivars. Under aphid infestation, the production of ethylene was highe r in cv. Frontera than in Aramir, the more aphid susceptible cultivar. Ethy lene production also increases with the degree of infestation. Maximum ethy lene evolution was detected after 16 hr when plants were infested with 10 o r more aphids. Comparing the two species of aphids. Schizaphis graminum ind uced more ethylene evolution than Rhopalosiphum padi. Infestation with S. g raminum increased hydrogen peroxide content and total soluble peroxidase ac tivity in cv. Frontera, with a maximum level of H2O2 observed after 20 min of infestation and the maximum in soluble peroxidase activity after 30 min of infestation. When noninfested barley seedlings from cv. Frontera were ex posed to ethylene, an increase in hydrogen peroxide and in total peroxidase activity was detected at levels similar to those of infested plants.