Induction of soluble and cell wall peroxidases by aphid infestation in barley

Peroxidase enzymes have been found in soluble, ionically bound, and covalen tly bound forms and have been implicated in several physiological processes in plants. This paper investigates the effect of aphid infestation on solu ble and bound-cell wall peroxidase activity and bound-cell wall isoform cha nges of barley plants. Peroxidase activity: was measured in control plants and plants infested with the aphid Schizaphis graminum (Rondani). The activ ity of soluble peroxidases increased with time of infestation, older plants being more affected than younger ones. The increase in bound-cell wall per oxidase activity as a function of age was higher in infested than in contro l plants, being higher in ionically bound than in covalently bound peroxida ses. When the aphids were removed from plants, the activities of both types of peroxidases decreased to control levels. Isoelectrofocusing analyses of the ionically bound peroxidases showed changes in the isoform pattern. A n ew isoform was induced by infestation. The activities of all covalently bou nd isoforms increased after infestation. The physiological implications of these changes are discussed.