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.