Chronology and elicitation of changes in peroxidase and phenylalanine ammonia-lyase activities in wounded wheat leaves in response to inoculation by Botrytis cinerea

Wounding wheat leaves induced increases in the activities of peroxidase (PO) and phenylalanine ammonia-lyase (PAL) which were further enhanced by inoculating the wounds with Botrytis cinerea. Subcellular fractionation of PO revealed no preferential stimulation of activity in any particular fraction by wounding alone or by inoculating intact or wounded leaves. Although the increases in PO and PAL activities induced by wounding were confined to wound areas, inoculation induced increases in both activities away from damaged tissue and thus in tissues distant from fungal hyphae.

PO activity was localised at infected wound margins in the cell walls and in degenerating cytoplasm of the leaf tissue. Some weaker activity was observed in fungal cell walls growing close to the wound edge.

Addition of heat-killed spores or a cell-free germination fluid of B. cinerea to wounds elicited increases in PO activity which were of similar magnitude to those elicited by living spores but PAL activity was stimulated to levels only around 10% that of the wound-inoculated response. Macerase-resistant rings of tissue were induced around wound margins by these fungal preparations, although the response was weaker than that of wounds inoculated with living spores.

Incubation of wheat leaf protoplasts with live spores, heat-killed spores or germination fluid of B. cinerea revealed no stimulation of either PO or PAL activities; in some cases inhibitions were observed.

It is postulated that inoculation of wheat leaf wound areas with B. cinerea does not merely augment an underlying injury response. Some form of fungal recognition is involved in the mediation of an infection response which diverts wheat leaf metabolism towards lignification.