An Elicitor of the Hypersensitive Lignification Response in Wheat Leaves Isolated from the Rust Fungus Puccinia graminis f. sp. tritici II. Induction of Enzymes Correlated with the Biosynthesis of Lignin

Abstract

The genuine biotic elicitor from germ tube walls of Puccinia graminis f. sp. tritici (Pgt-elicitor) induces lignification, preceded by an increase in phenylalanine ammonia-lyase (PAL) activity, when injected into the intercellular space of primary wheat leaves. This increase in PAL activity is accompanied by an increase in other enzyme activities of the general phenylpropanoid pathway and the specific pathway of lignin biosynthesis: 4-coumarate :CoA ligase (4CL), cinnamyl alcohol dehydrogenase (CAD) and peroxidase (PO). Total extractable activities of 4CL, CAD and PO do not differ significantly in resistant and susceptible near isogenic wheat lines, whereas the dose response curve of induced PAL activity shows significantly higher values in the resistant isoline. This difference is not observed after injection of other biotic and abiotic elicitors of the lignification response. Although total induced PO activities 24 h after elicitor treatment are equal in both isolines, the PO isoenzyme pattern of resistant plants differs markedly from that of susceptible plants. The patterns of PO isoenzymes in the compatible and incompatible interaction 48 h after inoculation with Puccinia graminis f. sp. tritici also show differences, which closely resemble those seen after injection of the Pgt-elicitor. The patterns observed after injection of an artificial biotic elicitor clearly differ from those of the natural interaction.