Several biotic and abiotic clicitors of the hypersensitive reaction in wheat leaves are described. The elicitors induce enhanced activity of phenylalanine ammonia-lyase with subsequent lignification, visible as a yellow autofluorescence. The deposited material stains positively with phloroglucinol. DEAE-dextran, epoxystearic acid and chitosan are strong elicitors, while the glucans tested have no activity. A biotic elicitor (genuine Pgt-elicitor) was isolated from the germ tube walls of uredospores of Puccinia graminis f. sp. tritici. The high molecular weight, water soluble elicitor is heat stable and unaffected by mild acid and mild alkaline treatments. It seems to be a glycoprotein with the carbohydrate moiety bearing the active residues, as indicated by periodate sensitivity and protease stability. The carbohydrate moiety consists mainly of glucose with some galactose and mannose. Upon ultrafiltration and gel chromatography elicitor activity was associated with fractions of molecular weight of more than 100 kD. When injected into the intercellular space of primary wheat leaves, the elicitor induces lignification, preceded by an increase in phenylalanine ammonia-lyase activity.
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Moerschbacher et al. (1986) studied this question.