The phytoalexin response in phaseolus vulgaris l.

This thesis concerns the initial events leading to the induction of the phytoalexin response in the Phaseolus vulgaris L. - Colletotrichum lindemuthianum L. host - pathogen interaction The phytoalexin response is an expression of the resistance of the host to further pathogen invasion. The visible expression of the phytoalexin response is hypersensitive necrosis. One of the initial events leading to the induction of the phytoalexin response is thought to be the induction of the first enzyme leading to the synthesis of phenylpropanoid phytoalexins, namely L-phenylalanine ammonia-lyase (PAL). Standard methods for determination of PAL activities were found to lead to measurements of both phenylalanine amino-transferase (PAT) and PAL activities together. Further, PAT was found to have a higher affinity for L-phenylalanine than PAL. An isotopic assay was devised for the accurate estimation of PAT and PAL activities separately using a specific inhibitor of PAT, L-aspartic acid. These experiments were carried out in a whole (intact) plant system. A rapidly isolated cell and protoplast system wa.s specially devised for isolation of the pathogen cell wall constituents responsible for the induction of the phytoalexin response. Special care was taken to minimise mechanical damage in these systems by optimising methods of purification, viability and intactness. The pathogen cell wall component responsible for the induction of the phytoalexin response was found to be an asialoglycoprotein. [To continue reading the abstract please see the pdf]