Sclerotinia Sclerotiorum: Phytotoxins and Metabolism of Phytoalexins
Chemical defences, i.e. phytoalexins, were elicited and isolated from a resistant plant (Erucastrum gallicum, dog mustard): indole-3-acetonitrile, arvelexin, 1-methoxyspirobrassinin and erucalexin (new phytoalexin, a structural isomer of 1-methoxyspirobrassinin). As well, the biotransformations of the phytoalexins brassinin, produced by rapeseed, canola and brown mustard plants, camalexin, and 6-methoxycamalexin, produced by wild crucifers like Arabidopsis thaliana, Capsella bursapastoris and Camelina sativa, were investigated. It was established that S. sclerotiorum could efficiently metabolize these phytoalexins using a remarkable glucosylation reaction of their indole ring. Overall, results of these biotransformation studies followed by antifungal bioassays indicated that metabolism of brassinin, camalexin, and 6-methoxycamalexin were detoxification processes. Analogues of these phytoalexins were designed based on structures of the detoxification products to probe the specificity or otherwise of the enzyme(s) involved in the metabolism of the phytoalexins. All the analogues tested were metabolized by the fungus though at slower rates. 6-Fluorocamalexin, one of the analogues, significantly slowed down the metabolism of brassinin both in cell cultures and in enzymatic assays with cell homogenates. Partial purification (five fold) of the brassinin detoxifying enzyme (brassinin glucosyltransferase) of S.sclerotiorum was achieved.
Advisor:Palmer, David; Hultin, Philip; Lin, Yen-Hen; Ward, Dale E.; Reid, Stephen
School:University of Saskatchewan
School Location:Canada - Saskatchewan
Source Type:Master's Thesis
Date of Publication:08/11/2008