Canadian Forest Service Publications
Silicon-mediated accumulation of flavonoid phytoalexins in cucumber. 1998. Fawe, A.; Abou-Zaid, M.M.; Menzie, J.G.; Bélanger, R.R. Phytopathology 88: 396-401.
Issued by: Great Lakes Forestry Centre
Catalog ID: 21679
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The controversial role of silicon in plant disease resistance, described mostly as a passive mechanical protection. has been addressed. Conclusive evidence is presented that silicon is involved in the increased resistance of cucumber to powdery mildew by enhancing the antifungal activity of infected leaves. This antifungal activity was attributable to the presence of low-molecular-weight metabolites. One of these metabolites, described here as a phytoalexin, was identified as a flavonol aglycone rharnnetin (3,5,3',4'-tetrahydroxy-7-0-methoxyflavone). This is the first repon of a phytoalexin for this chemical group in the plant kingdom and of a flavonol phytoalexin in cucumber, a chemical defense long believed to be nonexistent in the family Cucurbitaceae. The antifungal activity of leaf extracts was better expressed after acid hydrolysis, extending to another plant species the concept that some phytoalexins are synthesized as gJycosylated phytoalexins or their precursors.