Plants respond to stress using metabolic pathways that involve the production of various secondary metabolites. Phytoalexins are antimicrobial natural products produced in plants elicited with biotic and abiotic stress. These metabolites play an important role in the defence response of plants, and are part of their defence mechanisms. Crucifer plants (family Brassicaceae) are known to produce tryptophan-derived phytoalexins, with more than 45 metabolites discovered to date. In our on-going search for new sources of phytoalexins from crucifers, two cultivated species Nasturtium officinale (watercress), Barbarea verna (upland cress), and a wild species Erucastrum canariense were investigated. Abiotic elicitation of leaves of N. officinale and B. verna led to the production of several metabolites that were not detected in control plants. These metabolites were isolated and their structures were confirmed by synthesis. The metabolites were inhibitory against fungal pathogens, indicating them to be the novel phytoalexins nasturlexins and cyclonasturlexin. In addition, physically damaging leaves of E. canariense elicited a different group of metabolites that were isolated and characterized. Spectroscopic data analysis indicated them to be arabidopsides, a group of galacto-oxylipins that are derived from the jasmonate biosynthetic pathway. Further experiments investigated and correlated the production of these elicited metabolites in E. canariense upon wounding and other types of stress. Finally, biosynthetic experiments using stable isotope labelling suggest that cyclonasturlexin is derived from the tryptophan pathway via brassinin, an important phytoalexin in crucifers, whereas nasturlexins are biosynthesized from phenylalanine via gluconasturtiins and their corresponding isothiocyanates. The potential biosynthetic intermediates of these pathways will be presented and potential alternative pathways will be discussed. The discovery of new biosynthetic intermediates should facilitate the discovery of the corresponding biosynthetic enzymes and genes present in specific crucifer species

Chemical defence and novel biosynthetic pathways of phytoalexins in crucifers

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.