Metabolic Profiling of Root Exudates ofArabidopsisthaliana

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Abstract
This paper was withdrawn on October 7, 2009 ( J. Agric. Food Chem. 2009, 57 , 9346). In addition to accumulating biologically active chemicals, plant roots continuously produce and secrete compounds into their immediate rhizosphere. However, the mechanisms that drive and regulate root secretion of secondary metabolites are not fully understood. To enlighten two neglected areas of root biology, root secretion and secondary metabolism, an in vitro system implementing root-specific elicitation over a 48-day time course was developed. After roots of Arabidopsis thaliana had been elicited with salicylic acid, jasmonic acid, chitosan, and two fungal cell wall elicitors, the secondary metabolites subsequently secreted were profiled. High-performance liquid chromatography was used to metabolically profile compounds in the root exudates, and 289 possible secondary metabolites were quantified. The chemical structures of 10 compounds were further characterized by 1H and 13C NMR: butanoic acid, trans-cinnamic acid, o-coumaric acid, p-coumaric acid, ferulic acid, p-hydroxybenzamide, methyl p-hydroxybenzoate, 3-indolepropanoic acid, syringic acid, and vanillic acid. Several of these compounds exhibited a wide range of antimicrobial activity against both soil-borne bacteria and fungi at the concentration detected in the root exudates. Keywords: Arabidopsis thaliana; Brassicaceae; butanoic acid; trans-cinnamic acid; o-coumaric acid; p-coumaric acid; ferulic acid; p-hydroxybenzamide; methyl p-hydroxybenzoate; 3-indolepropanoic acid; syringic acid; vanillic acid; elicitation