A paper chromatographic method suitable for identification of the small amounts of coumarins and phenolic acids present in the uredospores of wheat stem rust was developed. By the use of the circular technique and a combination of three different solvent systems an adequate separation of all the substances was achieved. A preliminary development of the chromatogram with a solvent in which the test compounds were non-mobile facilitated identification and avoided the need for extensive preliminary fractionation of the extracts.Using this method the following compounds were identified in spore extracts: coumarin, umbelliferone, daphnetin, aesculetin, p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, o-coumaric acid, p-coumaric acid, ferulic acid, and caffeic acid; coumarin, p-hydroxybenzoic acid, vanillic acid, protocatechuic acid, o-coumaric acid, and ferulic acid were also present as glycosides; in addition scopoletin, gallic acid, syringic acid, and sinapic acid were detected after hydrolysis and are assumed to be present only in a bound form.In order to obtain some information about the role of these substances in the physiology of wheat stem rust, uredospores were germinated by being floated en masse on dilute aqueous solutions. Of the compounds tested, indoleacetic acid, coumarin, o-coumaric acid, protocatechuic acid, umbelliferone, and daphnetin gave a marked stimulation of germination at concentrations of 10–200 μg./ml. Caffeic acid, vanillic acid, p-hydroxybenzoic acid, ferulic acid, and ferulic acid β-glucoside had little effect or were strongly inhibitory.The stimulation of germination is attributed to the counteraction of a self-inhibitor released from the spores, and the possible significance of the compounds on the physiology of the rust and the host–parasite relationship is discussed.
Mechanisms of ferulic acid conversions to vanillic acid and guaiacol by Rhodotorula rubra.
