Isolation and Identification ofα-Tocopherol as an Inducer of the Parasitic Phase ofUstilago violacea

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Abstract
Plant extracts induce the smut fungi U. violacea, U. scabiosae and U. utriculosa to change from saprophytic, yeast-like growth to the parasitic, mycelial form. Previously, aqueous extracts were reported to be active when obtained from plant species that host a species of Ustilago but generally to be inactive when obtained from nonhost species. All tested plant species, hosts or nonhosts, had active extracts when extracted with methanol. The active agent is more soluble in methanol than in water, is universally distributed in angiosperms, and is possibly more available or accessible in hosts than in nonhosts. Four active peaks were found following reverse phase high performance liquid chromatography of leaf extracts of Silene alba, which is a host for U. violacea. One peak, found only in aqueous extracts, was weakly active after a 24-h delay and was identified as ascorbic acid. Some activity was also associated with peaks containing chlorophylls a and b obtained from methanolic extracts. The major activity was associated with a peak, purified from extracts of Pastinaca sativa and also found in S. alba, which was identified by UV absorption spectroscopy and mass spectrometry as .alpha.-tocopherol (vitamin E). Synthetic .alpha.-tocopherol and other tocopherols (.beta., .gamma., and .delta.) as well as phytol were all highly active and induced change to the mycelial growth form even at very low concentrations (107-10-8 M). The potential advantages of this system for further study of the mechanism of action of vitamin E, for bioassay of vitamin E, and for studies of the host/parasite relationship and smut control are discussed.