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Physiology and Biochemistry

Isolation and Identification of α-Tocopherol as an Inducer of the Parasitic Phase of Ustilago violacea. Alan J. Castle, Department of Plant Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7; Alan W. Day, Department of Plant Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7. Phytopathology 74:1194-1200. Accepted for publication 17 May 1984. Copyright 1984 The American Phytopathological Society. DOI: 10.1094/Phyto-74-1194.

Plant extracts induce the smut fungi Ustilago violacea, U. scabiosae, and U. utriculosa to change from saprophytic, yeastlike 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. However, we report here that all tested plant species, hosts or nonhosts, had active extracts when extracted with methanol. These results indicate that 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-hr 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 α-tocopherol (vitamin E). Synthetic α-tocopherol and other tocopherols (β, γ, and δ) as well as phytol were all highly active and induced change to the mycelial growth form even at very low concentrations (10- 7- 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.