When flowers smell fermented: The chemistry and ontogeny of yeasty floral scent in pawpaw (Asimina triloba : Annonaceae)

Floral scent plays important roles in basal angiosperms such as the pantropical woody family Annonaceae. The North American genus Asimina ( Adans.) ( Annonaceae) includes eight species of shrubs and small trees, of which Asimina triloba has the broadest and northernmost distribution. We characterized the yeastlike fragrance of these flowers using gas chromatography - mass spectrometry in natural populations in South Carolina. The odors of A. triloba and baker's yeast Saccharomyces cerevisiae shared ethanol, ethyl acetate, acetic acid, and other compounds but differed in relative amounts of 3-methyl-1-butanol, 3-OH-2-butanone, and butane-2,3-diol. Immature green flowers of A. triloba produced sesquiterpenes common to the foliage of many plants. In contrast, sexually mature flowers emitted fermentation volatiles, with additional nitrogenous compounds (androgynoecium) and butanediols ( outer corolla) emitted by male flowers. Some compounds were detected only when scent was sampled from at least 10 flowers. Chemical composition was more complex during day than night for immature and female flowers but not for males. Emission rates were fourfold greater in male than female flowers during the day but were comparable at night, perhaps because of overlapping gender expression. The yeasty odor of A. triloba is unusual in angiosperms and may serve to attract novel fly and beetle pollinators.