Fragrance chemistry, nocturnal rhythms and pollination "syndromes" in Nicotiana

GC-MS analyses of nocturnal and diurnal floral volatiles from nine tobacco species (Nicotiana; Solanaceae) resulted in the identification of 125 volatiles. including mono- and sesquiterpenoids, benzenoid and aliphatic alcohols, aldehydes and esters. Fragrance chemistry was species-specific during nocturnal emissions, whereas odors emitted diurnally were less distinct. All species emitted greater amounts of fragrance at night, regardless of pollinator affinity. However, these species differed markedly in odor complexity and emission rates, even among close relatives. Species-specific differences in emission rates per flower and per unit fresh or dry flower mass were significantly correlated; fragrance differences between species were not greatly affected by different forms of standardization. Flowers of hawkmoth-pollinated species emitted nitrogenous aldoximes and benzenoid esters on nocturnal rhythms. Four Nicotiana species in section Alatae sensu strictu have flowers that emit large amounts of 1,8 cineole, with smaller amounts of monoterpene hydrocarbons and alpha-terpineol on a nocturnal rhythm. This pattern suggests the activity of a single biosynthetic enzyme (1,8 cineole synthase) with major and minor products; however, several terpene synthase enzymes could contribute to total monoterpene emissions. Our analyses, combined with other studies of tobacco volatiles, suggest that phenotypic fragrance variation in Nicotiana is shaped by pollinator- and herbivore-mediated selection, biosynthetic pathway dynamics and shared evolutionary history. (C) 2003 Elsevier Science Ltd. All rights reserved.