Floral volatiles from Clarkia breweri and C. concinna ( Onagraceae ): Recent evolution of floral scent and moth pollination

Abstract

Clarkia breweri ( Onagraceae ) is the only species known in its genus to produce strong floral fragrance and to be pollinated by moths. We used gas chromatography-mass spectrometry (GC-MS) to identify 12 abundant compounds in the floral headspace from two inbred lines of C. breweri. These volatiles are derived from two biochemical pathways, one producing acyclic monoterpenes and their oxides, the other leading from phenylalanine to benzoate and its derivatives. Linalool and linalool oxide (pyran form) were the most abundant monoterpenoids, while linalool oxide (furan form) was present at lower concentrations. Of the aromatic compounds detected, benzyl acetate was most abundant, whereas benzyl benzoate, eugenol, methyl salicylate, and vanillin were present as minor constituents in all floral samples. The two inbred C. breweri lines differed for the presence of the additional benzenoid compounds isoeugenol, methyleugenol, methylisoeugenol, and veratraldehyde. We also analyzed floral headspace from C. concinna , the likely progenitor of C. breweri , whose flowers are odorless to the human nose. Ten volatiles (mostly terpenoids) were detected at low concentrations, but only when headspace was collected from 20 or more flowers at a time. Trans-β-ocimene was the most abundant floral compound identified from this species. Our data are consistent with the hypothesized recent evolution of floral scent production and moth pollination in C. breweri.