Mass spectral characterization of fatty acid amides from alfalfa trichomes and their deterrence against the potato leafhopper.

A homologous series of N-(3-methylbutyl)amides of normal saturated C14, C15, C16, C17 and C18 fatty acids were identified as major components of glandular trichome extracts from Medicago sativa G98A, an alfalfa genotype resistant to the potato leafhopper, Empoasca fabae. A second homologous series of N-(2-methylpropyl)amides of C14 through C18 normal fatty acids were minor components. Saturated free fatty acids C12, C13, C14, C15, C16, C17 and C18 were present in trace amounts, as was the N-(3-methylbutyl)amide of linoleic acid (C18:2). N-(3-methylbutyl)amides and N-(2-methylpropyl)amides of C14 through C18 fatty acids, along with the N-(3-methylbutyl)amide of linoleic acid, were synthesized and bioassayed for leafhopper deterrence by applying the compounds to the surface of a sachet containing an artificial diet. Leafhoppers were then offered a two-way choice between diet surfaces treated with the synthetic amides or an untreated control. N-(3-methylbutyl)amides and N-(2-methylpropyl)amides of C14 through C18 fatty acids did not deter leafhopper settling in a dose-dependent fashion. In contrast, when tested singly, N-(3-methylbutyl)amide of linoleic acid exhibited dose-dependent deterrence against leafhopper settling. Fatty acid amides localized in alfalfa glandular trichomes likely contribute to leafhopper resistance.

Bioactivity of lipophilic metabolites from glandular trichomes of Medicago sativa against the potato leafhopper.

Medicago sativa cv. G98A is highly resistant to the potato leafhopper, Empoascafabae. Glandular trichome extracts from G98A were fractionated using flash chromatography and tested for settling deterrency against the potato leafhopper. A fraction of intermediate polarity exhibited strong, dose-dependent deterrency when applied to the surface of an artificial diet sachet. Deterrency was not detected, however, when the fraction was applied to the internal surface of the sachet membrane (i.e., when contact was limited to only the leafhoppers' stylets). Major components of the highly deterrent fraction, determined by gas chromatography-mass spectrometry, were a homologous series of fatty acid amides C(n)H(2n+1)NO (n = 19-23) and trace components were 12:0, 13:0, 14:0, 15:0, 16:0, 17:0, 18:0, and possibly 18:1 free fatty acids. Deterrency declined slightly, but was still strong, after fatty acids were removed from crude extracts. When the crude extracts were separated further, a fraction containing only the fatty acid amides was also deterrent. Activity increased when this fraction was supplemented with authentic (C12:0 through C18:0, and C18:1) free fatty acids. However, the authentic free fatty acids were not deterrent when tested without the lipophilic amides. Fatty acid amides and free fatty acids in trichomes of M. sativa G98A may synergize and together function in deterring settling by the potato leafhopper.

Glandular trichome extracts from Medicago sativa deter settling by the potato leafhopper Empoasca fabae.

Extracts of glandular trichomes from Medicago sativa were tested for their ability to disrupt the settling behavior of the potato leafhopper, Empoasca fabae. Erect and procumbent glandular trichomes were mechanically isolated from stem sections of resistant genotype "G98A," and nonglandular trichomes were collected from susceptible cultivar "Ranger." Isolated trichomes were extracted with chloroform, acetone, and ethanol, and the resulting crude extracts were applied to the surface of a sachet containing an artificial diet. Leafhoppers were offered a two-way choice between crude trichome extracts from G98A and Ranger. All three of G98A solvent extracts caused various degrees of diet rejection, resulting in the crude Ranger trichome extracts being preferred over G98A extracts. Overall, the fewest leafhoppers settled on the ethanolic extracts. Additional bioassays documented a dose response associated with G98A ethanolic extracts when compared with Ranger trichome extracts and a solvent control. No difference in preference behavior was detected between Ranger trichome extracts and a solvent control. Gas chromatography-mass spectrometry analysis revealed a homologous series of nonvolatile fatty acid amides C(n)H(2n+1)NO (n = 19-23) unique to G98A glandular trichome extracts.

Geographic distribution of three alkaloid chemotypes of Croton lechleri.

Three known alkaloids, isoboldine (2), norisoboldine (1), and magnoflorine (8), have been isolated for the first time from Croton lechleri, a source of the wound healing latex "sangre de grado". An HPLC system was developed, and a large number of latex and leaf samples of C. lechleri from 22 sites in northern Peru and Ecuador were analyzed to gain an understanding of the natural variation in alkaloid content for the species. Up to six alkaloids were found to occur in the leaves including, in addition to those listed above, thaliporphine (3), glaucine (4), and taspine (9), whereas the latex contained only 9. Taspine (9) is the component that has been previously found to be responsible for the wound healing activity of C. lechleri latex, and its mean concentration throughout the range examined was found to be 9% of the latex by dry weight. In addition, three chemotypes are defined based on the alkaloid content of the leaves, and the geographic distribution of these chemotypes is discussed along with a quantitative analysis of the alkaloid content as a function of chemotype.