Receptor Neuron Discrimination of the Germacrene D Enantiomers in the Moth Helicoverpa armigera

Abstract

Plants release complex mixtures of volatiles, including chiral constituents. In the search for the biologically relevant plant odorants, gas chromatography linked to electrophysiological recordings from single receptor neurons has been employed. In heliothine moths, including the females of the Eurasian cotton bollworm moth Helicoverpa armigera, a major type of receptor neurons is identified, showing high sensitivity and selectivity for the sesquiterpene germacrene D. In the present study, gas chromatography with a chiral column linked to single cell recordings were performed. It was found that all germacrene D neurons belonged to one type; all responded to both enantiomers, but (-)-germacrene D had approximately 10 times stronger effect than (+)-germacrene D. Parallel dose-response curves for the two enantiomers were obtained by direct stimulations. The enantiomeric composition of germacrene D, which differed in six plant species and in different individuals of one species, was determined on the basis of the neuron responses. The results, showing the presence of one neuron type for receiving the information about germacrene D in the various plants, suggests that the two enantiomers mediate the same kind of information to the moth, but with different intensity.

Encoding of plant odour information in insects: peripheral and central mechanisms

“…For five of the types the most effective chemicals have been identified. Particularly interesting is the identification of a major neurone type, obtained in 80% of the recordings in H. virescens females and also in the related H. armigera females (Figure 1) (Røstelien et al, 2000a;Stranden et al, 2002). These neurones show a very high sensitivity and selectivity by responding to the sesquiterpene germacrene D at doses down to picograms.…”

“…Secondary responses were obtained at high concentrations to a few other chemically related sesquiterpenes. Another interesting feature is the enantioselectivity of the neurones responding bet- Stranden et al, 2002) ter to (−)-germacrene D than to the (+)-enantiomer; the two enantiomers having a ten times difference in stimulatory effect (Figure 1) . It suggests that the whole molecule, i.e., both the 10-carbon ring and the isopropyl group are important in the interaction with the receptor protein and that the direction of the isopropylgroup in relation to the carbon ring accounts for the different effect of the enantiomers.…”

Essential oil composition of sweet basil cultivars as affected by nitrogen and potassium fertilization

“…Eugenol, as one of the phenolic compounds characteristic of basil volatile oil, shows antioxidant (Juliani and Simon 2002) and antimicrobial activity (Ali et al 2005). Germacrene C and D, components from the group of sesquiterpene hydrocarbons, exhibit antimicrobial and insecticidal activity (Røstelien et al 2000;Stranden et al 2002).…”

Enantioselectivity of Projection Neurons Innervating Identified Olfactory Glomeruli

“…With a few exceptions (Wibe et al, 1998;Stranden et al, 2002Stranden et al, , 2003, however, little is known about the enantiospecificity of ORCs responding to nonpheromonal odor compounds. To our knowledge, no study in vertebrates or invertebrates has used intracellular recording to examine the enantioselectivity of PNs innervating identified glomeruli.…”