A photoaffinity-labeled green leaf volatile compound 'tricks' highly selective and sensitive insect olfactory receptor neurons

The sex pheromone of the scarab beetle, Phyllopertha diversa, is emitted by females and specifically detected by olfactory receptor neurons in the mal e and female antennae. Single sensillum recordings showed that, in contrast to the less sensitive pheromone sensilla in females, olfactory receptor ne urons in the male antennae had a low threshold (1 ng), which rivals those o f moths. The male and female antennae also possessed olfactory receptor neu rons specific for the detection of floral and green leaf volatile compounds . Detectors for the green leaf volatile (Z)-3-hexenyl acetate had a thresho ld (10 pg) far below the sensitivity of the pheromone-detecting machinery. In addition, these neurons showed a remarkable selectivity even when challe nged with related compounds at 10 000-fold higher concentrations. Surprisin gly, a diazo analog, (Z)-3-hexenyl diazoacetate, elicited slightly higher n ervous activity than the natural ligand in the neurons specific and selecti ve for (Z)-3-hexenyl acetate. The inability of the green leaf volatile-dete cting machinery to discriminate the photoaffinity-labeled compound from the natural product indicates that the synthetic ligand interacts with odorant -binding protein, odorant receptor and odorant-degrading enzyme as does the cognate ligand.