ANALYSIS OF MONOTERPENOIDS IN GLANDULAR TRICHOMES OF THE CATMINT NEPETA-RACEMOSA

Plants within the Lamiaceae are characterized by their production of e ssential oils, largely composed of monoterpenoids. They also possess o n their aerial surfaces different types of trichomes, including relati vely large peltate glandular trichomes. Observation of leaves of the c atmint Nepeta racemosa, using cryogenic scanning electron microscopy, showed that around 3000 peltate trichomes are present on a single expa nded leaf. An approach has been developed for sampling directly from t he subcuticular cavity of such trichomes, in order to characterize qua litatively and quantitatively their contents. Gland samples from Nepet a spp. were analysed by combined gas chromatography-mass spectrometry. These analyses have confirmed that the monoterpenoids characteristic of these species (nepetalactones) accumulate within the subcuticular c avity of peltate glandular trichomes. Qualitative analysis showed that three different nepetalactone stereoisomers were accumulated in diffe rent proportions in peltate glands from individual N. racemosa plants. Quantitative analysis showed that individual peltate glands accumulat e around 30 ng of nepetalactone by maturity, and that accumulation of nepetalactone probably occurs exclusively within this gland type.