Biosynthesis of linalyl acetate and other terpenes in lemon mint (Mentha aquatica var. citrata, Lamiaceae) glandular trichomes

摘要

The potential to produce and accumulate mono- and sesquiterperies in lemon mint (Mentha aquatica var. citrata) glandular trichomes was evaluated. Volatiles were extracted using methyl-tert-butyl ether or solid phase micro extraction and determined by gas chromatography-mass spectrometry. The main components of the essential oil of lemon mint are the monoterpene alcohol linalool and its ester linalyl acetate. Sesquiterpenes, such as elemol, (E)-caryophyllene, and germacrene D, as well as the monoterpenes 1,8-cineole, beta-myrcene, and beta-(E)-ocimene, are also prominent. Most of the essential oil is localized in the glands, as leaves devoid of trichomes had very low essential oil levels. The quantities of all these components per leaf increased during leaf development until reaching the third whorl, and then the levels remained steady. Conversely, the essential oil content per gram fresh weight decreased with leaf development, but the decrease was not statistically significant at p = .0.05. Desalted cell-free extracts derived from isolated glandular trichomes were able to convert geranyl diphosphate into linalool. Lower amounts of geranyl diphosphate were also converted to other monoterpenes such as myrcene, a-pinene, beta-pinene, limonene, beta-(E)-ocimene, and nerol. Furthermore, the extracts were able to convert farnesyl diphosphate into the sesquiterpene (E)-caryophyllene and lesser amounts of other sesquiterpenes such as delta-cadinene, alpha-humulene, beta-(E)-farnesene, and alpha-gurjunene. These cell-free extracts also efficiently catalyzed the formation of linalyl acetate from linalool and acetyl-coenzyme A. Our findings indicate that glandular trichomes of lemon mint, similar to other members of the Lamiaceae, contain unique enzymatic activities capable of the synthesis of mono- and sesquiterpene components of its essential oil.