Localization of the Biosynthesis and Accumulation of Monoterpenoids in Glandular Trichomes of Thyme

Abstract

Quantitative analyses of the essential oils in intact glandular trichomes isolated from thyme cotyledons by the use of an adhesive tape and a glass capillary tube showed that the content of thymol per cotyledon was approximately equal to the sum total of thymol in peltate glandular trichomes (PGTs) and capitate glandular trichomes (CGTs). The amounts of thymol and γ-terpinene in PGTs increased with time until 9 days after germination, when these monoterpenes were exclusively found in PGTs. The radioactivity of [U-¹⁴ C]-sucrose administered to cotyledonal segments was incorporated into γ-terpinene and thymol most actively by the peripheral part abundant in PGTs, whereas the incorporation was markedly decreased by a partial removal of PGTs from cotyledons. The cell-free extract of isolated PGTs was capable of cyclizing [¹⁴ C]-geranyl pyrophosphate into γ-terpinene, but this enzymatic reaction failed when PGTs were removed from cotyledons. These results indicate that the biosynthesis and accumulation of monoterpenes in thyme seedlings take place primarily in PGTs.

Key words

Thymus vulgaris - Labiatae - glandular trichome - essential oil - thymol - γ-terpinene - biosynthesis