Composition of Foeniculum vulgare cuticular waxes: Chain length and isomer distributions of compounds with mid-chain hydroxyl and carbonyl groups.

Plant cuticles are lipophilic surface coatings that protect above-ground organs against environmental stress. An important cuticle component is wax, typically composed of very-long-chain hydrocarbons with terminal or in-chain functional groups. The current study aimed to provide a comprehensive analysis of leaf and stem cuticular waxes of Foeniculum vulgare, with special emphasis on characteristic wax components with in-chain hydroxyls or carbonyls. The stem and leaf waxes had similar compositions, including common compound classes such as fatty acids, aldehydes, alcohols and alkyl esters. The wax mixtures were dominated by ketones, with mainly C27 and C29 chains and keto groups on C-10 and C-12. Other compounds with mid-chain functionalities were identified by GC-MS analyses, including sets of (i) free as well as esterified ketoacids and primary/secondary ketols, and (ii) sec. alcohols, prim./sec. diols and sec./sec. ketols. The chain length and isomer patterns of these diverse wax compounds have implications for potential biosynthesis mechanisms.