Extracellular lipids of Camelina sativa: Characterization of cutin and suberin reveals typical polyester monomers and unusual dicarboxylic fatty acids

Camelina sativa is relatively drought tolerant and requires less fertilizer than other oilseed crops. Various lipid- and phenolic-based extracellular barriers of plants help to protect them against biotic and abiotic stresses. These barriers, which consist of solvent-insoluble polymeric frameworks and solvent-extractable waxes, include the cuticle of aerial plant surfaces and suberized cell walls found, for example, in periderms and seed coats. Cutin, the polymeric matrix of the cuticle, and the aliphatic domain of suberin are fatty acid- and glycerol-based polyesters. These polyesters were investigated by base-catalyzed transesterification of C. sativa aerial and underground delipidated tissues followed by gas chromatographic analysis of the released monomer mixtures. Seed coat and root suberin had similar compositions, with 18-hydroxyoctadecenoic and 1,18-octadecenedioic fatty acids being the dominant species. Root suberin presented a typical lamellar ultrastructure, but seed coats showed almost imperceptible, faint dark bands. Leaf and stem lipid polyesters were composed of fatty acids (FA), 1,ω-dicarboxylic fatty acids (DCA), ω-hydroxy fatty acids (HFA) and hydroxycinnamic acids (HCA). Dihydroxypalmitic acid (DHP) and caffeic acid were the major constituents of leaf cutin, whereas stem cutin presented similar molar proportions in several monomers across the four classes. Unlike the leaf cuticle, the C. sativa stem cuticle presented lamellar structure by transmission electron microscopy. Flower cutin was dominated by DHP, did not contain aromatics, and presented substantial amounts (>30%) of hydroxylated 1,ω-dicarboxylic acids. We found striking differences between the lipid polyester monomer compositions of aerial tissues of C. sativa and that of its close relatives Arabidopsis thaliana and Brassica napus.