UBC Theses and Dissertations
Identification and quantification of surface wax compounds covering aerial organs of selected plant species Racovita, Radu C.
The cuticle is an external barrier of aerial plant organs that prevents desiccation. It is composed of hydrophobic waxes, i.e. complex mixtures of very-long-chain aliphatics, alicyclics and aromatics, lying on top of (epicuticular) and in between (intracuticular) a polyester matrix known as cutin. Wax compositions vary greatly between plant species, organs and tissues, both qualitatively and quantitatively. This thesis describes the identification and quantification of cuticular waxes of three plant species, including structure elucidation of novel compounds, chain length profiling, and wax compound distributions between intracuticular and epicuticular compartments for the first two species. Leaves of Aloe arborescens were found covered with 15 μg/cm² wax on the adaxial side and 36 μg/cm² on the abaxial side, with 3:2 and 1:1 ratios between epicuticular and intracuticular wax layers on each side, respectively. Along with ubiquitous wax compounds, three homologous series were identified as novel 3-hydroxy fatty acids (predominantly C₂₈), their methyl esters (predominantly C₂₈), and 2-alkanols (predominantly C₃₁), and their biosynthetic pathways were hypothesized based on structural similarities and homolog distributions. The adaxial side of young and old Phyllostachys aurea leaves was found covered with 1.7 to 1.9 μg/cm² each of epi- and intracuticular waxes. In addition to typical aliphatics and alicyclics, novel primary amides were identified, with their chain length profile peaking at C₃₀, and found exclusively in the epicuticular waxes, hence near the true plant surface. Flag leaves and peduncles of Triticum aestivum cv. Bethlehem were found covered with 16 and 49 μg/cm² wax, respectively, dominated by 1-alkanols in the case of the former and β-diketones and hydroxy-β-diketones for the latter. Along with previously reported wax classes, numerous new classes were identified as homologous series: 2-alkanol esters, benzyl esters, phenethyl esters, p-hydroxyphenethyl esters, secondary alcohols, primary/secondary diols and their esters, hydroxy- and oxo-2-alkanol esters, 4-alkylbutan-4-olides, internally methyl-branched alkanes, and 2,4-ketols. Other new compounds were found as single homologs: C₃₃ 2,4-diketone, C₃₁ mid-chain β-ketols, C₃₀ mid-chain α-ketols and α-diketone, as well as C₃₁ mid-chain ketones. Biosynthetic pathways are proposed in the thesis for the new compounds, based on common structural features and matching chain length patterns between related compound classes.
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