UBC Theses and Dissertations
Spatial distribution of cuticular wax compounds and cuticular water barrier properties using Cosmos bipinnatus and Arabidopsis thaliana as models Buschhaus, Christopher
Plant cuticles form an external barrier, primarily blocking water loss into the desiccating atmosphere but also inhibiting UV and pathogen penetration. Cuticles consist of hydrophobic wax – a complex mixture of very-long-chain aliphatics and alicyclics – on top of (epicuticular) and in between (intracuticular) the biopolymer cutin. Absolute and relative wax composition varies between species and organs. Considering the diversity of compounds and barrier functions, the question arises: How does each wax compound shape each function? This dissertation presents advancements using Cosmos bipinnatus and Arabidopsis thaliana in three research areas ranging from localization of compounds at the organ, cellular, and sub-cellular levels, to structural elucidation of novel compounds, and finally to functional characterization. Waxes from C. bipinnatus petals, stems, and leaves were shown to be distinct. Petal wax comprised mainly primary alcohols as well as novel 1,2- and 1,3-diols and ketols. These classes were dominated by C₂₂ and C ₂₄ chain lengths. The water resistances of the adaxial (3.0±0.3 x 10⁴ s/m) and abaxial (1.5±0.2 x 10⁴ s/m) surfaces of these petals were lower than average literature values for leaves but similar to fruit, suggesting that the wax composition on ephemeral organs creates a compromised water barrier. Lateral wax heterogeneity was shown for trichomes, which tended to have longer compound chain lengths and a higher percentage of alkanes, as compared to pavement cells in both leaves and stems of A. thaliana. Moreover, a meta-analysis synthesizing the epicuticular and intracuticular wax compositions of all species investigated to date showed vertical wax heterogeneity. Noticeably, cyclic compounds preferentially accumulated in intracuticular wax. This finding was confirmed by over-expression of AtLUP4 in Arabidopsis, which caused β-amyrin accumulation in the intracuticular but not epicuticular wax layer. The presence of β-amyrin reduced the intracuticular wax-caused water resistance (2.4±0.2 x 10³ s/m) to three-quarters of the control (3.4±0.5 x 10³ s/m) while the epicuticular wax resistance for the over-expressor (6.8±0.6 x 10³ s/m) equaled that of the control (6.6±0.9 x 10³ s/m). An understanding of how wax constituents affect cuticular functions will aid in breeding and designing plants capable of withstanding adverse biotic and abiotic conditions.
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