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UBC Theses and Dissertations

The diversity and biosynthesis of plant cuticular waxes Busta, Lucas Howard


Plants coat themselves in a cuticle to hinder transpiration across the vast surface areas they require for photosynthesis. The cuticle is made of cutin, a polyester, and cuticular waxes, aliphatic compounds that form the water barrier. Cuticles of model plants had been major targets for cuticular wax research, and knowledge of their surfaces is relatively advanced. However, this knowledge still does not answer crucial questions about relationships between wax structure and function. Limited studies of non-model species had provided glimpses of a much greater wax chemical structural diversity than that present on model plants. These also had hinted that diverse wax coverages and compositions exist on the surfaces of different species and different plant organs. Before relationships between structure and function can be established, the major dimensions of wax diversity must be described in more detail. To contribute, I aimed to describe wax structural and biological diversity in some model and non-model plant species. I examined the structural diversity of wax compound aliphatic tails and determined that branched compounds on Arabidopsis leaves are iso-branched and that certain wax biosynthesis enzymes can exhibit bias towards or against branched substrates. I also studied functional group diversity by performing a comprehensive literature search to codify our knowledge of wax compounds with secondary functions. I furthered our knowledge of wax coverage and composition on diverse biological surfaces by determining the structures of novel wax compounds from the moss Funaria hygrometrica and profiling the waxes from multiple F. hygrometrica surfaces to reveal that these moss cuticles have some similarities to those of flowering plants. By studying developing Arabidopsis leaves I found that their wax composition, but not coverage, is dynamic with time, pointing to functional optimization and synchronous cell expansion and wax production. This work highlights the importance of chain length specificity in wax biosynthesis, though the mechanisms by which such is achieved are unclear. It also confirms that secondary functional groups on wax molecules are installed by a variety of processes, that these are connected with biosynthetic chain length specificity and that both likely influence the physical and water barrier properties of the cuticle.

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