UBC Theses and Dissertations
Developmental cell biology of specialized metabolite production and storage in cannabis glandular trichomes Livingston, Samuel
Glandular trichomes on the flowers of Cannabis sativa L. (cannabis) produce and store a wealth of cannabinoids and terpenes, the metabolites consumed for both medicinal and recreational purposes around the world. Substantial progress has been made towards elucidating the enzymes involved in metabolite biosynthesis, as well as the diversity of metabolites produced. In contrast, we know very little about the cellular processes that facilitate the sheer abundance of metabolite biosynthesis and storage within the glandular trichomes. To fill this gap in knowledge, I used several microscopical approaches to assess the structure and composition of glandular trichomes throughout their development. A combination of fluorescence microscopy and scanning electron microscopy provided evidence that stalked trichomes develop from sessile-like trichomes during floral development, whereas bona fide sessile trichomes can be distinguished from a stalked trichome based on disc cell number, intrinsic fluorescence, and metabolite organization within their storage cavity. Evaluation of the glandular trichome ultrastructure with cryofixation sample preparation for transmission electron microscopy (TEM) led me to propose a new model of cannabinoid trafficking and secretion. An abundance of membrane contact sites near the apical plasma membrane suggests lipophilic metabolites may traffic from plastids to plasma membrane by partitioning into membrane bilayers and subsequent lipid exchange at membrane contact sites. The cell wall of the cannabis trichome was characterized using glycomic analysis followed by immunolocalization of cell wall-directed antibodies, which revealed dynamic changes in xyloglucan, pectin, and glycoproteins in the glandular trichome cell wall. Together, this thesis provides insights into the cell biology of cannabis glandular trichomes, in particular, how they produce and store abundant specialized metabolites.
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