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How trichomes make terpenes and cannabinoids in supercell pathways

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A study from the University of British Columbia froze trichomes with liquid nitrogen. Researchers peered into cryofixated Purple Kush cells with an electron microscope. Using modern techniques, they found new keys that better explain how trichomes make non-polar terpenes and cannabinoids without destroying plant cells. (1)

Cannabis plants produce acidic cannabinoids, such as THCa or CBDa. Acidic cannabinoids contain an extra little molecule of carboxylic acid (COOH). And trichomes are super-cellular lipid factories found on the outside of cannabis buds. However, specific highways and traffic lights along synthesis pathways inside the trichome remained hidden.

Trichomes and electron microscopy

Trichome diagram by Livingston et al. 2021 | Courtesy of The Plant Journal | Wiley. (2)

Sam Livingston, holding a Ph.D. in botany and plant biology, is a postdoc researcher with Professor Lacey Samuels and Keeling Lab at UBC. Professor Jon Page of UBC and Anadia Labs co-authored the recent trichome study. Lastly, Kim Rensing, Ph.D also collaborated on the project. In a phone call with this author, Sam described the importance their discovery (1) has in two worlds of cannabinoid production — botany and biosynthesis.

When I first started with this project, I was collecting a bunch of TEM (Transitional Electron Microscopy) data — really high resolution, high magnification images of the trichome. I wasn’t sure what to go looking for primarily because all of the research up until this point had been using what would be considered the conventional method of preserving cells.  

Sam Livingston, Postdoc. UBC Botany | Keeling Lab.

Chemically fixated cells

Modern hash producers can combine beautiful macro photography with lab tests to confirm the abundance of cannabinoid acids and terpenes in Capitate-Stalked trichomes. But scientists have been studying trichomes since the 1800s.

Sir Alexander Christison of Edinburgh and Georg Martius of Germany noted that soil nutrients affect cannabis’s resin-producing glands in 1851 and 1855, respectively. (3, 4) A century later, Dr. J. Bouquet studied the glandular cells under a microscope for the United Nations Office On Drugs And Crime. (5)

Research in the 1970s began to incorporate chemical fixation with traditional and electron microscopy to analyze trichomes. But, limitations stunt the traditional method of pickling cells in aldehydes and acids. (6)

Pickling cells with a bunch of aldehydes — which people might know from their biology classes in high school with formaldehyde — is a very slow process.

And just because you’ve immersed a glandular trichome inside these aldehydes doesn’t mean all the cellular processes have stopped. Sometimes things still move around inside the cell, giving you an erroneous idea of what’s actually happening in the living state of the cell.

Sam

Viewing trichomes like never before

Better techniques now published in Current Biology (1) helped discover routes that non-polar metabolites take through the trichome’s cellular landscape before turning into CBGa, and eventually THCa or CBDa. Sam and his peers used liquid nitrogen to preserve trichomes and freeze the entire cellular complex.

We used the most modern method of preserving trichomes. And that’s using cryofixation, basically using liquid nitrogen to freeze almost every process that’s inside the cell almost instantaneously. What we see on the TEM data is a snapshot of what was happening at the very moment before we froze [the trichome] in a cryopreserved state.

Sam

Sam stated their study proposes a new model — easily controlled in experiments — that explains how trichomes produce acidic cannabinoids and mono-terpenes. Importantly, their model uses a cellular context rather than a Petri dish.

As you might expect, what happens inside a cell is an incredibly complex environment. It is not at all like adding a little bit of Kool-Aid mix with some water and then stirring it up. What we have is millions and billions of different complexes and enzymes that are all competing for different energetic reactions. 

Sam

Trichomes — not so compartmentalized

Cannabis trichomes depend on transportation within their supercellular structure to make cannabinoids and terpenes. Production starts with CBGa in a polarized cell membrane and ends with THCa outside the cell wall, in a storage cavity. Moreover, Sam’s team discovered large porous bridges in cannabis cells that whole systems pass through, which is botanically unique.

They’re much larger than typical bridges found in almost every other plant cell that exists. Those [cells] are called plasmodesmata, and they have extremely small pore sizes. They allow water molecules and other very, very small molecules to exchange between cells. But what we saw in cannabis cells is that they’re large enough for whole plastids, mitochondria, and entire organelles to exchange from one cell to another.

That’s, in part, why we ended up proposing that this is not a collection of a bunch of single cells. This is just one huge supercell biofactory that is not compartmentalized. It’s all just one big unit working together to pump out as much THCa and CBDa as they can. 

Sam

Photo courtesy of Canva.

What is the physiological role that these bridges are playing? 

We really don’t have a good idea. We only know that it permits a lot of communication between these cells. And it may be a way of having a coordinated biosynthetic process happen all at once rather than having each cell work individually. 

Sam

According to Sam, the trichome’s many components, from the physical structure to the internal transportation system, prevent auto-toxicity. And while toxic effects are averted this way, internal mechanisms elucidated by the team are takeaways from the study. Companies can easily hack transporters within yeast cells designed for cannabinoid production. Otherwise, understanding the plant will help growers dump more acidic cannabinoids and terpenes from cannabis trichomes.

Stay tuned to learn more about the transportation in trichomes and how companies might be able to hack yeast cells to make more cannabinoids and terpenes.

Sources

  1. Samuel J. Livingston, Kim H. Rensing, Jonathan E. Page, A. Lacey Samuels. A polarized supercell produces specialized metabolites in cannabis trichomes. Current Biology, 2022;
  2. Livingston SJ, Quilichini TD, Booth JK, et al. Cannabis glandular trichomes alter morphology and metabolite content during flower maturation. Plant J. 2020;101(1):37-56. doi:10.1111/tpj.14516
  3. Christison, A. 1851. On the nature, history, action and uses of Indian Hemp.; printed in the Edinburgh Monthly Journal of Medical Science for July.
  4. Martius, G. 1855. Pharmacological and medicinal studies on hemp. Jungeund Sohn, Erlangen.
  5. BOUQUET, R.J. 1950. Cannabis. Bull. Narc. 2:14-30.
  6. Hammond, C.T., and Mahlberg, P.G. (1978). Ultrastructural development of capitate glandular hairs of Cannabis sativa L. (Cannabaceae). Am. J. Bot. 65, 140–151.





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