How trichomes make terpenes and cannabinoids in supercell pathways

A study from the University of British Columbia used liquid nitrogen to freeze trichomes. The researchers looked inside cryofixed 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 like THCa or CBDa. Acidic cannabinoids contain an additional small molecule of carboxylic acid (COOH). And trichomes are supercellular lipid factories found on the outside of cannabis buds. However, certain highways and traffic lights along synthetic pathways within the trichome remained hidden.

Trichomes and electron microscopy

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

Sam Livingston, with a Ph.D. in Botany and Plant Biology, is a postdoctoral researcher with Professor Lacey Samuels and Keeling Lab at UBC. Professor Jon Page of UBC and Anadia Labs were co-authors of the recent trichome study. Finally, Kim Rensing, Ph.D. on the project. In a phone call with this author, Sam described the importance of her discovery (1) in two worlds of cannabinoid production – botany and biosynthesis.

When I started this project, I collected a lot of TEM (Transitional Electron Microscopy) data – really high-resolution, high-magnification images of the trichomes. I wasn’t sure what to look for, especially since all of the research up to that point had worked with what would be considered a conventional cell preservation method.

Sam Livingston, postdoc. UBC Botany | Keeling Laboratory.

Chemically fixed cells

Modern hash makers can combine beautiful macro photography with lab testing to confirm the abundance of cannabinoid acids and terpenes in Capitate Stalked trichomes. But scientists have been studying trichomes since the 19th century.

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

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

Soaking cells with a bunch of aldehydes — which people might recognize from their high school biology class with formaldehyde — is a very slow process.

And just because you submerged a glandular trichome in these aldehydes doesn’t mean all cellular processes have stopped. Sometimes things are still moving inside the cell, giving you the wrong idea of ​​what is actually happening in the living state of the cell.

Sam

See trichomes like never before

Two-photon imaging scan of trichomes by Livingston et al. 2021| Courtesy of The Plant Journal | Wiley. (2)

Better techniques, now published in Current Biology (1), helped discover pathways that nonpolar metabolites take across the trichome’s cellular landscape before turning into CBGa and eventually THCa or CBDa. Sam and his colleagues used liquid nitrogen to preserve trichomes and freeze the entire cell complex.

We used the most modern method of trichome preservation. And that’s cryofixation, basically the use of liquid nitrogen to almost instantly freeze almost every process inside the cell. What we’re seeing on the TEM data is a snapshot of what was happening just before we froze [the trichome] in cryopreserved condition.

Sam

Sam explained that their study proposes a new model — easily controllable in experiments — that explains how trichomes produce acidic cannabinoids and monoterpenes. 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’s not at all like adding a little Kool-Aid mix with some water and then stirring. What we have are millions and billions of different complexes and enzymes all competing for different energetic reactions.

Sam

Trichomes – not so divided

Cannabis trichomes rely on transport 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. Additionally, Sam’s team discovered large porous bridges in cannabis cells that traverse entire systems, which is botanically unique.

They are much larger than typical bridges found in almost every other plant cell in existence. This [bridges] are called plasmodesmata and have extremely small pore sizes. They allow the exchange of water molecules and other very, very small molecules between cells. But what we have seen in cannabis cells is that they are large enough for entire plastids, mitochondria and entire organelles to be exchanged from one cell to another.

That’s partly why we ended up proposing that this isn’t a collection of individual cells. This is just a giant supercell biofactory that is not subdivided. It’s all just one big entity working together to pump out as much THCa and CBDa as possible.

Sam

Two-photon scans of two head trichomes. (2)

What physiological role do these bridges play?

We really don’t have a good idea. All we know is that it allows for a lot of communication between these cells. And it may be a way to run a coordinated biosynthetic process all at once, rather than having each cell work individually.

Sam Livingston

According to Sam, the many components of the trichome, from its physical structure to its internal transport system, prevent autotoxicity. And while toxic effects are averted in this way, the internal mechanisms elucidated by the team are lessons learned from the study. Companies can easily hack transporters inside yeast cells engineered for cannabinoid production. Otherwise, understanding the plant will help growers discard more acidic cannabinoids and terpenes from cannabis trichomes.

Stay tuned to learn more about trichome transport and how companies can potentially 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, Stand JK, et al. Cannabis glandular trichomes change 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, effects, and uses of Indian hemp.; printed in the Edinburgh Monthly Journal of Medical Science for July.
4. Martius, G. 1855. Pharmacological and Medical Studies on Hemp. Boy and son, Erlangen. pp. 29-30.
5. BOUQUET, RJ 1950. Cannabis. Bull. Narc. 2:14-30.
6. Hammond, CT, and Mahlberg, PG (1978). Ultrastructural development of the head gland hairs of Cannabis sativa L. (Cannabaceae). Am. J.Bot. 65, 140-151.