Deep Dive: Cannabis Trichomes are Cannabinoid Factories

This Deep Dive serves two roles: First as a homework assignment for the Cannabis Foundation: Part 1 course and second as part of Higher Learning's Deep Dive Subscription.

For Deep Dive subscribers: This Deep Dive serves as a research review that summarizes four peer-reviewed research studies on the topic of CBD for mood disorders. This article is a living document that is updated regularly based on the release of new research on this topic.

For students of Cannabis Foundation: Part 1, welcome to the first homework assignment for Module 1: Cannabis 1 > Lesson 4: Trichomes. In this assignment, students will learn about the chemistry and business significance of glandular trichomes. This assignment teaches students the results of a 2021 study about the trichomes of cannabis/hemp/marijuana plants that produce nearly all of the cannabinoids and terpenes within the plant.

This 2,000-word in-depth study summary teaches students the details of cannabis trichomes, including the purpose, function, and overall role of trichomes. It explains the three types of glandular trichomes (non-glandular trichomes also exist) and the factors that affect the terpene and cannabinoid yield of trichomes.

A September 2021 research study entitled "Cannabis Glandular Trichomes: A Cellular Metabolite Factory" that was published in the journal Frontiers in Plant Science provides an overview of "our current understanding of cannabis glandular trichomes and their metabolite products to identify current gaps in knowledge and to outline future research directions." The study involved researchers from Germany, Israel, and China.

The researchers noted the need to validate the results of previous research on the plant is critical due to the lack of "uniform standards" employed in past studies. It also noted the need to replace the current misinformation surrounding marijuana "production 'folklore'" with solid science and evidence-based procedures "is paramount, yet challenging due to the impact of genotype [genetics] and growing environment."

The scientists also spotlighted the "decades-long stigma surrounding cannabis" and its role in generating and maintaining "the misconceptions surrounding the plant."

The study noted that "the key compounds of Cannabis plants are cannabinoids, which are produced by stalked glandular trichomes located on female flowers." It explained that trichomes appear on the plant surface, are not limited to the cannabis species, and provide "a variety of functions and benefits to the plant" that include "affecting leaf temperature and photosynthesis or more complicated functions, such as pest-deterrence via their physical structures or production of compounds."

"The nearly microscopic trichomes glands that appear on mature flowers of female cannabis plants are the sole source of cannabinoids and terpenes."

The research reported that "trichomes develop a secretory cavity between secretory disk cells and the cuticle where secondary metabolites, including cannabinoids and terpenes, are deposited and stored." In other words, the nearly microscopic trichomes glands that appear most on the mature flowers of female cannabis plants are the sole source of the cannabinoids and terpenes that are so coveted by cannabis consumers—be they medical or lifestyle (adult-use or recreational) consumers.

"While male plants produce small amounts of cannabinoids...the primary products are the female flowers clustered in inflorescences ("inflorescences" are defined by Merriam-Webster as "the mode of development and arrangement of flowers on an axis" and "the budding and unfolding of blossoms").

Image courtesy Darryl Glubczynski

The study explained that the glandular trichomes produce important "metabolites" such as "tetrahydrocannabinolic acid (THCA), cannabidiolic acid (CBDA), terpenes, and flavonoids" and that the volumes and relative ratios (profiles) of these chemicals "are influenced by genetics and the cultivation environment, highlighting the importance of controlled conditions for cannabis cultivation."

The scientists proposed that the mainstream society is beginning to accept the medicinal uses of cannabis and the cannabinoids that the herb produces that is supported by "peer-reviewed research and clinical trials." This is resulting in an increase in "the global demand for medicinal cannabis products" that is pressuring cultivators "to improve control over the concentration of specific cannabis metabolites."

The study reported that commercial cultivation strategies "need to be centered around trichomes as the 'factories' of the plant." The study's authors noted that trichomes are "ultimately responsible for yield and quality control" and that it is, therefore, important for the cannabis industry to "advance our understanding of how [trichomes], specifically, are affected by these efforts, as well as to investigate new approaches to broaden the scope of possible cost-effective applications for improving yield."

The researchers noted that trichome glands are certainly not exclusive to the cannabis plant species and that they can be found "across the plant kingdom."

The researchers noted that trichome glands are certainly not exclusive to the cannabis plant species and that they can be found "across the plant kingdom, displaying a stunning variety of shapes and properties." All trichomes "arise from the epidermis [outer skin] on [the] vegetative and reproductive organs of plants" and that there are two general types of these glands: Secretory and non-secretory.

Cannabis trichomes are secretory, meaning that they manufacture, or secrete, certain metabolites and other chemical compounds. In the case of cannabis and hemp, these metabolites manifest as medicinal cannabinoids (including cannabidiol, or CBD) and tetrahydrocannabinol, or THC) and aromatic terpenes.

The study emphasized that genetic studies of the cannabis plant and, more specifically, many characteristics of glandular trichomes "are imperative to investigate the factors that influence trichome development in cannabis, both within and between cultivars [strains]." It argued that commercial cannabis cultivators and their customers will suffer without "precise cannabis trichome control."

Microscopic trichome image

The study identified a "plethora of cannabinoids" that have been discovered to be produced by the glandular trichomes of marijuana, many of which have only recently been identified. As of late 2021, the total known number of cannabinoids is "just over 110," which the study reports "can be divided into 11 subclasses." All of these cannabinoids are exclusive to the cannabis species and are produced by no other plant.

Hemp oils contain more monoterpenes and "score better on olfactory evaluations than oils containing more sesquiterpenes."

Terpenes, which "impart floral aroma and flavor," number approximately 120 from cannabis and are broadly categorized as either monoterpenes (the most simple and molecularly light variety of terpene) or sesquiterpenes (a considerably more complex molecule).

Interestingly, the research noted that hemp oils contain more monoterpenes and "score better on olfactory evaluations than oils containing more sesquiterpenes." However, the study also noted that oils that contain a mix of both monoterpenes and sesquiterpenes "scored highest on scent tests."

The study explained that, in the past, the scientific literature described three types of trichomes: Capitate-sessile, capitate-stalked, and bulbous and that this assessment was based on morphology (shape and size) and "structural assessments [determined] by scanning electron microscopy."

Bulbous trichomes are small and low, the sessile variety is "comprised of a globular head on a very short stalk," and stalked trichomes feature "a larger globular head on a long stalk." Most important for commercial cultivators and industry professionals, of the three varieties of trichomes, the stalked type "produce the greatest amount of cannabinoids."

Important for commercial cultivators and industry professionals, of the three varieties of trichomes, the stalked type "produce the greatest amount of cannabinoids."

The research noted that "a recent [2019] study on trichome anatomy revealed that sessile trichomes on vegetative leaves consistently have exactly eight secretory disk cells, while stalked glandular trichomes on mature flowers have 12–16" and that these numbers are consistent across hemp and drug-type [delta-9 THC-bearing marijuana] varieties.

(A) An individual inflorescence, with majority of the organs covered in stalked glandular trichomes. Arrow indicates cluster of calyces and bracts covered with trichomes. (B) Dark field micrograph of stalked glandular trichomes protruding from calyx epidermis. Biosynthesis of secondary metabolites occurs in the secretory disk cells lining the base of the globular trichome head. The metabolites are stored in the clear subcuticular cavity above the secretory disk cells; this cavity will turn milky white to dark brown over the course of flower maturity. (C) Graphic illustration of stalked glandular trichome structure.

The study explained that two varieties of sessile trichomes exist, one that is expressed on the vegetative leaves and other non-flower areas of the plant and another that populates the immature flowers and eventually grows into the stalked variety. In the past, researchers considered all sessile trichomes to be the same because they did not understand that the flower-based (calyx-based) versions are merely juveniles that will morph into "adult" stalked versions as the plant matures and approaches harvest.

(Because the research behind this trichome insight was published as recently as 2019, prior scientific investigations often employ incorrect labels and descriptions of these important elements of cannabis plant anatomy.)

The study emphasized that environmental factors cause a particular cultivar (also called chemovars or chemotypes) to alter its production of metabolites such as cannabinoids and terpenes. This variability in trichome production dynamics is not limited to environmental conditions, including temperature, fertilization, humidity, and particularly light type (source) and intensity (as well as a host of other important conditions).

"Flowers sampled from the upper region of the plant produce significantly greater quantities of cannabinoids and terpenes than lower positions."

"For example, flowers sampled from the upper region of the plant produce significantly greater quantities of cannabinoids and terpenes than lower positions," stated the research, identifying "light source and plant maturity" as "important factors influencing the concentration and/or amounts" of terpenes and cannabinoids.

The study's authors lamented the fact that "knowledge regarding how these factors influence growth and trichome formation is limited" and that the emerging cannabis industry must "produce scientific evidence to support links between metabolite production and environmental factors."

While noting that trichomes are most dense on the flowers of the plant, the study explained that this is likely "to protect the reproductive organs" of the plant to help it propagate and to ensure the survival of the species. Because one of the main evolutionary functions of trichomes and the terpenes and cannabinoids that they produce is to protect the plant from sun damage, "genotypes that originate from closer to the equator will produce higher levels of cannabinoids due to the higher incidence of UVB radiation in that region."

It is theorized that terpenes "act as deterrents against [pests and predators]" and that the monoterpenes α-pinene and limonene repel insects and "are present in higher concentrations in the flowers [of the plant] while sesquiterpenes, which are bitter to mammals, have greater concentrations in the lower leaves."

Terpenes "act as deterrents against [pests and predators]" and that the monoterpenes α-pinene and limonene repel insects.

The scientists explained that the viscosity of the gooey resin produced by cannabis trichomes is determined by the "ratio of monoterpenes to sesquiterpenes" and that the cannabinoid acidic precursors cannabigerolic acid (CBGA) and THCA "are toxic to insects" to protect the plant "and critical tissues like flowers as they develop."

While one of the evolutionary function of terpenes is protection of the plant via a reduction in "the risk of pest-related damage," cannabinoids convey a wide range of potential medicinal properties for humans, including antimicrobial characteristics. In fact, ten "key cannabinoids" have "significant antibacterial activity against several methicillin-resistant Staphylococcus aureus strains."

These cannabinoids include "THC, CBD, cannabichromene (CBC), cannabigerol (CBG), and cannabinol (CBN) and their acid precursor forms" (THCA, cannabidiolic acid (CBDA), cannabichromenic acid (CBCA), CBGA, and cannabinolic acid (CBNA).

Cannabinoids produced by trichomes include "CBC, CBD, CBG, CBN, and THC and their acid precursor forms" CBCA, CBDA, CBGA, CBNA, and THCA.

The study reported that cannabinoids, "including those that are typically secreted in low concentrations, have a broad range of benefits, acting both within and outside the plant [in humans]." It noted that more than 200 cannabinoid and terpene compounds, combined, have been identified and that the "costs for producing this vast number of secondary metabolites must be investigated to elucidate their individual benefits and roles in plant function."

The study called for further research to produce the scientific evidence that is "required to prove that these compounds are not simply by-products of other biological processes, but truly have a primary role in defense mechanisms." Importantly, the research recommended that future studies "should not only include cannabis cultivars that are the result of centuries of breeding, but also naturally occurring types that are not products of human selection activity, though these are rarely available."

The study's authors reported that trichomes "in other plant species have been well characterized in recent decades" and that it is important that "our understanding of cannabis trichomes reach similar levels of comprehension."

"The more we understand about trichomes, the more applicable our knowledge of this plant will be to those along the chain of production and consumption."

The scientists stated that the ability for commercial cannabis cultivators to "consistently replicate specific [cannabinoid and terpene] concentrations and combinations" produced by glandular trichomes would deliver great "benefits for both producers, medical practitioners, and consumers."

"The more we understand about trichomes, the more applicable our knowledge of this plant will be to those along the chain of production and consumption," concluded the researchers.

View the original study.