Updated: Nov 5
This homework assignment from Lesson 4: Trichomes from Module 1: Cannabis of our forthcoming Cannabis Foundation course gives prospective students and human resources managers a preview of the training delivered to students in preparation for certification testing.
An August 2019 study entitled "Cannabis Glandular Trichomes Alter Morphology and Metabolite Content During Flower Maturation" that was published in The Plant Journal explored the biochemical nature and lifecycle of the trichome glands that are the source of all cannabinoids and terpenes produced by hemp and cannabis.
Magnified view of stalked trichomes (multi-photon microscopy)
The study reported that its goal was to "proceed beyond the known surface features of cannabis glandular trichomes by characterizing their internal anatomy [and] biochemistry." It also stated a goal of testing the hypothesis that "stalked trichomes develop from sessile-like precursors" and whether these glands are specialized in terms of their metabolic actions, with certain types possibly focusing on production of particular terpenes and cannabinoids.
The research noted that, despite a global multibillion dollar industry that has emerged around the cannabinoids and terpenes produced by trichome glands, "the properties and relative contributions of the different types of cannabis glandular trichomes remain poorly understood."
Female plants most abundantly produce trichomes that are "consumed for medicinal and recreational purposes based on the properties of their specialized metabolites (i.e. cannabinoids and terpenes)."
The scientists explained that it is the female plants that most abundantly produce trichomes that are "consumed for medicinal and recreational purposes based on the properties of their specialized metabolites (i.e. cannabinoids and terpenes)," adding that "male flowers are typically not consumed for recreational or medical purposes due to the scarcity of glandular trichomes."
Trichomes visible to the naked eye
The research noted that the trichome glands synthesize cannabinoids that include "tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA)." Officially called acidic precursors, THCA and CBDA are converted to their more famous neutral versions, tetrahydrocannabinol (THC) and cannabidiol (CBD) (sometimes called the "active" or "bioactive" versions), via a chemical process involving heat called decarboxylation.
"The research noted that the trichome glands of cannabis synthesize cannabinoids and terpenes."
The study reported that terpenes "include monoterpenes and sesquiterpenes" [and] contribute to the fragrance of cannabis flowers and cannabis products.
Three Types of Cannabis Trichomes
The study noted that three types of trichomes exist and differ based on their "surface morphology." Sessile and stalked varieties are regarded as the "major" and most important types of trichomes.
Bulbous: Smallest in size; produce limited specialized metabolites.
Sessile: Feature "a short stalk and a globose head comprised of a multicellular disc of secretory cells and a subcuticular metabolite storage cavity."
Stalked: Shape very similar to sessile trichomes, but "slightly larger" and feature a "globose head elevated several hundred microns above the epidermal surface by a multicellular stalk."
Based on the similarity of sessile and stalked trichomes, some research investigations have categorized them as variations on a single category. Other scientists have proposed the theory that sessile trichomes are merely "a premature stage of stalked trichome development."
The study's authors reported that it "remains unclear if stalked trichomes are distinct from sessile trichomes simply by the presence or absence of a stalk, or whether stalked and sessile trichomes have additional unique characteristics" that help differentiate them.
The research observed that trichomes, regardless of type, are most dense on the calyx of the plant. Merriam-Webster defines calyx as the "usually green outer whorl of a flower consisting of separate or fused sepals" (sepals are defined as "one of the modified leaves comprising a calyx").
The research observed that trichomes, regardless of type, are most dense on the calyx of the plant.
The study found that sessile and stalked trichomes differ in terms of the number of secretory cells featured, with the sessile variety (that does not morph into the stalked type) found only on vegetative leaves, not flowers, and having "exactly eight cells." Stalked trichomes, on the contrary, featured "the largest and most variable number of cells in the secretory disc."
Stalked Trichomes Dominate
In mature plants, the study found that the number of stalked trichomes "dominated" that of sessile and bulbous varieties. "Throughout the development of the calyx, the proportion of stalked trichomes increased from less than 30 percent to 80–90 percent on the most mature calyces," reported the research.
The scientists stated that their data "support the hypothesis that stalked trichomes develop from sessile glandular trichomes" and concluded that stalked trichomes "dominate the pharmacological and sensory properties of cannabis flowers."
The study surmised that, on calyces, sessile trichomes represent "premature stalked trichomes." Interestingly, the scientists noted that, although most sessile trichomes on immature flowers "appear destined to become stalked as the calyx matures, a scant subpopulation of sessile trichomes persisted."
Trichomes Rich in Cannabinoids & Terpenes
The research reiterated what was already known: Trichomes produce large volumes of cannabinoids and terpenes (among other compounds). Of these, it noted "a substantial increase in monoterpenes during calyx maturation." Monoterpenes are the most simple type of terpene molecule. Overall, the hemp and cannabis cultivars tested revealed significant variation in terms of terpene profile.
"Trichomes on flower calyces contain mostly monoterpenes and those appearing on vegetative leaves feature mostly sesquiterpenes."
Trichomes located on the calyces populating the flowers of the herb were found to contain mostly monoterpenes, but those appearing on vegetative leaves featured mostly sesquiterpenes—a more complex and significantly larger terpene molecule. Overall, the trichomes of flowers and leaves were found to be very similar, although flowers featured many more trichomes than vegetative leaves and these trichomes typically produced greater volumes of cannabinoids.
Stalked vs. Sessile Trichomes
The study theorized that different types of trichomes may specialize in production of particular types of terpenes or terpene profiles. Stalked trichomes "were dominated by monoterpenes (92 percent of all terpene production) and featured a ratio of monoterpenes to sesquiterpenes of more than 12:1. In contrast, sessile trichomes found on vegetative leaves "contained very low monoterpenes compared to sesquiterpenes."
(a) Flowering female plant; inset: isolated floral cluster containing numerous calyces bearing densely populated trichomes; (b) calyx and styles of an individual female flower; (c) calyx of female flower; (d–f) Cryo-SEM images of the three types of cannabis trichomes: Stalked (d), sessile (e), and bulbous (f).
The research determined some differences between sessile trichomes that develop into the stalked type (on the calyx) and those that do not (on vegetative leaves) and remain sessile for their entire life. "The bona fide sessile trichomes found on anthers and vegetative leaves, which do not develop into stalked trichomes, have chemically distinct terpene profiles from the premature stalked and mature stalked glandular trichomes of cannabis flowers."
"The sessile trichomes found on vegetative leaves, which do not develop into stalked trichomes, have chemically distinct terpene profiles."
The study also revealed that stalked trichomes on mature cannabis flowers feature "a globular head consisting of an enlarged disc of greater than eight secretory cells," while sessile trichomes found on vegetative leaves "have exactly eight secretory cells" and feature fewer cannabinoids "and higher proportions of sesquiterpenes."
The scientists concluded that the glandular trichomes of cannabis and hemp "represent natural cell factories" and produce "large quantities of specialized metabolites" such as terpenes and cannabinoids.
"The findings presented here reveal that the sessile and stalked trichomes of cannabis differ not only in whether they sit on a large stalk or directly on the epidermal surface, but they also have distinct fluorescent properties, number of cells in their secretory disc, and terpene profiles."
"The stalked trichomes that densely cover the economically important cannabis flowers develop from transitory sessile-like precursors during floral development."
"Our findings support the hypothesis that the stalked glandular trichomes that densely cover the economically important cannabis flowers develop from transitory sessile-like precursors during floral development," declared the scientist. They summarized that the sessile trichomes appearing on flowers "are anatomically and biochemically distinct from sessile trichome types on anthers and vegetative leaves."
The study's authors suggested that further research into the "unique properties of these biotechnologically important structures and the genes that are highly expressed within them" is needed and that this provides "new opportunities for molecular breeding, targeted engineering, informed harvest timing, and optimized processing of this important plant."
View the original study.