Cannabinoids and Where To Find Them
I wonder if, besides staring intently at your food and thinking, "This is so pretty," have you ever wondered where the magical chemicals in those delicate little florets on your joint or smoker come from?
Today, we're going to talk about the "icing" on cannabis flowers—the story of strawberry daifuku ice cream and lollipops!
Eh...icing? !
Look closely at a blooming hemp flower, and you'll see dense, frosty specks of it, like a mint ice cream covered in frosting. Get even closer, and you'll notice some of these "frosting" resemble tiny lollipops, with a stem at the bottom and a large head at the top; others resemble strawberry daifuku ice cream spread on the leaf surface. These are today's featured subjects—capitate glandular trichomes!
What are capitate glandular trichomes?
Throughout the long history of evolution, plants have developed a variety of structures to enhance their survival, and trichomes are one of them. These furry creatures provide numerous benefits, such as protecting against herbivores and insects, protecting against excessive ultraviolet radiation, maintaining temperature and humidity, and reducing infection by plant pathogens. These hairs, each with its own distinct functions, often have distinct appearances and are therefore often used by taxonomists to identify species.
Hairs can be composed of either a single cell (unicellular) or multiple cells (multicellular). Hairs are divided into two types based on the presence or absence of glands: simple/non-glandular trichomes (STs), which do not secrete; glandular-secreting trichomes (GSTs), which secrete.
The most significant and distinctive feature of glandular hairs is their ability to synthesize and secrete large quantities of metabolites (relative to their size), leading to their being described as the plant's "chemical factories." Glandular hairs typically consist of a stalk and a "glandular head," resembling small lollipops stuck to the leaf epidermis. However, sessile, branched, short, or long hairs can also be found. Depending on the size of the head and the length of the stalk, glandular hairs can be further divided into peltate and capitate types.
The frosting on cannabis flowers is actually three different types of glandular trichomes:
- Stalked capitulum glandular trichomes
- Sessile capitulum glandular trichomes
- Bulbous glandular trichomes
What are their metabolites and what do they do?
The metabolites secreted by these secretory hairs are primarily terpenoids, but also include phenylpropanoids, flavonoids, methyl ketones, and acylsugars. These compounds play an essential role in plant defense.
Terpenoids, for example, are the most common and abundant compounds found in glandular hairs. In plants of the genus Petunia (Petunia Juss.), the loss of insecticides secreted by the hairs can make the plant more susceptible to pests. Terpenoids in tomato hairs can also enhance the plant's ability to resist plant pathogens.
Acylsugars are found in the hairs of nearly all species in the Solanaceae family. These molecules act as natural surfactants, making plant leaves sticky and trapping harmful insects, even suffocating them. Wild tobacco plants, such as Nicotiana attenuata*, also use acylsugars as a defensive measure. They prefer to grow in desolate areas following wildfires. Predictably, there's no vegetation there, and anyone who ventures out will be doomed. Consequently, they face a multitude of pathogens and over twenty species of herbivorous insects, presenting a formidable challenge for survival.
They utilize acyl sugars in a somewhat unique way. The larvae of the tobacco hawkmoth (Manduca sexta*) consume acyl sugar-containing exudates from their glandular hairs while feasting on tobacco. When these sugars pass through the high pH of the hawkmoth's digestive tract, they deesterify branched-chain fatty acids, giving the larvae their distinctive odor, both in their feces and on their bodies. This scent attracts ants (Pogonomyrmex rugosus) and removes these plant-eating creatures. You're so good, Nicotiana attenuata!
That head-shaped... hair... Oh well, what does it have to do with whether I fly or not?
Seeing this, you smart people should be able to imagine what's next... and you're right! Cannabinoids familiar to pilots, such as THCA (tetrahydrocannabinolic acid) and CBDA (cannabidiolic acid), are secreted by glandular hairs on the female inflorescence. Terpenes, which give different strains their distinctive aromas, are also secreted by these hairs.
As I mentioned earlier, there are three different types of glandular hairs in cannabis. Are there any differences in their metabolites?
Is a lollipop actually just Daifuku ice cream with an extra bamboo stick?
Previous studies have found that of the three types of cannabis glandular hairs, stalked hairs have slightly larger heads than sessile hairs, while bulbous hairs have the smallest head size. Other studies have found that stalked and sessile hairs share many characteristics, leading some to hypothesize that sessile hairs may represent a pre-mature form of stalked hairs.
In 2020, a Canadian research team used various methods to investigate the feasibility of this hypothesis in cannabis plants from the Finola variety. They also sought to determine whether there were differences in the metabolite composition of stalked and sessile hairs. Finola, with its shorter plant height and rapid flowering, was a suitable candidate for this study.
Let's take a look at the results!
Three kinds of glandular hairs in a shrimp dish
To preserve the complete appearance of the glandular hairs, the research team used cryo-scanning electron microscopy (cryo-SEM) to observe the original appearance of the three types of glandular hairs. The results showed that the heads of stalked trichomes are elevated by a multicellular stalk, while sessile trichomes sit directly on the surface, perfectly resembling strawberry daifuku ice cream. Globular trichomes are smaller and have smaller storage cavities.
The storage cavity here refers to the head of the trichome, where the cells store their metabolites after secretion. Other studies have shown that the diameter of the glandular hairs of medical cannabis (high-THC) varieties is significantly larger than that of industrial cannabis (low-THC), suggesting an evolutionary trend caused by breeding.
What do metabolites look like inside the head?
The research team used fluorescence microscopy and transmission electron microscopy (TEM) to investigate the distribution of metabolites within the cavity. In addition to the three types of glandular hairs, hairs on leaves and male flowers were also included for comparison.
Fluorescence microscopy revealed that the sessile and globular glandular hairs emitted blue-shifted fluorescence (Figures b and f), while the sessile glandular hairs on the calyx of female flowers, leaves, and stamens emitted red-shifted fluorescence (Figures c, d, e). Previous studies have shown that strong blue-shifted fluorescence indicates high cannabinoid content, and have shown that of these different hair types, stalked glandular hairs have the highest cannabinoid content.
Similar results have been observed in the high-THCA varieties "Purple Kush" (https://www.leafly.com/strains/purple-kush) and "Hindu Kush" (https://www.leafly.com/strains/hindu-kush), where the autofluorescence of the stalked glandular hairs is a large, blue hue.
In addition, observations using a transmission electron microscope revealed that the cavities of the sessile glandular hairs were filled with numerous small droplets. The cavity of stalked glandular hairs is filled with a single, large droplet.
Do stalked glandular hairs have more secretory cells?
The number of cells in sessile glandular hairs on mature leaves is 8 (21 samples, each with 8 cells), and in mature calyxes is also 8 (14 samples, 11 of which had 8 cells). On the other hand, the number of cells in stalked glandular hairs on mature calyxes ranges from 12 to 16. This suggests that stalked glandular hairs have more secretory cells.
Is there a higher proportion of stalked glandular hairs?
If stalked glandular hairs develop from sessile glandular hairs, then we should see a gradual increase in the number of stalked glandular hairs as the flower matures.
The results showed that as flowers mature, the proportion of stalked glandular hairs on the calyx increases from 30% to 80-90%, and the calyx length and the proportion of stalked glandular hairs are positively correlated and statistically significant. This indicates that the more mature the calyx, the higher the proportion of stalked glandular hairs, supporting the hypothesis that stalked glandular hairs develop from sessile glandular hairs.
Chemical Composition
If sessile glandular hairs are the precursors of stalked glandular hairs, then the biochemical composition of sessile glandular hairs on the calyx should be closer to that of stalked glandular hairs than to the hairs on leaves or the sessile glandular hairs on stamens.
The research team used immature calyxes, mature calyxes, and leaves to test this hypothesis. They injected the material into pentane and extracted the material from the storage cavity using microcapillaries for chemical composition analysis.
Results showed that as the calyx matures, the monoterpenes content and the monoterpenes-to-sesquiterpenes ratio increase significantly, and the total cannabinoid content (both CBD and THC) increases. Furthermore, chemical analysis revealed distinct terpene profiles in the leaves and calyx.
Gene Expression
Transcriptome analysis revealed that the expression of genes in the three types of glandular trichomes was significantly higher than in other parts of the plant, with the majority of the expressed genes involved in monoterpenoid and cannabinoid synthesis.
Comparing the gene expression levels of the three types of glandular trichomes, the expression of certain specific genes was significantly higher in stalked and sessile trichomes than in bulbous trichomes.
This suggests that glandular hairs not only produce large quantities of cannabinoids but are also specialized as factories for secreting monoterpenoid-rich terpenes.
Furthermore, the similarities in the transcriptomes of pre- and post-maturation stalked hairs further support the hypothesis that stalked hairs developed from sessile hairs.
Summarizing the Research Results
I'm sure everyone's lost their minds after reading this, but that's okay, I was too 🫠 Let's summarize the experimental results.
- The blue-shifted fluorescence produced by shining light on stalked glandular hairs indicates a high content of cannabinoids.
- The number of secretory cells in stalked glandular hairs is greater than that in sessile glandular hairs.
- The proportion of stalked glandular hairs on the calyx increases as the flower matures.
- The terpene composition of the trichomes on the calyx and leaves differs.
- The cannabinoid and terpene contents in stalked glandular hairs are significantly higher than those in sessile glandular hairs.
- Genetic expression of calyx trichome height is associated with monoterpene and cannabinoid synthesis.
Combining these experimental results, the research team believes that the hypothesis that sessile glandular trichomes develop from sessile glandular trichomes is valid, and that the trichomes on female flowers have distinct appearance and chemical composition compared to those on leaves and male flowers.
Summary
We've discussed what glandular trichomes are, their importance to plants, and finally reviewed recent research on the icing on cannabis flowers.
Research confirms that the glandular trichomes on cannabis flowers are important producers of cannabinoids and terpenes (Popo: I'm not ruling it out). Furthermore, in addition to their appearance, sessile and sessile glandular trichomes also have different numbers of secretory cells and different terpene compositions. Furthermore, mature trichomes produce more and more fragrant cannabinoids and terpenes!
A small story with a big moral: smoke the mature stuff, not the tender grass.
Next time before your flight, take a moment to examine these exquisite lollipops and Daifuku ice cream! (Although it might be dried out and twisted.)
Use weed wisely, and have a safe trip.
References
- O-Acyl Sugars Protect a Wild Tobacco from Both Native Fungal Pathogens and a Specialist Herbivore
- Plant Glandular Trichomes - Natural Cell Factories of High Biotechnological Interest
- Cannabis glandular trichomes alter morphology and metabolite content during flower
- Secreting Glandular Trichomes: More than Just Hairs
