By: Jacob Haas
If you start with the right building blocks, you can build magnificent cathedrals. The building blocks can come from humble sources: even in the Cathedral at Cologne, some bricks are made of slimy mud and pretty stained glass windows from tiny, useless, sand.
Natural things, too, have to be built by smaller things. From the bodies of many plants and animals just tiny compounds called terpenes. They are produced by a variety of plants, particularly evergreen trees, but also by termites and butterflies. They look sappy, sticky, meager and probably useless, but they glisten, and this sparkly hints at their enormous value. It turns out that they are a versatile, valuable and nearly ubiquitous building block for all kinds of magnificent things. With terpenes are built the rubber in some tires, many of the fragrances you encounter — including the smell of a hoppy beer. Terpenes even make some of the steroids inside your favorite athletes. Yes, Sammy Sosa may have built his career on terpenes. The terpene farnesene, which can be found in many plants and insects, has great potential as a renewable carbon building block, and is currently being mass-produced by a genetically modified yeast, which instead of producing alcohol produces this compound (Schofer et al. 2014). Terpenes can also serve as signaling chemicals for the plant cell, and as antimicrobials, and are oftentimes found in soaps and hygienic products.
If we want to do a more competent job of building tires, brewing beer, and making soaps out of terpenes, it might help to know something more about what the terpene is. Terpenes and terpenoids are the most common group of chemicals produced by plants, constructed from a common building block called isoprene, which is a simple five carbon molecule (Zwenger and Basu 2008)(figure3). Terpenoids can be thought of as modified terpenes, usually with added or removed methyl groups (CH3), accompanied by the presence of oxygen atoms in the molecule (Zwenger and Basu 2008). Limonene, in the top panel of figure 2, is a terpene, while the others are considered terpenoids.
A natural, common producer of terpenes and terpenoids and other chemicals, many of which have valuable commercial applications (Schilmiller et al. 2008), is a structure called the trichome. Trichomes our tiny outgrowths on the surface of the plant that come in a variety of shapes and sizes and carry out specialized functions, such as defense against herbivores. The structures are found in numerous plants for many different species, including the tomato.
These complex chemical factories, the trichomes, are also found in Cannabis plant. Trichomes cover the Cannabis plant’s flowers, stems and leaves (figure 1A). Cannabis has three distinct types of trichomes varying in size, density and location. The most common type of trichome, and the one that is of most interest, is capitate stalked trichome (figure 1b). The capitate stalked trichome usually consists of a small stalk and a glandular head filled with secretory cells, or cells that release a particular substance (Tissier 2012). Other less important trichomes are the capitate sessile and the bulbous trichome (figures 1c and D, respectively).
A variety of techniques are used to study trichomes, no matter what plant they come from. Usually the first step involves knocking off or separating the trichome from the rest of the plant material. A more advanced procedure incorporates laser microdissection to study the different parts of the trichome (Tissier 2012; Happyana et al. 2013). Once collected, our knowledge of genomics (the study of genomes, all of the genes of an organism) coupled with transcriptomics (the study of the products from the genes that will become proteins) can be applied to obtain genetic and protein data. This data is useful for the characterization of genes involved in chemical production.
However, there are some difficulties when it comes to studying glandular trichomes, such as finding a suitable model organism. Cannabis is a good candidate to study trichomes, due to the sheer amount of trichomes produced. But, mostly due to its legal status over the past six decades, Cannabis lacks a significant pool of genomic and transcriptomic data, making it harder to study.
The tomato looks like a stronger competitor based on current research (Tissier 2012; Happyana et al. 2013) that has set a strong foundation for the study of this agriculturally significant crop. The tomato has several well-developed databases, which establish the regions of the genome that are expressed, or, as we biologists call them, expressed sequence tag sites (ESTs), specifically for glandular trichomes. Other databases track insertion of new genes into the genome and mutations. On top of all that, the tomato is easily transformed, meaning that the plant can readily take up DNA from its environment, making it susceptible to genetic alteration (Tissier 2012).
But we here suggest that Cannabis not be ruled out as a suitable model organism to study.
Although research on the Cannabis plant has been virtually nonexistent over the past half-century, due to its legal status, the loosening of the laws is beginning to allow science to study this very interesting and helpful crop. Our work at the Cannabis Genomic Research Initiative (CGRI) will provide resources for those who wish to further their knowledge of the Cannabis plant and its trichome function and development. Ultimately, the development of an ultrahigh density genetic map (a genomic tool that allows us to understand the physical location of genes within a genome) will allow us to understand how the trichomes produce these important chemical compounds with a greater resolution and will enable us to more accurately pinpoint novel genes for the generation of these substances.
THCA (delta-9 tetrahidrocanabinnodiol) and other cannabinoids fall under the broad category of terpenoids, which is home to over 25,000 different chemicals (Zwenger and Baru 2008). Cannabinoids are chemicals that interact specifically with the endocannabinoid system within the human brain. All cannabinoids are terpenoids, although of course not all terpenoids are cannabinoids; as everyone knows, you cannot get high by smoking a conifer.
But trichomes are one of the star players when it comes to marijuana production; growers debate about trichome color; many suggest harvesting their plants when the trichomes are milky or when amber heads start appearing. It’s a general rule of thumb that the longer your plans are left up, the more Amber trichomes you will acquire, and a more sedative effect will be felt due to a larger number of THCA breakdown products, such as CBN (Cannabinol). But this is mostly folk wisdom. A truer understanding of trichomes could yield smokable trichomes with more specific, predictable medicinal properties.
Trichomes in Cannabis are currently being explored not just for their medicinal and psychoactive properties, but for their potential in renewable resources and synthesis of important pharmaceuticals or other biochemicals. Studying the specific terpenes in marijuana will help us to understand terpenes more generally. Harnessing the power of the trichome will enable us to invest in renewable chemical technology with direct applications to chemical, pharmaceutical, and agricultural industries, making textiles, fuels and food.
Put simply, through our work at CGRI, we will develop the tools needed to better understand cannabis, the terpenes it produces, and also terpenes more generally. Hemp has a lot to contribute, so please help us understand more about trichomes. Donate to CGRI’s research at the Agricultural Genomics Foundation, a nonprofit organization that aims to help CGRI’s cannabis investigation. Donations are tax-exempt.
As the laws change, we’re learning that Cannabis is more than the one-dimensional intoxicant that movies and music usually make it out to be. Cannabis plants — like tomatoes — are beautiful plants in and of themselves; like intricate temples built by nature. And like any nave, chapel or church, they are built on very simple bricks. Some of the tomato and the cannabis plant’s most important bricks aren’t made of mud or sand but of compounds called terpenes. If we can understand more about these bricks, we might understand more about how nature builds its temples, and we might even be able to fashion beautiful natural cathedrals of our own.
- Happyana, N., S. Agnolet, R. Muntendam, A. Van Dam, B. Schneider, and O. Kayser. 2013. Analysis of cannabinoids in laser-microdissected trichomes of medicinal Cannabis sativa using LCMS and cryogenic NMR. Phytochemistry 87:51-59.
- Schilmiller, A. L., R. L. Last, and E. Pichersky. 2008. Harnessing plant trichome biochemistry for the production of useful compounds. The Plant Journal 54:702-711.
- Schofer, S. J., D. J. McPhee, N. Moriguchi, Y. Yamana, B. Chapman, K. Hirata, and Y. Uehara. 2014. Biofene, a renewable monomer for elastomer materials with novel properties: Polymer development, characterization and use. Rubber World 250.
- Tissier, A. 2012. Glandular trichomes: what comes after expressed sequence tags? The Plant Journal 70:51-68.
- Zwenger, S. and C. Basu. 2008. Plant terpenoids: applications and future potentials. Biotechnol Mol Biol Rev 3:1-7