Cannabis plants are known for being sticky and smelly. These two traits are attributed to structures called glandular trichomes. In dried cannabis, you might notice these as the crystals that cover cannabis flowers. Trichomes contain cannabinoids as well as odorous molecules called terpenes. Scientifically, we call these “secondary metabolites” because they are molecules that are not critical to plant function and development but play a supporting role. In nature, cannabinoids and terpenes help to repel herbivores, pests, and pathogens. For cannabis consumers, they offer biological effects as well as sensory effects like giving cannabis strains unique smells and flavors.

Cannabis Breeding and Genetics

Cannabis has a long history of cultivation and domestication [1]. Early on, it was noticed that you could selectively breed plants with desirable effects to strengthen those effects. While some cultures targeted increased seed or fiber production in hemp, others sought to increase the psychoactive effects of marijuana. This divergence in types of cannabis began thousands of years ago and continues today. Through selective breeding, genetic traits are isolated and enhanced. In the case of cannabinoid potency, chromosome 9 holds the key. Different variations of genes on this chromosome lead to cannabis plants with differing cannabinoid profiles and more or less potential potency.

Cannabinoid Biosynthesis

Glandular trichomes can be thought of as the “chemical factories” of the cannabis plant [1]. They manufacture, store, and excrete secondary metabolites. This occurs through two biosynthetic pathways. The first pathway creates a type of molecule called a polyketide. Polykeytide synthesis produces the components that are needed to synthesize cannabinoids, namely olivetolic acid (OA). The second pathway is the methylerythritol 4-phosphate (MEP) pathway. This pathway synthesizes two compounds (isopentenyl diphosphate and dimethyl allyl diphosphate) that combine to form geranyl pyrophosphate (GPP). GPP is the monoterpene portion in cannabinoid synthesis.

Together, OA and GPP create cannabigerolic acid (CBGA). CBGA is the precursor to all other cannabinoids like tetrahydrocannabinolic acid (THCA) and cannabidiolic acid (CBDA). Prior to heat exposure or degradation, cannabinoids are all in their “inactive” form which is an acid. However, a small amount of conversion does occur in the exterior cell wall of the trichomes where these cannabinoids are synthesized and stored.

Enhancing Cannabis Potency

Along with genetic potential, environmental factors like lighting and nutrition also play a big role in glandular trichome development and the synthesis of cannabinoids [1]. While many are aware of the benefits of good lighting and proper nutrient feeding, there are other compounds that can also be used to alter cannabinoid development. Plant hormones like gibberellic acid, methyl jasmonate, and salicylic acid impact cannabinoid synthesis and are examples of materials used to encourage productivity in cannabis plants. The statin compound mevinolin can be used to inhibit THC production and polyploidization treatments can enhance CBD production without impacting THC.

Breeding Better Cannabis

Cannabis has many potential applications in and outside of medicine. While recreational marijuana growers are mainly concerned with enhancing THC potency, hemp growers need to minimize THC production and maximize CBD production. Medicinal cannabis growers might seek to create more balanced strains that balance the psychoactive and non-psychoactive benefits of cannabis for health conditions. In any of these cases, breeders can benefit from understanding the process of cannabinoid biosynthesis and experimenting with the use of novel inputs like plant hormones in addition to their traditional approaches.

References

  1. Xie, Z., Mi, Y., Kong, L., Gao, M., Chen, S., Chen, W., … & Xu, Z. (2023). Cannabis sativa: origin and history, glandular trichome development, and cannabinoid biosynthesis. Horticulture Research, uhad150.

https://academic.oup.com/hr/advance-article-pdf/doi/10.1093/hr/uhad150/50961844/uhad150.pdf

Sabine Downer
Author: Sabine Downer