The essential oil industry is a billion-dollar-a-year business that doesn’t show any signs of slowing down. Essential oils derived from plants, including mint, basil and thyme, are key ingredients in products such as medicines, aromatic fragrances and flavorings.
Demand for these products has been the driving force behind countless research studies conducted with the goal of understanding how and why plants produce these unique chemical compounds, and how growers can enhance the production of these compounds. The research begins with the glandular trichome.
Glandular trichomes are tiny, specialized, hair-like formations found on the epidermis of plant stems and leaves. At the tip of the hairs are glandular cells that produce, store and eventually secrete exudates such as essential oils. Nearly all plant species produce some sort of hair-like formation, but only about 30% of vascular plants have the ability to create these sought-after substances.
Glandular trichomes come in several different shapes that are highly species-specific, to the point where they are often a characteristic used in the classification and identification of a plant species.
The different types of glandular trichome exudates include terpenoids, phenylpropenes, flavonoids and methyl ketones. To understand what these unique chemical compounds are, we must first address why they are produced.
The Secondary Metabolism
Glandular trichomes are not directly connected to a plant’s vascular system and therefore are not products of a plant’s primary metabolism. Primary metabolites—products of the primary metabolism—are compounds that play an important role in the basic life functions that allow plants to properly complete their full growth cycle, such as respiration, reproduction, cell division and growth.
Secondary metabolite compounds, such as the exudates secreted by glandular trichomes, are not directly involved in these essential functions, but they do serve an important purpose. Secondary metabolite compounds are believed to play a major role in a plant’s ability to adapt to the dangers of their environment.
These compounds provide a level of defense against possible antagonists with antifungal, antibiotic and antiviral properties. These properties are the reason these compounds are sought after for medicinal purposes.
Not only do secondary metabolites help protect plants from microscopic assailants, but they also help protect them from various insects and animals because some of the compounds secreted can cause severe discomfort when ingested. In addition, they also contain UV ray-absorbing compounds that protect the leaves from potential harm from sunlight.
For years, scientists have been working on ways to increase glandular trichome production in numerous plant species in an effort to collect as much of the desired essential oils from one plant as physically possible.
Since glandular trichomes are the result of a plant’s protective measure against a danger in the environment, the question is how do we simulate a stressful situation in nature to enhance the production of these secondary metabolites on our plants at home?
Simulating a Stressful Situation
A plant’s glandular trichome production potential is the result of genetics developed through interactions with the surrounding environment. Plants that evolved in a more threatening environment generally have a higher level of glandular trichome production. But through certain stimuli, production levels can be increased in the home garden.
I would never suggest releasing harmful pests into a controlled growing environment, but there are ways to cause physical stress to a plant without greatly harming the growth cycle. Older leaves and branches can be cut to make the plant think that it is under attack.
Growers can also supplement with artificial UVA or UVB lighting in an effort to simulate some environmental stressors. In nature, UV radiation from the sun can reduce the rate of photosynthesis in the leaves, which can directly affect a plant’s ability to grow properly. The trichomes produced by the plant help protect it from different types of UV radiation. Supplementing with UV indoors should, theoretically, have the same affect.
There are also several fertilizer supplement products that are marketed as having the ability to enhance glandular trichome production. I have used a few on my culinary herb garden with satisfactory results, but judging by the product labels, it is hard to pinpoint the active ingredient or ingredients that provide such results.
Studies have shown that the naturally occurring plant hormone jasmonate plays an important role in triggering the pathways that create secondary metabolites and scientist have figured out how to create, in a lab, a synthetic version of the hormone which is called jasmonic acid.
However, a grower should show due diligence and research any possible harms when considering using a growth regulating hormone of any type, especially if the plant is intended for eventual human consumption.
Glandular trichomes are the product of a plant striving to survive in an often-unforgiving environment. But to humans, they represent so much more. Though we use them for their beneficial medicinal properties, we also enjoy their delicious flavors and amazing aromas. Substances created within glandular trichomes enhance our daily lives and prove that, no matter what, we are still strongly attached to the plants we grow and the nature that surrounds us.