Cannabis – Know the trichomes

    31-Jan-2020
Dr Sona A Pungavkar
Trichomesare living cells,found on the surface of the Cannabis plants, usually on the flowers, but can also be seen on the stems and leaves. These are outgrowths of the epidermis, resembling hairs. These are shaped differently ranging from thin branches, to star shape, short and curly or long and straight. Trichomes cause the glistening appearance of the tips of the Cannabis plant and also it’s sticky feel. These appear as crystals or frost, having a whitish appearance
The trichomes have protective functions as the mammalian hair, including protection from insects, animals, wind, frost and to avoid water loss by providing a cover.
Trichomes can be non-glandular and glandular. Non-glandular trichomes predominantly have a protective function and do not produce the psychoactive compounds.
Three main types of glandular trichomes are found in the Cannabis plant. These include bulbous, capitate–sessile and capitate-stalked.
Bulbous trichomes are the smallest types of glandular trichomes and are hardly visible to the naked eye. These measure 10-30 micrometers in length and are less abundant of the three. Each bulbous trichome is constituted by few cells in a short stalk and a bulb-like tip, which secretes the sticky material or the resin.
Capitate sessile trichomes are medium in size measuring between 25 to 100 micrometers in length. These are more abundant than the bulbous variety, covering the Cannabis plant. A single cell stalk and a round gland at the tip makes up the capitate sessile trichome. The gland at the top is made up of few cells giving it a rosette appearance.
Capitate stalked trichomes are the largest of the three measuring from 50 to 500 micrometers. These are also the most abundant and also produce higher concentrations of the Cannabinoids and other compounds. Appearing at the time of flowering, these trichomes coat the calyces, which are found around the newly formed buds. These can be visualised with the naked eye, as having elongated stalks with swollen glandular heads. The growers concentrate on these trichomes to assess the time for harvesting.
The glandular trichomes produce the main ingredients of the compounds, namely the  cannabinoids, terpenes, and flavonoids, including THC and other phytocannabinoids. We already know that phyocannabinoids produced by the cannabis plant produce numerous psychotropic and therapeutic effects by interacting with the endocannabinoid receptor system of the body. Terpenesand flavonoids are compounds predominantly providing the aroma and flavors and enhance the effect of the phytocannabinoids.  
Cannabinoids, terpenes, and flavonoids are produced within the trichome cells through biosynthesis. This process utilizes specific enzymes,which initiate and continue chemical reactions on simple substrates to produce complex molecules.
On a molecular level, the activity is as follows. Enzymes in the cells of the trichomesbind to one or two small molecules (substrates), attach the substrates to each other, then pass the small molecule down to another enzyme that processes it, making small changes to the small molecule (cyclization).
The first cannabinoid to be formed is CBGA or cannabigerolic acid from a biosynthetic reaction that joined two smaller pieces together. It contains a carboxylic acid group.
CBGA is the precursor to other natural phytocannabinoids, getting converted into THCA, CBDA, or CBCA via the respective enzyme.
On heating, carboxylic acid groups spontaneously break off the cannabinoid structures, forming carbon dioxide (CO2) gas.
This process is called decarboxylation and involves the loss of the acidic group.
For example, decarboxylated CBGA becomes CBG and THCA becomes THC. It is a degradation process and does not require enzymes and occurs after the plant is harvested.
So, the presence or absence and concentration of a certain enzyme will determine the predominance of a certain cannabinoid in a given strain.
When cannabis flower is harvested at the correct time and dried adequately, the most prominent cannabinoids will be the acidic forms of the cannabinoids (THCA, CBDA, CBCA, or CBGA). When treated with heat, as during smoking or manufacturing edibles, these molecules undergo decarboxylation. The decarboxylatedproducts include delta-9-THC, cannabidiol (CBD), and cannabichromene (CBC).
All these processes happen in the trichomes. As the trichomes are small, magnifying instruments are used to look for a clear or cloudy appearance. When the trichomes appear amber in colour, these are already ripe.
The appearance of the trichomes is important to decide the time for harvesting.When the pistils or the stalks appear white, it is too early to harvest.
Harvesting when 60-70% of trichomesare dark, allows for high levels of THC in the plant extract, while when more than 70 % of the trichomesare dark THC is converted into CBN, which has a more calming and anti-anxiety effect. This knowledge helps in choosing a strain with a particular cannabinoid in higher concentration. The goal is, usually, to harvest at a time when THC content is highest
The author is a Cannabis researcher, a senior radiologist and Vice President, Cannabis Health and Sciences.