About Elicitors

When discussing medicinal oil producing crops there are two production parameters that need to considered. Firstly, there are the yield parameters (harvest weight) and, secondly, there is the crop quality parameters (i.e. essential oil percentages).  Factors that influence outcomes regarding these two parameters can be quite different.  In simple terms, preventing any plant stress, of any kind, promotes optimum harvest weight while, in some cases, carefully promoting stress at the right points of the crop cycle can increase essential oil production without compromising yields.

What is an Elicitor?

Many of the medically useful compounds produced by plants are the result of the plant stress response. Stress may be the result of biotic or abiotic sources. Biotic sources of stress are caused by living organisms, such as a fungal pathogen or a feeding insect. Compounds produced by living organisms, such as fungal wall derivatives or signalling molecules can also be sources of biotic stress. Abiotic stress arises from non-biological stresses, such as nutrient deficiency, shortage of water or salinity. When a plant is exposed to stressors, which are also called elicitors, enzymatic pathways are induced which alter the content of secondary metabolites. This is especially true for compounds which are well known for pharmacological activity, such as terpenoids, alkaloids, and phenylproponoids.

Cannabinoids are closely related to some terpenoids which protect plants under stress. Cannabinoids and terpenoids share a similar biochemical pathway. Isopentenyl pyrophosphate (IPP) is the basic building block of all terpenoids and is produced either in the cytosol and mitochondria through the Mevalonate pathway or in the plastids through the Mevalonate-independent pathway. The Mevalonate-independent pathway is the source of all mono-, di-, and tetraterpenes which include many essential oil components. In cannabinoid synthesis, geranyl pyrophosphate (GPP) from the Mevalonate-independent pathway is combined with olivetolic acid (OA), a product of the polyketide pathway, to produce cannabigerolic acid (CBGA). CBGA is then converted to more commonly known cannabinoids such as THCA and CBDA through various synthases. Carotenoids and xanthophylls, which are also produced through the Mevalonate-independent pathway, are involved in mitigating photo-oxidative damage caused by environmental stress. Stressors like drought elicit the formation of reactive oxygen species (ROS) in the chloroplasts. Production of antioxidant compounds in the chloroplasts such as carotenoids and the xanthophylls is up-regulated in stressed plants to prevent cell damage. This may also be the case for other terpenes with antioxidant properties. Environmental stressors which normally up-regulate terpenoid synthesis and accumulation may do the same for some cannabinoids because of their related biochemical origins.

Therefore, controlled exposure to stress is shown to be an effective method to increase the production of some secondary metabolites in cannabis. For example, treatment with UV-B radiation, which is not utilized in photosynthesis, is shown to increase THC concentration[1] while drought induced stress is shown to increase essential oil production while not impacting on flower yield weight, if handled correctly.

For example, a 2018 PhD thesis (University of Guelph) on the cultivation of cannabis found:

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“Controlled application of drought can increase secondary metabolite concentrations in essential oil-producing crops. Drought increased the concentration of major cannabinoids tetrahydrocannabinol acid (THCA) and cannabidiolic acid (CBDA) by 12% and 13%, respectively, compared to the control. Further, yield per unit growing area of THCA was 43% higher than the control, CBDA yield was 47% higher, Δ9-tetrahydrocannabinol (THC) yield was 50% higher and cannabidiol (CBD) yield was 67% higher…. Increases in secondary metabolite concentration due to drought stress usually coincides with reduced growth; however, this was not the case in the study in which there was no difference in yield between drought and control groups.  Controlled drought stress may therefore be an effective horticultural management technique to maximize both floral weight and cannabinoid yield in cannabis, although results may differ with cannabis or cultivar chemotype.” [2]

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Elicitor Molecules which Activate Defence Pathways

Accumulation of defensive secondary metabolites is a well-studied strategy of plants against various adversary environmental stresses, and it especially occurs in plants exposed to pathogens or elicitors. Pathogens or elicitors stimulate biosynthesis of defensive secondary metabolites through various signal transduction pathways.

Among these pathways is the jasmonate (JA) pathway, the salicylic acid pathway and the abscisic acid (ABA) pathway.  Jasmonic acid (JA), abscisic acid (ABA) and salicylic acid (SA) play important roles in plant defense systems.

Elicitor molecules such as salicylic acid (SA) and methyl jasmonate (MJ) are known to induce the production of secondary metabolites when added to culture medium (Shanks and Morgan 1999) and promote the production of terpenes (Penuelas et al. 2007), while application of abscisic acid (ABA) to flowering cannabis plants has been shown to increase THC while reducing some terpenes.[3] Through carefully activating the defence pathways in plants, at the right point of the crop cycle, growers are able to improve crop quality.

Resin Finish was developed over several years through North American based crop trials where the final quality and quantity of end product was evaluated through essential oil lab analysis. What was discovered was that by activating two of the key defense pathways in the plant towards the end of the crop cycle THC percentage is increased by 8 – 12% and CBD by 5 – 10% in many cultivars.

A Warning on Elicitation

Eliciting higher oil production comes down to inducing a stress response in medicinal plants. The problem with this is that plant stress can very easily result in reduced yields. For example, drought stress is linked to significant yield losses.  For this reason, growers SHOULD NOT randomly induce stress in the hope of getting higher oil yields. Elicitation must be handled very carefully to ensure that higher oil production occurs while yields ARE NOT impacted.

Another issue also presents in that some genetics (particularly some landraces and poly hybrids) are prone to turning hermaphrodite under stress. As a result, stress induction might be the last thing a grower wants to do with some genetics.

Resin Finish was developed with these issues in mind. Because it is used during the very latter stages of the crop cycle, yield losses won’t occur and the potential for hermaphrodite plants is negated.

Note: all actives used by Med-Tek products are carefully considered, researched and tested. We NEVER use potentially harmful to human health actives. Resin Finish, therefore, contains no synthetic chemical actives that pose risk to end consumer health.

References

[1] Lydon, J., a H. Teramura, and C.B. Coffman. 1987. UV-B radiation effects on photosynthesis, growth and cannabinoid production of two Cannabis sativa chemotypes. Photochem. Photobiol. 46:201–206.

[2] Deron M. Caplan. Propagation and Root Zone Management for Controlled Environment Cannabis Production. PhD thesis, University of Guelph, 2018

[3] Mansouri, H. Asrar, Z. Szopa, J.  Effects of ABA on primary terpenoids and Δ⁹-tetrahydrocannabinol in Cannabis sativa L. at flowering stage. Plant Growth Regulation 2009 Vol.58 No.3 pp.269-277 ref.42