UVB and THC Production
Pate, D.W., 1994. Chemical ecology of Cannabis. Journal of the International Hemp Association 2: 29, 32-37.
The production of cannabinoids and their associated terpenes in Cannabis is subject to environmental influences as well as hereditary determinants. Their biosynthesis occurs in specialized glands populating the surface of all aerial structures of the plant. These compounds apparently serve as defensive agents in a variety of antidessication, antimicrobial, antifeedant and UV-B pigmentation roles. In addition, the more intense ambient UV-B of the tropics, in combination with the UV-B lability of cannabidiol, may have influenced the evolution of an alternative biogenetic route from cannabigerol to tetrahydrocannabinol in some varieties.
Another stress to which plants are subject results from their daily exposure to sunlight. While necessary to sustain photosynthesis, natural light contains biologically destructive ultraviolet radiation. This selective pressure has apparently affected the evolution of certain defenses, among them, a chemical screening functionally analogous to the pigmentation of human skin. A preliminary investigation (Pate 1983) indicated that, in areas of high ultraviolet radiation exposure, the UV-B (280-315 nm) absorption properties of THC may have conferred an evolutionary advantage to Cannabis capable of greater production of this compound from biogenetic precursor CBD. The extent to which this production is also influenced by environmental UV-B induced stress has been experimentally determined by Lydon et al. (1987). Their experiments demonstrate that under conditions of high UV-B exposure, drug-type Cannabis produces significantly greater quantities of THC. They have also demonstrated the chemical lability of CBD upon exposure to UV-B (Lydon and Teramura 1987), in contrast to the stability of THC and CBC. However, studies by Brenneisen (1984) have shown only a minor difference in UV-B absorption between THC and CBD, and the absorptive properties of CBC proved considerably greater than either. Perhaps the relationship between the cannabinoids and UV-B is not so direct as first supposed. Two other explanations must now be considered. Even if CBD absorbs on par with THC, in areas of high ambient UV-B, the former compound may be more rapidly degraded. This could lower the availability of CBD present or render it the less energetically efficient compound to produce by the plant. Alternatively, the greater UV-B absorbency of CBC compared to THC and the relative stability of CBC compared to CBD might nominate this compound as the protective screening substance. The presence of large amounts of THC would then have to be explained as merely an accumulated storage compound at the end of the enzyme-mediated cannabinoid pathway. However, further work is required to resolve the fact that Lydon’s (1985) experiments did not show a commensurate increase in CBC production with increased UV-B exposure.
This CBC pigmentation hypothesis would imply the development of an alternative to the accepted biochemical pathway from CBG to THC via CBD. Until 1973 (Turner and Hadley 1973), separation of CBD and CBC by gas chromatography was difficult to accomplish, so that many peaks identified as CBD in the preceding literature may in fact have been CBC. Indeed, it has been noted (De Faubert Maunder 1970) and corroborated by GC/MS (Turner and Hadley 1973) that some tropical drug strains of Cannabis do not contain any CBD at all, yet have an abundance of THC. This phenomenon has not been observed for northern temperate varieties of Cannabis. Absence of CBD has led some authors (De Faubert Maunder 1970, Turner and Hadley 1973) to speculate that another biogenetic route to THC is involved. Facts scattered through the literature do indeed indicate a possible alternative. Holley et al. (1975) have shown that Mississippi-grown plants contain a considerable content of CBC, often in excess of the CBD present. In some examples, either CBD or CBC was absent, but in no case were plants devoid of both. Their analysis of material grown in Mexico and Costa Rica served to accentuate this trend. Only one example actually grown in their respective countries revealed the presence of any CBD, although appreciable quantities of CBC were found. The reverse seemed true as well. Seed from Mexican material devoid of CBD was planted in Mississippi and produced plants containing CBD.
Could CBC be involved in an alternate biogenetic route to THC? Yagen and Mechoulam (1969) have synthesized THC (albeit in low yield) directly from CBC. The method used was similar to the acid catalyzed cyclization of CBD to THC (Gaoni and Mechoulam 1966). Reaction by-products included cannabicyclol, delta-8-THC and delta-4,8-iso-THC, all products which have been found in analyses of Cannabis (e.g., Novotny et al. 1976). Finally, radioisotope tracer studies (Shoyama et al. 1975) have uncovered the intriguing fact that radiolabeled CBG fed to a very low THC-producing strain of Cannabis is found as CBD, but when fed to high THC-producing plants, appeared only as CBC and THC. Labeled CBD fed to a Mexican example of these latter plants likewise appeared as THC. Unfortunately, radiolabeled CBC was not fed to their plants, apparently in the belief that CBC branched off the biogenetic pathway at CBD and dead ended. Their research indicated that incorporation of labeled CBG into CBD or CBC was age dependent. Vogelman et al. (1988) likewise report that the developmental stage of seedlings, as well as their exposure to light, affects the occurrence of CBG, CBC or THC in Mexican Cannabis. No CBD was reported.
Ultra-violet B light is a spectrum of light that is invisible to us but is visible to insects and some other organisms. In humans it causes suntan and sunburn and is implicated in the formation of eye cataracts. It is the light emitted by tanning bulbs.
UVB light also affects marijuana potency. The potency of high quality marijuana increases in direct ratio to the amount of UVB light it receives. This is very significant. In California, where the medical dispensaries operate in an unrestricted market; many dispensaries reject fall harvested outdoor material as inferior. They have found it lacks the potency of indoor crops and is a harsh smoke. However, when they were presented with marijuana grown outdoors but forced to ripen August 10, they accepted it as if it were indoor because of its high potency and lack of harshness. I think the harshness results from cool nights.
Indoors, under fluorescent and HPS lamps, gardens receive little UV-B light. Metal halides emit a bit more. However, there are ways of supplying your garden with UV-B light. Tanning lamps work, that is, lamps that tan people, because of the UV-B light they emit. Using tanning lamps will increase the THC content of the crop. Reptiles and lizards require the spectrum to stay healthy. So the spectrum usually comprises about 10 percent of their output. If you want to try tanning lamps they are available on the Internet. Use between 5-10 percent of your total wattage to these lamps. For a 1000-watt garden use 100 watts of special lighting. The Solis-Tek 10K metal halide bulb emits a tremendous amount of UVB and measured with a specific UVB meter, the SolarMeter 6.2,
Adding UV-B light to your garden will enhance your marijuana naturally, without “special formulas” and chemicals.
Although the chemistry of Cannabis has come under extensive investigation, more work is needed to probe the relationship of its resin to biotic and abiotic factors in the environment. Glandular trichomes are production sites for the bulk of secondary compounds present. It is probable that the cannabinoids and associated terpenes serve as defensive agents in a variety of antidessication, antimicrobial, antifeedant and UV-B pigmentation roles. UV-B selection pressures seem responsible for the distribution of THC-rich Cannabis varieties in areas of high ambient radiation, and may have influenced the evolution of an alternate biogenetic pathway from CBG to THC in some of these strains. Though environmental stresses appear to be a direct stimulus for enhanced chemical production by individual plants, it must be cautioned that such stresses may also skew data by hastening development of the highly glandular flowering structures. Future studies will require careful and representative sampling to assure meaningful results.
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