Cannabinoids and Terpenes: How Production of Photo-Protectants Can Be Manipulated to Enhance Cannabis sativa L. Phytochemistry

Abstract

Cannabis sativa L. is cultivated for its secondary metabolites, of which the cannabinoids have documented health benefits and growing pharmaceutical potential. Recent legal cannabis production in North America and Europe has been accompanied by an increase in reported findings for optimization of naturally occurring and synthetic cannabinoid production. Of the many environmental cues that can be manipulated during plant growth in controlled environments, cannabis cultivation with different lighting spectra indicates differential production and accumulation of medically important cannabinoids, including Δ⁹-tetrahydrocannabinol (Δ⁹-THC), cannabidiol (CBD), and cannabigerol (CBG), as well as terpenes and flavonoids. Ultraviolet (UV) radiation shows potential in stimulating cannabinoid biosynthesis in cannabis trichomes and pre-harvest or post-harvest UV treatment merits further exploration to determine if plant secondary metabolite accumulation could be enhanced in this manner. Visible LED light can augment THC and terpene accumulation, but not CBD. Well-designed experiments with light wavelengths other than blue and red light will provide more insight into light-dependent regulatory and molecular pathways in cannabis. Lighting strategies such as subcanopy lighting and varied light spectra at different developmental stages can lower energy consumption and optimize cannabis PSM production. Although evidence demonstrates that secondary metabolites in cannabis may be modulated by the light spectrum like other plant species, several questions remain for cannabinoid production pathways in this fast-paced and growing industry. In summarizing recent research progress on light spectra and secondary metabolites in cannabis, along with pertinent light responses in model plant species, future research directions are presented.

Keywords: light emitting diode; light spectrum; light wavelength; photobiology; secondary metabolites; tetrahydrocannabinol; ultraviolet.

Figure 1

A simplified overview of cannabinoid and terpene biosynthesis pathways in cannabis (Cannabis sativa L.), derived from recent reviews (Hazekamp, ; Degenhardt et al., ; Sirikantaramas and Taura, ; Jin et al., 2019). Enzymes are in dashed line box. Enzymes in shaded blue boxes are upregulated by UV radiation and blue light in Lamiaceae. Cannabis precursor (shade blue): CBDA, cannabidiolic acid; DMAPP, dimethylallyl pyrophosphate; G3P, glyceraldehyde 3-phosphate; GPP, geranyl pyrophosphate; GPPS, geranyl pyrophosphate synthase; MEP, methylerythritol phosphate; PT4, geranylpyrophosphate: olivetolate geranyltransferase 4; IPP, isopentenyl diphosphate; IPPi, isopentenyl-diphosphate delta-isomerase; OA, olivetolic acid; OAC, olivetolic acid cyclase; TK, tetraketide; TKS, tetraketide synthase. Cannabinoid (shade red): CBC, cannabichromene; CBCA, cannabichromentic acid; CBCAS, cannabichromentic acid synthase; CBDAS, cannabidiolic acid synthase; CBD, cannabidiol; CBG, cannabigerol; CBGA, cannabigerolic acid; CBL, cannabicyclol; CBLA, cannabicyclolic acid; CBN, cannabinol; CBNA: cannabinolic acid; Δ⁸-THC, Δ⁸-tetrahydrocannabinol; Δ⁹-THC (or THC), Δ⁹-tetrahydrocannabinol; THCA, tetrahydrocannabinolic acid. Terpene precursor (shade orange): FPP, farnesyl diphosphate; FPPS, farnesyl diphosphate synthase; MEV, mevalonate; TPS, terpene synthase.

Figure 2

A simplified overview of the cannabis flavonoids, cannflavin A&B, pathway(s) in cannabis (Cannabis sativa L.), derived from Flores-Sanchez and Verpoorte (2008b) and Rea et al. (2019). Enzymes are in dashed line box. Enzymes in shaded blue boxes are upregulated by UV radiation in Arabidopsis thaliana. Dashed arrows represent proposed enzymatic reactions. CHS, chalcone synthase; CHI, chalcone isomerase; CsOMT21, C. sativa L. O-methyltransferase 21; CsPT3, C. sativa L. prenyltransferase 3; C4H, cinnamate 4-hydroxylase; C3H, p-coumaroyl-CoA 3-hydroxylase; FNS, flavone synthase; F3'H, flavonoid 3'-hydrolase; HEDS or HvCHS, homoeriodictyol/eriodictyol synthase; OMT, SAM-methyltransferase; PAL, phenylalanine ammonia-lyase; 4CL, 4-Coumarate:CoA ligase.

Figure 3

The impact of wavelengths on Cannabis sativa L. PSM responses, with corresponding photoreceptors (↑: increase, Δ: varying depended on light treatments, ↓: decrease, ?: unknown).