LED lighting affects the composition and biological activity of Cannabis sativa secondary metabolites

Growth conditions are expected to alter the relative and absolute content of the hundreds of phytochemicals produced by Cannabis sativa L.; some of these possess biological activity on the human body. However, relatively little information exists regarding the effects of different light regimes on the composition of C. sativa secondary metabolites and thus on their biological activity. In this study, we investigated how light quality influences the production and final content of secondary metabolites, as well as their bioactive properties. Toward these, plant growth and blooming were carried out at different illumination conditions, utilizing light-emitting diode (LED) fixtures vs. conventional fluorescent and high-pressure sodium (HPS) lamps as controls. Inflorescences were sampled at different time points along the blooming; extract compositions were analyzed by HPLC and GC/MS, and the biological activity of the extracted material was assessed using cell viability assays. We found that growth and blooming under LED illumination considerably changed shoot architecture and inflorescence mass. Moreover, the content of cannabinoids, terpenes, and alkanes were altered in the inflorescences of LED-grown plants during the flowering period as well as in the harvested flowers. In particular, significantly higher quantities of cannabigerolic acid accumulated in the inflorescences that flowered under LED fixtures, with a cannabigerolic acid to Δ9-tetrahydrocannabinolic acid (CBGA:THCA) ratio of 1:2 as opposed to 1:16 when grown under HPS. Notably, the cytotoxic activities of extracts derived from plants grown under the different illumination regimes were different, with extracts from LED-grown plants possessing higher cytotoxicity along the flowering stage. Our results thus indicate that the transition to indoor growth of C. sativa under LED lighting, which can have significant impacts on cannabinoid and terpene content, and also on the bioactive properties of the plant extracts, should proceed with thorough consideration.