The Effects of Light, Salt, and Osmotic Stress on Mesembryanthemum tortuosum Growth and Mesembrine-Type Alkaloid Production In Vitro.

Mesembryanthemum tortuosum is a valuable South African medicinal plant. A wide range of pharmacological and therapeutic actions have been ascribed to the plants' mesembrine-type alkaloids. Alkaloids are naturally produced in minute quantities in plants; however, production is often increased in stress conditions. This study aimed to determine the effects of abiotic stress on M. tortuosum growth and mesembrine-type alkaloid production. Light (0, 8, 16, and 24 h), salt (0, 50, 100, and 200 μM NaCl), and osmotic stress (0, 25, 50, and 100 g L^-1 polyethylene glycol; PEG) were applied to M. tortuosum cultures in vitro. Growth effects were recorded after 28 days. Alkaloid extracts were analyzed with UPLC-MS. Total mesembrine-type alkaloid contents were significantly increased by 0 h light and 100 g l^-1 PEG (9.16 ± 0.12 and 6.74 ± 0.30 μg mg^-1 DW, respectively), in comparison to the controls (2.93 ± 0.16 and 3.73 ± 0.014 μg mg^-1 DW, respectively). Zero h light allowed for more optimal plantlet growth than osmotic stress treatments. Growth effects and conservation of secondary metabolite pools in the presence of salt confirmed that M. tortuosum has a halophytic nature. Abiotic stress application is a simplistic and inexpensive method of enhancing mesembrine-type alkaloid production in M. tortuosum. With some modification, these methods could prove valuable to small- and large-scale growers of M. tortuosum, along with biotechnologists and pharmaceutical companies. The growing need for commercial availability of these phytochemicals could possibly be satiated with the appropriate use of the stress conditions described.