The alkaloid brachycerine is induced by ultraviolet radiation and is a singlet oxygen quencher.

Abstract

The effects of ultraviolet (UV) radiation on chlorophyll content and accumulation of the anti-inflammatory monoterpene-indole alkaloid brachycerine in plants and calli of Psychotria brachyceras (Rubiaceae) were investigated. In this study, we also investigated a protective role for brachycerine against stress conditions. Calli and tip cuttings incubated in nutrient media were daily supplemented with 4 or 16 h of UV. High-performance liquid chromatography analyses of methanolic extracts showed only traces of brachycerine in irradiated aseptic cultures, with no alkaloid being observed in control calli. In cuttings, a 10-fold increase in brachycerine content was seen after exposure for 16 h to UV-C, whereas a 4 h daily supplementation doubled the amount of the alkaloid in leaves. Exposure to a UV-B source also doubled the alkaloid yield. In vitro brachycerine was able to quench singlet oxygen. The data indicate a potential protective role for brachycerine against UV radiation, acting as a UV filter (absorption peaks are within the UV range) and a reactive oxygen species scavenger. In addition, UV radiation may be used to increase yields of this compound of pharmaceutical interest.