Adventitious root cultures of Castilleja tenuiflora Benth. as a source of phenylethanoid glycosides

Castilleja tenuiflora is a highly valued medicinal plant that grows in pine-oak woods in Mexico. In this study, we identified for the first time verbascoside and isoverbascoside as the major phenylethanoid glycosides (PhGs) in C. tenuiflora. These compounds have proven biological activities, including anti-inflammatory, antioxidant, and cytotoxic activities, which may be related to the traditional uses of this plant. We developed a reverse-phase high-performance liquid chromatography (RP-HPLC) procedure to analyze PhGs, and determined their concentrations in various different tissues of wild plants. Verbascoside accumulated mainly in roots and inflorescences (9.23 and 7.88 mg g⁻¹ dry biomass, respectively), while isoverbascoside accumulated mainly in the roots (7.13 mg g⁻¹ dry biomass). To provide an alternative source of material for production of bioactive compounds, we established in vitro adventitious root cultures in which roots were grown in B5 medium containing either 10 μM indole 3-acetic acid (IAA) or 10 μM α-naphthaleneacetic acid (NAA). The greatest dry biomass yield (30 g L⁻¹) was achieved at 30 days after transfer of roots into IAA-containing medium. The highest specific yields of PhGs were also obtained using this auxin; the maximum level of verbascoside was 14.62 mg g⁻¹ dry root biomass (438.6 mg L⁻¹) at 30 days after root transfer, and the maximum yield of isoverbascoside was 37.32 mg g⁻¹ dry root biomass (522.48 mg L⁻¹) at 23 days after root transfer. Adventitious root cultures of C. tenuiflora are a promising system for further studies on scale-up and phenylethanoid glycosides biosynthesis.