The influence of light quality on the production of bioactive metabolites - verbascoside, isoverbascoside and phenolic acids and the content of photosynthetic pigments in biomass of Verbena officinalis L. cultured in vitro

Abstract

In vitro callus cultures of Verbena officinalis L. were maintained on solid Murashige and Skoog medium, enriched with 1 mg dm^-3 BA and 1 mg dm^-3 IBA under LED lights (red, blue, red/blue 70%/30%), in darkness and under control fluorescent lamps. The measurements of 2 phenylpropanoid glycosides (verbascoside and isoverbascoside) and 23 phenolic acids were performed in methanolic extracts from the biomass collected after 2-, 3- and 4-week growth cycles using the HPLC-DAD method. The presence of verbascoside, isoverbascoside and additionaly 7 phenolic acids (protocatechuic, chlorogenic, vanillic, caffeic, ferulic, o-coumaric and m-coumaric acids) was confirmed in all extracts. Blue and red/blue lights stimulated the accumulation of verbascoside (max. of 6716 and 6023 mg 100 g^-1 DW after a 4-week growth cycle) and isoverbascoside (max. 333 and 379 mg 100 g^-1 DW also after 4 weeks). The maximum amounts of verbascoside and isoverbascoside were respectively 1.8- and 7.0-fold higher than under the control conditions. Phenolic acids were accumulated in different amounts, and the maximum total amounts ranged from 36 to 65 mg 100 g^-1 DW. LED lights also stimulated their accumulation in comparison with darkness and control. The main phenolic acids included: m-coumaric acid (max. 39 mg 100 g^-1 DW), ferulic acid (max. 12 mg 100 g^-1 DW), and protocatechuic acid (max. 13 mg 100 g^-1 DW). Additionally, the quantities of photosynthetic pigments (chlorophyll a, b and carotenoids) were estimated in acetonic extracts using spectrophotometry. Red/blue light stimulated the biosynthesis of pigments (max. total content 287 μg g^-1 FW after 4-week growth cycles). This is the first study describing the effect of LED lights on the production of phenylpropanoid glycosides and phenolic acids in V. officinalis callus cultures. Very high amounts of verbascoside and isoverbascoside are interesting from a practical point of view.

Keywords: Callus cultures; HPLC-DAD analysis; Light-emitting diode light; Monochromatic light; Phenolic acids; Phenylpropanoid glycosides; Photosynthetic pigments; Vervain.