In vitro regenerative potential and metabolite profiles of two Centaurium tenuiflorum phenotypes differing in flower colour

Centaurium tenuiflorum (fam. Gentianaceae) is an annual herb rich in highly-valuable bioactive metabolites, predominately xanthones and secoiridoids. The metabolomes of the aerial parts of slender centaury resemble those of C. erythraea, a species widely used in traditional medicine for treating mild dyspeptic and gastrointestinal complaints and temporary loss of appetite. This research aimed to develop an efficient clonal propagation protocol for two C. tenuiflorum chemotypes corresponding to the white-flowered (CtW) and pink-flowered (CtP) phenotypes, which is a prerequisite for the development and optimisation of biotechnological processes to produce bioactive metabolites. No spontaneous regeneration of CtP and CtW shoots occurred in either the solid or liquid half-strength MS culture media, and both were accompanied by tissue necrosis and browning. Supplementation of the culture medium or the pretreatment of the explants with anti-browning agents, i.e. activated charcoal, PVP, ascorbic acid, caffeic acid, citric acid or silver nitrate, all at various concentrations, did not enhance the regeneration efficacy or prevent the tissue browning. In contrast, the addition of plant growth regulators promoted high-frequency shoot initiation from both the root and leaf explants, and effectively induced rooting. The optimal conditions for the clonal propagation of both the CtP and CtW genotypes was a liquid basal medium containing 1 mg L-1 TDZ and 1 mg L-1 IAA at the proliferation stage, and a solid basal medium containing 1 mg L-1 IAA at the rooting stage. Although no significant differences between the regenerative capacity of the CtP and CtW genotypes were observed, targeted metabolomics data clearly distinguish the two chemotypes. The present study highlights the active production of xanthones and secoiridoids in the C. tenuiflorum regenerated shoots and their intensive exudation into the surrounding culture medium. Among the ten targeted metabolites, polyphenolics from the groups of xanthones and phenolic acids, highly abundant in both the C. tenuiflorum tissue and the culture media, were recognised as the main contributors to the tissue browning. The study demonstrates an efficient approach for recovering xanthones, phenolic acids, and secoiridoids from liquid culture media and highlights its potential as a promising source of bioactive compounds.