In vitro culture of Atraphaxis frutescens (L.) K. Koch: effects of D-mannitol and pH on a propagation coefficient, secondary-metabolite levels, and antiradical activity

Species of the genus Atraphaxis are xerophytic shrubs growing in steppe and semidesert habitats on various soil types, including saline ones. Despite much interest in Atraphaxis species as sources of phenolic and polyphenolic compounds, information on approaches to the cultivation of these plants’ tissues is not available in the literature. In this study, an in vitro technology of A. frutescens propagation was developed for the first time. The Murashige and Skoog (MS) medium supplemented with 0.5 µM 6-benzylaminopurine was chosen as optimal. Microshoots were successfully rooted on the ½ MS medium without auxins or supplemented with 1 µM indole-3-butyric acid. All the media regarding the in vitro propagation contained 3% of sucrose and 0.6% of agar. The subcultivation period was 30 days. The A. frutescens in vitro culture showed resistance to osmotic stress (up to 150 mM D-mannitol) and to a wide pH range: 3.8 to 8.3. Under the influence of the culture medium, there was an increase in concentrations of catechins, tannins, phenolic acids, and saponins and in the total phenolic content and a decrease in the levels of flavonols as compared to a natural sample. Cultivation of samples on culture media with D-mannitol reduced the levels of flavonols and phenolic acids as compared to a control medium. The highest concentrations of tannins, catechins, and flavonols were noted at pH 8.3, and the same was true for saponins at pH 3.8. Meanwhile, no significant correlations were found between phenolic compounds and antiradical activity. Thus, in vitro culture of A. frutescens microshoots can serve as an alternative source of valuable classes of secondary metabolites such as catechins, tannins, saponins, and phenolic acids. In future studies, to create large-scale in vitro systems of A. frutescens , the selection of a proper bioreactor type and optimization of process parameters will be crucial for maximizing secondary-metabolite production. Key Message This is the first report of an efficient in vitro methodology for Atraphaxis frutescens propagation and offers a tool for implementation of its conservation and for obtaining valuable secondary metabolites.