Adventitious root cultures of Arnebia euchroma: A sustainable alternative for the production of natural pigments.

Arnebia euchroma is a valuable Himalayan herb, whose roots are savagely harvested from the wild to extract red naphthoquinone pigments with applications in food, cosmetic and pharmaceutical industries. The primary objective of this study was to induce A. euchroma adventitious roots and use the same for the production of naphthoquinone pigments. A number of media and auxin types were tried for the formation of adventitious roots from leaves of A. euchroma under in vitro conditions. The data showed 100% root induction on semi-solid Schenk & Hildebrandt (SH) medium fortified with 2.5 mg/L indole-3-butyric acid (IBA) after 4-weeks of culture. Thereafter, factors like inoculum density and sucrose concentration were optimized to maximize adventitious root growth and pigment production in liquid shake flask cultures. The results revealed a significantly high root biomass (7.00 ± 0.25 g/L dry weight (DW)) and pigment (192.92 ± 1.61 mg/g DW) yield in SH medium having 10 g/L inoculum density, 0.5 mg/L IBA and 5% sucrose concentration. In addition, the cultivation of adventitious roots in Balloon-Type Bubble Bioreactor (5 L cap.) was also done, which showed comparably lower root biomass (4.33 ± 0.09 g/L DW) yield to shake flask culturing, however, resulted in higher pigments accumulation (195.36 ± 1.95 mg/g DW). The chemical profile of in vitro induced adventitious roots cultivated in shake flask and bioreactor was also compared with parent plant rhizome using Ultra Performance Liquid Chromatography. As per the results, deoxyshikonin and β, β-dimethylacrylshikonin were found to be the key pigments in adventitious roots, although shikonin was not detectable which otherwise also present in parent plant rhizomes. Considering the shorter cultivation cycle (4-weeks) and regenerative potential of induced adventitious roots along with comparable metabolic profile, the developed process seems to be a feasible alternative for the production of natural pigments. [Display omitted] • An efficient in vitro protocol for adventitious root induction was developed. • In vitro process has a significantly low cultivation period (4-weeks). • Induced adventitious roots were found competent enough as a regenerative substitute for producing naphthoquinone pigments. [ABSTRACT FROM AUTHOR]