Establishment of Cajanus cajan (Linn.) Millsp. cell suspension cultures as an effective in vitro platform for the production of pharmacologically active phenolic compounds

Phenolic compounds are validated to be the pharmacologically active phytochemicals in Cajanus cajan (Linn.) Millsp. leaves (CCLs) and the medicinal product (Tongluo Shenggu capsules, TSCs) thereof. For the first time, C. cajan cell suspension cultures (CCSCs) were established as an effective in vitro platform for the production of phenolic compounds. Callus was induced from C. cajan leaves by 2.0 mg/L 2,4-D, 5.0 mg/L α-NAA, and 0.1 mg/L Kn, and then subcultured on MS solid medium supplemented with 1.5 mg/L 2,4-D, 3.0 mg/L α-NAA, and 0.25 mg/L Kn. Culture conditions of a selected high-productive callus line (CCCL VII) were systematically optimized in terms of biomass productivity and phenolic yield, and eleven target compounds were identified and quantified by ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). Under the optimal culture conditions (MS liquid medium, sucrose concentration 3.5 %, temperature 26 °C, inoculum size 3.0 %, and time 49 day), CCSCs produced the highest level of total phenolics (3462.99 μg/g DW) along with the maximum biomass productivity (10.03 g/L), which was higher than the phenolic yield in field-grown CCLs (3288.81 μg/g DW). Notably, CCSCs exhibited superiority in the content of the most valuable compound cajaninstilbene acid (2858.76 μg/g DW) as compared with CCLs (2114.60 μg/g DW). Also, CCSCs were discovered to be more abundant in genistin and genistein as against both CCLs and TSCs. This work concluded that CCSCs might be attractive alternative sources for the production of phenolic compounds with potential uses in pharmaceutical/nutraceutical industries.