Interactive effects of zinc oxide nano particles and different light regimes on growth and silymarin biosynthesis in callus cultures of Silybum marianum L.

Silybum marianum L. commonly known as milk thistle is a medicinally potent plant with a multitude of pharmacological applications. The present investigations demonstrated the effects of Zinc Oxide nanoparticles (ZnO NPs) on callus growth and biosynthesis of silymarin in milk thistle under various light conditions. The callus cultures developed on Murashige and Skoog (MS) basal media containing ZnO NPs (0.15 mg/L), under the dark condition maintained for two weeks, followed by transference into normal light produced the maximum callus fresh weight (2294 mg/L FW). Further, the metabolite profiling revealed that ZnO NPs significantly augmented the production of silymarin and upregulated the antioxidant system in the callus cultures. Maximum TPC (total phenolic content: 37 +/- 0.20 mg/g DW), TFC (total flavonoid content: 8.9 +/- 0.023), DPPH antioxidant activity (91.5 +/- 1.75%), Superoxide dismutase activity (SOD: 4.1 +/- 0.045 nM/min/mg FW) and the highest silymarin content (14.6 +/- 0.023 mg/g DW) were recorded in the callus cultures developed on MS media supplemented with solitary ZnO NPs (0.15 mg/L). While the callus culture evolved in presence of only PGRs (2,4 D and BA: 2 mg/L, each) accumulated the lesser fresh weight (562 mg/L FW). A higher concentration of ZnO NPs (0.15 mg/L) enhanced the secondary metabolite accumulation and silymarin content in the callus of Silybum marianum. This is the first standardized protocol to be applied on the industrial level for the production of silymarin.