Enhanced antioxidant activity in Curcuma caesia Roxb. microrhizomes treated with silver nanoparticles

Curcuma caesia Roxb. is a highly valuable, endangered herb of therapeutic importance that resides in their rhizomes. In the present investigation, the effect of ½ strength liquid Murashige and Skoog (MS) medium supplemented with 1 mg/l Indole-3-butyric acid (IBA) and different sucrose concentrations (1.5%, 3%, 6%, 9%, or 12%) was studied on microrhizomes induction of C. caesia. The shoot length, root length and microrhizomes dry weight of C. caesia decreased significantly at 6% sucrose and above. When compared to the control (1.5% sucrose), the current water content significantly decreased at 6% sucrose. The optimum concentration for in vitro microrhizomes induction in C. caesia was 6% sucrose. Therefore for further experiments, the 6% sucrose was used. We also studied the effect of silver nanoparticles (AgNP) on microrhizome induction and antioxidant activity in C. caesia cultures. Field-grown C. caesia rhizomes extract was used in the green synthesis of AgNP. The synthesized AgNP was further characterized through scanning electron microscopy and X-ray diffraction. The AgNP, ranging from 0, 0.025, 0.05, 0.075 or 0.1 mg/l was supplemented in ½ strength liquid MS medium with 6% sucrose and 1 mg/l IBA. The MS medium with 0.05 mg/l AgNP found with significant morphological changes in C. caesia cultures (root number, root length and microrhizomes fresh weight). For the total phenolic and total terpenoids content estimation as well as for antioxidant activity analysis, the extracts of un-treated cultures (6% sucrose + 1 mg/l IBA, without AgNP), AgNP treated cultures (6% sucrose + 1 mg/l IBA with 0.025 and 0.05 mg/l AgNP) was used. The 0.025 and 0.05 mg/l AgNP enhanced the phenolic and terpenoid content in the cultures compared to the field-grown mother plant. The antioxidant activity of the cultures treated with AgNP also increased compared to un-treated cultures and field-grown mother plant. The Gas Chromatography-Mass Spectrometry (GC-MS) analysis revealed that the extract treated with 0.05 mg/l AgNP had increased production of monoterpene (camphor) and sesquiterpenes (β-elemenone and curcumenone). These increased terpenes could be responsible for the enhanced antioxidant activity of C. caesia cultures.