Enhancement of Phenolic and Polyacetylene Production in Chinese Lobelia (Lobelia chinensis Lour.) Plant Suspension Culture by Employing Silver, Iron Oxide Nanoparticles and Multiwalled Carbon Nanotubes as Elicitors

Silver nanoparticles (AgNPs), iron oxide nanoparticles (Fe2O4NPs), and multiwalled carbon nanotubes (MWCNTs) are widely used in various applications, such as biomedicine, environmental remediation, and agriculture. In addition, these nanomaterials can affect the production of bioactive compounds in plants that have pharmacological activities. In the current study, the in vitro plant cultures of Chinese lobelia (Lobelia chinensis Lour.) were established in MS medium and treated with 0, 12.5, 25, 37.5, and 50 mg L−1 AgNPs or Fe2O4NPs, or MWCNTs. Initially, plants were grown for four weeks without any elicitors, and after that, the cultures were treated with nano-elicitors for one week. After five weeks, the effects of nano-elicitors were estimated on growth, total phenolic, flavonoids, polyacetylenes, and ABTS/DPPH/FRAP antioxidant activity was investigated. The results showed that lower levels of AgNPs (25 mg L−1), Fe2O4NPs (25 mg L−1), and MWCNTs (12.5 mg L−1) favored the accumulation of fresh and dry biomass. Whereas, 37.5 mg L−1 AgNPs, 25 mg L−1 Fe2O4NPs, and 37.5 mg L−1 MWCNTs enhanced the accumulation of total phenolics, flavonoids, specific phenolic compounds including chlorogenic acid, catechin, phloretic acid, coumaric acid, salicylic acid, naringin, myricetin, linarin, and polyacetylenes viz. lobetylonin and lobetyolin in higher concentrations. The plant extracts elicited by nanomaterials also depicted very good antioxidant activities according to ABTS, DPPH, and FRAP assays. These results suggest that specific nanomaterials, and at specific levels, could be used for the production of bioactive compounds from shoot cultures of Chinese lobelia.