Efficient regeneration of shoots and roots in graphene oxide and carbon nanotubes mediated callus cultures: A qualitative and quantitative study

The applications of nanomaterials have been assessed for the regeneration of plants and secondary metabolite content. The purpose of this study was to investigate the effects of carbon nanotubes and reduced graphene oxide nanosheets on callus cultures of Fagonia indica. We aimed to assess for the first time whether reduced graphene oxide and carbon nanotubes causes plant regeneration in the absence of plant growth regulators. The callus cultures of Fagonia indica were grown in Murashige and Skoog media enriched with different concentrations of nanomaterials to examine their effect on its regeneration, biomass accumulation, and phytochemical content. Morphological and biochemical responses are measured upon interaction with nanomaterials at different time periods. Results show that calli treated with the highest concentration of carbon nanotubes showed regeneration, while the media containing reduced graphene oxide induces regeneration of shoots and roots at all concentrations. Moreover, the callus growth and biomass accumulation were increased upon addition of both nanomaterials, but the significant results are obtained at low concentration (1 mg/L and 2 mg/L). The media containing carbon nanotubes at a concentration of 2 mg/L produced the maximum biomass yield (FW= 0.7914 g, DW= 0.067 g), whereas the media containing reduced graphene oxide at a concentration of 1 mg/L produced the lowest yield (FW= 6.02985 g, DW= 0.3405 g). The highest total phenolic and flavonoid content values are obtained at the highest concentration of nanomaterials. However, the callus treated with reduced graphene oxide showed increased total phenolic content (107.4 µg GAE/mL) and total flavonoid content (8.06 µg QE/mL) as compared to total phenolic content (32.3 µg GAE/mL) and total flavonoid content (7.11 µg Q/mL) observed in callus treated with carbon nanotubes. Further, the data from High-Performance Liquid Chromatography shows that carbon nanotubes alone have the potential to trigger the pathways of secondary metabolism while reduced graphene oxide triggers only the production of Quercetin and Gallic acid. This study gives the first evidence that the use of reduced graphene oxide gives better results than carbon nanotubes as an elicitor for inducing plant regeneration, biomass accumulation, and the in vitro biosynthesis of valuable secondary metabolites.