Dose-dependent Effects of Bio-AgNPs on <i>Rubia tinctorum</i> Callus and Root Biomass

Silver nanoparticles have frequently been used in many areas of biotechnology. These nanomaterials, especially biologically synthetized silver nanoparticles (bio-AgNPs), have some beneficial effects on plant biosystems because of their ethylene-inhibiting and auxin-stimulating effects which make them practical and cost-effective alternatives for synthetic plant growth regulators. The variety of the plants' responses to bio-AgNPs is dose-dependent, and the effects show a wide variety for every plant, explant and culture types. In our study, bio-AgNPs derived from Syzygium aromaticum flowers were used in stem cultures of Rubia tinctorum. At 0-30 mg/L concentrations, their efficacies were evaluated on the basis of biomass and chemical accumulations. Bio-AgNPs affected the growth parameters and content of biomass depending on their concentrations. The highest biomass accumulations were detected at 10 mg/L concentration (up to 3.4 times higher compared to control). Callus and root regenerations were triggered at 5 and 10 mg/L concentrations. Total phenolic concentrations were detected at the highest level (16.54 and 18.86 mg GAE/g, respectively) at 15 mg/l concentration, whereas total flavonoid concentrations were the highest at 15 and 20 mg/L concentrations (5.63 and 5.42 mg QE/g, respectively). Total antioxidant capacity and radical scavenging activity enhanced in response to bio-AgNPs. The highest total antioxidant capacity was detected at 107.53 mg AAE/g at 1 mg/L concentration in root biomass (1.6 times higher than the control). Total anthraquinone concentrations reached their highest values at 30 mg/L bio-AgNP concentration in both callus and root tissues. The results revealed that bio-AgNPs acted as elicitors or/and biomass enhancers in response to their concentrations.