Iron oxide nanoparticles and light intensity modulate biomass, antioxidant capacity and anti-leishmanial activity in callus cultures of Artemisia scoparia

Iron oxide nanoparticles (FeO-NPs) have gained global attention as bio safe elicitors for incrementing medicinal metabolites in plants. This study, for the first time evaluated the effects of FeO-NPs under varying light intensities to enhance growth, biomass and production of anti-leishmanial natural products in Artemisia scoparia cell cultures. Results showed that optimal levels of FeO-NPs (10-15 mg/L) significantly enhanced callus growth attributes and metabolites production on solid MS media. Highest callus induction frequency (92%) and biomass accumulation (33 g/L), were observed in explants treated with 15 mg/L FeO-NPs combined with 1.5 mg/L 2,4-D. However, higher levels of Total phenolic content (TPC:37 mg GAE/g DW), Total flavonoid content (TFC:9.2 mg QE/g DW) and DPPH antioxidant activity (88%) respectively, were recorded in callus cultures grown at 15 mg/L FeO-NPs alone. In shake flasks, maximum callus biomass accumulation (191 g/L) was observed on day 24 of the growth curve, when cell cultures were treated with 15 mg/L FeO-NPs combined with 1.5 mg/L 2,4-D and maintained in darkness for ten days followed by exposure to normal light conditions. Antioxidant potential of cell suspension cultures was significantly enhanced compared to callus grown on solid media with the highest values of TPC (57 mg GAE/g DW), TFC (8.9 mg QE/g DW) and antioxidant activity (91%) were observed. Phenylalanine ammonia-lyase activity (PAL) was found to inversely correlate with biomass and antioxidant metabolites production. Significant variations in antioxidant enzymes activities were detected in cell cultures subjected to different light regimens, with dark pre-treatment followed by light exposure induced the highest superoxide dismutase (SOD; 4.1 U/mg protein) and peroxidase (POD; 4.5 U/mg protein) activities. Cultures grown in complete darkness also resulted in substantial expression of SOD, POD, catalase (CAT) and ascorbate peroxidase (APx) enzymes. Nonetheless, the antileishmanial potential of the cell cultures was evaluated and the putative metabolites responsible for this activity were identified and quantified through the robust Gas chromatography- mass spectrometry (GC-MS) analysis.