Iron oxide nanoparticle-mediated elicitation enhances secondary metabolite production, antioxidant activity, and gene expression in Melia azedarach L

Melia azedarach L. is an important medicinal plant with various biological activities, such as antidiabetic, antibacterial, antifungal, analgesic, and anticancer. The effect of iron oxide nanoparticles on the contents of azadirachtin, lupeol, stigmasterol, mevalonic acid, and squalene metabolites, expression of genes involved in their synthesis pathway, and the activity of some antioxidants in M. azedarach cell suspension culture has not been extensively studied. The impact of iron oxide nanoparticles at different concentrations (0, 20, 40, and 60 mg/L) and sampling times (3, 6, and 9 days) on cell suspension growth, production, and accumulation of the metabolites, expression of MOF1 and SQS1 genes, and antioxidant enzyme activity was investigated. Also, response surface methodology was used to optimize the applied treatment to achieve maximum accumulation of the secondary metabolites. The results of the RSM showed that the optimal conditions for achieving maximum accumulation of azidarichtin and squalene were a concentration of 20 mg/L of iron oxide nanoparticles on days 8.1 and 5.6 of sampling, respectively, and for lupeol, the optimal conditions were 39.2 mg/L of iron oxide nanoparticles and a sampling time of 4.5 days. The results showed that the highest expression levels of Mof1 and SQS1 genes, with an increase of 30.83 and 10.25-fold compared to the control, were observed under the treatment where squalene accumulation reached its highest level. In addition, the highest proline content, total flavonoid content, and phenol content were found for the 60 mg/L iron oxide nanoparticles and 6 days of sampling, 20 mg/L iron oxide nanoparticles and 9 days of sampling, and 40 mg/L iron oxide nanoparticles and 3 days of sampling, respectively. The catalase and superoxide dismutase enzymes showed the maximum activity in the 20 mg/L iron oxide nanoparticle and 6 days of sampling. The results suggest that optimized iron oxide nanoparticle treatments are associated with enhanced growth, metabolite accumulation, antioxidant activity, and expression of selected biosynthetic genes.