Influence of Heavy Metals (Cu, Cr, Zn) on Antioxidant Potential in Emilia sonchifolia (L.) DC

Heavy metal contamination poses significant threats to plant physiology and secondary metabolite production. This study investigated the effects of copper (Cu), chromium (Cr), and zinc (Zn) on the antioxidant defense system of Emilia sonchifolia, a medicinal plant with therapeutic potential. Hydroponically grown plants were exposed to metal concentrations ranging from 25–125 ppm for 30 days. Antioxidant responses were evaluated through DPPH radical scavenging assays and superoxide dismutase (SOD) activity measurements. Results revealed metal-specific and concentration-dependent effects. Cu exhibited a hormetic response, with peak antioxidant activity at 50 ppm (lowest IC50 = 4.77 µg/mL; highest SOD activity = +42% vs control), followed by decline at higher concentrations. Cr demonstrated consistently toxic effects, with antioxidant capacity progressively decreasing (IC50 increased 4.4-fold at 125 ppm) and SOD activity declining by 62% at highest exposure. Zn showed optimal enhancement at 50–75 ppm (IC50 = 5.87 µg/mL; SOD +33%), but reduced efficacy beyond 100 ppm. Two-way ANOVA confirmed significant interactive effects of metal type × concentration (p < 0.001). These findings demonstrate that while moderate Cu and Zn can stimulate antioxidant defenses, Cr is uniformly detrimental, providing critical insights for cultivating medicinal plants in metal-contaminated environments and assessing their pharmacological potential under stress conditions.