Sustainable nanotechnology: differential roles of green-synthesised and metallic ZnO nanoparticles in swiss chard

The use of nanoparticles (NPs) in agriculture requires a thorough investigation of their effects on plant antioxidant systems, metal accumulation, and growth. With the escalating global population and food demand, it is important to conduct comprehensive studies to understand the implications of NPs on plants before using them to enhance agricultural output and quality. This study aims to elucidate the impact of metal-based (M-) and green-synthesized (G-) ZnO NPs on Swiss chard’s (Beta vulgaris L. var ‘Barese’) enzymatic and non-enzymatic antioxidant properties, mineral accumulation, growth parameters, and hazard quotients. Swiss chards were grown hydroponically in controlled environment agriculture and sprayed with the appropriate NPs. M-ZnO NPs (< 50 nm) at concentrations of 200 and 400 ppm suspensions were prepared in ultrapure water, and the G-ZnO NPs (< 50 nm) at concentrations of 200 and 400 ppm suspensions were prepared using dried Quercus robur bark extract. Results revealed that a 400 ppm suspension of G-ZnO NPs positively affected non-enzymatic antioxidants. Compared to the control, the TPC increased by 28%, DPPH by 23%, ABTS by 15%, FRAP by 3%, violaxanthin by 9%, lutein by 10%, chlorophyll b by 12%, chlorophyll a by 10%, and β-carotene by over 21%. G-ZnO NPs increased the activity of SOD and DHAR by 40% and 7%, while the suspension of M-ZnO NPs at a concentration of 400 ppm affected SOD, GR, MDHAR, CAT, and APX by increasing their activity by 15, 13, 6, 76, and 77% respectively. G-ZnO NPs had a positive effect on increasing the amounts of Ca, K, Mg, Na, P, S, Fe, Mn, and Zn through 36, 7, 15, 3, 43, 71, 74, 67, and 82%, respectively, compared to untreated plants. The accumulation of Zn in leaves increased by 190% when exposed to a 400 ppm M-ZnO NPs suspension compared to untreated plants. This study contributes new knowledge about the effect of differently synthesized nanoparticles on plant antioxidant systems and mineral accumulation.