Modulation of antioxidant systems and photosynthetic machinery by foliar-applied ZnO nanoparticles in cadmium-stressed mung bean (Vigna radiata L.)

Agricultural soil contamination with cadmium (Cd) presents a significant threat to plant growth and food security. Nanotechnology offers innovative approaches to mitigate the adverse effects of heavy metal stress on plants. This study investigated the impact of foliar-applied zinc oxide nanoparticles (ZnO-NPs) on mung bean (Vigna radiata L.) plants subjected to Cd stress. To induce Cd stress in mung bean plants, varying concentrations of cadmium were applied: control (no Cd), 50 µM, and 100 µM, using cadmium chloride (CdCl2) as the source. ZnO-NPs were administered via foliar spraying at different concentrations (40 and 80 mg/L). Mung bean varieties, NIAB Mung 2011 (NM-2011) and NIAB Mung 2021 (NM-2021), were treated with ZnO-NPs under Cd stress conditions. Our results demonstrated that ZnO-NPs significantly mitigated the detrimental effects of Cd stress on mung bean cultivars. The application of ZnO-NPs (80 mg/L) notably enhanced plant growth under both 50 µM and 100 µM Cd stress levels. The findings revealed a dose-dependent effect, with optimal ZnO-NPs concentrations promoting superior shoot (17%) and root growth (20%); increased chlorophyll content (total chlorophyll 39%, chlorophyll a 38%, chlorophyll b 41%, carotenoids 40%), indicating improved photosynthetic performance. ZnO-NPs also elevated the activity of antioxidant enzymes such as superoxide dismutase (SOD) (32%), catalase (CAT) (19%), ascorbate peroxidase (APX) (35%) and peroxidase (POD) (26%), and reduced oxidative stress induced by Cd toxicity also along with decreased lipid peroxidation (MDA 35%, H2O2 63%). These findings underscore the potential of nanotechnology-based strategies to enhance plant resilience to heavy metal stress, which is crucial for sustainable agricultural practices. Further investigation is warranted to elucidate the underlying mechanisms and assess the long-term impacts of ZnO-NPs on plant growth and cadmium stress alleviation.