Integrated physiological, metabolomic, and transcriptomic responses of maize (Zea mays) and soybean (Glycine max) to nanoplastic-induced stress

The widespread use and degradation of agricultural plastics lead to the accumulation of nanoplastics (NPs) and soil contamination, posing growing risks to agroecosystems. This study investigated the differential physiological and molecular responses of maize (Zea mays) and soybean (Glycine max) to polyethylene nanoparticles (PE-NPs) and polypropylene nanoparticles (PP-NPs), each within the size range of 20–50 nm, at concentrations of 50 and 500 mg/kg of soil. Over a 45-day exposure period, at 500 mg/kg concentration, both NPs types significantly suppressed plant height and fresh biomass in both maize and soybean, with PP-NPs demonstrating greater toxicity in soybean than in maize. At 500 mg/kg, both crops accumulated high levels of both NPs types in their roots, triggering oxidative stress as evidenced by elevated malondialdehyde levels and a significant decline in catalase activity, which compromised root membrane integrity, antioxidant defense mechanisms, and nutrient availability. However, maize's higher photosynthetic efficiency, more vigorous root growth, and greater metabolic exudation made it more resilient to the NPs stress than soybean. To compare the molecular responses of maize and soybean, we conducted a multi-omics analysis of plants exposed to 500 mg/kg PP-NPs. The results showed a significant disruption of purine metabolism and phenylpropanoid biosynthesis in both plants, with the effect more pronounced in soybean. Soybean exhibited strong downregulation of adenosine deaminase and adenylate kinase, with reduced levels of xanthine, inosine, and uric acid. Notable alterations in the expression of key enzymes, such as phenylalanine ammonia-lyase, trans-cinnamate 4-monooxygenase, and peroxidase in both plants indicate a substantial impact on phenylpropanoid biosynthesis and its downstream flavonoid and lignin precursors. These findings reveal the distinct physiological and multi-omics responses underlying the resilience of maize and soybean to nanoplastic-contaminated soils.