大豆における生物学的利用可能な老化ポリスチレン微小プラスチック濃度の植物毒性および代謝再プログラミングの規定

Microplastic (MP) contamination in soils poses a growing risk, yet the effects of environmentally aged MPs on crops remain unclear. Here, we investigated polystyrene (PS) MPs (average size 4.65 ± 3.01 μm) prepared via sequential dry-wet milling and thermal annealing (95 °C) to mimic natural aging. Characterization confirmed aged-like properties, including high surface roughness, crystallinity (0.397), and carbonyl index (0.63). In pot experiments, PS MPs accumulated exclusively in soybean roots (444-688 μg/g; PS1.0 > PS1.5 > PS0.5) but not in leaves. Phytotoxic effects correlated with the internalized (bioavailable) concentration of MPs: PS0.5 showed negligible impact, whereas PS1.0 severely reduced biomass and triggered the strongest oxidative stress (ROS +204 %, MDA +118 %). Sucrose content declined sharply under PS1.0 (-77.9 %) and PS1.5 (-55.1 %), linking oxidative stress to impaired carbon allocation. Metabolomic profiling revealed broad reprogramming of carbohydrate and defense pathways, with sucrose and galactose metabolism disrupted at PS1.0, and lipid-related defenses enriched at PS1.5. These findings establish a standardized protocol for producing environmentally relevant aged MPs and demonstrate that their phytotoxicity is governed by oxidative stress-driven carbon reallocation in a bioavailable concentration-dependent manner.