Characteristics and Mechanism of Polystyrene Microplastic Uptake and Transport in Maize Seeds and Seedlings

ObjectiveThis study aimed to investigate the absorption and transport characteristics and mechanism of microplastics of different concentrations and particle sizes in maize seeds and seedlings.MethodMaize was used as the test material and fluorescent-labelled polystyrene microplastics (PS-MPs) microspheres were added to the seeds during germination and to the seedlings during hydroponic exposure. This platform quantified growth-suppressive impacts of the test compound on germinative capacity and early seedling establishment, and clarified its mechanism of action.ResultThe effects of microplastics on the germination of maize seeds and the growth of seedlings exhibited significant dependence on concentration and particle size. At the seed germination stage, when examined using laser confocal electron microscopy, it was found that PS-MPs fluorescent microspheres were enriched at the position of the root hairs on the embryonic root. Furthermore, some of the microspheres penetrated the root epidermis and entered the cortical tissue, ultimately reaching the xylem vessels that are responsible for transporting water and nutrients. Their presence in these critical conductive tissues disrupted the seed germination process and induced oxidative damage. This experiment demonstrated that low concentrations (20 mg·L–1) of fluorescent PS-MPs promoted germination, whereas medium-to-high concentrations (50 and 100 mg·L–1) inhibited it.ConclusionThis study verified the internalization and shootward translocation of microplastics in maize plants and provided preliminary insights into the absorption and translocation characteristics of microplastics within maize plants. It also sheded light on the toxic mechanisms of microplastics on maize, providing a vital experimental basis for understanding the migration and transformation patterns of microplastics within plants, thus providing scientific evidence with which to assess the impact of microplastics on agricultural ecosystems and food safety.