Translocation of polystyrene nanoplastics in distinct plant species: Novel insight from a split-root system and transcriptomic analysis

Nanoplastics (NPs) can be absorbed by crop roots and translocated to shoots, but whether the process follows a unidirectional pathway in different plant species remains unclear. This study investigated the translocation and accumulation of europium-labeled polystyrene NPs in cucumber (dicot) and maize (monocot) seedlings using a split-root system. The results showed that NP accumulation was highest in exposed roots (E-R), followed by unexposed roots (UE-R), and then shoots in both plants. In cucumber, NP accumulation in E-R was 26.84 % higher than in maize; while in maize, the translocation factor from shoot to UE-R was 4.45 times greater than in cucumber. TEM images confirmed NP transport from root to shoot via xylem, while confocal images showed the redistribution of NPs from shoot to root via phloem. AgNO treatment (5-50 μmol L) revealed aquaporin-mediated regulation of NP accumulation, with concentration-dependent increases of 30.37-220.7 % in cucumber roots and 36.38-53.65 % in maize shoots. Transcriptomic analysis revealed that NP accumulation interacted with aquaporin gene expression, where differential regulation of tonoplast intrinsic, plasma membrane intrinsic, and nodulin 26-like intrinsic proteins drove translocation differences. This study offers critical insights into the "root-to-shoot-to-root" translocation of NPs, informing crop safety assessments amid global plastic pollution.