Disruption of auxin homeostasis by negatively charged nanoplastics inhibits plant primary root development

Nanoplastics, commonly found with varying charge states in the environment, represent an emerging pollutant with the potential to be absorbed by terrestrial plants, negatively affecting their growth, especially root growth. However, the underlying mechanisms by which surface charge modifications affect root growth remain poorly understood. We investigated the impact of polystyrene nanoplastics with different surface charges on the growth and development of roots, and identified the cellular response pathways triggered by nanoplastics and molecular mechanisms with the help of transcriptomics sequencing, confocal microscopy observation, and molecular docking simulation. The results showed that strong inhibitory effects of negatively charged nanoplastics on development of root meristem zone. Additionally, it downregulated genes associated with stem cell niche activity and mitotic processes. Transcriptomic analysis highlighted the significant suppression of key pathways related to phytohormone signaling and transmembrane transporter protein activity. Molecular docking further demonstrated that negatively charged nanoplastics preferentially bind to polar auxin efflux transporter PIN proteins, leading to excessive auxin accumulation at root tip and impairing auxin redistribution, thereby disrupting gravitropic growth. This research offers valuable insights into how differently charged nanoplastics influence root growth and provides guidance for the ecological risk assessment of nanoplastics and the sustainable development of agriculture.