Clathrin-mediated endocytosis governs CdS nanoparticle internalization in rice (Oryza sativa L.) roots

Cadmium sulfide (CdS) precipitation in anaerobic paddy soils is widely recognized as a critical mechanism limiting Cd uptake by rice (Oryza sativa L.). However, the potential uptake of dispersed CdS nanoparticles (NPs) and their cellular internalization mechanisms in rice roots remain poorly understood. In this study, we investigated the internalization mechanisms of CdS NPs in hydroponically grown rice seedlings. Transmission electron microscopy analysis confirmed the internalization of CdS NPs into the cytoplasm of root cells. Pharmacological inhibitor assays identified clathrin-mediated endocytosis (CME) as the dominant internalization pathway. Consistently, knockout of CLATHRIN LIGHT CHAIN 2 (OsCLC2), encoding an essential component in CME pathway, reduced CdS NP accumulation in rice roots by 59.7 %-62.1 % compared to wild-type plants. Furthermore, root hairs were established as the primary site for CdS NP entry, as evidenced by increased clathrin-coated vesicles and their colocalization with the membrane dye FM4-64 following CdS NP exposure. Collectively, these results demonstrate that the CME pathway in root hairs facilitates CdS NP internalization, uncovering a previously underestimated ecological risk of these NPs in rice and advancing mechanistic understanding of NP uptake in plant roots.