Cell wall: An important medium regulating the aggregation of quantum dots in maize (Zea mays L.) seedlings

Quantum dots (QDs) find various applications in many fields, leading to increasing concerns regarding their uptake and subsequent interaction with plant body. Cell wall (CW), serving as a first target place that interacts with xenobiotic substances into plant body, its role in regulating the QDs cellular uptake needs to be explored. In the present study, maize (Zea mays L.) seedlings were hydroponically exposed to PEG-COOH-CdS/ZnS QDs (QDs-PEG-COOH) and MPA-CdS/ZnS QDs (QDs-MPA) functionalized with negatively charged and neutral coatings, respectively. Uptake rate of QDs-PEG-COOH was approximately 3.5 times lower than that of QDs-MPA due to electrostatic repulsion to the negatively charged root CW. Both types of QDs had obvious aggregation on surfaces of taproot, lateral root and fibrous root, and QDs-MPA aggregates were approximately 1.8 times larger than QDs-PEG-COOH aggregates. The strong hydrogen bond formed by hydroxyl group in cellulose of CW and carboxyl group on surface coatings of QDs-PEG-COOH constituted the key mechanism for QDs-PEG-COOH aggregation, while conjugated C˭C chains between lignin and QDs-MPA dominated the occurrences of QDs-MPA aggregation. Results of this work highlight the importance of plant CW in regulating uptake rate and aggregation of QDs, potentially limiting their internalization into plant body and introduction into food webs.