Polymer nanoparticles pass the plant interface

Abstract

As agriculture strives to feed an ever-increasing number of people, it must adapt to cope with climate change. It is also clear that our biosphere is suffering from an increasing burden of anthropogenic waste which includes minute plastic particles. It is not yet known whether plants will accumulate such micro- and nanoplastic materials, nor how their surface properties might influence uptake. Therefore, we prepared well-defined block copolymer nanoparticles with a range of different sizes (Dh = 20 - 100 nm) and surface chemistries by aqueous dispersion polymerisation using different functional macro chain transfer agents. A BODIPY fluorophore was then incorporated via hydrazone formation and uptake of these fluorescent nanoparticles into intact roots and protoplasts of Arabidopsis thaliana was investigated using confocal microscopy. Where uptake was seen, it was inversely proportional to nanoparticle size. Positively charged particles accumulated around root surfaces and were not taken up by roots or protoplasts, whereas negatively charged nanoparticles accumulated slowly in protoplasts and roots, becoming prominent over time in the xylem of intact roots. Neutral nanoparticles exhibited early, rapid penetration into plant roots and protoplasts, but lower xylem loads relative to the negative nanoparticles. These behaviours differ from those recorded in animal cells and our results show that, despite robust cell walls, plants are vulnerable to nanoplastic particles in the water and soil. The data form both a platform for understanding plastic waste in the farmed environment, and may also be used constructively for the design of precision delivery systems for crop protection products. Significance StatementSustainable food production must keep pace with the growing global population, as well as adapt to climate change and other anthropogenic insults. It has become clear that micro-and nanoscale plastics are accumulating in all parts of the biosphere and we have set out to study how vulnerable plants are to such waste. We show that the size and surface properties of the designed plastics significantly affect both their speed of uptake and distribution within intact roots. Crucially, it is clear that rigid cell walls around plant cells are no barrier to the smallest particles and these pass into the plants vasculature. Our results relate to plastic waste but can also be used to develop precision vehicles for crop protection.