Engineered nanomaterials and plant interactions: uptake, translocation, transformation and physiological effects
Alvarez, Pedro J.J.
Doctor of Philosophy
The increasing likelihood of engineered nanomaterial (ENM) releases to the environment and their potential applications in agriculture highlight the importance of understanding ENM interactions with plants, which are cornerstone of most ecosystems. This study investigated how silver nanoparticles (Ag NPs) of different sizes affect plant growth over a wide range of concentrations and how coating charge affects quantum dots (QDs) uptake, translocation and transformation within woody plants. Even though both Ag NPs (5, 10, and 25 nm) and silver ion (Ag+) were phytotoxic to poplars and Arabidopsis above a specific concentration, a stimulatory effect was observed on root elongation, fresh weight and evapotranspiration of both plants at a narrow range of sub-lethal concentrations. Plants were most susceptible to the toxic effects of Ag+, but Ag NPs also showed some toxicity at higher concentrations and this susceptibility increased with decreasing Ag NP size. Both poplars and Arabidopsis accumulated silver, but silver distribution in shoot organs varied between plant species. Arabidopsis accumulated silver primarily in leaves (at ten-fold higher concentrations than in the stem or flower tissues), whereas poplars accumulated silver at similar concentrations in leaves and stems. Uptake of cationic QDs by poplar was faster than anionic QDs, possibly due to electrostatic attraction of cationic QDs to the negatively charged root cell wall. QDs aggregated upon root uptake, and their translocation to poplar shoots was likely limited by the endodermis. After 2-day exposure, both cationic and anionic coatings were likely degraded from the internalized QDs inside the plant, leading to the aggregation of the metallic cores and a “red-shift” of fluorescence. The fluorescence of cationic QD aggregates inside roots was stable through the 11-day exposure period, while that of the anionic QD aggregates was quenched probably due to destabilization of the coating inside the plant, even though these QDs were more stable in the hydroponic solution. Overall, the phyto-stimulatory effect observed in this study precludes the generalization of the phytotoxicity of Ag NPs. The QDs study highlights the importance of coating properties in the rate and extent to which NPs are assimilated by plants and potentially introduced into food webs.