Morphological, proteomic and metabolomic insight into the effect of cerium dioxide nanoparticles to Phaseolus vulgaris L. under soil or foliar application

Chemically synthesized nanoparticles (NPs) arewidely used in industry and concern over their impact on the environment is rising. In this study, greenhouse grown bean (Phaseolus vulgaris L.) plants were treated with CeO2 NPs suspensions at 0, 250, 500, 1000, and 2000 mg L−1 either aerially by spraying or via soil application. At 15 days after treatment, plants were analyzed for Ce uptake, morphological and biochemical assays, as well as high-resolutionmass spectrometry basedmetabolomics and proteomics. The results fromICP-MS assays showed a dose dependent absorption, uptake and translocation of Ce through both roots and leaves; Ce content increased from0.68 up to 1894 mg kg−1 following spray application,while concentrationswere three orders lower following soil application (0.59 to 2.19mg kg−1). Electrolyte leakage increased with NPs rate, from 25.2% to 70.3% and from 24.8% to 32.9% following spray and soil application, respectively. Spraying lowered stomatal density (from 337 to 113 permm2) and increased stomatal length (from 12.8 to 19.4 μm), and altered photosynthesis and electron transport chain biochemicalmachinery. The increase in Ce content induced accumulation of osmolites (proline increased from 0.54 to 0.65 mg/g under spray application), phytosiderophores (muconate and mugineate compounds showed increase fold-changes N16) and proteins involved in folding or turnover. NPs application induced membrane damage, as evidenced by the increase in membrane lipids degradates and by the increase in electrolyte leakage, and caused oxidative stress. Most of the responses were not linear but dose-dependent, whereas metabolic disruption is expected at the highest NPs dosage. Both proteomics and metabolomics highlighted a stronger effect of CeO2 NPs spraying, as compared to soil application. High concentrations of NPs in the environment have been confirmed to pose toxicity concern towards plants, although important differences could be highlighted between aerial deposition and soil contamination.