Studies on plant cell toxicity of luminescent silica nanoparticles (Cs 2 [Mo 6 Br 14 ]@SiO 2 ) and its constitutive components

As part of the risk evaluation before potential applications of nanomaterials, phytotoxicity of newly designed multifunctional silica nanoparticles (CMB@SiO 2 , average diameter of 47 nm) and their components, i.e., molybdenum octahedral cluster bromide units (CMB, 1 nm) and SiO 2 nanoparticles (nSiO 2 , 29 nm), has been studied using photosynthetic Arabidopsis thaliana cell suspension cultures. CMB clusters presented toxic effects on plant cells, inhibiting cell growth and negatively affecting cell viability and photosynthetic efficiency. Nevertheless, we showed that neither nSiO 2 nor CMB@SiO 2 have any significant effect on cell growth and viability or photosynthetic efficiency. At least, part of the harmful impact of CMB clusters could be ascribed to their capacity to generate an oxidative stress since lipid peroxidation greatly increased after CMB exposure, which was not the case for nSiO 2 or CMB@SiO 2 treatments. Exposure of cells to CMB clusters also leads to the induction of several enzymatic antioxidant activities (i.e., superoxide dismutase, guaiacol peroxidase, glutathione peroxidase, glutathione reductase, and glutathione S-transferase activities) compared to control and the other treatments. Finally, using electron microscopy, we showed that Arabidopsis cells internalize CMB clusters and both silica nanoparticles, the latter through, most likely, endocytosis-like pathway as nanoparticles were mainly found incorporated into vesicles. Graphical Abstract