Cell Walls Are Remodeled to Alleviate nY₂O₃ Cytotoxicity by Elaborate Regulation of <i>de Novo</i> Synthesis and Vesicular Transport.

Abstract

Yttrium oxide nanoparticles (nY₂O₃), one of the broadly used rare earth nanoparticles, can interact with plants and possibly cause plant health and environmental impacts, but the plant defense response particularly at the nanoparticle-cell interface is largely unknown. To elucidate this, Bright Yellow 2 (BY-2) tobacco (<i>Nicotiana tabacum</i> L.) suspension-cultured cells were exposed to 50 mg L^-1 nY₂O₃ (30 nm) for 12 h. Although 42.2% of the nY₂O₃ remained outside of protoplasts, nY₂O₃ could still traverse the cell wall and was partially deposited inside the vacuole. In addition to growth inhibition, morphological and compositional changes in cell walls occurred. Together with a locally thickened (7-13-fold) cell wall, increased content (up to 58%) of pectin and reduction in (up to 29%) hemicellulose were observed. Transcriptome analysis revealed that genes involved in cell wall metabolism and remodeling were highly regulated in response to nY₂O₃ stress. Expression of genes for pectin synthesis and degradation was up- and down-regulated by 31-78% and 13-42%, respectively, and genes for xyloglucan and pectin modifications were up- and down-regulated by 82% and 81-92%, respectively. Interestingly, vesicle trafficking seemed to be activated, enabling the repair and defense against nY₂O₃ disturbance. Our findings indicate that, although nY₂O₃ generated toxicity on BY-2 cells, it is very likely that during the recovery process cell wall remodeling was initiated to gain resistance to nY₂O₃ stress, demonstrating the plant's cellular regulatory machinery regarding repair and adaptation to nanoparticles like nY₂O₃.