Cell Walls Are Remodeled to Alleviate nYO Cytotoxicity by Elaborate Regulation of Synthesis and Vesicular Transport.

Yttrium oxide nanoparticles (nYO), 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 ( L.) suspension-cultured cells were exposed to 50 mg L nYO (30 nm) for 12 h. Although 42.2% of the nYO remained outside of protoplasts, nYO 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 nYO 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 nYO disturbance. Our findings indicate that, although nYO generated toxicity on BY-2 cells, it is very likely that during the recovery process cell wall remodeling was initiated to gain resistance to nYO stress, demonstrating the plant's cellular regulatory machinery regarding repair and adaptation to nanoparticles like nYO.