Improvement of leaf K retention is a shared mechanism behind CeO and MnO nanoparticles improved rapeseed salt tolerance.

Salinity is a global issue limiting efficient agricultural production. Nanobiotechnology has been emerged as an effective approach to improve plant salt tolerance. However, little known is about the shared mechanisms between different nanomaterials-enabled plant salt tolerance. In this study, we found that both PNC [polyacrylic acid coated nanoceria (CeO nanoparticles)] and PMO (polyacrylic acid coated MnO nanoparticles) nanozymes improved rapeseed salt tolerance. PNC and PMO treated rapeseed plants showed significantly fresh weight, dry weight, higher chlorophyll content, Fv/Fm, and carbon assimilation rate than control plants under salt stress. Results from confocal imaging with reactive oxygen species (ROS) fluorescent dye and histochemical staining experiments showed that the ROS over-accumulation level in PNC and PMO treated rapeseed was significantly lower than control plants under salt stress. Confocal imaging results with K fluorescent dye showed that significantly higher cytosolic and vacuolar K signals were observed in PNC and PMO treated rapeseed than control plants under salt stress. This is further confirmed by leaf K content data. Furthermore, we found that PNC and PMO treated rapeseed showed significantly lower cytosolic Na signals than control plants under salt stress. While, compared with significantly higher vacuolar Na signals in PNC treated plants, PMO treated rapeseed showed significantly lower vacuolar Na signals than control plants under salt stress. These results are further supported by qPCR results of genes of Na and K transport. Overall, our results suggest that besides maintaining ROS homeostasis, improvement of leaf K retention could be a shared mechanism in nano-improved plant salt tolerance.