Improvement of leaf K⁺ retention is a shared mechanism behind CeO₂ and Mn₃O₄ nanoparticles improved rapeseed salt...

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 (CeO₂ nanoparticles)] and PMO (polyacrylic acid coated Mn₃O₄ 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.