Nanomaterial-modulated cellular sodium extrusion and vacuolar sequestration for salt tolerance

Nanomaterials can induce plant tolerance to abiotic environmental stresses, whereas the sensing mechanism and the resulting response at the cellular level need further exploration. Bright Yellow 2 tobacco (Nicotiana tabacum L.) suspension-cultured cells challenged with 100 mM NaCl were exposed to increasing doses (0.05, 0.1, and 0.5 mg L⁻¹) of nano-CeO₂ (nCeO₂) or nitrogen-doped carbon dots (N-CDs). nCeO₂ at 0.1 mg L⁻¹ or N-CDs at 0.5 mg L⁻¹ were optimal for alleviating salt stress and nCeO₂ was superior to N-CDs. Notably, the expression of genes (IPUT1, SOS3, SOS2, and SOS1) involved in Na⁺-GIPC perception-Na⁺-extrusion was stimulated (5.3-fold) after nCeO₂ exposure for 4 h, and NHX1 encoding Na⁺ vacuolar sequestration was induced by 7.8-fold after N-CDs treatment for 6 h. Subsequently, the net Ca²⁺ influx and Na⁺ efflux were strongly promoted by 293.6% and 191.3% after incubation with nCeO₂, while no obvious Na⁺ extrusion but the transient K⁺ influx (by 3.0-fold) was observed for N-CDs. The downstream metabolic modifications in fatty acids, or amino acids and carbohydrates could favor the adaptation to salt stress. This work reveals the specific nanomaterial-induced early cell perception and signaling cascade, contributing to the nano-based agricultural practices for combating salt stress.