Nano-cerium oxide enhances salt stress tolerance in Tamarix chinensis by regulating antioxidant defense, phenylpropanoid biosynthesis and phytohormone balance

Soil salinization imposes notable limitations on plant growth and land use. Nanotechnology is a promising strategy to mitigate salt stress. Studies on nanoparticle-regulated salt tolerance have rarely focused on Tamarix chinensis ( T. chinensis ), a halophyte adapted to moderate to severe saline-alkali soil. This study used a multimodal approach encompassing physiology, ultrastructure observation, ion detection, transcriptome sequencing, and phytohormone quantification to clarify the effect and underlying mechanisms of cerium dioxide nanoparticles (CeO 2 NPs) on the mitigation of salt stress in T. chinensis . The results revealed that CeO 2 NPs markedly restored biomass (90.9%), chlorophyll content (28.0%), and root development (110-120%) of T. chinensis under salt stress, and reduced cellular ultrastructural damage. Higher total cerium was detected in roots than in leaves, and salt stress increased tissue total cerium levels. It was found to regulate ion homeostasis by lowering the Na + /K + ratio and enhancing the accumulation of soluble sugars. Moreover, CeO 2 NPs have been indicated to scavenge excessive ROS by lowering hydrogen peroxide and MDA levels and boosting POD/SOD activities by roughly 2.6-3.5 fold, which was associated with enhanced plant antioxidant capacity and lowered levels of reactive oxygen species derived oxidative damage. Transcriptome analysis identified differentially expressed genes enriched in phenylpropanoid biosynthesis, flavonoid biosynthesis, and plant hormone signal transduction pathways. CeO 2 NPs have been demonstrated to modulate the levels of the phytohormones abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA), with a concurrent decrease in ABA (80%) and JA (48%), and an increase in SA (159%). These effects have been indicated to reverse the aberrant expression of important genes within the three pathways mentioned above under salt stress conditions. In conclusion, CeO 2 NPs mediated salt stress mitigation in T. chinensis may be associated with enhanced antioxidant defense systems, alterations in phenylpropanoid flavonoid biosynthesis, and shifts in phytohormone homeostasis and signal transduction. This study offers a theoretical justification for using a nanotechnology-based strategy in halophyte cultivation for saline land development.