Foliar Spraying of CeO2 Nanoparticles Enhances High-Temperature Tolerance in Herbaceous Peony Via Regulating Antioxidant Systems and Lignin Accumulation: Integrated Physiological, Biochemical, and Transcriptomic Evidence

Cerium dioxide nanoparticles (CeO2-NPs) possess unique redox and catalytic properties that effectively alleviate plant oxidative stress caused by adverse environmental conditions. However, the molecular mechanisms by which CeO2-NPs mediate high-temperature tolerance in plants remain poorly understood. In this work, we integrated physiological detection, transcriptome profiling, and virus-induced gene silencing verification to explore the protective effect and underlying mechanism of foliar-applied CeO2-NPs under heat stress. The results showed that 17.2 mg/L CeO2-NPs maintained chloroplast stability and photosynthetic performance, inhibited chlorophyll and lignin degradation, and reduced the level of ROS accumulation and lipid peroxidation. Physiological data revealed that relative electrical conductivity and malondialdehyde content in the control were 1.66- and 2.63-fold higher than those in the CeO2-NP group. Meanwhile, CeO2-NP treatment significantly increased SOD, POD, and APX activities by 1.56, 1.43, and 1.87 times, respectively. Heat stress reduced lignin content by 57.83% in the control but only by 19.40% with CeO2-NP application. Further transcriptomic and functional validation demonstrated that CeO2-NPs enhanced thermotolerance by upregulating PlPrx56 to promote antioxidant capacity and inducing PlCAD1 to maintain lignin accumulation. This study elucidates the dual molecular pathway of CeO2NPs-mediated plant heat tolerance and provides a promising nanomaterial strategy for improving plant stress adaptability in agricultural production.