Fe3O4 nanozyme as a novel plant growth promoter for enhancing salt tolerance in cucumber seedlings: integrated analysis of growth physiology and transcriptional metabolism

Abstract

Salt stress is one of the most significant factors limiting the output and quality of cucumber. The emergence of nanomaterials offers a new approach for overcoming the current limitations in non-biological stress management and achieving high-yield agriculture. Herein, we develop a PEG-modified Fe₃O₄ nanozyme (FNPs-G) and investigate its effect on the salt tolerance of cucumber seeds and seedlings. The results showed that FNPs-G significantly increased the germination rate by approximately 50% and promoted embryonic root growth (7.2% increase). Under salt stress, the foliar application of FNPs-G enhanced salt tolerance by increasing POD and CAT activities (38% and 17.4%, respectively), elevating proline (54.6%) and soluble sugar (3.13-fold) levels, and reducing H₂O₂ (24.6%) and MDA (33.8%) accumulation. The results of transcriptional and metabolic analyses indicate that the foliar application of FNPs-G can further mitigate salt stress in cucumber by enhancing phenylalanine metabolism, phenylpropanoid biosynthesis, and steroid biosynthesis. It also significantly facilitates tyrosine and arginine biosynthesis and upregulates the expression of genes encoding intracellular hydrolases and oxidoreductases, thereby maintaining cellular homeostasis. This study provides a theoretical and mechanistic basis for future investigations into the potential effects of FNPs-G during the fruiting stage and their influence on fruit quality under saline conditions.