Spermidine Improves Freezing Tolerance by Regulating H₂O₂ in Brassica napus L

Low temperature is a common abiotic stress that causes significant damage to crop production. Polyamines (PAs) are a class of aliphatic amine compounds that serve as regulatory molecules involved in plant growth, development, and response to abiotic and biotic stresses. In this study, we found that the exogenous application of two concentrations of spermidine (Spd) significantly enhanced the freezing tolerance of three differently matured rapeseed (Brassica napus L.) varieties, as manifested by higher survival rates, lower freezing injury indexes, and reduced H₂O₂ content. RNA-seq and qRT-PCR analyses showed that Spd enhanced the freezing tolerance of rapeseed by regulating genes related to the PA metabolic pathway and antioxidant mechanism, and generally inhibited the expression of genes related to the JA signaling pathway. This study provides a reference basis for understanding the functionality and molecular mechanisms of polyamines in the response of rapeseed to freezing stress.