24-Epibrassinolide treatment alleviates frost damage of apple flower via regulating proline, ROS, and energy metabolism.

Frost damage to apple flowers significantly affects both the quality and yield of apples, potentially leading to substantial economic losses. This study investigates the application of the environmentally friendly plant hormone 24-epibrassinolide (EBR) on apple flowers to assess its effects under frost stress conditions. The findings indicate that exogenous EBR treatment maintained favorable flower morphology, mitigated pistil browning, and reduced ion leakage. Furthermore, EBR enhanced the ICE-CBF-COR signaling pathway and increased proline accumulation by modulating gene expression and enzyme activity involved in proline metabolism, promoting osmotic adjustment ability of cells. Furthermore, EBR treatment retarded the increase of HO, O, and malonaldehyde (MDA), and increased the enzymatic activity and gene expression of antioxidant enzymes such as superoxide dismutase (SOD), Catalase (CAT), ascorbate peroxidase (APX) and peroxidase (POD), thereby augmenting the antioxidant capacity of tissues. Additionally, the study found that exogenous EBR reduced AMP content, promoted ATP content and energy charge level, improved succinic dehydrogenase (SDH), cytochrome oxidase (CCO), H-ATPase, Ca-ATPase enzyme activity, and enhanced the energy supply of the cells. Consequently, we hypothesized that EBR treatment could enhance the frost resistance in apple flowers by synergistically ameliorating cold signaling, osmotic adjustment, antioxidant capacity, and energy status.