Exogenous 24-Epibrassinolide Alleviates Postharvest Chilling Injury in Green Pepper Fruit Associated with Enhanced Antioxidant Defense and Reduced Membrane Damage

Green pepper is highly susceptible to chilling stress during extended low-temperature storage. This study examined the physiological responses and associated transcriptional changes in postharvest green pepper fruit following exogenous 24-epibrassinolide (EBR) treatment. After treatment with 15 μmol·L−1 EBR, fruits were maintained at 4.0 ± 1.0 °C for 25 d. Chilling injury, quality attributes, reactive oxygen species (ROS) accumulation, enzymatic and non-enzymatic antioxidant defenses, and membrane damage-related parameters were monitored, and transcriptomic profiling was performed at 25 d. EBR treatment reduced chilling injury and weight loss and delayed softening and storage-related quality deterioration. It also helped maintain antioxidant defenses, limited O2•− production and H2O2 and malondialdehyde (MDA) accumulation, and lowered relative electrical conductivity and phospholipase D (PLD) and lipoxygenase (LOX) activities. Transcriptomic analysis identified EBR-associated changes in processes involving cell wall remodeling, stress responses and signaling, ROS production, and membrane lipid-related functions. These results indicate that improved chilling tolerance in EBR-treated green pepper is closely associated with sustained antioxidant defenses, lower ROS accumulation, and reduced membrane damage, while the transcriptomic data provide additional molecular clues linked to these physiological responses.