Exogenous progesterone treatment alleviates chilling injury in postharvest banana fruit associated with induction of alternative oxidase and antioxidant defense

•Progesterone (10−5 M) was effective in reducing chilling injury in banana fruit.•Application of progesterone reduced the generation of reactive oxygen species.•Progesterone advanced the induction of alternative oxidase.•Progesterone improved the enzyme and non-enzymatic antioxidant defenses. The effects of exogenous progesterone (PROG) on chilling injury (CI) in postharvest banana fruit were investigated. Concentration screening tests showed that 10−5 mol/l PROG was most effective in reducing CI in banana fruit stored for 25 d at 5 ± 1 °C, but did not markly increase PROG content of pulps. This PROG treatment significantly reduced the electrolyte leakage, levels of malondialdehyde, O2− production rate and H2O2 contents in banana compared with control fruit. The PROG treatment caused an early induction of alternative oxidase (AOX) at the transcript and protein level to reduce the generation of O2− and H2O2. PROG treatment also enhanced the transcript levels and activities of antioxidant enzymes and maintained higher levels of reduced glutathione and ascorbic acid than the control fruit. These results suggested that PROG attenuating CI in banana fruit may be attributed to the induction of AOX and the improvement of enzyme and non-enzymatic antioxidant defenses.