AcePosF21 positively alleviates ROS damage by cold stress in kiwifruit. A) The expression level of AcePosF21 in WT and transgenic calli of AcePosF21-overexpression lines under 25 °C (control) or 4 °C (cold stress) for 6 h. B) The variation of fluorescence intensity showed the difference in ROS content among WT, AcePosF21-overexpression, and mutant calli of kiwifruit after cold treatment (4 °C) for 6 h. C–G) The content of O₂^.−C), H₂O₂D), electrolyte leakage E), MDA F) and proline G) of wild-type, AcePosF21-overexpression, and mutant calli under 25 °C (control) or 4 °C (cold stress) for 6 h. Error bars indicate ± SD in the above experiments (n = 3 to 4). Significant differences were detected by t-test (*P < 0.05; **P < 0.01; ***P < 0.001).