Salicylic acid mitigates 'Hayward' kiwifruit chilling injury by regulating hormone and proline metabolism, as well as maintaining cellular structure

The 'Hayward' kiwifruit is extremely susceptible to chilling injury (CI) during the late stages of cold storage, thus limiting its storage quality and life. Therefore, mitigating the losses caused by CI is imperative. Salicylic acid (SA) has been demonstrated to mitigate CI in fruit and vegetables. In this study, we conducted a comparative analysis of proline metabolism, key endogenous hormone levels, as well as the effects on cell structure and membrane lipid oxidation in kiwifruit treated with 1 mM SA during low-temperature storage. The results showed that SA could attenuate lipoxygenase (LOX) activity, enhance catalase (CAT) activity, suppress the elevation of malondialdehyde (MDA) content, mitigate starch granule degradation in cells, and preserve cell structure integrity. Moreover, SA was found to enhance proline biosynthesis by activating ornithine transaminase (OAT) and pyrroline-5-carboxylate synthase (P5CS) while concurrently suppressing proline dehydrogenase (PDH) activity. Additionally, exogenous SA increased endogenous levels of both SA and abscisic acid (ABA), while simultaneously decreasing the concentration of gibberellic acid (GA) in fruit. In conclusion, exogenous SA treatment could alleviate the development of CI in kiwifruit by maintaining cell structure, promoting proline synthesis, and balancing endogenous hormone content. Our study offers a theoretical foundation for understanding the mechanism by which SA mitigates cold damage in kiwifruit, and provides novel insights into the low-temperature preservation of kiwifruit.