Postharvest heat treatment delays fruit ripening and softening by <i>S</i>-nitrosylation of PpACO1 in peach

Abstract Objectives: Ethylene plays a pivotal role in the processes of fruit ripening and senescence. Heat treatment has a significant impact on maintaining fruit quality and extending shelf life, while the precise mechanism by which heat treatment prolongs the storage life of melting peach remains to be elucidated. Materials and Methods: Two melting peach varieties, ‘Hujingmilu’ (HJML) and ‘Yulu’ (YL), were treated with hot water at 45 °C for 10 min to explore the effect of postharvest heat treatment during storage and its regulatory mechanism. Results: The enzymatic activities of polygalacturonase (PG) and 1-aminocyclopropane-1-carboxylate (ACC) oxidase (ACO) were inhibited by heat treatment, and the transcript level of PGM was reduced, while PpACO1 was not affected by heat treatment. Moreover, the protein abundance of PpACO1 was not inhibited by heat treatment. Interestingly, nitric oxide (NO) content significantly increased in heat-treated fruit as the S-nitrosylation level of total protein increased. An in vitro assay indicated that PpACO1 could be S-nitrosylated with a reduction of ACO enzymatic activity, suggesting that NO-mediated S-nitrosylation of PpACO1 may be involved in reducing ethylene emission by heat treatment. Conclusions: These findings demonstrated that postharvest heat treatment can lead to an increase in NO content, resulting in S-nitrosylation of PpACO1, thus slowing down endogenous ethylene production and effectively delaying postharvest ripening and softening of fruit.