Endogenous ABA accelerates apple softening during postharvest ripening

Ethylene is considered the main hormone involved in the ripening of climacteric fruit including apples. However, the contribution of other hormones to the regulation of climacteric fruit ripening has become more relevant in recent times. Indeed, abscisic acid (ABA) is able to trigger ethylene production in some climacteric fruit such as pear and peach. Nevertheless, scarce information is available regarding the role of abscisic acid (ABA) on apple ripening. In this study, we analysed the evolution of ethylene, ABA and ripening related traits (colour, firmness, soluble and starch among others) in ‘Golden Reinders’ apples under three ripening scenarios after reaching the commercial harvest date (CHD): on-tree, off-tree and post-cold storage ripening. Our data revealed that the autocatalytic ethylene production in ‘Golden Reinders’ apples was only triggered when the fruit ripened detached from the tree (off-tree and post-cold storage scenarios) without a clear involvement of ABA. However, ethylene itself was not able to trigger ripening-related changes including softening unless ABA levels raised. Collectively, our results point out that after the activation of ethylene metabolism, ABA may trigger or at least accelerate softening and other ripening-related changes during postharvest ripening of ‘Golden Reinders’ apples.