Ethylene and abscisic acid play a key role in modulating apple ripening after harvest and after cold-storage

An autocatalytic burst in ethylene production generally accompanies ripening of detached apple fruit. However, if apples are left to ripen attached to the tree, some cultivars, will not experience this autocatalytic ethylene production and the fruit will never acquire the organoleptic properties of detached ripened fruit. Accordingly, the present study aimed to understand how the hormonal crosstalk regulates ripening in ‘Golden Reinders’ apples, ripened on-tree, detached from the tree or after a period of cold storage, following the commercial harvest date. Our results showed that during on-tree ripening, ethylene production remained low, and no significant changes were observed in fruit colour or firmness. In fruit ripened detached from the tree, ethylene production was preceded by an increase of indole 3-acetic acid (IAA) and gibberellic acid (GA3) levels, whereas a cold-induced accumulation of jasmonic acid (JA) seemed to induce an earlier initiation of the climacteric burst in fruit ripened after cold storage. In both postharvest conditions, the accumulation of abscisic acid (ABA) may be either needed or facilitating the action of ethylene on triggering some ripening-related changes, pointing out the importance of both hormones in mediating apple ripening. In contrast, changes in sugars and ROS/antioxidants did not vary among the different ripening scenarios suggesting that none of the measured compounds may act as signalling molecules during apple ripening. Collectively, our results highlight that ethylene together with ABA played a crucial role in triggering ripening-related changes during postharvest ripening of ‘Golden Reinders’ apples.