Proteomic Changes in 'Ambrosia' Apple Fruit during Cold Storage in Response to Delayed Cooling Treatment

Abstract

‘Ambrosia’ is one of the emerging apple cultivars that have been gaining popularity in North America due to its superior eating quality. An effective postharvest storage regime has been established for optimal storage and quality maintenance. Unfortunately, a postharvest physiological disorder has often been reported which shows symptoms similar to low temperature induced soft scald in ‘Honeycrisp’. Therefore, a delayed cooling strategy has been developed and implemented as a successful and economical method to mitigate this disorder. In order to reveal the molecular mechanism of soft scald development and delayed cooling in combating this low temperature induced disorder, a quantitative proteomic investigation employing stable isotope dimethylation labeling by peptides was conducted on ‘Ambrosia’ apples from three commercial orchards in BC, Canada after 1 and 3 month storage. Changes in protein abundance in association with disorder development and in response to delayed cooling treatment were found. Among the quantified proteins, 380 and 425 proteins were common to three biological replicates after 1 and 3 month storage; respectively. Among them, the abundance of 47 and 57 proteins were found to be significantly changed in response to delayed cooling as compared with normal cold storage for 1 and 3 months, respectively. Principal component analysis (PCA) revealed groups of proteins that play a major role in response to delayed cooling. These identified proteins were functionally annotated using MAPMAN software, which identified glycolysis, lipid metabolism, amino acids (including GABA shunt), hormone response, stress and signaling, redox and glutathione metabolism as the major pathways influenced by the delayed cooling treatment. A significant correlation between protein changes and aroma volatile production was also found. These detailed results will be presented in a separate abstract. This study demonstrates the potential mechanism of the biological effect of delayed cooling on apple fruit at the proteomic level. It also provides in-depth insight on molecular mechanisms of the delayed cooling treatment in apples.