Proteomic Approach to Study Scald Disorder of Apples

Apple “scald” is a physiological disorder and still causing significant economical loss of fruit industry. Despite for the extensive physiological and biochemical studies, the mechanism of scald development is still unknown. In this study, we applied 2-DE (2-dimensional electrophoresis) to separate the apple fruit peel proteins and stained with SYPRO Ruby. After gel analysis to identify up and down regulated spots, significantly spots were excised from gels and identified with electrospray ionization tandem mass spectrometry (ESI-MS/MS).  “Red Delicious” fruit were harvested before the climacteric stage, with internal ethylene concentration below 0.1-0.2 µl/L. After harvest, fruit were divided into three groups, including control, DPA and 1-MCP treatment. DPA (2000 μl/L) and 1-MCP (1.0 μl/L) were applied. Fruit were stored under cold air and CA (3.0 kPa  +1.0 kPa CO₂) at 0-1°C for 4 and 6 months.  Scald development was evaluated immediately after removal from storage, or after an additional 7 days at 22 °C. A total of 900, 851, and 954 spots have been visualized for the control, DPA and 1-MCP treated fruits, respectively. Substantial quantitative and qualitative differences in protein profiles were shown. At day 0, there were 16, 28 and 29 proteins associated with the scald, DPA and 1-MCP treatments, respectively. Among them, three proteins were consistently present in fruit treated with DPA or 1-MCP. At day7, 134 proteins were found to be specific to DPA treatment, while 71 proteins were common to both the DPA and 1-MCP treatments. LC/MS identification was conducted on day 0 samples, and 5, 17 and 17 proteins from control, DPA and 1-MCP respectively, were putatively identified and annotated. At this stage of this study, we speculate that DPA and 1-MCP might have their own unique function against scald, but may also share a common mechanism by protecting fruit tissue from oxidative stress damage caused by H₂O₂ and/or ROS. Identification of proteins related to scald development or to treatments inhibiting scald will give new insights to understand the development of scald and further design the strategies to prevent this disorder.