Studies on the Relationship of the Development of Bitter Pit in Apple Fruits with the Contents of Calcium and Magnesium and the Activities of Antioxidant Enzymes Studies on the Relationship of the Development of Bitter Pit in Apple Fruits with the Contents of Calcium and Magnesium and the Activities of Antioxidant Enzymes Effects of 1-MCP on Physiological Changes of ‘Jonagold’Apples at Ambient Temperature after Harvest