Cloning, Expression and Transformation of hGLR Gene in Malus hupehensis var. pingyiensis Effect of Calcium on the Functions of Antioxidant Systems and Mitochondria in Malus hupehensis var. pingyiensis Roots under Acid Treatment Responses of Root Morphology and Architecture in Malus hupehensis var. pingyiensis Seedlings to Cadmium Chloride