The Character of MhHSP70 from Malus hupehensis and Its Response to the Stress of Cadmium and Osmosis The Character of MhHSP70 from Malus hupehensis and Its Response to the Stress of Cadmium and Osmosis Differential Expression of Anti-apoptotic Genes in Extensive and Absorbing Roots of Malus hupehensis and Their Response to 2,4-D