Modified Method for PCR Cloning of Soluble Acid Invertase Gene in Sorghum bicolor Purification, Biochemical and Immunological Characterization of Acid Invertases from Apple Fruit Establishment of Detection System for Soluble Acid Invertase Activity in Lilium davidii var. unicolor Bulb Establishment of Detection System for Soluble Acid Invertase Activity in Lilium davidii var. unicolor Bulb