Effect of postharvest calcium chloride treatments on tissue water relations, cell wall calcium levels and postharvest life of 'Golden Delicious' apples

摘要

Changes in tissue water relations, cell wall Ca concentrations and physical properties of Ca-treated and untreated Golden Delicious apple fruits were monitored for up to 8 months postharvest storage at 0deg C. Ca-treated fruits were pressure-infiltrated with CaCl2 at 0.07-0.34 mol/litre, which reduced fruit softening and air space volume of fruit in a concentration-dependent manner. Turgor potential-related stress within the fruit persisted during storage and was higher in Ca-treated than in untreatedfruits. Fruits that were pressure-infiltrated with CaCl2 solutions between 0.14 and 0.20 mol/litre and then waxed showed no peel injury. At Ca concentrations up to 0.20 mol/litre, cell-wall-bound Ca approached saturation whereas soluble Ca showed a linear dependence. At higher external Ca concentrations, only soluble Ca in the tissue increased. During 8 months of cold storage, cell wall Ca-binding capacity increased by up to 48%. The osmotic potential of apples harvested over 3 seasons ranged from -1.32 to -2.33 MPa. In tissue discs, turgor potential changes caused by adjusting the osmolality of the incubation solution with CaCl2 or sorbitol were accompanied by changes in the osmotic and water potentials of the tissue. In CaCl2 solutions up to 0.34 mol/litre, turgor potential was >=0.6 MPa in tissue incubated in 0.14 or 0.17 mol/litre CaCl2 solutions and was more than 3 times higher than in tissues incubated in low (<=0.03 mol/litre) or high (>=0.27 mol/litre) concentrations of CaCl2. At osmotically equivalent concentrations, turgor potential was up to 40% higher in Ca- than in sorbitol-treated tissue. Postharvest treatment with 0.14 to 0.20 mol/litre CaCl2 solutions were best for maintaining fruit water relations and storage life of Golden Delicious apples.