Ion Relations of Apple Fruit Tissue During Fruit Development and Ripening. III. Calcium Uptake

Abstract

The ability of discs of apple cortical tissue to take up calcium from salt solutions declined during fruit development. This was true for both the cellular and free-space components of uptake. The extent of reduction was greatest in the slow, linear phase of uptake, which in young fruit had a metabolic component inhibited at 4°C. Free-space uptake contributed some 80% of the total uptake capacity and dominated calcium loss in wash-out experiments. The magnitude of calcium uptake was reduced in the presence of 10-3 M magnesium but not by equivalent concentrations of potassium. Because of the low rate of calcium uptake into the cytoplasm and vacuole, we suggest that the greatest effect of calcium treatments used to control disorders such as bitter pit is to change the extracellular environment.