Histological Effects of Calcium Chloride in Stored Apples

Mature apples (Malus domestica Borkh. cv. Golden Delicious) were immersed for 2 min in 0, 0.14, 0.27, or 0.41 mol·L-1 (0, 2%, 4%, or 6%, respectively) aqueous solutions (w/v) of CaCl₂ at 0 or 68.95 kPa, and were stored at 0 °C. Histological samples of peel/cortex were taken at harvest and at four monthly intervals in storage. Paraffin sections were stained with an aqueous mixture of alcian blue 8GX, safaranin 0 and Bismark brown Y, or with the periodic acid-Schiff (PAS) reaction. No histological difference was observed in fruit treated with 2% CaCl₂ compared with those pressure-infiltrated with greater amounts of Ca. Fruits pressure-infiltrated with 6% CaCl₂ exhibited the greatest amount of flattened epidermal cells and hypodermal cavities. Cuticles were also affected at the higher CaCl₂ treatment levels (with regard to staining with Bismark brown), becoming more condensed and uniform. Cuticle and hypodermis were stained differentially with PAS in the 6% CaCl₂ treatment. All tissues, including the cuticle, were stained magenta red, indicating a possible chemical alteration of the cuticle and the underlying tissue by Ca.