Enhanced cell wall integrity: Ca plays a crucial role in maintaining the integrity of cell walls by promoting the cross-linking of pectin molecules and the formation of calcium pectate. Stronger cell walls can better withstand the turgor pressure that builds up in the fruit, reducing the risk of cracking.
Regulation of water relations: Ca application can influence water relations in sweet cherries by reducing water uptake and transpiration. This effect is attributed to the role of Ca in closing stomata, thereby controlling water loss and maintaining a more favorable water balance within the fruit. Reduced water uptake helps prevent excessive turgor pressure, which can lead to cracking.
Modulation of enzymatic activities: Ca is involved in the regulation of various enzymatic activities related to cell wall metabolism and fruit softening. It has been suggested that Ca application can inhibit the activity of cell wall-degrading enzymes, such as polygalacturonase, which contribute to fruit softening and weakening of the cell walls. By preserving the integrity of the cell walls, Ca application reduces the susceptibility to cracking.
Antioxidant defense: Ca has antioxidant properties and can mitigate oxidative stress in sweet cherries. It helps neutralize reactive oxygen species (ROS) that can damage cell membranes and contribute to fruit deterioration. By reducing oxidative stress, Ca application maintains membrane integrity and protects the fruit from cracking.
In addition to these mechanisms, Ca also influences other physiological processes in sweet cherries, such as fruit growth, sugar accumulation, and ripening. It is likely that the combination of these effects contributes to the overall reduction in macrocracking observed in Ca-treated sweet cherries. Further research is needed to fully elucidate the mechanisms by which Ca exerts its protective effects against macrocracking in sweet cherries.
