Changes in enzymes involved in photosynthesis and other metabolic processes in the fruit of Opuntia ficus-indica during growth and ripening

The aim of this study was to investigate changes in the abundance of a number of enzymes in the peel, coreand seeds of fruits of Opuntia ficus-indica (L.) Miller during development. The enzymes studied were phosphoenolpyruvatecarboxylase (PEPC; EC: 4.1.1.31), ribulose-1,5-bisphosphate carboxylase/oxygenase(RUBISCO; EC: 4.1.1.39), aldolase (EC: 4.1.2.13), pyruvate, orthophosphate dikinase (PPDK; EC: 2.7.9.1),phosphoenolpyruvate carboxykinase (PEPCK; EC: 4.1.1.49) and aspartate aminotransferase (AspAT; EC:2.6.1.1). To detect these enzymes, antibodies specific for each enzyme were used to probe Western blotsof sodium dodecyl sulphate polyacrylamide gels. Fruit weight increased throughout development, andduring ripening there was both an accumulation of total soluble solids and a decrease in both total titratableacidity and chlorophyll content. In the early stages of its growth the polypeptide pattern and enzymecomposition of the fruit chlorenchyma was similar to that of the cladode. In the peel of the fruit PEPC,RUBISCO, plastidic aldolase and PPDK decreased to undetectable amounts as ripening progressed. PEPCKwas not detected in either the chlorenchyma of the fruit or cladode. This showed that O. ficus-indica isnot a PEPCK type CAM plant and that in this fruit PEPCK is not involved in the metabolism of organicacids. Cytosolic aldolase and AspAT were present in both the peel and core throughout development.The seeds accumulated storage proteins before the fruit ripened, and the abundance of all the enzymesstudied declined once the accumulation of storage proteins was complete.