CO2-GAS EXCHANGE OF ATTACHED FRUIT IN APPLES
Photosynthesis was high in young apple fruits and decreased to low levels at fruit ripeness. Apple fruit are able to refix CO2 via PEPC (phosphoenol pyruvatecarboxylase) and PEPCK.(phosphoenol pyruvatecarboxykinase). By this means a large portion of the internal CO2 can be recovered and saved, especially if assimilate supply from the leaves is restricted or at high light intensity. However, at all developmental stages of the fruit more CO2 will be lost by respiration than gained by CO2-fixation. This is pronounced at early fruit development and at maturity.
Lenz, F. (1989). CO2-GAS EXCHANGE OF ATTACHED FRUIT IN APPLES. Acta Hortic. 240, 217-220