The Organic Acid Metabolism of Cox's Orange Pippin Apples

Abstract

The basic respirations (CO₂-output and O₂-uptake) of Cox's Orange Pippin apples and of the peel tissue prepared from them were compared in fruit in various stages of development, both initially and after storage at 12°C. Both show the same general trend, although as the apples become mature the peak value of the respiration climacteric tends to rise in the whole fruit and fall in the peel. The effect of adding malate or citrate on the respiration of the same samples of peel was studied. Three broad stages of development were observed. During the first stage (petal fall to 60 days after) the metabolic pattern appears to be different from the two later stages. Here O₂-uptake as well as C₂-output are influenced by the addition of both malate and, to a considerably less extent, citrate. In stage 2 (60–125 days from petal fall), the malate effect (CO₂-output) is small until after detachment from the tree, when it rises sharply. In stage 3 (125 days to full maturity) the malate effect follows the course expected for earlier work, namely, it develops at the same time as the climacteric rise in respiration. The possible reasons for the different behaviour of the peel at the three stages is discussed. Results were similar in general trend for Cox's Orange Pippin apples grown on different rootstocks and under different cultural conditions. It is suggested that the malate effect is most active in the epidermal and hypodermal tissues of the fruit.