Development of ACC oxidase activity during maturation and ripening of ‘Paulared’, ‘Empire’ and ‘Law Rome’ apples

Abstract

Abstract The development of ACC oxidase activity was investigated in three cultivars of apple ( Malus domestica Borkh.), ‘Paulared’, ‘Empire’ and ‘Law Rome’, as typifying early, mid-season and late cultivars, respectively, during maturation and ripening. Fruits were selected at progressive stages of development of the autogenous ethylene climacteric during maturation and ripening on the tree. The level of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene was used as a relative measure of the activity of ACC synthase and the ability of fruit tissue to convert ACC to ethylene was used as a measure of the activity of ACC oxidase, the ethylene forming enzyme. ‘Paulared’ fruits accumulated high levels of ACC as the autogenous ethylene climacteric began and this was associated with slow development of ACC oxidase activity. ‘Law Rome’ apples showed ACC oxidase activity early in the development of the ethylene climacteric but this was associated with accumulation of low levels of ACC in fruits. ‘Empire’ fruits were found to be intermediate between the early and late cultivars. ACC oxidase activity of fruits of the three cultivars was found to increase concurrently with or subsequent to the accumulation of ethylene to ca. 0.1 μl 1 −1 in the internal atmosphere of the fruit. Thus, the ACC content of the fruit was found to be a function of the development of ACC synthase activity as well as the relative activity of ACC oxidase. The levels of these activities were cultivar dependent. Differential sequestering of ACC into malonyl ACC by malonyl Co A-ACC transferase among the three cultivars may also account for the wide disparity in changes in ACC content with maturation but this was not investigated.