COMPARISON IN ETHYLENE BIOSYNTHESIS AMONG ATTACHED AND DETACHED FRUITS OF SEVERAL APPLE CULTIVARS DURING MATURATION

The internal ethylene concentrations (IEC), 1-aminocyclopropane-1-carb oxylate (ACC) and N-malonyl-ACC (MACC) contents, ACC synthase and ACC oxidase activities were measured on several attached and detached frui ts of apple (Malus domestica Borkh.) cultivars during maturation. The purpose was to investigate the ability of fruits of 'Starking Deliciou s', 'Senshu' (mid-season) and 'Golden Delicious' and 'Fuji' (late seas on) to synthesize ethylene. The attached fruits of 'Starking Delicious ' and 'Golden delicious' contained high IEC (40-100 mu l . L-1), where as 'Senshu' and 'Fuji' contained low IEC (<10 mu l . L-1). The results of ACC content, ACC synthase anc ACC oxidase activities indicated tha t ACC synthase activity and ACC content were limiting factors of IEC i n three cultivars except 'Starking Delicious'. IEC in attached fruits of 'Starking Delicious' had no correlation with these. IEC in detached fruits of all cultivars increased after 1-2 weeks in storage; and the value consistently exceeded IEC in attached fruits. The physiological reason, however, was not clarified by the changes of enzymes activiti es. It was indicated that detaching the fruit from the tree triggered the elevation of IEC, because the fruit was taken off before IEC incre ased. MACC content in attached fruits was almost constant during the m aturation stage in all cultivars, but that in detached fruits increase d several-fold during storage at 20 degrees C.