ETHYLENE BIOSYNTHESIS IN BANANA FRUIT - EVOLUTION OF EFE ACTIVITY AND ACC LEVELS IN PEEL AND PULP DURING RIPENING

In the methionine cycle, ethylene biosynthesis is controlled by the content of 1-aminocyclopropane-1-carboxylic acid (ACC) and its conversion to ethylene by ethylene forming enyzme (EFE). In bananas, before the onset of ripening, EFE activity is low in both peel and pulp. Immediately after the rise in ethylene production, EFE activity in pulp increases to a maximum which coincides with the ethylene peak. It then decreases following the same pattern as ethylene. In peel, however, EFE activity remains low during the peak of ethylene production, but then increases along with the respiratory climacteric. Free ACC in pulp increases at the same time as ethylene, reaching its maximum later, then decreases while the level of malonyl ACC (MACC) increases. In peel, free ACC remains low, while MACC considerably increases after the ethylene peak. The role of peel and pulp on ripening is discussed. It is suggested that EFE activity in the pulp is a key factor to start the autocatalytic ethylene production.