DEVELOPMENTAL REGULATION OF THE EXPRESSION OF ALCOHOL-DEHYDROGENASE IN RIPENING TOMATO FRUITS

In each of 5 tomato (Lycopersicon esculentum Mill) cultivars examined, alcohol dehydrogenase (E.C.1.1.1.1) specific activity decreased during the early stages of ripening and then increased in the postclimacteric period. Alcohol dehydrogenase specific activity also increased when immature, mature or pink fruit were placed in an atmosphere of 3% (V/V) oxygen. Measurements of oxygen in the internal tissues and the respiratory quotient throughout ripening established that fruit ripening in air does not suffer an oxygen stress. Increases in alcohol dehydrogenase activity were also observed in pink fruit exposed to 10% (V/V) carbon dioxide. Such atmospheres are known to result in a lowering of the cytoplasmic pH in plants and it is suggested that alcohol dehydrogenase activity is induced during ripening in response to cytoplasmic acid stress. The increased ADH activity during ripening may contribute to flavor development.