RIPENING PHYSIOLOGY OF FRUIT FROM TRANSGENIC TOMATO (LYCOPERSICON-ESCULENTUM) PLANTS WITH REDUCED ETHYLENE SYNTHESIS

The physiological effects of reduced ethylene synthesis in a transgeni c tomato (Lycopersicon esculentum) line expressing 1-aminocyclopropane -1-carboxylic acid (ACC) deaminase enzyme have been examined. Fruit fr om the transgenic line 5673 ripen significantly slower than control fr uit when removed from the vine early in ripening. In contrast, fruit t hat remain attached to the plants ripen much more rapidly, exhibiting little delay relative to the control. Ethylene determinations on attac hed fruit revealed that there was significantly more internal ethylene in attached than detached fruit. The higher ethylene content can full y account for the observed faster on-the-vine ripening. All of the dat a are consistent with a catalytic role for ethylene in promoting many, although not all, aspects of fruit ripening. Biochemical analyses of transgenic fruit indicated no significant differences from controls in the levels of ACC oxidase or polygalacturonase. Because transgenic fr uit are significantly firmer than controls, this last result indicates that other enzymes may have a significant role in fruit softening.