Polygalacturonase in Tomato Fruits and the Induction of Ripening

Endopolygalacturonase (EC 3.2.1.15) activity, endopolygalacturonase protein detected immunologically and water-soluble uronide were measured in tomato fruit samples (cv. Rutgers) at different stages of ripening. Endopolygalacturonase activity and endopolygalacturonase protein were only detected in samples in which ripening had been initiated for 2 or more days. Enzyme activity and enzyme protein increased during ripening and were highly correlated. A high molecular weight form of the enzyme appeared 2 or 3 days after ripening was initiated. Lower molecular weight forms of endopolygalacturonase appeared later and eventually accounted for most of the enzyme protein. The content of water-soluble uronide did not increase until fruit had been ripening for 4 or more days. It is concluded that endopolygalacturonase is not involved in the initiation of ripening.