Senescence in higher plants involves a series of physiological processes integrated within developmental programme which normally lead to the loss of the maternal plant or most of its organs. After senescence the plant is prepared to start the next generation. One of the facts related to senescence is the softening and failure of cell cohesion in some tissues belonging to certain organs. The present review examines several aspects of the biochemistry and molecular biology of polygalacturonases. These enzymes catalyzes the hydrolytic cleavage of α-(1-4) galacturonan linkages and are involved in the large changes in pectine structure that accompany to senescence. This update will focus mainly on the ripening phases of fruits, dehiscence and abscission, as well as the role of ethylene in the regulatory mechanism of this enzymatic activity.
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