Morphological and Anatomical changes during abscission:
Leaf abscission takes place at the base of the petiole which is marked internally by a distinct zone of few layers of thin-walled cells arranged transversely. This zone is called the abscission zone or abscission layer. An abscission layer is greenish-grey in color and is formed by rows of cells of 2 to 15 cells thick. The cells of the abscission layer separate due to the dissolution of the middle lamella and primary wall of cells by the activity of enzymes pectinase and cellulase resulting in the loosening of cells. Tyloses are also formed blocking the conducting vessels. Degrading of chlorophyll occurs leading to the change in the color of leaves, leaf detachment from the plant, and leaf fall. After abscission, the outer layer of cells becomes suberized by the development of periderm.
