The process of separation of leaves, flowers, and fruits from the plant is called abscission. It is essential, when these parts are removed that the plant seals off its vascular system to prevent loss of water and nutrients and to exclude bacteria, fungal sporesand other pathogens. An abscission zone, a layer of specialized cells is formed at the base of each part before it is lost, to separate it form the main body. The cells in this layer die and become hardened by the deposition of ligning and suberin. So, by the time the leaf or fruit drops, the vascular system has been
It takes place at the base of the petiole which is internally marked by a distinct zone of few layers of thin-walled cells arranged transversally across the petiolar base. This zone is called as the abscission zone or abscission layer (Fig). The cells of the abscission layer is separate from each other due to the dissolution of middle lamella and also the primary cellulose walls under the influence of the increased of the increased activity of the enzymes pectinase and cellulase. At this stage the petiole remains attached to the stem only by vascular elements and very soon due to its own weight and pressure of wind, is detached from the stem. The broken vascular elements are soon plugged with tyloses or gums.
Abscission is controlled by abscisic acid (ABA), a growth regulator synthesized primarily in chloroplasts. It is a general inhibitor of many processes, and the abscission layer forms and hardens under its direction.
1. Itsheds off the senescent and dead parts of the plants.
2. It also sheds off ripe fruits, which helps in their dispersaland further life cycle of the plant.
3. In lower plants, shedding of vegetative parts, such as gemmae or plantlets helps in vegetative propagation.