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The process whereby a plant sheds one of its parts. Leaves, flowers, seeds, and fruits are parts commonly abscised. Almost any plant part, from very small buds and bracts to branches several inches in diameter, may be abscised by some species. However, other species, including many annual plants, may show little abscission, especially of leaves.

Abscission may be of value to the plant in several ways. It can be a process of self-pruning, removing injured, diseased, or senescent parts. It permits the dispersal of seeds and other reproductive structures. It facilitates the recycling of mineral nutrients to the soil. It functions to maintain homeostasis in the plant, keeping in balance leaves and roots, and vegetative and reproductive parts.

In most plants the process of abscission is restricted to an abscission zone at the base of an organ (see illustration); here separation is brought about by the disintegration of the walls of a special layer of cells, the separation layer. The portion of the abscission zone which remains on the plant commonly develops into a corky protective layer that becomes continuous with the cork of the stem.

Diagrams of the abscission zone of a leafenlarge picture
Diagrams of the abscission zone of a leaf

Auxin applied experimentally to the distal (organ) side of an abscission zone retards abscission, while auxin applied to the proximal (stem) side accelerates abscission. The gibberellins are growth hormones which influence abscission. When applied to young fruits or to leaves, they tend to promote growth, delay maturation, and thereby indirectly prevent or delay abscission. Abscisic acid has the ability to promote abscission and senescence and to retard growth. Small amounts of ethylene have profound effects on the growth of plants and can distort and reduce growth and promote senescence and abscission.

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A physiological process promoted by abscisic acid whereby plants shed a part, such as a leaf, flower, seed, or fruit.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Dispersal begins when the fruit (and sometimes the enclosing calyx) abscises from the mother plant.
The waxy cuticle of each gland encapsulates the sticky resin until it is needed for protection from herbivory (or to attract humans who disseminate it) and abscise readily as a convenient way of delivering its evolutionarily common allelopathic aromatic constituents, in addition to its evolutionarily unique cannabinoids.
The females oviposit on young fruit, often causing it to abscise (Quaintance & Jenne 1912; Snapp 1930).
are soon to abscise (Glinwood & Pettersson, 2000; Karban, 2007).
If the assimilate supply to a boll drops below a threshold level during the first 2 wk after anthesis, then that boll would probably abscise. However, if the assimilate supply is above the retain threshold level but below the optimum level, then the boll will remain but its fiber quality may suffer.
Second, the margins of the valves abscise, again beginning at the distal end of the nut, splitting the husk into four valves.
Regardless of many production practices involved in protection of fruiting forms on these positions, they can still abscise because of insect feeding or physiological stress (Guinn, 1982).
These are branches that form and develop concurrent with the RGU on which they form but that are strictly reproductive and abscise after fruiting.
Although most leaves abscise by bud-break the following growing season, a small fraction remain, especially in the interior of larger, older trees, into much of the next growing season.
It is thought that mature seeds start to abscise before the later-formed seeds become ripe (Kreft, 1989a).
Leaves began to abscise on the experimental tree on 31 March 1992, and on that date we collected all marked leaves and returned them to the laboratory.