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Related to abscission: abscission layer, abscission zone


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 ?
According to Reich and Borchert (1984) and Borchert, Rivera and Hagnauer (2002), leaf abscission represents a response to water stress, and so it is involved in the capacity to withstand water loss, which varies according to the tree species found in the Caatinga (QUIRINO, 2006).
[18] stated the formation of abscission layer at the stem point lead to fruit drop from unbalanced of auxins, cytokinins and gibberellins.
Premature abscission of leaves in response to herbivory is a common general response of woody plants (Zvereva & Kozlov 2014) and can be related to the rate of photosynthesis occurring in a leaf; once it drops below a certain level, abscission may occur in order to prevent a drain on water and nutrients from outweighing the contribution of fixed carbon (Hensel et al.
(2004) observed higher diameter increase in Handroanthus umbellatus (Sond.) Mattos during the flooding and rain periods, and no growth or negative growth in the dry season which coincided with leaf abscission of older leaves and production of reproductive structures in a flooded forest in the Atlantic Rainforest in Rio de Janeiro, Brazil.
Abscission is the process in which organs are separated from the parent plant; this process involves multiple changes in cell structure, metabolism, and gene expression [1].
Many authors have reported different protocols for in vitro culture of potato using different explants and different cultivars (Roest and Bokelman, 1976; Martel and de Garcia, 1992; de Garcia and Martinez, 1995; Seabrook and Douglass, 2001; Vargas et al., 2005); however, ethylene produced by tissue, callus and plantlets in closed vessels may lead to abnormal plantlet growth, hyperhydricity, abnormal branching in vitro, epinasty, leaf and flower bud abscission, diminution of foliar area (Turhan, 2004; Mullins et al., 2006; Zobayed et al., 2001; Zobayed, 2005; Hazarika, 2006; Steinitz et al., 2010; Giridhar, 2004; Dang and Wei, 2009; Jackson et al., 1991).
The decrease in the percentage of nitrogen observed from April on reflects the period of maturation, senescence and leaf abscission, what was previously reported by Leitao & Silva (2004) in the evaluation of mineral compartmentalization in the phenophases of Ouratea spectabilis (Mart.) Engl.
This abscission layer is constructed so as to prevent the tree from "bleeding to death'' when the leaves detach from the tree.
Artificial lighting isn't strong enough to induce photosynthesis, but it can affect the production of phytocrome, a pigment that absorbs red wavelengths to help plants with dormancy, seed germination and abscission (the natural detachment of parts, such as leaves or fruit).
Under these conditions, the senescence rate was 50% slower (150 days) than in explants cultured in medium with SA and AgN[O.sub.3] (100 days), which was reinforced by a marked chlorosis and faster leaf abscission.