abscission

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Abscission

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.

abscission

[ab′sizh·ən]
(botany)
A physiological process promoted by abscisic acid whereby plants shed a part, such as a leaf, flower, seed, or fruit.
References in periodicals archive ?
The females oviposit on young fruit, often causing it to abscise (Quaintance & Jenne 1912; Snapp 1930).
These branches develop from buds that remain dormant for some period, then flower and abscise from the branch; they do not form part of the vegetative architecture of the tree.
The early collection was necessary because pods of Cercidium microphyllum abscise and drop from canopies in early July, before most M.
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.
A second is passive and time dependent, whereby squares that would abscise for reasons other than insect damage are instead retained, replacing those lost to insect damage.
But as stressed by Greene and Johnson (1989), wind-dispersed diaspores preferentially abscise at higher wind speeds.
1-4), and in yellow leaves that were ready to abscise (Egli, 1997).
buds are much stronger sinks than flowers, which receive only minimal photosynthate support regardless of whether they abscise or develop into fruits (Pate and Farrington, 1981).
As plants mature, they abscise their cotyledonary leaves and expand their true leaves.
Several studies have shown that young squares are more prone to abscise as a result of environmental stress than old squares and bolls (McMichael and Guinn, 1980; Ungar et al.
MRSA infections can cause abscises and high fever, symptoms that require vancomycin, but if there is resistance, the patient's body will not respond," said Dr Shershad.