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).
Second, the margins of the valves abscise, again beginning at the distal end of the nut, splitting the husk into four valves.
These are branches that form and develop concurrent with the RGU on which they form but that are strictly reproductive and abscise after fruiting.
It may have the same limitations as a natural enemy of pepper weevil in that infested floral buds and immature fruits often abscise (Cano & Alcacio 1894; Walker 1905; Pratt 1907; Elmore et al.