Abscission


Abscission

Abscission (from Latin abscindere, from ab- ‘off, away’ + scindere ‘to cut’) is the shedding of a body part. It most commonly refers to the process by which a plant intentionally drops one or more of its parts, such as a leaf, fruit, flower or seed, though the term is also used to describe the shedding of a claw by an animal.

Use

A plant will abscise a part either to discard a member that is no longer necessary, such as a leaf during autumn, or a flower following fertilisation, or for the purposes of reproduction. Most deciduous plants drop their leaves by abscission before winter, while evergreen plants continuously abscise their leaves. Another form of abscission is fruit drop, when a plant abscises fruit while still immature, in order to conserve resources needed to bring the remaining fruit to maturity. If a leaf is damaged a plant may also abscise it to conserve water or photosynthetic efficiency, depending on the 'costs' to the plant as a whole. The abscission layer is a greenish grayish color.

Types

In deciduous trees, an abscission zone, also called a separation zone, is formed at the base of the petiole. It is composed of a top layer which has cells with weak walls, and a bottom layer which expands in the autumn, breaking the weak walls of the cells in the top layer. This allows the leaf to be shed.

In woody plants, an abscission layer is formed composed of parenchyma cells bounded on both sides with cork. This layer is found at the base of the leaf petioles in woody angiosperms and gymnosperms and because of the disintegration of the parenchyma layer, the organ, such as a leaf or bark, is separated from the parent plant. Abscission is a natural process of plant growth induced by the plant, in contrast to decaying or falling off due to other causes.

The liberation of a fungal spore by the withering away of an adjoining layer is also called abscission.

Hormone involvement

The gaseous plant hormone ethylene can stimulate abscission. While researchers originally believed abscisic acid to be the hormone that stimulated abscission (for which the hormone was named), it was later proven that it does not play a primary role.Fact|date=September 2007

Auxin is a plant hormone which can prevent the formation of abscission layers and premature fruit drop. Auxin is also believed to play a part in the shedding of leaves and their autumn color change. This happens due to continuous release of auxin in a young leaf; however, as leaves gets old and auxin supply dwindles, an abscission layer forms and leaves shed. In woody plants preparing to shed their leaves, the abscission zone or layer cuts off the movement of auxin from the leaf blade to the leaf. Fact|date=September 2007

ee also

*Marcescence, the retention of normally shed plant parts

External links

* [http://www.microscopyu.com/galleries/confocal/abscission.html Absission layer microscopy]


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Look at other dictionaries:

  • abscission — ● abscission nom féminin (latin abscissio, de abscindere, couper) Rupture normale du pédoncule des feuilles d automne ou des fruits mûrs, entraînant leur chute. ⇒ABSCISION, ABSCISSION, subst. fém. CHIR., vieilli. Synon. de excision, action de… …   Encyclopédie Universelle

  • Abscission — Ab*scis sion, n. [L. abscissio. See {Abscind}.] 1. The act or process of cutting off. Not to be cured without the abscission of a member. Jer. Taylor. [1913 Webster] 2. The state of being cut off. Sir T. Browne. [1913 Webster] 3. (Rhet.) A figure …   The Collaborative International Dictionary of English

  • abscission — index cancellation Burton s Legal Thesaurus. William C. Burton. 2006 …   Law dictionary

  • abscission — (n.) removal or cutting away, early 15c., from L. abscissionem (nom. abscissio) a cutting off, noun of action from pp. stem of abscindere (see ABSCISSA (Cf. abscissa)) …   Etymology dictionary

  • abscission — [ab sizh′ən] n. [ME abscisioun < L abscissio: see ABSCISSA] 1. a cutting off, as by surgery 2. the normal separation of fruit, leaves, etc. from plants by the development of a thin layer of pithy cells at the base of their stems …   English World dictionary

  • Abscission — Abszission bezeichnet das Abwerfen von Blättern, Früchten und anderen Pflanzenteilen wie Laub und Blütenknospen, Zweigen, Stacheln, Dornen oder Blütenständen. Man spricht daher auch vom Blattfall, Fruchtfall, Laubfall, Knospenfall, Blütenfall.… …   Deutsch Wikipedia

  • abscission — noun Etymology: Middle English abscisioun, from Anglo French abscission, Latin abscission , abscissio, from abscindere Date: 15th century 1. the act or process of cutting off ; removal 2. the natural separation of flowers …   New Collegiate Dictionary

  • Abscission — L abscission est le processus par lequel un fruit ou une feuille se détache de l arbre (s effeuille). Elle dépend de l équilibre entre plusieurs régulateurs de croissance aux effets antagoniste. L auxine et les brassinostéroïdes ont un effet… …   Wikipédia en Français

  • abscission — /ab sizh euhn, sish /, n. 1. the act of cutting off; sudden termination. 2. Bot. the normal separation of flowers, fruit, and leaves from plants. [1605 15; < L abscission (s. of abscissio). See ABSCISSA, ION] * * * …   Universalium

  • abscission — noun a) The act or process of cutting off. Not to be cured without the abscission of a member. b) The state of being cut off. See Also: abscise, abscisic, abscisic acid, abscisin, abscissin …   Wiktionary


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