Abscission
Abscission (from
In plants
Function
A plant will abscise a part either to discard a member that is no longer necessary, such as a leaf during
Abscission can also occur in premature leaves as a means of
Process
Abscission occurs in a series of three events: 1) resorption, 2) protective layer formation, and 3) detachment.[2] Steps 2 and 3 may occur in either order depending on the species.[2]
Resorption
Resorption involves degrading
Protective layer formation
Cells under the abscission zone divide and form a layer of cork cells.[5] Situated on both sides of the abscission zone are layers of parenchyma cells, which produce and inject suberin and lignin under the abscission zone into the new layer of cork cells.[5] Suberin and lignin create a durable and waterproof layer for the plant once the organ is detached.[5]
Detachment
This step can occur in a variety of ways depending on the species but always occurs at the abscission zone.
Mechanisms
Structural
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 that has cells with weak walls, and a bottom layer that expands in the autumn, breaking the weak walls of the cells in the top layer. This allows the leaf to be shed.[7]
Lack of chlorophyll as a trigger
The reduction of chlorophyll production in leaves due to decreased sunlight in the autumn explains why some leaves turn yellow. However, the yellow color can attract aphids, so some trees turn the leaves red instead by injecting a bright pigment.[8] The loss of chlorophyll may also contribute to the abscission process.[citation needed]
Chemical
A variety of
Hormonal
While researchers originally believed
In animals
See: Moulting, Autotomy, Claw (Mammals)
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See also
- Marcescence, the retention of normally shed plant parts
References
- ^ Williams, A.G., & T.G. Whitham (1986). Premature leaf abscission: an induced plant defense against gall aphids. Ecology, 67(6), 1619-1627.
- ^ a b c Addicott, F.T. 1982. Abscission. University of California Press, London, England.
- ^ a b c d Keskitalo, J., G. Bergguist, P. Gardestrom, and S. Jansson. 2005. A Cellular Timetable of Autumn Senescence. Plant Phys. 139 : 1635-1648.
- ^ Hopkins, W.G. and N.P.A. Huner. 2009. Introduction to Plant Physiology. Fourth edition. Wiley & Sons, Hoboken, NJ.
- ^ a b c Kozlowski, T.T. 1973. Shedding of Plant Parts. Academic Press, New York, NY.
- ^ a b c d e Solomon, E.P., L.R. Berg., and D.W. Martin. 2011. Biology. Ninth edition, Brooks/Cole, Belmont, CA.
- ISSN 0002-9122.
- ^ Highfield, Roger (22 Sep 2008). "Why leaves fall off trees is discovered". Telegraph.co.uk. The Daily Telegraph. Retrieved 1 Nov 2009.
- ^ a b Sakamoto, M., I. Munemura, R. Tomita, & K. Kobayashi (2008). Reactive oxygen species in leaf abscission signaling. Plant Signal Behavior, 3(11), 1014-1015.