WordNet

the act of cutting something off (同)cutting off
shedding of flowers and leaves and fruit following formation of scar tissue in a plant
the bodily process of discharging waste matter (同)evacuation, excretion, excreting, voiding
the murder of a competitor (同)liquidation
the act of removing or getting rid of something (同)riddance
the act of removing an unknown mathematical quantity by combining equations
analysis of a problem into alternative possibilities followed by the systematic rejection of unacceptable alternatives (同)reasoning by elimination
remove from a contest or race; "The cyclist has eliminated all the competitors in the race"
kill in large numbers; "the plague wiped out an entire population" (同)annihilate, extinguish, eradicate, wipe_out, decimate, carry off
remove (an unknown variable) from two or more equations
separate (a small unit) from a larger, especially for a special assignment; "detach a regiment"
come to be detached; "His retina detached and he had to be rushed into surgery" (同)come_off, come_away
cause to become detached or separated; take off; "detach the skin from the chicken before you eat it"
the act of releasing from an attachment or connection (同)disengagement
a small unit of troops of special composition
shed flowers and leaves and fruit following formation of a scar tissue
remove or separate by abscission

PrepTutorEJDIC

切除,切断;分離,離脱
(…の)除去,削除《+『of』+『名』》 / (競技の)予選
(…から)…‘を'『取り除く』,削除する(get rid of)《+『名』+『from』+『名』》 / …‘を'考慮に入れない,無視する(disregard)
(…から)…‘を'引き離す,分離する,取り外す《+『名』+『from』+『名』》 / (特別任務に)〈部隊・軍艦など〉‘を'派遣する,分遣する
〈U〉(…から…を)分離すること,取り外すこと《+『of』+『名』+『from』+『名』》 / 〈U〉超然としていること / 〈U〉私心(偏見)のないこと / 〈C〉(特別の任務を帯びた)分遣隊,特派部隊
〈葉などが〉(枝から)離れる

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/10/11 23:58:30」(JST)

wiki en

[Wiki en表示]

Leaf litter on the forest floor. Annual autumn leaf drop in temperate zones is caused by the abscission of the mature leaves from the growth season in response to the approach of cold winter weather.

Abscission (from the Latin ab, meaning away, and scindere, meaning to cut) is the shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed. In zoology, abscission is the intentional shedding of a body part, such as the shedding of a claw, husk, or the autotomy of a tail to evade a predator. In mycology, it is the liberation of a fungal spore. In cell biology, abscission refers to the separation of two daughter cells at the completion of cytokinesis.

In plants

Function

Abscission of the hypanthium during development of a nectarine fruit

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, whereas 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.

Abscission can also occur in premature leaves as a means of plant defense. Premature leaf abscission has been shown to occur in response to infestation by gall aphids. By abscising leaves that have been made host to aphid galls, plants have been shown to massively diminish the pest population, as 98% of aphids in abscised galls died. The abscission is selective, and the chance of dropping leaves increases as the number of galls increase. A leaf with three or more galls was four times more likely to abscise than a leaf with one, and 20 times as likely to be dropped as a leaf without any galls.^[1]

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.

Lack of chlorophyll as a trigger

Streptocarpus leaf showing abscission line in response to reduced day length

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.^[2] The loss of chlorophyll may also contribute to the abscission process.

Chemical

A variety of reactive oxygen species (ROS) are generated by plants during times of stress (biotic and abiotic) including UV light, cool temperatures, excessive light, pathogens, parasites, and high salinity. The presence and continuous production of these ROS causes disruption in the homeostasis of the cellular components, leading to metabolic dysfunction and expression of cell wall-degrading enzymes (WDEs).^[3]

Hormonal

While researchers originally believed abscisic acid to be the hormone that stimulates abscission (for which the hormone was named), it was later proven that it does not play a primary role. In fact, auxin, a plant hormone, and ethylene have been implicated as prominent regulators of abscission signaling. The two compounds work in a synergistic fashion: As the auxin levels decrease, the flux of auxin to the abscission zone is reduced. Exhaustion of auxin makes the abscission zone sensitive to ethylene. When the plant is then exposed to ethylene, gene expression of cell wall-degrading enzymes such as cellulase and polygalacturonase are activated. However, this is not to say that ethylene directly activates WDE gene expression, because the elements responsible for detecting ethylene have not been found in the gene’s promoter region.^[3] Dwindling auxin levels have also been implicated in autumn-leaf color change.

In animals

References

^ Williams, A.G., & T.G. Whitham (1986). Premature leaf abscission: an induced plant defense against gall aphids. Ecology, 67(6), 1619-1627.
^ 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.

External links

Absission layer microscopy

This biology article is a stub. You can help Wikipedia by expanding it.

English Journal

Beclin-1 knockdown shows abscission failure but not autophagy defect during oocyte meiotic maturation.

You SY1, Park YS1, Jeon HJ1, Cho DH2, Jeon HB3, Kim SH4, Chang JW5, Kim JS6, Oh JS1.
Cell cycle (Georgetown, Tex.).Cell Cycle.2016 May 5:0. [Epub ahead of print]
Cytokinesis is the final step in cell division that results in the separation of a parent cell into daughter cells. Unlike somatic cells that undergo symmetric division, meiotic division is highly asymmetric, allowing the preservation of maternal resources for embryo development. Beclin-1/BECN1, the
PMID 27149384

Leaf structural traits of tropical woody species resistant to cement dust.

Siqueira-Silva AI1, Pereira EG2, Modolo LV3, Paiva EA3.
Environmental science and pollution research international.Environ Sci Pollut Res Int.2016 May 5. [Epub ahead of print]
Cement industries located nearby limestone outcrops in Brazil have contributed to the coating of cement dust over native plant species. However, little is known about the extent of the response of tropical woody plants to such environmental pollutant particularly during the first stages of plant dev
PMID 27146683

The Aurora-B-dependent NoCut checkpoint prevents damage of anaphase bridges after DNA replication stress.

Amaral N1,2, Vendrell A1,2, Funaya C3, Idrissi FZ4, Maier M1,2, Kumar A1,2, Neurohr G1, Colomina N5, Torres-Rosell J5, Geli MI3, Mendoza M1,2.
Nature cell biology.Nat Cell Biol.2016 May;18(5):516-26. doi: 10.1038/ncb3343. Epub 2016 Apr 25.
Anaphase chromatin bridges can lead to chromosome breakage if not properly resolved before completion of cytokinesis. The NoCut checkpoint, which depends on Aurora B at the spindle midzone, delays abscission in response to chromosome segregation defects in yeast and animal cells. How chromatin bridg
PMID 27111841

Clks 1, 2 and 4 prevent chromatin breakage by regulating the Aurora B-dependent abscission checkpoint.

Petsalaki E1, Zachos G1.
Nature communications.Nat Commun.2016 Apr 29;7:11451. doi: 10.1038/ncomms11451.
When chromatin is trapped at the intercellular bridge, cells delay completion of cytokinesis (abscission) to prevent chromosome breakage. Here we show that inhibition of Cdc-like kinases (Clks) 1, 2 or 4 accelerates midbody resolution in normally segregating cells and correlates with premature absci
PMID 27126587