関: cotyledon、seed leaf、seed leaves

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embryonic leaf in seed-bearing plants (同)seed_leaf

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(種子の)子葉

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/08/22 05:21:48」(JST)

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Schematic image of wheat coleoptile (above) and flag leaf (below).

Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses. Coleoptiles have two vascular bundles, one on either side. Unlike the flag leaves rolled up within, the pre-emergent coleoptile does not accumulate significant protochlorophyll or carotenoids, and so it is generally very pale. Some preemergent coleoptiles do, however, accumulate purple anthocyanin pigments.

Coleoptiles consist of very similar cells that are all specialised to fast stretch growth. They do not divide, but increase in size as they accumulate more water. Coleoptiles also have water vessels (frequently two) along the axis to provide a water supply.

When a coleoptile reaches the surface, it stops growing and the flag leaves penetrate its top, continuing to grow along. The wheat coleoptile is most developed in the third day of the germination (if in the darkness).

Tropisms

Early experiments on phototropism using coleoptiles suggested that plants grow towards light because plant cells on the darker side elongate more than those on the lighter side. In 1880 Charles Darwin and his son, Francis found that coleoptiles only bend towards the light when their tips are exposed.^[1] Therefore the tips must contain the photoreceptor cells although the bending takes place lower down on the shoot. A chemical messenger or hormone called auxin moves down the dark side of the shoot and stimulates growth on that side. The natural plant hormone responsible for phototropism is now known to be indoleacetic acid (IAA).

The Cholodny-Went model is named after Frits Warmolt Went of the California Institute of Technology and the Russian scientist N. Cholodny, who reached the same conclusion independently in 1937. It describes the phototropic and gravitropic properties of emerging shoots of monocotyledons. The model proposes that auxin, a plant growth hormone, is synthesized in the coleoptile tip, which senses light or gravity and will send the auxin down the appropriate side of the shoot. This causes asymmetric growth of one side of the plant. As a result, the plant shoot will begin to bend toward a light source or toward the surface.^[2]

Coleoptiles also exhibit strong geotropic reaction, always growing upward and correcting direction after reorientation. Geotropic reaction is regulated by light (more exactly by phytochrome action).

References

^ Darwin, C. R. (1880). The Power of Movement in Plants. London: Murray.
^ Rashotte et al. (February 2000). "Basipetal Auxin Transport Is Required for Gravitropism in Roots of Arabidopsis". Plant Physiology 122 (2): 481–490. doi:10.1104/pp.122.2.481.

External links

Media related to Coleoptiles at Wikimedia Commons

English Journal

DEFECTIVE KERNEL 1 promotes and maintains plant epidermal differentiation.

Galletti R1, Johnson KL2, Scofield S3, San-Bento R4, Watt AM2, Murray JA3, Ingram GC1.
Development (Cambridge, England).Development.2015 May 7. pii: dev.122325. [Epub ahead of print]
During plant epidermal development, many cell types are generated from protodermal cells, a process requiring complex co-ordination of cell division, growth, endoreduplication and the acquisition of differentiated cellular morphologies. Here we show that the Arabidopsis phytocalpain DEFECTIVE KERNEL
PMID 25953348

Interaction of cold radiofrequency plasma with seeds of beans (Phaseolus vulgaris).

Bormashenko E1, Shapira Y2, Grynyov R3, Whyman G3, Bormashenko Y3, Drori E4.
Journal of experimental botany.J Exp Bot.2015 May 6. pii: erv206. [Epub ahead of print]
The impact of cold radiofrequency air plasma on the wetting properties and water imbibition of beans (Phaseolus vulgaris) was studied. The influence of plasma on wetting of a cotyledon and seed coat (testa) was elucidated. It was established that cold plasma treatment leads to hydrophilization of th
PMID 25948708

Placental transfer of rilpivirine in an ex vivo human cotyledon perfusion model.

Mandelbrot L1, Duro D2, Belissa E3, Peytavin G4.
Antimicrobial agents and chemotherapy.Antimicrob Agents Chemother.2015 May;59(5):2901-3. doi: 10.1128/AAC.00075-15. Epub 2015 Feb 17.
Placental transfers of the HIV nonnucleoside reverse transcriptase inhibitor rilpivirine were investigated in 8 term human cotyledons perfused with rilpivirine (400 ng/ml) in the maternal-to-fetal direction. The mean fetal transfer rate (FTR) (fetal/maternal concentration at steady state from 15 to
PMID 25691637