Coleoptile

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).

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

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

  1. ^ Darwin, C. R. (1880). The Power of Movement in Plants. London: Murray.
  2. ^ 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. PMC 58885.

External links

Ann Cotten

Ann Cotten (born 1982, Ames, Iowa) is an American-born Austrian writer.

Auxin

Auxins (plural of auxin ) are a class of plant hormones (or plant growth regulators) with some morphogen-like characteristics. Auxins have a cardinal role in coordination of many growth and behavioral processes in the plant's life cycle and are essential for plant body development. Auxins and their role in plant growth were first described by the Dutch biologist Frits Warmolt Went. Kenneth V. Thimann was the first to isolate one of these phytohormones and determine its chemical structure as indole-3-acetic acid (IAA). Went and Thimann co-authored a book on plant hormones, Phytohormones, in 1937.

BBCH-scale (rice)

The BBCH-scale (rice) identifies the phenological development stages of rice Oryza sativa. It is a plant species specific version of the BBCH-scale.

1 A leaf is unfolded when its ligule is visible or the tip of the next leaf is visible

2 Tillering or stem elongation may occur earlier than stage 13; in this case continue with stages 21 or 30

3 If stem elongation begins before the end of tillering continue with stage 30

4 Flowering usually starts before stage 55; continue with principal stage 6

BBCH-scale (weed)

The BBCH-scale (weed) identifies the phenological development stages of weed species. It is a plant species specific version of the BBCH-scale.

D = Dicotyledons

G = Gramineae

M = Monocotyledons

P = Perennial plants

V = Development from vegetative parts or propagated organs

No code letter is used if the description applies to all groups of plants.

Cereal growth staging scales

Cereal growth staging scales attempt to objectively measure the growth of cereals.

Cholodny–Went model

In botany, the Cholodny–Went model, proposed in 1927, is an early model describing tropism in emerging shoots of monocotyledons, including the tendencies for the shoot to grow towards light (phototropism) and the roots to grow downward (gravitropism).

In both cases the directional growth is considered to be due to asymmetrical distribution of auxin, a plant growth hormone.

Although the model has been criticized and continues to be refined, it has largely stood the test of time.

Clinostat

A clinostat is a device which uses rotation to negate the effects of gravitational pull on plant growth (gravitropism) and development (gravimorphism). It has also been used to study the effects of microgravity on cell cultures and animal embryos.

Common bunt

Common bunt, also known as stinking smut and covered smut, is a disease of both spring and winter wheats. It is caused by two very closely related fungi, Tilletia tritici (syn. Tilletia caries) and T. laevis (syn. T. foetida).

Cotyledon

A cotyledon (; "seed leaf" from Latin cotyledon, from Greek: κοτυληδών kotylēdōn, gen.: κοτυληδόνος kotylēdonos, from κοτύλη kotýlē "cup, bowl") is a significant part of the embryo within the seed of a plant, and is defined by the Oxford English Dictionary as "The primary leaf in the embryo of the higher plants (Phanerogams); the seed-leaf." Upon germination, the cotyledon may become the embryonic first leaves of a seedling. The number of cotyledons present is one characteristic used by botanists to classify the flowering plants (angiosperms). Species with one cotyledon are called monocotyledonous ("monocots"). Plants with two embryonic leaves are termed dicotyledonous ("dicots").

In the case of dicot seedlings whose cotyledons are photosynthetic, the cotyledons are functionally similar to leaves. However, true leaves and cotyledons are developmentally distinct. Cotyledons are formed during embryogenesis, along with the root and shoot meristems, and are therefore present in the seed prior to germination. True leaves, however, are formed post-embryonically (i.e. after germination) from the shoot apical meristem, which is responsible for generating subsequent aerial portions of the plant.

The cotyledon of grasses and many other monocotyledons is a highly modified leaf composed of a scutellum and a coleoptile. The scutellum is a tissue within the seed that is specialized to absorb stored food from the adjacent endosperm. The coleoptile is a protective cap that covers the plumule (precursor to the stem and leaves of the plant).

Gymnosperm seedlings also have cotyledons, and these are often variable in number (multicotyledonous), with from 2 to 24 cotyledons forming a whorl at the top of the hypocotyl (the embryonic stem) surrounding the plumule. Within each species, there is often still some variation in cotyledon numbers, e.g. Monterey pine (Pinus radiata) seedlings have 5–9, and Jeffrey pine (Pinus jeffreyi) 7–13 (Mirov 1967), but other species are more fixed, with e.g. Mediterranean cypress always having just two cotyledons. The highest number reported is for big-cone pinyon (Pinus maximartinezii), with 24 (Farjon & Styles 1997).

The cotyledons may be ephemeral, lasting only days after emergence, or persistent, enduring at least a year on the plant. The cotyledons contain (or in the case of gymnosperms and monocotyledons, have access to) the stored food reserves of the seed. As these reserves are used up, the cotyledons may turn green and begin photosynthesis, or may wither as the first true leaves take over food production for the seedling.

Frits Warmolt Went

For his father, also a botanist, see Frits the father Went.Frits Warmolt Went (May 18, 1903 – May 1, 1990) was a Dutch biologist whose 1928 experiment demonstrated the existence of auxin in plants.

Went's father was the prominent Dutch botanist F.A.F.C. Went. After graduating from the University of Utrecht, Holland in 1927 with a dissertation on the effects of the plant hormone auxin, Went then worked as a plant pathologist in the research labs of the Royal Botanical Garden in Buitenzorg, Dutch East Indies (now Bogor, Indonesia) from 1927 to 1933. He then took a position at Caltech in Pasadena, California, first researching plant hormones. His interest gradually shifted to environmental influences on plant growth. At Caltech he was among the first to demonstrate the importance of hormones in plant growth and development. He played an important role in the development of synthetic plant hormones, which then became the basis of much of the agricultural chemical industry.

Frees is known for the Cholodny-Went model, named after Went and the Soviet scientist N. Cholodny.

They proposed it in 1937, after coming independently to the same conclusions.

This is an early model describing the phototropic and gravitropic properties of emerging shoots of monocotyledons. It 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.Funded by generous donors, Went constructed a series of greenhouses at Caltech in which he could vary light conditions, humidity, temperature, air quality and other variables. In 1949 this led to him to construct a large new complex of climate-controlled rooms called the Earhart Plant Research Laboratory, also known as the "phytotron." Here he produced foundational research of the effects of air pollution on plant growth.

In 1958 Went was appointed director of the Missouri Botanical Garden and professor of Botany at Washington University in St Louis, at a point where he had become a world recognized authority on plant growth. He moved from Pasadena to St. Louis with his wife Catharina and their two children, Hans and Anneka. After the opening of the Climatron, the worlld's first geodesic dome greenhouse, Went’s vision of a renewed Missouri Botanical Garden eventually came into conflict with that of its Board of Trustees, and he resigned as director in 1963. After two years as simply Professor of Botany at Washington University, in 1965 he then became director of the Desert Research Institute at the University of Nevada-Reno, where he continued his research on desert plants for the remainder of his career, and on occasion lectured in the Department of Biology, University of Nevada-Reno. He remained active in many fields of botany until his death in 1990.

Germination

Germination is the process by which an organism grows from a seed or similar structure. The most common example of germination is the sprouting of a seedling from a seed of an angiosperm or gymnosperm. In addition, the growth of a sporeling from a spore, such as the spores of hyphae from fungal spores, is also germination. Thus, in a general sense, germination can be thought of as anything expanding into greater being from a small existence or germ.

Glucuronoarabinoxylan endo-1,4-beta-xylanase

Glucuronoarabinoxylan endo-1,4-beta-xylanase (EC 3.2.1.136, feraxan endoxylanase, feraxanase, endoarabinoxylanase, glucuronoxylan xylohydrolase, glucuronoxylanase, glucuronoxylan xylanohydrolase, glucuronoarabinoxylan 1,4-beta-D-xylanohydrolase) is an enzyme with systematic name glucuronoarabinoxylan 4-beta-D-xylanohydrolase. This enzyme catalyses the following chemical reaction

Endohydrolysis of (1->4)-beta-D-xylosyl links in some glucuronoarabinoxylansThis enzyme has high activity towards feruloylated arabinoxylans.

Hypocotyl

The hypocotyl (short for "hypocotyledonous stem", meaning "below seed leaf") is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root).

Indole-3-acetaldehyde oxidase

In enzymology, an indole-3-acetaldehyde oxidase (EC 1.2.3.7) is an enzyme that catalyzes the chemical reaction

(indol-3-yl)acetaldehyde + H2O + O2 (indol-3-yl)acetate + H2O2

The 3 substrates of this enzyme are (indol-3-yl)acetaldehyde, H2O, and O2, whereas its two products are (indol-3-yl)acetate and H2O2.

This enzyme belongs to the family of oxidoreductases, specifically those acting on the aldehyde or oxo group of donor with oxygen as acceptor. The systematic name of this enzyme class is (indol-3-yl)acetaldehyde:oxygen oxidoreductase. Other names in common use include indoleacetaldehyde oxidase, IAAld oxidase, AO1, and indole-3-acetaldehyde:oxygen oxidoreductase. This enzyme participates in tryptophan metabolism. It has 3 cofactors: FAD, Heme, and Molybdenum.

Nikolai Cholodny

Nikolai Grigoryevich Cholodny (Russian: Никола́й Григо́рьевич Холо́дный; 22 June 1882 – 4 May 1953) was an influential microbiologist who worked at the University of Kiev, Ukraine in the USSR during the 1930s.

He is known for the Cholodny–Went model, which he developed independently with Frits Warmolt Went of the California Institute of Technology.

Despite being associated with the same theory, the two men never actually met.Cholodny worked in the A.V. Fomin Botanical Garden, attached to the University of Kiev.

He was one of the pioneers of the concept that microbes adhere to surfaces,

using the technique of first placing glass slides in earth for a measured time period,

then using a microscope to examine the slides.

The Prokaryote Leptothrix cholodnii is named after him.

In 1927 Cholodny proposed that the cells of the coleoptile are first polarized under the influence of uneven exposure to light, so growth hormone can diffuse more rapidly towards the side in the shade than in any other direction.

Went reached the same conclusion in 1928, and the two scientists' names have been attached to the controversial Cholodny-Went theory.

Photomorphogenesis

In developmental biology, photomorphogenesis is light-mediated development, where plant growth patterns respond to the light spectrum. This is a completely separate process from photosynthesis where light is used as a source of energy. Phytochromes, cryptochromes, and phototropins are photochromic sensory receptors that restrict the photomorphogenic effect of light to the UV-A, UV-B, blue, and red portions of the electromagnetic spectrum.The photomorphogenesis of plants is often studied by using tightly frequency-controlled light sources to grow the plants. There are at least three stages of plant development where photomorphogenesis occurs: seed germination, seedling development, and the switch from the vegetative to the flowering stage (photoperiodism).Most research on photomorphogenesis comes from plants, it occurs in several kingdoms: Fungi, Monera, Protista, and Plantae.

Phototropism

Phototropism is the growth of an organism which responds to a light stimulus, it Is called phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light have a chemical called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the farthest side from the light. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism (skototropism). Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth. Roots usually exhibit negative phototropism, although gravitropism may play a larger role in root behavior and growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them. The combination of phototropism and gravitropism allow plants to grow in the correct direction.

Scald (barley disease)

Scald is common disease of barley in temperate regions. It is caused by the fungus Rhynchosporium secalis and can cause significant yield losses in cooler, wet seasons.

Tropism

A tropism (from Greek τρόπος, tropos, "a turning") is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus (as opposed to nastic movements which are non-directional responses). Viruses and other pathogens also affect what is called "host tropism", "tissue tropism", or "cell tropism", or in which case tropism refers to the way in which different viruses/pathogens have evolved to preferentially target specific host species, specific tissue, or specific cell types within those species. Tropisms are usually named for the stimulus involved (for example, a phototropism is a reaction to sunlight) and may be either positive (towards the stimulus) or negative (away from the stimulus).

Tropisms occur in four sequential steps. First, there is a perception to a stimulus, which is usually beneficiary to the plant. Next, signal transduction occurs. This leads to auxin redistribution at the cellular level and finally, the growth response occurs.

Tropisms are typically associated with plants (although not necessarily restricted to them). Where an organism is capable of directed physical movement (motility), movement or activity in response to a specific stimulus is more likely to be regarded by behaviorists as a taxis (directional response) or a kinesis (non-directional response).

In English, the word tropism is used to indicate an action done without cognitive thought: However, "tropism" in this sense has a proper, although non-scientific, meaning as an innate tendency, natural inclination, or propensity to act in a certain manner towards a certain stimulus.

In botany, the Cholodny–Went model, proposed in 1927, is an early model describing tropism in emerging shoots of monocotyledons, including the tendencies for the stalk to grow towards light (phototropism) and the roots to grow downward (gravitropism).

In both cases the directional growth is considered to be due to asymmetrical distribution of auxin, a plant growth hormone.

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