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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2012/07/09 17:11:15」(JST)

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In developmental biology, photomorphogenesis is light-mediated development. The photomorphogenesis of plants is often studied by using tightly-frequency-controlled light sources to grow the plants.

Germination

Light has profound effects on the development of plants. The light-mediated changes in plant growth and development are called photomorphogenesis. The most striking effects of light are observed when a germinating seedling emerges from the soil and is exposed to light for the first time.

Normally the seedling radicle (root) emerges first from the seed, and the shoot appears as the root becomes established. Later, with growth of the shoot (particularly when it merges into the light) there is increased secondary root formation and branching. This coordinated progression of developmental responses are early manifestations of correlative growth phenomena where the root affects the growth of the shoot and vice versa. To a large degree, these coordinated differential growth responses are hormone mediated.

In the absence of light, plants develop an etiolated growth pattern. Etiolation of the seedling adapts it to emerging from the soil.

Comparison of dark-grown (etiolated) and light-grown (de-etiolated) seedlings

Photoreceptor systems in plants

Plants use phytochrome to detect and respond to red and far-red wavelengths.

Phytochromes are proteins with a light absorbing pigment attached (chromophore).

The chromophore is a linear tetrapyrrole called phytochromobilin.

The phytochrome apoprotein is synthesized in the Pr form. Upon binding the chromophore, the holoprotein becomes sensitive to light. If it absorbs red light it will change conformation to the biologically active Pfr form. The Pfr form can absorb far red light and switch back to the Pr form.

Most plants have multiple phytochromes encoded by different genes. The different forms of phytochrome control different responses but there is also a lot of redundancy so that in the absence of one phytochrome, another may take on the missing functions.

Arabidopsis has 5 phytochromes - PHYA, PHYB, PHYC, PHYD, PHYE

Molecular analyses of phytochrome and phytochrome-like genes in higher plants (ferns, mosses, algae) and photosynthetic bacteria have shown that phytochromes evolved from prokaryotic photoreceptors that predated the origin of plants.

Blue light systems

As for the red/far-red system, plants contain multiple blue light photoreceptors which have different functions.

Based on studies with action spectra, mutants and molecular analyses, it has been determined that higher plants contain at least 4, and probably 5, different blue light photoreceptors.

Cryptochromes were the first blue light receptors to be isolated and characterized from any organism. The proteins use a flavin as a chromophore. The cryptochromes have evolved from microbial DNA-photolyase, an enzyme that carries out light-dependent repair of UV damaged DNA.

Two cryptochromes have been identified in plants.

Cryptochromes control stem elongation, leaf expansion, circadian rhythms and flowering time.

In addition to blue light, cryptochromes also perceive long wavelength UV irradiation (UV-A).

Phototropin is the blue light photoreceptor that controls phototropism. It also uses flavin as chromophore. Only one phototropin has been identified so far (NPH1). Phototropin also perceives long wavelength UV irradiation (UV-A) in addition to blue light.

Recent experiments indicate that a 4th blue light receptor exists that uses a carotenoid as a chromophore. This new photoreceptor controls blue light induction of stomatal opening. However, the gene and protein have not yet been found.

Other blue light responses exist that seem to function in plants that are missing the cryptochrome, phototropin and carotenoid photoreceptors suggesting that at least one more will be found.

Since the cryptochromes were discovered in plants, several labs have identified homologous genes and photoreceptors in a number of other organisms, including humans, mice and flies. It appears that in mammals and flies, the cryptochromes function in entrainment of the biological clock. Indeed, in flies, a cryptochrome may be a functional part of the clock mechanism.

UV systems

Based on various responses to UV light, it is assumed that there are UV-specific photoreceptor...

References

External links

Photomorphogenesis

English Journal

Light and COP1 regulate level of overexpressed DET1 protein.

Ly V1, Collister DT1, Fonseca E1, Liao TS1, Schroeder DF2.
Plant science : an international journal of experimental plant biology.Plant Sci.2015 Feb;231:114-23. doi: 10.1016/j.plantsci.2014.11.011. Epub 2014 Dec 4.
de-etiolated 1 (det1) and constitutive photomorphogenic 1 (cop1) were initially identified as constitutively photomorphogenic Arabidopsis mutants, exhibiting light-grown phenotypes in the dark. Subsequently, both were shown to be components of Damaged DNA Binding protein 1 (DDB1)/CULLIN4-type comple
PMID 25575996

Searching for the mechanism of signalling by plant photoreceptor cryptochrome.

Müller P1, Bouly JP2.
FEBS letters.FEBS Lett.2015 Jan 16;589(2):189-92. doi: 10.1016/j.febslet.2014.12.008. Epub 2014 Dec 11.
Even though the plant photoreceptors cryptochromes were discovered more than 20years ago, the mechanism through which they transduce light signals to their partner molecules such as COP1 (Constitutive Photomorphogenic 1) or SPA1 (Suppressor of Phytochrome A) still remains to be established. We propo
PMID 25500270

Carotenoid Metabolism in Plants.

Nisar N1, Li L2, Lu S3, Khin NC1, Pogson BJ4.
Molecular plant.Mol Plant.2015 Jan 5;8(1):68-82. doi: 10.1016/j.molp.2014.12.007. Epub 2014 Dec 17.
Carotenoids are mostly C40 terpenoids, a class of hydrocarbons that participate in various biological processes in plants, such as photosynthesis, photomorphogenesis, photoprotection, and development. Carotenoids also serve as precursors for two plant hormones and a diverse set of apocarotenoids. Th
PMID 25578273

Japanese Journal

A Circadian Clock- and PIF4-Mediated Double Coincidence Mechanism is Implicated in the Thermosensitive Photoperiodic Control of Plant Architectures in Arabidopsis thaliana

Nomoto Yuichi,Kubozono Saori,Miyachi Miki [他]
Plant and Cell Physiology 53(11), 1965-1973, 2012-11
NAID 40019500757

Circadian Clock- and PIF4-Controlled Plant Growth : A Coincidence Mechanism Directly Integrates a Hormone Signaling Network into the Photoperiodic Control of Plant Architectures in Arabidopsis thaliana