phototropism


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phototropism

1. the growth response of plant parts to the stimulus of light, producing a bending towards the light source
2. the response of animals to light: sometimes used as another word for phototaxis

Phototropism

 

change in the direction of growth of plant organs under the influence of illumination from one side. In positive phototropism, the stem bends toward the light source. In plagiotropism, or diatropism, the leaf blades move at an angle toward the falling light. In negative phototropism the plant organs bend in a direction opposite to the light source (for example, ivy stems and the apices of certain roots). The same organ may be positively phototropic to weak light, negatively phototropic to intense light, and not at all phototropic to light of medium intensity.

Plant species differ in their capacity for phototropism. Phototropic responses may change even in plants of the same species: in young individuals the responses are always stronger, given the same conditions, than in older plants. Phototropism may manifest itself only in the young organs of a plant. In stems and leaves the phenomenon leads to uniform leaf distribution, so that the leaves shade each other only slightly. Positive phototropism and negative geotropism enable the apices of sprouts to emerge to the soil surface even when the seeds have been planted very deeply.

The process of phototropism includes a series of successive reactions: perception of a light stimulus, excitation of cells and tissues, transmission of excitation to cells and tissues of the growth zone of the organ, and intensification or diminution of cell and tissue growth in the growth zone. Perception of the light stimulus is effected by a specific photoactive complex that includes carotenoids and flavin. Transmission of the excitation through the plant occurs with the participation of bioelectric currents and plant hormones known as auxins. (For a discussion of the mechanisms of these processes, see.)

The manifestations of phototropism depends on the spectral composition of the illumination. Maximum phototropic sensitivity in plants has been found in the absorption spectra of yellow and orange pigments—carotenoids and flavins. It is conjectured that photosensitive proteins containing the pigments perceive the light stimulus. Carotenoid “eyes” have also been found in certain unicellular algae displaying phototaxis and in the sporangiophores of fungi capable of phototropism.

REFERENCES

Darwin, C. “Sposobnosf k dvizheniiu u rastenii.” Soch., vol. 8. Moscow-Leningrad, 1941.
Thimann, K. V., and G. M. Curry. “Phototropism.” In Symposium on Light and Life. Baltimore, 1961. Pages 646–70.

phototropism

[fō′tä·trə‚piz·əm]
(botany)
A growth-mediated response of a plant to stimulation by visible light.
(solid-state physics)
A reversible change in the structure of a solid exposed to light or other radiant energy, accompanied by a change in color. Also known as phototropy.
References in periodicals archive ?
It was found that when several of the PIN and kinase components were missing, plant growth was completely unresponsive to the light signals that trigger phototropism.
This bending response to light is called phototropism, and other tropisms include a response to gravity (geotropism) and a response to touch (thigmotropism).
Plant responses to light include amount and direction of growth and development as well as timing and amount of flowering, color development in fruit, and plant movements, or phototropisms.
Phototropism is the influence of varying durations of light on plant growth and development.
Phototropism is an involuntary orientation in which a light is an orienting stimulus.
The phototropism of the flight of bees is the example discussed there.
When a cut flower curves or bends in the direction of light, as do anemones, this phenomenon is specifically called phototropism, from the Greek words photo (light) and trope (turning).
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urchins showed a heightened negative phototropism in response to
Red, together with the extreme red (peaks between 710-740nm) are responsible for the processes of morphogenesis, while blue, violet (peaks between 400-425nm) and ultraviolet (peaks between 280-400nm) activate phototropism (KAMPF, 2005; MAJEROWICZ & PERES, 2008).
2005) found that pediveligers of the variegated scallop Chlamys varia had positive phototropism.
Auxin is the first plant hormone studied and it has been correlated with several developmental processes like root initiation, apical dominance, plant growth, geotropism and phototropism and fruit development (Paciorek & Friml, 2006).