Phototropism - History Of Phototropism Research, Cholodny-went Theory, The Photoreceptor Pigment, Phototropism In Other Organisms
movement orientation light source
Phototropism is the orientation of an organism in response to asymmetric illumination. Phototropism is commonly observed in the stems of higher plants, which grow bent toward a light source. Phototropism can be positive (bending toward a light source) or negative (bending away from a light source), depending on the organism and nature of the illumination. Phototropism and other tropisms are different from nastic movements, which are also common in plants. A tropism is the orientation of an organism in response to an external stimulus in which the stimulus determines the orientation of the movement. A nastic movement is a growth movement in which the stimulus does not determine the orientation of the movement.
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Plant physiologists have investigated phototropism for over 100 years. The best known early research on phototropism was by Charles Darwin, who reported his experiments in a book published in 1880, The Power of Movement in Plants. Although Darwin was better known for his earlier books on evolution (The Origin of Species and The Descent of Man), this book was an important contribution to plant phys…
These and other experiments by Went led to what has become known as the Cholodny-Went theory of tropic curvature. In terms of phototropism, the Cholodny-Went theory proposes that (a) auxin is synthesized in the coleoptile tip; (b) the coleoptile tip perceives the asymmetric illumination and this causes auxin to move into the un-irradiated side; (c) auxin moves down the coleoptile so that lower reg…
There has also been an active search for the identity of the photoreceptor pigment, an aspect of phototropism not covered by the Cholodny-Went theory. In the 1930s, many researchers believed the photoreceptor was a carotenoid, a class of mostly orange plant pigments. They argued that carotenoids strongly absorb blue light and phototropism is most effectively elicited by blue light. Furthermore, re…
While phototropism has been most intensively studied in higher plants, many other organisms also exhibit phototropism. Phototropism occurs in the filaments and rhizoids of algae, germ tubes and protonemas of mosses, rhizoids and protonemas of ferns, spore-bearing stalks of certain fungi, and numerous other organisms. Many phototropism experiments have been performed on Phycomyces blakesleeanus, a …
Laboratory studies of phototropism have a bearing upon the life of plants in nature. It is advantageous for a young seedling, such as a coleoptile, to bend toward the light so that its leaves can intercept more sunlight for photosynthesis and grow faster. Phototropism is also related to solar tracking, the orientation of a plant's leaves in response to the Sun. Unlike the response in coleop…
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