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auxin

auxin (ôk´sĬn), plant hormone that regulates the amount, type, and direction of plant growth. Auxins include both naturally occurring substances and related synthetic compounds that have similar effects. Auxins are found in all members of the plant kingdom. They are most abundantly produced in growth areas (meristem), e.g., root and shoot tips, but are also produced elsewhere, e.g., in the stems and leaves. The method of dispersal throughout the plant body is not yet fully understood. Auxins affect numerous plant processes, e.g., cell division and elongation, autumnal loss of leaves, and the formation of buds, roots, flowers, and fruit. They are also responsible for many forms of tropism. It is known that phototropism is due to the inhibition of auxins by light; the cells on that side of a plant exposed to light do not divide or grow as quickly as those on the shaded side, and thus the plant grows toward the light source. Auxins are widely used commercially to produce more vigorous growth, to promote flowering and fruiting and also root formation in plants not easily propagated by stem cuttings, to retard fruit drop, and to produce seedless varieties (e.g., of tomatoes) by parthenogenetic fruiting. Only minute amounts of auxins occur naturally, and synthetic auxins (e.g., 2,4-D) must be administered in carefully prescribed doses, since excessive concentration produces usually fatal abnormalities. However, different species of plants react to different amounts of auxins, a fact used to advantage as a method of weed control. The principal natural auxin is indoleacetic acid; other common but less frequent plant hormones include the gibberellins, lactones, and kinins.

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auxin

auxin A hormone that promotes longitudinal growth in the cells of higher plants. Typically, low concentrations of auxin promote growth whereas high concentrations inhibit it. Auxins are produced at the growing points of stems and roots, and promote growth by increasing the rate of cell elongation rather than that of cell division. They are involved in the curvature of parts of the plant towards light (phototropism) or gravity (geotropism), and the initiation of cambium activity in association with cytokinins; and they may control fruit growth or leaf fall, and inhibition of lateral-bud development in favour of apical buds. A natural example of an auxin is indole-3-acetic acid (IAA), which has been isolated from fungi and bacteria, and from the endosperm of corn, as well as from urine and saliva in humans. Auxins have also been synthesized, and are widely used to regulate growth in a variety of plants of agricultural and horticultural importance. Some of these may have differential effects on different plants. For example 2, 4-dichlorophenoxyacetic acid (2, 4-D) is toxic to dicotyledons (see DICOTYLEDONEAE) but not to monocotyledons (see MONOCOTYLEDONEAE), and is used to control weeds in cereal crops and lawns.

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"auxin." A Dictionary of Plant Sciences. . Encyclopedia.com. 10 Dec. 2017 <http://www.encyclopedia.com>.

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"auxin." A Dictionary of Plant Sciences. . Retrieved December 10, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/auxin

auxin

auxin Any of a group of plant growth substances responsible for such processes as the promotion of growth by cell enlargement, the maintenance of apical dominance, and the initiation of root formation in cuttings. Auxins are also involved in suppressing the abscission of leaves, fruit, or other plant organs and in the development of flowers and fruits. Naturally occurring auxins, principally indoleacetic acid (IAA), are synthesized in actively growing regions of the plant, from where they are transported to other parts of the plant. IAA is stored in the plant in an inactive form, conjugated (attached) to various compounds, such as myo-inositol. Synthetic auxins include 2,4-D, which is used as a weedkiller, and indolebutyric acid and naphthaleneacetic acid, which are sold in preparations of ‘rooting hormones’.

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"auxin." A Dictionary of Biology. . Encyclopedia.com. 10 Dec. 2017 <http://www.encyclopedia.com>.

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auxin

auxin Plant hormone produced mainly in the growing tips of plant stems. Auxins accelerate plant growth by stimulating cell division and enlargement, and by interacting with other hormones. Actions include the elongation of cells in geotropism and phototropism (by increasing the elasticity of cell walls, allowing the cells to take up more water), fruit drop and leaf fall. See also gibberellin

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"auxin." World Encyclopedia. . Encyclopedia.com. 10 Dec. 2017 <http://www.encyclopedia.com>.

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"auxin." World Encyclopedia. . Retrieved December 10, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/auxin

auxin

aux·in / ˈôksin/ • n. a plant hormone that causes the elongation of cells in shoots and is involved in regulating plant growth.

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"auxin." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 10 Dec. 2017 <http://www.encyclopedia.com>.

"auxin." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (December 10, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/auxin

"auxin." The Oxford Pocket Dictionary of Current English. . Retrieved December 10, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/auxin