auxin


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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 tropismtropism
, involuntary response of an organism, or part of an organism, involving orientation toward (positive tropism) or away from (negative tropism) one or more external stimuli.
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. 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 weedweed,
common term for any wild plant, particularly an undesired plant, growing in cultivated ground, where it competes with crop plants for soil nutrients and water. In their natural habitat, wildflowers and herbs not only provide beauty but function in many useful ways, e.g.
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 control. The principal natural auxin is indoleacetic acid; other common but less frequent plant hormones include the gibberellins, lactones, and kinins.

auxin

[′ȯk·sən]
(biochemistry)
Any organic compound which promotes plant growth along the longitudinal axis when applied to shoots free from indigenous growth-promoting substances.
References in periodicals archive ?
The effect of auxin type on secondary metabolite synthesis was studied in the tissue culture of Ecballium elaterium.
Whether you are planting vegetable seedlings, bare-root roses or fruit trees, transplanting established garden specimens from one location to another, or propagating plants by stem cuttings or division, auxin will accelerate development of new roots.
Investigations on the synthetic auxin residues of greenhouse tomatoes.
Various environmental factors influence auxin biosynthesis by rhizobacteria in pure culture and in soil (Purushothaman et al.
The auxin study was conducted on a plant called Arabidopsis, the first for which the entire genome has been sequenced.
When light hits outer flower petals it triggers a hormone (function-controlling chemical) called auxin that causes cells to grow and expand.
Peroxidases are also thought to be involved in the metabolism of auxin (Ludwig-Muller and Hilgenberg 1992).
A YOUR rubber tree has only one stem because side shoots are suppressed by a chemical called an auxin produced in the growing tip.
According to Waaland (1981), the advantages of algae as a biofertilizer are that they: (1) are free of weed seeds and fungal spores which can harm terrestrial crops, (2) are good sources of trace elements, and (3) can regulate crop growth and ripening because of the auxin, cytokinin, and gibberellin associated with them.
Beltsville, Md 20705) have genetically altered the levels of auxin, a hormone which causes a tomato to grow and ripen.
Of the five major plant hormones, auxin has been known the longest and is probably the most important.
These compounds may interfere in auxin metabolism, change membrane penetrance, influence respiration and oxidative phosphorylation or protein synthesis [4].