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 ?
Because auxin is produced at the highest point of a stem, an elegant way to thwart or redirect apical dominance without having to prune off any part of a shoot is to bend it down.
The greater reduction in height due auxin herbicide exposure in [V.sub.5] is attributed to the greater injury in early stage compared to late stage, and to the fact that in the [R.sub.2] stage the growth in height has already been completed.
This superiority is related to the ability of this group of bacteria to produce indolacetic acid (AIA) (Baudoin et al., 2010), the most abundant natural auxin (plant hormone) present in plants and responsible for cell differentiation and adventitious root emission (Dartora et al., 2013, Mercier, 2008); making possible to affirm that there was a synergic effect between bacteria and IBA for the percentage of rooted cuttings.
To determine which ARF genes potentially work on different developmental processes, the temporal-spatial expression pattern in vegetative organs (2nd, 3rd, and 4th internode and leaves) and expression response to auxin treatment in seedlings were determined by real-time PCR (qRT-PCR).
The cuttings usually respond to concentrations of auxin in a typical way, showing a progressive increase in the number and quality of roots formed with each increase in concentration auxin reaching a peak, from which a descent begins in response due to toxicity (Mesen, 1998).
In present study, rooting was significantly affected by auxin concentration, highest number of root per cutting, rooting length; root fresh and dry weight was achieved at 400 mg kg-1 IBA solution.
Balko et al., "The discovery of Arylex[TM] active and Rinskor[TM] active: Two novel auxin herbicides," Bioorganic & Medicinal Chemistry, vol.
TAS3 tasiRNAs negatively regulate ARFs (auxin response factors) that is necessary for proper plant development [44-48].
Synthetic auxin (2,4-D and NAA) at 5 mg/L treatment during the flowering also reduced the fruit drop and enhanced the quality.C and V-shaped girdling 3 weeks before flowering increased number of flowers and reduced the premature fruit drop of wax apple fruits.