auxin


Also found in: Dictionary, Thesaurus, Medical, Wikipedia.

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.
..... Click the link for more information.
. 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.
..... Click the link for more information.
 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 presence of IAM indicates that the TRP [right arrow] IAM [right arrow] IAA pathway of auxin biosynthesis might be active in these rhizobacteria.
Auxin performs its functions by stimulating gene expression--that is, it turns genes on and off.
The same amount of auxin that promotes cell elongation in shoots can inhibit growth in roots (Figure 4-5).
If we can determine how auxin is made in a plant, then we can change the concentration, or level.
We identified an Abscisic acid (ABA) inducible protein PHV A1 gene and auxin response factor 12 and 25 genes highly expressed in stem tips.
For auxin treatments, the highest number of leaves per cutting was obtained treated with 400 mg kg-1 IBA solution followed by 200 mg kg-1 and lowest number of leaves per cutting without IBA treatments (control).
Determination of Auxin Biosynthesis: Three isolates of Rhizobium species (Cp1, Cp2 and Cp3) were screened for their auxin biosynthesis potential with and without L-TRP.
2007) evidenced that despite increasing concentrations of NaCl reducing the length and DM of shoot and root systems, the addition of auxin indoleacetic acid (AIA) during the germination period promoted an increase in shoot length and dry matter in three Triticum aestivum (L.
A Tares, Effect of Gibberellin and Auxin on Parthenocarpic Fruit Growth Induction in the CV Micro-Tom of Tomato, J.
The classical phytohormone auxin (indole3 acetic acid) was produced and secreted by different strains of purple nonsulphur bacteria (Sasikala and Ramana, 1995 and Rajashekar et al.
During the present study, an elaborative experiment was carried out to optimize the effect of auxin on rooting of Stevia rebaudiana cuttings as well as on the vigor of developing shoots.