auxin


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auxin

(awk′sĭn) [Gr. auxe, increase]
A substance that promotes growth in plant cells and tissues.

auxin

a type of plant growth-regulating substance involved in the growth of cells and several other functions. The most important auxin is indolacetic acid (IAA; see Fig. 194 ), but many other substances have been classified as auxins, using a BIO-ASSAY method developed by Fritz WENT.

The effects of auxins depend on their concentration in the plant. They are most concentrated at the shoot tip and least concentrated in the root, except for small amounts at the root tip. The major effects of auxin are summarized below:

  1. Encourages cell growth by elongation, producing a softening of the MIDDLE LAMELLAE of cell walls.
  2. Stimulates cell division in the PHLOEM of the VASCULAR BUNDLES, so encouraging new growth.
  3. Promotes positive PHOTOTROPISM in shoots by growth of tissues towards the light source.
  4. Promotes GEOTROPISM in all parts of the plant (positive in roots, negative in shoots, due to unequal distributions of the hormone).
  5. Induces APICAL DOMINANCE by suppressing lateral buds.
  6. Induces lateral root formation.
  7. Stimulates fruit development, enabling seedless fruits to be produced artificially. (h) Suppresses ABSCISSION in leaves and fruit. (i) Encourages the formation of wound tissues in injured or diseased plants.

    Auxins have a number of commercial uses, e.g. to promote the rooting of cuttings, regulate plant height, induce flower formation and control fruit set and fruit drop.

auxin

plant hormone.
References in periodicals archive ?
In conclusion, this study reveals that inoculation with specific auxin-producing microorganisms and/or amendment with L-TRP was effective in promoting auxin accumulation in soil, even in the presence of indigenous microflora but with different efficiency.
Estelle maintains that identifying these proteins is important because "understanding how auxin works may allow us to manipulate plant growth in desirable ways.
The ability of auxin to promote and inhibit plant growth explains why shoots grow upward and roots grow downward (Figure 4-6).
During ripening, auxin degrades to low levels, often resulting in overripening.
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.
Plate Experiment: To test the response of Rhizobium specie (chickpea) on wheat, isolate having the highest auxin biosynthesis potential (Cp3) was used in plate experiment (root-shoot elongation assay).
Moreover, it is also possible that the maintenance of DM values in roots in the +NB treatment, and even the increase of this variable at the concentration of 50 mM NaCl can be partly attributed to the combined action of cytokinin and auxin, considering that under salinity conditions these phytohormones can stimulate cellular elongation and increase biomass allocation into the roots (Albacete et al.
Feron, The Solanum Lycopersicum Auxin Response Factor 7 (SlARF7) Regulates Auxin Signaling During Tomato Fruit Set and Development, Plant J.
In a study Wiesmann and Epstein (1988) noticed that all the stages of rooting were linked directly or indirectly, with changes in endogenous auxin concentrations and later on similar results were reported (Heloir et al.
For in vitro rooting of shoots obtained during the multiplication phase, it was found that adding auxin to the culture medium did not influence the induction of root formation, since there were no statistical differences between the various treatments.