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(awk′sĭn) [Gr. auxe, increase]
A substance that promotes growth in plant cells and tissues.
Medical Dictionary, © 2009 Farlex and Partners


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.

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005
References in periodicals archive ?
This quick and simple check to auxin flow not only causes growth to falter briefly, but also awakens lateral buds that were dormant.
The auxin efflux carrier protein plays proactive and critical role in development of root system in plants.
(2010), the root growth process is regulated by hormonal factors, where auxins are responsible for cell division, while cytokines act in cell differentiation.
(2013); ROBINSON et al., (2013a, 2013b) and SOLOMON & BRADLEY, 2014, who reported that soybean exposure to auxin herbicides drift causes significant more crop injury when applied during vegetative than reproductive stage.
However, artificial activation of auxin biosynthesis in the embryo cells, which are normally unable to produce this hormone in early stages of development, allowed the embryos to develop normally without a maternal auxin supply.
In this sense, the objective of this work was to evaluate the use of auxin, calcium and Azospririllum brasilense on rooting of semihardwood olive cuttings.
Because of their important roles in auxin signaling pathways, which are indispensable to plant growth and development, ARF gene families have been studied in many plant species.
The purpose of treating cuttings with growth regulators is to increase the percentage of rooting, reduce root initiation time and improve the quality of the formed root system (Cachique et al., 2011), being IBA the most effective auxin to induce rooting of cuttings in most species.
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).
Previous research has documented many consequences associated with auxin herbicide drift onto soybean, such as fewer seeds per pod, lower seed quality, pod malformation, and reduced yield [16-18] as well as reduced growth when exposed to drift rates of auxin herbicides, all of which were documented in this study.