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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 ?
Therefore, it can be very easy to make up a fresh batch of homemade rooting compound whenever you need to plant some new cuttings.
Then, remove the needles from the bottom two-thirds of the cuttings, dip them in a rooting compound and, using a putty knife and a straight edge, make a slice in the sand the width of the propagation bed.
Just cut below a healthy new leaf joint, dip into a specialist rooting compound and plant in 3ins pots of compost.