Apical dominance

Many conifers show particularly strong apical dominance, strongest of all in the family Araucariaceae, showing a single erect central trunk with strongly differentiated horizontal branching. Cuttings of Araucariaceae species taken from a side branch will not develop erect growth. Araucaria heterophylla, South Durras, New South Wales, Australia.

In plant physiology, apical dominance is the phenomenon whereby the main central stem of the plant is dominant over (i.e., grows more strongly than) other side stems; on a branch the main stem of the branch is further dominant over its own side branchlets.

Typically, the end of a shoot contains an apical bud, which is the location where shoot growth occurs. The apical bud produces IAA, an auxin that inhibits growth of the lateral buds further down on the stem. When the apical bud is removed, the lowered IAA concentration allows the lateral buds to grow and produce new shoots, which compete to become the lead growth. Pruning techniques such as coppicing and pollarding make use of this natural response to damage to direct plant growth and produce a desired shape, size, and/or productivity level for the plant.

Weeping larch showing growth habit is lacking apical dominance.

Some fruit trees have strong apical dominance, and young trees can become "leggy", with poor side limb development. Apical dominance can be reduced in this case, or in cases where limbs are broken off by accident, by cutting off the auxin flow above side buds that one wishes to stimulate. This is often done by orchardists for young trees.

Occasionally, strong apical dominance is advantageous, as in the "Ballerina" apple trees. These trees are intended to be grown in small gardens, and their strong apical dominance combined with a dwarfing rootstock gives a compact narrow tree with very short fruiting side branches.

See also

• Meristem
• Fruit trees pruning

References

• Thimann, Kenneth V.; Skoog, Folke (1933). "Studies on the growth hormone of plants: III. The inhibiting action of the growth hormone on bud development.". Proceeding National Academy Sciences (USA) 19: 714–716. http://www.pnas.org/content/19/7/714.full.pdf+html. Retrieved 2011-10-18. 

• Dun, Elizabeth Ann; Ferguson, Brett James; Beveridge, Christine Anne (2006). "Apical Dominance and Shoot Branching. Divergent Opinions or Divergent Mechanisms?". Plant Physiology 142: 812–819. doi:10.1104/pp.106.086868. http://www.plantphysiol.org/content/142/3/812.full. Retrieved 2011-10-15.