Auxin and the power of the proteasome in plants.

Auxins, mainly indole-3-acetic acid (IAA), play a critical role in numerous plant growth processes, including embryo development, root and flower development, vascular differentiation, stem elongation, apical dominance, and tropic responses. Charles Darwin and his son Francis performed some of the earliest work relating to the effect of auxin on plant growth with their experiments on phototropism (bending of plants toward a light source) in oat ( Avena sativa ) and canary grass ( Phalaris canariensis ). Their experiments, reported in the monograph entitled “The Power of Movement in Plants,” led them to the conclusion that “some influence” was transmitted from the upper to the lower part of the seedlings, causing them to bend (Darwin, 1880). This “influence” was isolated in 1926 by Frits W. Went in his famous experiments with oat coleoptiles and later named auxin (Went, 1935). The diverse effects of auxin on plant growth are mainly the result of auxin’s effect on cell elongation, cell division, or cell differentiation and are dependent on the control of auxin biosynthesis and degradation and the polar transport to and the perception of auxin at the site of action. Although much has been discovered regarding the effects and regulation of auxins on plant growth since the Darwin experiments, there is much that remains unknown.