Exogenous Auxin Effects on Lateral Bud Outgrowth in Decapitated Shoots

In 1933 Thimann and Skoog demonstrated exogenous auxin repression of lateral bud outgrowth in decapitated shoots of Vicia faba . This evidence has given strong support for a role of auxin in apical dominance. Most, but not all, investigators have confirmed Thimann and Skoog's results. In the present study, auxin treatments were carried out on ten different species or plant types, many of which were treated with auxin in different forms, media and under different light conditions. The Thimann–Skoog experiment did work for most species (i.e. exogenous auxin did repress bud outgrowth) including the dgt tomato mutant which is known to be insensitive to auxin in certain responses. Toxic auxin symptoms were observed in some but not all species. The Thimann–Skoog experiment did not work for greenhouse-grown Coleus or for Arabidopsis . Light was shown to reduce apical dominance in Coleus and Ipomoea nil .