Exogenous Auxin Effects on Lateral Bud Outgrowth in Decapitated Shoots

In 1933 Thimann and Skoog demonstrated exogenous auxin repressionof lateral bud outgrowth in decapitated shoots ofVicia faba. This evidence has given strong support for a role of auxinin apical dominance. Most, but not all, investigators have confirmedThimann and Skoog's results. In the present study, auxin treatmentswere carried out on ten different species or plant types, manyof which were treated with auxin in different forms, media andunder different light conditions. The Thimann–Skoog experimentdid work for most species (i.e. exogenous auxin did repressbud outgrowth) including thedgt tomato mutant which is knownto be insensitive to auxin in certain responses. Toxic auxinsymptoms were observed in some but not all species. The Thimann–Skoogexperiment did not work for greenhouse-grownColeus or forArabidopsis. Light was shown to reduce apical dominance inColeus andIpomoeanil . apical dominance; lateral bud outgrowth; axillary bud; auxin; IAA; decapitation; Vicia faba ; Ipomoea nil ; Pisum sativum ; Phaseolus vulgaris ; Lycopersion exculentum ; dgt ; Coleus blumei ; Arabidopsis thaliana ; Helianthus annuus ; Thimann–Skoog