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DEVELOPMENT AND HORMONE ACTION

Auxin Dynamics after Decapitation Are Not Correlated with the Initial Growth of Axillary Buds¹

Australian Research Council Centre of Excellence for Integrative Legume Research, and School of Integrative Biology, The University of Queensland, St. Lucia, Queensland, 4072, Australia (S.E.M., M.C.H.C., S.K., C.A.B.); and School of Plant Science, University of Tasmania, Hobart, Tasmania, 7001, Australia (J.J.R.)

One of the first and most enduring roles identified for the plant hormone auxin is the mediation of apical dominance. Many reports have claimed that reduced stem indole-3-acetic acid (IAA) levels and/or reduced basipetal IAA transport directly or indirectly initiate bud growth in decapitated plants. We have tested whether auxin inhibits the initial stage of bud release, or subsequent stages, in garden pea (Pisum sativum) by providing a rigorous examination of the dynamics of auxin level, auxin transport, and axillary bud growth. We demonstrate that after decapitation, initial bud growth occurs prior to changes in IAA level or transport in surrounding stem tissue and is not prevented by an acropetal supply of exogenous auxin. We also show that auxin transport inhibitors cause a similar auxin depletion as decapitation, but do not stimulate bud growth within our experimental time-frame. These results indicate that decapitation may trigger initial bud growth via an auxin-independent mechanism. We propose that auxin operates after this initial stage, mediating apical dominance via autoregulation of buds that are already in transition toward sustained growth.

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.058743.

^* Corresponding author; e-mail c.beveridge{at}botany.uq.edu.au; fax 61–7–3365–1699.

Received December 23, 2004; returned for revision March 16, 2005; accepted March 19, 2005.

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