JXB Advance Access published online on April 29, 2007
Journal of Experimental Botany, doi:10.1093/jxb/erm063
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© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)
RESEARCH PAPER |
Cumulative activation of axillary buds by nodal roots in Trifolium repens L.
AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand
* To whom correspondence should be addressed. E-mail: mike.hay{at}agresearch.co.nz
In Trifolium repens the rate of outgrowth of an axillary bud was closely correlated with its duration of exposure to a nearby nodal root. The dose-dependent nature of this relationship, over 0–22 d, is consistent with the concept that axillary buds are cumulatively activated by a root signal (RS) such that the longer they receive the signal the higher is their level of activation and hence their rate of outgrowth. Furthermore, the activation level attained by a bud was subsequently retained following the excision of the nodal root providing the source of its activation: its rate of growth 3–6 weeks after root excision still reflected the initial level of activation of the bud. Thus, once activated, a bud required relatively little RS to maintain its rate of outgrowth, implying that activation involves the establishment of an autonomous control mechanism within the bud itself. This provides an explanation of how a strongly activated apical bud can continue growth at relatively low RS levels when it is distanced from its nearest root system, while at the same time the prevailing low RS environment leads to weak activation of the axillary buds emerging from it.
Key words: Axillary bud outgrowth, branch development, bud activation, bud emergence, cumulative activation, nodal roots, root signals, stem elongation, Trifolium repens
Received 29 November 2006; Revised 19 February 2007 Accepted 5 March 2007
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