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JXB Advance Access originally published online on March 28, 2008
Journal of Experimental Botany 2008 59(6):1163-1173; doi:10.1093/jxb/ern043
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© 2008 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

Regulation of shoot branching patterns by the basal root system: towards a predictive model

R. G. Thomas and M. J. M. Hay*

AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand

* To whom correspondence should be addressed. E-mail: mike.hay{at}agresearch.co.nz

This study aimed to underpin the development of a generic predictive model of the regulation of shoot branching by roots in nodally rooting perennial prostrate-stemmed species using knowledge gained from physiological studies of Trifolium repens. Experiment 1 demonstrated that the net stimulatory influence from the basal rooted region of the plant on growth of newly emerging axillary buds on the primary stem decreased as their phytomeric distance from the basal root system increased. Experiment 2 found that at any one time the distribution of net root stimulus (NRS) to the apical bud on the primary stem and all lateral branches was fairly uniform within a single plant. Thus, although NRS availability was uniform throughout the shoot system at any point in time, it progressively decreased as shoot apical buds grew away from the basal root system. Based on these findings, a preliminary predictive model of the physiological regulation of branching pattern was developed. This model can explain the decline in growth rate of buds on a primary stem as it grows away from its basal root system but not the rapid progressive decline in secondary branch development on successive lateral branches. Thus knowledge of NRS availability to emerging buds is not, by itself, a sufficient basis from which to construct a predictive model. In addition, it seems that the ability of an emerging bud to become activated in response to its local NRS availability is, at least in part, directly influenced by the activation level of its parent apical bud. The experimental testing of this hypothesis, required for continued development of the model, is proceeding.

Key words: Axillary bud outgrowth, branch development, bud activation, intra-plant variation, nodal roots, prostrate clonal herbs, root signals, Trifolium repens

Received 11 September 2007; Revised 25 November 2007 Accepted 18 January 2008


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