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AOBPreview published online on August 22, 2006
Annals of Botany, doi:10.1093/aob/mcl177
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© The Author 2006. Published by Oxford University Press on behalf of the Annals of Botany Company. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
Received December 14, 2005
Revised February 3, 2006
Accepted July 5, 2006

Article

Onset of Sheath Extension and Duration of Lamina Extension are Major Determinants of the Response of Maize Lamina Length to Plant Density

BRUNO ANDRIEU 1 *, JONATHAN HILLIER 2, and COLIN BIRCH 3

1 Institut National de la Recherche Agronomique, Unité Environnement et Grandes Cultures, 78850 Thiverval-Grignon, France
2 Institut National de la Recherche Agronomique, Unité Environnement et Grandes Cultures, 78850 Thiverval-Grignon, France; Present address: University College London, Department of Geography, 26, Bedford Way London WC1H 0AP, UK
3 The University of Queensland, Gatton, 4343 Qld, Australia

* To whom correspondence should be addressed.
BRUNO ANDRIEU, E-mail: Bruno.Andrieu{at}grignon.inra.fr


  Abstract

• Background and Aims Plants regulate their architecture strongly in response to density, and there is evidence that this involves changes in the duration of leaf extension. This questions the approximation, central in crop models, that development follows a fixed thermal time schedule. The aim of this research is to investigate, using maize as a model, how the kinetics of extension of grass leaves change with density, and to propose directions for inclusion of this regulation in plant models.

• Methods Periodic dissection of plants allowed the establishment of the kinetics of lamina and sheath extension for two contrasting sowing densities. The temperature of the growing zone was measured with thermocouples. Two-phase (exponential plus linear) models were fitted to the data, allowing analysis of the timing of the phase changes of extension, and the extension rate of sheaths and blades during both phases.

• Key Results The duration of lamina extension dictated the variation in lamina length between treatments. The lower phytomers were longer at high density, with delayed onset of sheath extension allowing more time for the lamina to extend. In the upper phytomers--which were shorter at high density--the laminae had a lower relative extension rate (RER) in the exponential phase and delayed onset of linear extension, and less time available for extension since early sheath extension was not delayed.

• Conclusions The relative timing of the onset of fast extension of the lamina with that of sheath development is the main determinant of the response of lamina length to density. Evidence is presented that the contrasting behaviour of lower and upper phytomers is related to differing regulation of sheath ontogeny before and after panicle initiation. A conceptual model is proposed to explain how the observed asynchrony between lamina and sheath development is regulated.

Keywords: Co-ordination, emergence, leaf extension, kinetics, lamina, leaf, ligule, ontogeny, plant architecture, primordium, sheath, Zea mays, RER, LER.
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