Primary root growth: a biophysical model of auxin-related control
Andrés Chavarría-Krauser A B C , Willi Jäger B and Ulrich Schurr AA ICG-III (Phytosphere), Research Center Jülich, 52425 Jülich, Germany.
B Institute of Applied Mathematics, University of Heidelberg, INF 294, 69120 Heidelberg, Germany.
C Corresponding author. Email: a.chavarria@fz-juelich.de
Functional Plant Biology 32(9) 849-862 https://doi.org/10.1071/FP05033
Submitted: 11 February 2005 Accepted: 9 May 2005 Published: 26 August 2005
Abstract
Plant hormones control many aspects of plant development and play an important role in root growth. Many plant reactions, such as gravitropism and hydrotropism, rely on growth as a driving motor and hormones as signals. Thus, modelling the effects of hormones on expanding root tips is an essential step in understanding plant roots. Here we achieve a connection between root growth and hormone distribution by extending a model of root tip growth, which describes the tip as a string of dividing and expanding cells. In contrast to a former model, a biophysical growth equation relates the cell wall extensibility, the osmotic potential and the yield threshold to the relative growth rate. This equation is used in combination with a refined hormone model including active auxin transport. The model assumes that the wall extensibility is determined by the concentration of a wall enzyme, whose production and degradation are assumed to be controlled by auxin and cytokinin. Investigation of the effects of auxin on the relative growth rate distribution thus becomes possible. Solving the equations numerically allows us to test the reaction of the model to changes in auxin production. Results are validated with measurements found in literature.
Keywords: auxin, gravitropism, hormone, model, root growth.
Acknowledgments
We thank Peter Minchin, Maja Christ, Uwe Rascher, Elizabeth Ainsworth, Hanno Scharr, Kate Morrissey and Achim Walter for their comments on this manuscript. We also thank Georg Dreissen for his assistance in evaluating the data.
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