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A model for water transport in the stele of plant roots

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Summary

The mechanism of water movement across roots is, as yet, not well understood. Some workable black box theories have already been proposed. They, however, assumed unrealistic cell membranes with low values of σ, or were based on a poor anatomical knowledge of roots. The role of root stele in solute and water transport seems to be especially uncertain. An attempted explanation of the nature of root exudation and root pressure by applying the apoplast canal theory (Katou andFurumoto 1986 a, b) to transport in the root stele is given. The canal equations are solved for boundary conditions based on anatomical and physiological knowledge of the root stele. It is found that the symplast cell membrane, cell wall and net solute transport into the wall apoplast are the essential constituents of the canal system. Numerical analysis shows that the canal system enables the coupled transport of solutes and water into a xylem vessel, and the development of root pressure beyond the level predicted by the osmotic potential difference between the ambient medium and the exudate. Observations on root exudation and root pressure previously reported seem to be explained quite well. It is concluded that the movement of water in the root stele although apparently active is essentially osmotic.

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Abbreviations

J exv :

volume exudation per root surface

J0 :

non-osmotic exudation

Lr :

overall radial hydraulic conductivity of an excised root

σ:

reflection coefficient

Δ Cs :

difference in the osmotic concentration between the bathing medium and the exudate

R:

gas constant

T:

absolute temperature

CK :

molar concentration of K+

CCl :

molar concentration of Cl−

Cj :

molar concentration of ion species j

Pj :

membrane permeability of ion j

zj :

valence of ion j

F:

Faraday constant

Vix :

intracellular electric potential with reference to the canal

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Authors and Affiliations

  1. Department of Earth Sciences, Faculty of Science, Nagoya University, Nagoya

    M. Furumoto

  2. Biological Institute, Faculty of Science, Nagoya University, Chikusa-ku, Nagoya 464, Japan

    K. Katou & T. Taura

Authors
  1. K. Katou
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  2. T. Taura
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  3. M. Furumoto
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Katou, K., Taura, T. & Furumoto, M. A model for water transport in the stele of plant roots. Protoplasma 140, 123–132 (1987). https://doi.org/10.1007/BF01273721

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  • DOI: https://doi.org/10.1007/BF01273721

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