Journal of Experimental Botany, Vol. 53, No. 373, pp. 1411-1419,
June 2002
© 2002 Oxford University Press
Original Papers |
Revisiting the Münch pressureflow hypothesis for long-distance transport of carbohydrates: modelling the dynamics of solute transport inside a semipermeable tube
Horticultural Research, Batchelor Research Centre, Private Bag 11030, Palmerston North, New Zealand
A mathematical model of the Münch pressureflow hypothesis for long-distance transport of carbohydrates via sieve tubes is constructed using the NavierStokes equation for the motion of a viscous fluid and the van't Hoff equation for osmotic pressure. Assuming spatial dimensions that are appropriate for a sieve tube and ensuring suitable initial profiles of the solute concentration and solution velocity lets the model become mathematically tractable and concise. In the steady-state case, it is shown via an analytical expression that the solute flux is diffusion-like with the apparent diffusivity coefficient being proportional to the local solute concentration and around seven orders of magnitude greater than a diffusivity coefficient for sucrose in water. It is also shown that, in the steady-state case, the hydraulic conductivity over one metre can be calculated explicitly from the tube radius and physical constants and so can be compared with experimentally determined values. In the time-dependent case, it is shown via numerical simulations that the solute (or water) can simultaneously travel in opposite directions at different locations along the tube and, similarly, change direction of travel over time at a particular location along the tube.
Key words: Münch pressureflow hypothesis, NavierStokes equation, phloem transport, van't Hoff equation.
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