The carbon needed for growth of plants is produced in the form of sugars by photosynthesis in the leaves. It is then transported in the sieve cells, which in trees run in the innermost layer of the bark, the so-called phloem, from the leaves to the new shoots and fruits and all the way down to the roots. According to the Münch hypothesis from the 30’ies, this transport is driven by osmotic pressure differences due to the differences in sugar concentrations between the sources (leaves) to the sinks, where sugar is consumed. The relevant sugar concentrations and the corresponding pressures are hard to measure on living trees and so-far the Münch hypothesis has only been indirectly tested. It remains an outstanding problem in plant physiology to what extent the Münch mechanism can account for long distance sugar transport in trees.
To learn more about the feasibility of such flows, we have recently studied osmotically driven flows both experimentally and theoretically in collaboration with groups at Harvard University, Washington State University and University of Copenhagen. The references are given below.
Osmotically driven pipe flows and their relation to sugar transport in plants
K.H. Jensen, E. Rio, R. Hansen, C. Clanet, and T. Bohr:
Journal of Fluid Mechanics 636, 371-396 (2009) ( pdf)
Osmotically driven flows in microchannels separated by a semipermeable membrane
K.H. Jensen, J. Lee, T. Bohr, and H. Bruus: Lab On a Chip 9, 2093-2099 (2009) ( pdf)
Self-consistent unstirred layers in osmotically driven flows
K. Hartvig Jensen, T. Bohr, and H. Bruus:
Journal of Fluid Mechanics 662, 197-208 (2010) ( pdf)
Optimality of the Münch mechanism for translocation of sugars in plants
K. Hartvig Jensen, J. Lee, T. Bohr, H. Bruus, N.M. Holbrook, and M.A. Zwieniecki
Journal of the Royal Society Interface 8, 1155-1165 (2011) ( pdf)
Analytic solutions and universal properties of sugar loading models in Münch phloem flow
K. H. Jensen, K. Berg-Sørensen, S. M. M. Friis, and T. Bohr
Journal of Theoretical Biology 304, 286-296 (2012) ( pdf)
Universality of Phloem Transport in Seed Plants
K. H. Jensen, J. Liesche , T. Bohr, and A. S. Schulz
Plant, Cell & Environment 35, 1065-1075 (2012) ( pdf)
Modeling the hydrodynamics of phloem sieve plates
K.H. Jensen, D.L. Mullendore, N.M. Holbrook, T. Bohr, M. Knoblauch, and H. Bruus
frontiers in Plant Science 3, article 151 (2012) ( pdf)
The Efficiency of Osmotic Pipe Flows, L. S. Haaning, K. H. Jensen, C. Helix Nielsen, K. Berg-Sørensen and T. Bohr, submitted to Physical Review E. (pdf)