Summary
A steady-state model of solution flow in a tubular semipermeable membrane is developed for an arbitrary distribution of solute sources and sinks along the translocation path. It is demonstrated that the volume-flow mechanism of phloem transport depends only on the two assumptions: 1. that the plasmalemma of the sieve tube is a differentially permeable membrane, and 2. that sugars are actively secreted into and absorbed from the lumen of the sieve tube. It is shown that in the absence of a pressure gradient, there is a negligible concentration gradient over most of the translocation path. However, in the presence of a pressure gradient a small concentration gradient develops as a result of the continually changing chemical potential of water along the direction of solution flow. For Poiseuille flow the concentration gradient is approximately proportional to the mean stream velocity.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Crafts, A. S., Crisp, C. E.: Phloem transport in plants. San Francisco: Freeman 1971
Diamond, J. M., Bossert, W. H.: Standing gradient osmotic flow. J. gen. Physiol. 50, 2061–2083 (1967)
Eschrich, W., Evert, R. F., Young, J. H.: Solution flow in tubular semipermeable membranes. Planta (Berl.) 107, 279–300 (1972)
Evert, R. F., Eschrich, W., Eichhorn, S. E.: P−protein distribution in mature sieve elements of Cucurbita maxima. Planta (Berl.) 109, 193–210 (1973)
Katchalsky, A., Curran, P. F.: Nonequilibrium thermodynamics in biophysics. Cambridge, Mass., USA: Harvard Univ. Press 1965
Kleinig, H., Dörr, I., Weber, C., Kollmann, R.: Filamentous proteins from plant sieve tubes. Nature (Lond.) New Biol. 229, 152–153 (1971)
Mason, T. G., Maskell, E. J.: Studies in the transport of carbohydrates in the cotton plant. Ann. Bot. 42, 572–636 (1928)
Münch, E.: Die Stoffbewegungen in der Pflanze. Jena: Fischer 1930
Sabnis, D. D., Hart, J. W.: P−protein in sieve elements. I. Ultrastructure after treatment with vinblastine and colchicine. Planta (Berl.) 109, 127–133 (1973)
Spanner, D. C.: Transport in the phloem. Nature (Lond.) 232, 157–160 (1971)
Tammes, P. M. L., Die, J. van, Ie, T. S.: Studies on phloem exudation from Yucca flaccida Haw. VIII. Fluid mechanics and exudation. Acta bot. neerl. 20, 245–252 (1971)
Thaine, R.: Movement of sugars through plants by cytoplasmic pumping. Nature (Lond.) 222, 873–875 (1969)
Weatherley, P. E.: Solution flow in tubular semi-permeable membranes. Planta (Berl.) 110, 183–187 (1973)
Williamson, R. E.: An investigation of the contractile protein hypothesis of phloem translocation. Planta (Berl.) 106, 149–159 (1972)
Wooding, F. B. P.: P protein and microtubular systems in Nicotiana callus phloem. Planta (Berl.) 85, 284–298 (1969)
Worley, J. F.: Evidence in support of “open” sieve tube pores. Protoplasma (Wien) 76, 129–132 (1973)
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Young, J.H., Evert, R.F. & Eschrich, W. On the volume-flow mechanism of phloem transport. Planta 113, 355–366 (1973). https://doi.org/10.1007/BF00387318
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF00387318