Abstract
An evaluation was made of the extent which a Münch-type pressure flow mechanism (i.e., osmotically-generated pressure flow) might contribute to phloem transport in soybean. Estimates of sucrose concentrations in source (leaf) and sink (root) sieve tubes were obtained by a negativestaining procedure. Water potential measurements of the leaf and of the nutrient solution allowed calculation of the turgor pressures in source and sink sieve tubes. The turgor difference between source and sink sieve tubes was compared to that required to drive translocation at the observed velocity between the source and sink, as measured by [14C] photosynthate movement. Sieve-tube conductivity was calculated from the sieve-tube dimensions, assuming an essentially unobstructed pathway. In three experiments, the sucrose concentration was consistently higher in source sieve tubes (an average of 11.5%) than in sink sieve tubes (an average of 5.3%). The ratio of these values (2.3:1) agreed reasonably well with an earlier ratio for source/sink sieve tube concentrations of 1.8:1, obtained by quantitative microautoradiography. The resulting calculated turgor difference (an average of 4.1 bars) was adequate to drive a pressure flow mechanism at the observed translocation velocities (calculated to require a turgor difference of 1.2 to 4.6 bars). No other force need be presumed to be involved.
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References
Boyer, J.S.: Resistances to water transport in soybean, bean and sunflower. Crop Sci. 11, 403–407 (1971)
Boyer, J.S., Knipling, E.B.: Isopiestic technique for measuring leaf water potentials with a thermocouple psychrometer. Proc. Natl. Acad. Sci. USA 54, 1044–1051 (1965)
Fife, J.M., Price, C., Fife D.C.: Some properties of phloem exudate collected from root of sugar beet. Plant Physiol. 37, 791–792 (1962)
Fisher, D.B.: Structure of functional soybean sieve elements. Plant Physiol. 56, 555–569 (1975)
Fisher, D.B.: Histochemical approaches to water-soluble compounds and their application to problems in translocation. In: Transport and Transfer Processes in Plants. pp. 237–246, Wardlaw, I.F., Passioura, J.B., eds. New York: Academic Press 1976
Fisher, D.B.: The estimation of sugar concentrations in individual sieve tube elements by negative staining. Plant 139, 19–24 (1978)
Fisher, D.B.: Housley, T.L.: The retention of water-soluble compounds during freeze-substitution and microautoradiography. Plant Physiol. 49, 166–171 (1972)
Housley, T.L., Fisher, D.B.: Estimation of osmotic gradients in soybean sieve tubes. Qualified support for the Münch hypothesis. Plant Physiol. 59, 701–706 (1977)
Michel, B.E.: A miniature stem thermocouple hygrometer. Plant Physiol. 60, 645–647 (1977)
Münch, E.: Die Stoffbewegungen in der Pflanze. Jena: Fischer 1930
Pate, J.S.: Exchange of solutes between phloem and xylem and circulation in the whole plant. In: Transport in Plants. I. Phloem Transport, pp. 451–473, Zimmermann, M.H., Milburn, J.A., eds. (Encycl. Plant Physiol., N.S., Pirson, A., Zimmermann, M.H., eds., vol. 1) Berlin-Heidelberg-New York: Springer 1975
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Fisher, D.B. An evaluation of the Münch hypothesis for phloem transport in soybean. Planta 139, 25–28 (1978). https://doi.org/10.1007/BF00390805
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DOI: https://doi.org/10.1007/BF00390805