Phloem hydrostatic pressure relates to solute loading rate: a direct test of the Münch hypothesis

Functional Plant Biology : FPB
Nick GouldP E H Minchin

Abstract

According to the Münch hypothesis, a flow of solution through the sieve tubes is driven by a hydrostatic pressure difference between the source (or collection) phloem and the sink (or release) phloem. A high hydrostatic pressure is maintained in the collection phloem by the active uptake of sugar and other solutes, with a concomitant inflow of water. A lower pressure is maintained in the release phloem through solute unloading. In this work we directly test the role of solute uptake in creating the hydrostatic pressure associated with phloem flow. Solute loading into the phloem of mature leaves of barley and sow thistle was reduced by replacing the air supply with nitrogen gas. Hydrostatic pressure in adjacent sieve elements was measured with a sieve-element pressure probe, a cell pressure probe glued to the exuding stylet of aphids that had been feeding from the phloem. Sieve element sap was sampled by aphid stylectomy; sap osmotic pressure was determined by picolitre osmometry and its sugar concentration by enzyme-linked fluorescence assays. Samples were taken with a time resolution of ~2-3 min. In accordance with Münch's proposal a drop in osmotic and hydrostatic pressure in the source phloem following treatment of the sourc...Continue Reading

References

Jul 4, 2002·Journal of Experimental Botany·P E H MinchinO A Koroleva
Sep 1, 1977·Plant Physiology·M G JonesO H Lowry
May 1, 2004·Functional Plant Biology : FPB·Nick GouldPhilip J White
Nov 1, 2004·Functional Plant Biology : FPB·Nick GouldMichael R Thorpe

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Citations

Feb 24, 2010·Journal of Experimental Botany·Veerle De Schepper, Kathy Steppe
Jul 15, 2015·Tree Physiology·Sebastian PfautschMaurizio Mencuccini
Dec 7, 2017·Nature Plants·Jessica A SavageN Michele Holbrook
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Aug 1, 2014·Functional Plant Biology : FPB·Yann SalmonNina Buchmann
Oct 10, 2013·Journal of Experimental Botany·Veerle De SchepperKathy Steppe
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May 1, 2007·Functional Plant Biology : FPB·Winfried S PetersMichael Knoblauch
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Jul 29, 2021·Plant Science : an International Journal of Experimental Plant Biology·Xiao-Yang WeiDavid W McCurdy
Jun 15, 2010·Comptes rendus biologies·Sylvie DinantJulia Kehr

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Methods Mentioned

BETA
electron microscopy
enzyme-linked fluorescence assay

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