Register      Login
Functional Plant Biology Functional Plant Biology Society
Plant function and evolutionary biology
RESEARCH ARTICLE

Direct measurements of sieve element hydrostatic pressure reveal strong regulation after pathway blockage

Nick Gould A D , Peter E. H. Minchin A B and Michael R. Thorpe A C
+ Author Affiliations
- Author Affiliations

A University of Waikato, Department of Biology, Hamilton, NZ.

B Current address: ICG-III Phytosphëre, Forschungszentrum Jülich, D 52425, Jülich, Germany.

C Current address: Chemistry Department, Building 555, Brookhaven National Laboratory, Upton, NY 11973, USA.

D Corresponding author; email: ngould@waikato.ac.nz

Functional Plant Biology 31(10) 987-993 https://doi.org/10.1071/FP04058
Submitted: 18 March 2004  Accepted: 22 June 2004   Published: 14 October 2004

Abstract

According to the Münch hypothesis, solution flow through the phloem is driven by a hydrostatic pressure gradient. At the source, a high hydrostatic pressure is generated in the collection phloem by active loading of solutes, which causes a concomitant passive flow of water, generating a high turgor pressure. At the sink, solute unloading from the phloem keeps the turgor pressure low, generating a source-to-sink hydrostatic pressure gradient. Localised changes in loading and unloading of solutes along the length of the transport phloem can compensate for small, short-term changes in phloem loading at the source, and thus, maintain phloem flow to the sink tissue. We tested directly the hydrostatic pressure regulation of the sieve tube by relating changes in sieve tube hydrostatic pressure to changes in solute flow through the sieve tube. A sudden phloem blockage was induced (by localised chilling of a 1-cm length of stem tissue) while sieve-tube-sap osmotic pressure, sucrose concentration, hydrostatic pressure and flow of recent photosynthate were observed in vivo both upstream and downstream of the block. The results are discussed in relation to the Münch hypothesis of solution flow, sieve tube hydrostatic pressure regulation and the mechanism behind the cold-block phenomenon.

Keywords: aphid stylectomy, chilling response, phloem pressure probe, single-cell sampling, 11C.


Acknowledgments

This work was funded through the Marsden Fund (Royal Society, NZ). We thank Professors Roy Daniels and Warwick Silvester at the University of Waikato for providing a laboratory space and support in conducting this work.


References


Fisher DB, Frame JM (1984) A guide to the use of the exuding stylet technique in phloem physiology. Planta 161, 385–393. open url image1

Grange RI, Peel AJ (1978) Evidence for solution flow in the phloem of willow. Planta 138, 15–23. open url image1

Hammel HT (1968) Measurement of turgor pressure and its gradient in the phloem of oak. Plant Physiology 43, 1042–1048. open url image1

Hayes PM, Patrick JW, Offler CE (1987) The cellular pathway of radial transfer of photosynthates in stems of Phaseolus vulgaris L.: effects of cellular plasmolysis and p-chloromercuribenzene sulphonic acid. Annals of Botany 56, 125–138. open url image1

Jones MGK, Outlaw WH, Lowry OH (1977) Enzymic assay of 10−7 to 10−14 moles of sucrose in plant tissues. Plant Physiology 60, 379–383. open url image1

Knoblauch M, Peters WS, Ehlers K, van Bel AJE (2001) Reversible calcium-regulated stopcocks in legume sieve tubes. The Plant Cell 13, 1221–1230.
Crossref | GoogleScholarGoogle Scholar | PubMed | open url image1

Lang A (1983) Turgor-regulated translocation. Plant, Cell and Environment 6, 683–689. open url image1

Lang A, Minchin PEH (1986) Phylogenetic distribution and mechanism of translocation inhibition by chilling. Journal of Experimental Botany 37, 389–398. open url image1

McQueen JC (2003) ‘Carbohydrate storage and remobilisation: the mechanisms involved in woody stem tissue of apple trees.’ PhD thesis. (The University of Waikato: NZ)

Malone M, Leigh RA, Tomos AD (1989) Extraction and analysis of sap from individual wheat leaf cells: the effect of sampling speed on the osmotic pressure of extracted sap. Plant, Cell and Environment 12, 919–926. open url image1

Minchin PEH, Thorpe MR (1983) A rate of cooling response in phloem translocation. Journal of Experimental Botany 34, 529–536. open url image1

Minchin PEH, Thorpe MR (1984) Apoplastic unloading into the stem of bean. Journal of Experimental Botany 35, 538–550. open url image1

Minchin PEH, Thorpe MR (1987) Measurement of unloading and reloading of photo-assimilate within the stem of bean. Journal of Experimental Botany 38, 211–220. open url image1

Minchin PEH, Lang A, Thorpe MR (1983) Dynamics of cold induced inhibition of phloem transport. Journal of Experimental Botany 34, 156–162. open url image1

Minchin PEH, Ryan KG, Thorpe MR (1984) Further evidence of apoplastic unloading into the stem of bean: identification of the phloem buffering pool. Journal of Experimental Botany 35, 1744–1753. open url image1

Pickard WF, Minchin PEH (1990) The transient inhibition of phloem translocation in Phaseolus vulgaris by abrupt temperature drops, vibration, and electric shock. Journal of Experimental Botany 41, 1361–1369. open url image1

Plieth C, Hansen UP, Knight H, Knight MR (1999) Temperature sensing by plants: the primary characteristics of signal perception and calcium response. The Plant Journal 18, 491–497.
Crossref | GoogleScholarGoogle Scholar | PubMed | open url image1

Thompson MV, Holbrook NM (2004) Scaling phloem transport: information transmission. Plant, Cell and Environment 27, 509–519. open url image1

Thorpe MR, Minchin PEH (1996) Mechanisms of long- and short-distance transport from source to sinks. ‘Photoassimilate distribution in plants and crops — source-sink relationships’. (Eds E Zamski, AA Schaffer) pp. 261–282. (Marcel Dekker Inc., New York)

Thorpe MR, Minchin PEH, Gould N, McQueen J () The stem apoplast: a potential communication channel in plant growth regulation. ‘Vascular transport in plants’. (Eds NM Holbrook, MA Zwieniecki) (Elsevier Academic Publishing: Jordan Hill, UK)

van Bel AJE (2003) The phloem, a miracle of ingenuity. Plant, Cell and Environment 26, 125–149.
Crossref | GoogleScholarGoogle Scholar | open url image1

Weatherley PE, Peel AJ, Hill GP (1959) The physiology of the sieve tube. Preliminary experiments with aphid mouth parts. Journal of Experimental Botany 10, 1–16. open url image1

Wright JP, Fisher DB (1983) Estimation of the volumetric elastic modulus and membrane hydraulic conductivity of willow sieve tubes. Plant Physiology 73, 1042–1047. open url image1