Phloem transport and differential unloading in pea seedlings after source and sink manipulations

Planta ◽  
1994 ◽  
Vol 192 (2) ◽  
pp. 239-248 ◽  
Author(s):  
Alexander Schulz
Keyword(s):  
Phloem Transport ◽  
Pea Seedlings ◽  
Source And Sink

scholarly journals Testing the Münch hypothesis of long distance phloem transport in plants

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Michael Knoblauch ◽  
Jan Knoblauch ◽  
Daniel L Mullendore ◽  
Jessica A Savage ◽  
Benjamin A Babst ◽  
...  
Keyword(s):  
Strong Support ◽  
Sieve Tube ◽  
Phloem Transport ◽  
Plant Tissues ◽  
Long Distance ◽  
Pressure Flow ◽  
Long Distance Transport ◽  
Sieve Tubes ◽  
Distance Transport ◽  
Source And Sink

Long distance transport in plants occurs in sieve tubes of the phloem. The pressure flow hypothesis introduced by Ernst Münch in 1930 describes a mechanism of osmotically generated pressure differentials that are supposed to drive the movement of sugars and other solutes in the phloem, but this hypothesis has long faced major challenges. The key issue is whether the conductance of sieve tubes, including sieve plate pores, is sufficient to allow pressure flow. We show that with increasing distance between source and sink, sieve tube conductivity and turgor increases dramatically in Ipomoea nil. Our results provide strong support for the Münch hypothesis, while providing new tools for the investigation of one of the least understood plant tissues.

Consequences of phloem pathway unloading/reloading on equilibrium flows between source and sink: a modelling approach

2017 ◽  
Vol 44 (5) ◽  
pp. 507 ◽  
Author(s):  
Peter E. H. Minchin ◽  
André Lacointe
Keyword(s):  
Large Fraction ◽  
Phloem Transport ◽  
Solute Concentration ◽  
Sources And Sinks ◽  
Pressure Profiles ◽  
Flow Mechanisms ◽  
Source Sink ◽  
Pressure Driven Flow ◽  
Source And Sink ◽  
Modelling Approach

It is now accepted that the transport phloem, linking major sources and sinks, is leaky, and this leakage can be considerable. Hence for phloem transport to function over the long distances observed, a large fraction of this unloaded photosynthate must be reloaded. A fraction of this unloaded solute is used to maintain tissues surrounding the phloem, as well as being stored. Also, pathway unloading/reloading acts as a short-term buffer to source and sink changes. In this work we present the first attempt to include both pathway unloading and reloading of carbohydrate in the modelling of pressure driven flow to determine if this has any significant effect upon source–sink dynamics. Our results indicated that the flow does not follow Poiseuille dynamics, and that pathway unloading alters the solute concentration and hydrostatic pressure profiles. Hence, measurement of either of these without considerable other detail tells us very little about the flow mechanisms. With adequate reloading along the pathway, the effects of pathway unloading can completely compensate for, making the entire system look like one with no pathway unloading.

Modelling phloem transport within a pruned dwarf bean: a 2-source-3-sink system

2011 ◽  
Vol 38 (2) ◽  
pp. 127 ◽  
Author(s):  
Michael R. Thorpe ◽  
André Lacointe ◽  
Peter E. H. Minchin
Keyword(s):  
Mechanistic Model ◽  
Phloem Transport ◽  
Phaseolus Vulgaris L ◽  
Model Predictions ◽  
Complex Architectures ◽  
Treatment Responses ◽  
Model Platform ◽  
Bidirectional Flow ◽  
Source And Sink ◽  
Dwarf Bean

A mechanistic model of carbon partitioning, based on the Münch hypothesis of phloem transport and implemented with PIAF-Münch modelling platform (Lacointe and Minchin 2008), was tested for an architecture more complex than any tested previously. Using 11C to label photosynthate, responses in transport of photosynthate within a heavily pruned dwarf bean plant (Phaseolus vulgaris L.) to changes in source and sink activities were compared with model predictions. The observed treatment responses were successfully predicted. However, the observations could not be completely explained if the modelled stem contained only one phloem pathway: tracer from a labelled leaf was always detected in both shoot apex and root, whichever of the two leaves was labelled. This shows that bidirectional flow occurred within the stem, with solute moving simultaneously in both directions. Nevertheless, a model architecture with very little more complexity could incorporate such bidirectional flow. We concluded that the model could explain the observations, and that the PIAF-Münch model platform can be expected to describe partitioning in even more complex architectures.

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