Consequences of phloem pathway unloading/reloading on equilibrium flows between source and sink: a modelling approach
Peter E. H. Minchin A D and André Lacointe B CA The New Zealand Institute for Plant and Food Research Ltd (PFR), 412 No. 1 Rd, Te Puke 3182, New Zealand.
B UCA, INRA, UMR PIAF, F-63000 Clermont-Ferrand, France.
C Clermont Université, Université Blaise Pascal, UMR547 PIAF, Clermont-Ferrand, France.
D Corresponding author. Email: peter.minchin@plantandfood.co.nz
Functional Plant Biology 44(5) 507-514 https://doi.org/10.1071/FP16354
Submitted: 13 June 2016 Accepted: 12 January 2017 Published: 23 February 2017
Abstract
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.
Additional keywords: modelling, Münch, pathway reloading, pathway unloading, phloem transport.
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