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Elife. 2017 Feb 23;6. pii: e24125. doi: 10.7554/eLife.24125.

Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle.

Author information

1
School of Biological Sciences, Washington State University, Pullman, United States.
2
Department of Physics, Technical University of Denmark, Lyngby, Denmark.
3
Department of Biological and Medical Sciences, Oxford Brookes University, Headington, Oxford, United Kingdom.
4
Institute of Molecular Plant Science, University of Edinburgh, Edinburgh, United Kingdom.
5
Sainsbury Laboratory, University of Cambridge, Cambridge, United Kingdom.
6
Department of Plant and Soil Sciences, Delaware Biotechnology Institute, University of Delaware, Newark, United States.

Abstract

In plants, a complex mixture of solutes and macromolecules is transported by the phloem. Here, we examined how solutes and macromolecules are separated when they exit the phloem during the unloading process. We used a combination of approaches (non-invasive imaging, 3D-electron microscopy, and mathematical modelling) to show that phloem unloading of solutes in Arabidopsis roots occurs through plasmodesmata by a combination of mass flow and diffusion (convective phloem unloading). During unloading, solutes and proteins are diverted into the phloem-pole pericycle, a tissue connected to the protophloem by a unique class of 'funnel plasmodesmata'. While solutes are unloaded without restriction, large proteins are released through funnel plasmodesmata in discrete pulses, a phenomenon we refer to as 'batch unloading'. Unlike solutes, these proteins remain restricted to the phloem-pole pericycle. Our data demonstrate a major role for the phloem-pole pericycle in regulating phloem unloading in roots.

KEYWORDS:

A. thaliana; funnel plasmodesmata; long distance signaling; phloem; phloem pole pericycle; phloem unloading; plant biology; protophloem

PMID:
28230527
PMCID:
PMC5365319
DOI:
10.7554/eLife.24125
[Indexed for MEDLINE]
Free PMC Article

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