Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle
- Washington State University, United States
- Technical University of Denmark, Denmark
- Oxford Brookes University, United Kingdom
- University of Edinburgh, United Kingdom
- University of Cambridge, United Kingdom
- University of Delaware, 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.
Article and author information
Author details
Alexander G Monteith
Funding
National Science Foundation (1146500)
- Michael Knoblauch
Biotechnology and Biological Sciences Research Council
- Karl John Oparka
Carlsbergfondet
- Kaare H Jensen
Villum Fonden (13166)
- Kaare H Jensen
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2017, Ross-Elliott et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle
eLife 6:e24125.
https://doi.org/10.7554/eLife.24125
