Passive phloem loading and long-distance transport in a synthetic tree-on-a-chip
Name
Manuscript_revised_Feb21.pdf
Description
Accepted version
Size
1.49 MB
Format
Adobe PDF
Checksum (MD5)
ca1ba0304637a46927c97324fde9c0dc
Author(s)
Comtet, Jean
Jensen, Kaare H
Turgeon, Robert
Stroock, Abraham D
Hosoi, AE
Date Issued
2017
Journal
Nature Plants
Publisher
Springer Science and Business Media LLC
Version
Author's final manuscript
Abstract
© 2017 Macmillan Publishers Limited, part of Springer Nature. All rights reserved. Vascular plants rely on differences in osmotic pressure to export sugars from regions of synthesis (mature leaves) to sugar sinks (roots, fruits). In this process, known as Münch pressure flow, the loading of sugars from photosynthetic cells to the export conduit (the phloem) is crucial, as it sets the pressure head necessary to power long-distance transport. Whereas most herbaceous plants use active mechanisms to increase phloem sugar concentration above that of the photosynthetic cells, in most tree species, for which transport distances are largest, loading seems, counterintuitively, to occur by means of passive symplastic diffusion from the mesophyll to the phloem. Here, we use a synthetic microfluidic model of a passive loader to explore the non-linear dynamics that arise during export and determine the ability of passive loading to drive long-distance transport. We first demonstrate that in our device, the phloem concentration is set by the balance between the resistances to diffusive loading from the source and convective export through the phloem. Convection-limited export corresponds to classical models of Münch transport, where the phloem concentration is close to that of the source; in contrast, diffusion-limited export leads to small phloem concentrations and weak scaling of flow rates with hydraulic resistance. We then show that the effective regime of convection-limited export is predominant in plants with large transport resistances and low xylem pressures. Moreover, hydrostatic pressures developed in our synthetic passive loader can reach botanically relevant values as high as 10 bars. We conclude that passive loading is sufficient to drive long-distance transport in large plants, and that trees are well suited to take full advantage of passive phloem loading strategies.
MIT Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
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DOI of Published Version
https://doi.org/10.1038/NPLANTS.2017.32
