Phloem unloading in Arabidopsis roots is convective and regulated by the phloem- pole pericycle
Date
2017-02-23
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Publisher
eLIFE Sciences Publications
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.
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Citation
Ross-Elliott, Timothy J., et al. "Phloem unloading in Arabidopsis roots is convective and regulated by the phloem-pole pericycle." Elife 6 (2017): e24125.