PHLOEM UNLOADING: Sieve Element Unloading and Post-Sieve Element Transport

PHLOEM UNLOADING: Sieve Element Unloading and Post-Sieve Element Transport ▪ Abstract The transport events from the sieve elements to the sites of utilization within the recipient sink cells contribute to phloem unloading. The phenomenon links sink metabolism and/or compartmentation with phloem transport to, and partitioning between, sinks. The nature of the linkage depends upon the cellular pathway and mechanism of unloading. The common unloading pathway is symplasmic, with an apoplasmic step at or beyond the sieve element boundary reserved for specialized situations. Plasmodesmal conductivity exerts the primary control over symplasmic transport that occurs by diffusion with bulk flow anticipated to be of increasing significance as import rate rises. In the case of an apoplasmic step, efflux across the plasma membranes of the vascular cells occurs by simple diffusion, whereas efflux from nonvascular cells of developing seeds is facilitated and, in some cases, energy coupled. Accumulation of sugars from the sink apoplasm universally occurs by a plasma membrane–bound sugar/proton symport mechanism. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Annual Review of Plant Biology Annual Reviews

PHLOEM UNLOADING: Sieve Element Unloading and Post-Sieve Element Transport

Annual Review of Plant Biology, Volume 48 (1) – Jun 1, 1997

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Publisher
Annual Reviews
Copyright
Copyright © 1997 by Annual Reviews Inc. All rights reserved
Subject
Review Articles
ISSN
1040-2519
D.O.I.
10.1146/annurev.arplant.48.1.191
Publisher site
See Article on Publisher Site

Abstract

▪ Abstract The transport events from the sieve elements to the sites of utilization within the recipient sink cells contribute to phloem unloading. The phenomenon links sink metabolism and/or compartmentation with phloem transport to, and partitioning between, sinks. The nature of the linkage depends upon the cellular pathway and mechanism of unloading. The common unloading pathway is symplasmic, with an apoplasmic step at or beyond the sieve element boundary reserved for specialized situations. Plasmodesmal conductivity exerts the primary control over symplasmic transport that occurs by diffusion with bulk flow anticipated to be of increasing significance as import rate rises. In the case of an apoplasmic step, efflux across the plasma membranes of the vascular cells occurs by simple diffusion, whereas efflux from nonvascular cells of developing seeds is facilitated and, in some cases, energy coupled. Accumulation of sugars from the sink apoplasm universally occurs by a plasma membrane–bound sugar/proton symport mechanism.

Journal

Annual Review of Plant BiologyAnnual Reviews

Published: Jun 1, 1997

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