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Related Experiment Videos

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

J. W. Patrick1

  • 1Department of Biological Sciences, The University of Newcastle, New South Wales 2308, Australia.

Annual Review of Plant Physiology and Plant Molecular Biology
|June 1, 1997
PubMed
Summary

Phloem unloading is a vital process linking plant transport and sink metabolism. Understanding symplasmic and apoplasmic pathways is key to nutrient partitioning in plants.

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Area of Science:

  • Plant Physiology
  • Molecular Biology
  • Biochemistry

Background:

  • Phloem unloading connects phloem transport to sink metabolism and nutrient partitioning.
  • The cellular pathway and mechanism of unloading dictate the nature of this linkage.
  • Symplasmic unloading is common, while apoplasmic steps are specialized.

Purpose of the Study:

  • To elucidate the mechanisms and pathways of phloem unloading.
  • To understand the regulation of transport from sieve elements to sink cells.
  • To investigate the role of plasmodesmata and membrane transport in nutrient allocation.

Main Methods:

  • Analysis of transport pathways (symplasmic vs. apoplasmic).
  • Investigation of plasmodesmal conductivity and its role in diffusion and bulk flow.

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  • Characterization of membrane transport mechanisms (diffusion, facilitated, energy-coupled).

    • Main Results:

    • Symplasmic unloading is the predominant pathway, regulated by plasmodesmal conductivity.
    • Bulk flow becomes significant with increasing import rates.
    • Apoplasmic unloading involves diffusion, facilitated, or energy-coupled transport across plasma membranes.
    • Sugar accumulation in the sink apoplasm utilizes sugar/proton symport.

    Conclusions:

    • Phloem unloading is a complex process involving regulated transport across cellular compartments.
    • Plasmodesmata and plasma membrane transporters are critical for efficient nutrient delivery to sinks.
    • Understanding these mechanisms is crucial for optimizing plant growth and crop yield.