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Short-distance Transport of Resources02:12

Short-distance Transport of Resources

Short-distance transport refers to transport that occurs over a distance of just 2-3 cells, crossing the plasma membrane in the process. Small uncharged molecules, such as oxygen, carbon dioxide, and water, can diffuse across the plasma membrane on their own. In contrast, ions and larger molecules require the assistance of transport proteins due to their charge or size. Transport across membranes also occurs within individual cells, playing a variety of essential roles for the plant as a whole.
Xylem and Transpiration-driven Transport of Resources02:03

Xylem and Transpiration-driven Transport of Resources

The xylem of vascular plants distributes water and dissolved minerals that are taken up by the roots to the rest of the plant. The cells that transport xylem sap are dead upon maturity, and the movement of xylem sap is a passive process.
Phloem and Sugar Transport02:02

Phloem and Sugar Transport

Like many living organisms, plants have tissues that specialize in specific plant functions. For example, shoots are well adapted to rapid growth, while roots are structured to acquire resources efficiently. However, sugar production is primarily restricted to the photosynthetic cells that reside in the leaves of angiosperm plants. Sugar and other resources are transported from photosynthetic tissues to other specialized tissues by a process called translocation.
The Apoplast and Symplast01:46

The Apoplast and Symplast

Plant growth depends on its ability to take up water and dissolved minerals from the soil. The root system of every plant is equipped with the necessary tissues to facilitate the entry of water and solutes. The plant tissues involved in the transport of water and minerals have two major compartments - the apoplast and the symplast. The apoplast includes everything outside the plasma membrane of living cells and consists of cell walls, extracellular spaces, xylem, phloem, and tracheids. The...
Delivery Pathways to the Lysosome01:36

Delivery Pathways to the Lysosome

Eukaryotic cells use different mechanisms to eliminate toxic waste obsolete and worn-out substances. Lysosomes play a pivotal role in this, and hence, these substances are carried to the lysosome from other parts of the cell and extracellular space through different pathways. The most elaborately studied pathways to the lysosome are the endocytic pathways.
Endocytosis
In endocytosis, the cell membrane takes up macromolecules and particles from the surrounding medium. Clathrin-mediated...
Membrane Asymmetry Regulating Transporters01:19

Membrane Asymmetry Regulating Transporters

Enzymes like flippase, floppase, and scramblase transfer phospholipids from one layer to another in the membrane, thereby affecting membrane asymmetry.
Flippase
Eukaryotic flippases are type-IV P-type ATPases or P4-ATPases belonging to P-type ATPase family proteins that are membrane-bound pumps involved in the ATP-mediated transport of ions and molecules across the membrane. Flippases flip specific phospholipids from the outer to the inner leaflet of a membrane. All P4-ATPases have one...

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Related Experiment Video

Updated: Jun 1, 2026

Technique for Studying Arthropod and Microbial Communities within Tree Tissues
05:30

Technique for Studying Arthropod and Microbial Communities within Tree Tissues

Published on: November 16, 2014

What is Phloem unloading?

K J Oparka1

  • 1Department of Cellular and Environmental Physiology, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, United Kingdom.

Plant Physiology
|October 1, 1990
PubMed
Summary
This summary is machine-generated.

Phloem unloading mechanisms remain unclear, with difficulty distinguishing transport across cell boundaries. Research highlights complexities in sugar movement within plant sinks, necessitating further investigation into symplastic and apoplastic pathways.

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Published on: January 9, 2018

Area of Science:

  • Plant Physiology
  • Molecular Biology
  • Biochemistry

Background:

  • Distinguishing phloem unloading events at the sieve element/companion cell (SE/CC) boundary from subsequent short-distance transport in parenchyma cells is challenging.
  • Previous research suggests symplastic unloading in storage and utilization sinks, but evidence for apoplastic unloading is equivocal.
  • The role of apoplastic acid invertase in phloem unloading is also debated.

Purpose of the Study:

  • To critically evaluate current understanding of phloem unloading pathways in plant sinks.
  • To address the ambiguity surrounding symplastic versus apoplastic unloading mechanisms.
  • To highlight the complexities of sugar transport post-unloading and identify future research directions.

Main Methods:

  • Review and synthesis of existing scientific literature on phloem unloading.
  • Analysis of indirect evidence for symplastic and apoplastic transport routes.
  • Discussion of experimental challenges in pinpointing solute exchange sites.

Main Results:

  • Indirect evidence supports symplastic unloading in many sink types.
  • Evidence for apoplastic phloem unloading is inconclusive, and the role of apoplastic acid invertase is unclear.
  • The ability of sink cells to accumulate sugars from the apoplast is complicated by potential symplastic continuity.

Conclusions:

  • The precise sites of symplast/apoplast solute exchange during phloem unloading are difficult to determine.
  • The post-unloading pathway in sinks is complex and varies significantly.
  • Further research is needed to elucidate the mechanisms and locations of phloem unloading and sugar transport.