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02:02Phloem 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.
01:46The 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...
02:12Short-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.
01:23Transcellular Transport of Solutes
Transcellular transport of solutes is the movement of substances like monosaccharides and amino acids through polarized cells. This transport mechanism is primarily seen in epithelial and endothelial cells aided by membrane transport proteins such as channels and transporters. The tight junctions between these cells confine the membrane proteins to the two sides of the cell. The epithelial cells have distinct apical and basolateral domains. In contrast, the endothelial cells show the luminal...
02:03Xylem 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.
02:34Water and Mineral Acquisition
Specialized tissues in plant roots have evolved to capture water, minerals, and some ions from the soil. Roots exhibit a variety of branching patterns that facilitate this process. The outermost root cells have specialized structures called root hairs that increase the root surface, thus increasing soil contact. Water can passively cross into roots, as the concentration of water in the soil is higher than that of the root tissue. Minerals, in contrast, are actively transported into root cells.
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Related Experiment Video
Updated: Jun 14, 2026
09:38
Collection and Analysis of Arabidopsis Phloem Exudates Using the EDTA-facilitated Method
Published on: October 23, 2013
The phloem pathway: new issues and old debates.
1Institut National de la Recherche Agronomique, institut Jean-Pierre-Bourgin, route de St-Cyr, Versailles cedex, France. dinant@versailles.inra.fr
Comptes Rendus Biologies
|April 8, 2010
Summary
The plant phloem transports nutrients and signals, with recent studies revealing complex molecular trafficking and long-distance communication. Phloem
Area of Science:
- Plant Biology
- Molecular Biology
- Plant Physiology
Background:
- The phloem is crucial for plant development, nutrient distribution, and interorgan communication.
- Recent research has identified diverse molecules, including proteins, RNAs, and metabolites, within phloem sap, suggesting signaling roles.
- Understanding phloem transport and signaling is key to plant science.
Purpose of the Study:
- To review recent breakthroughs in phloem transport and signaling mechanisms.
- To highlight the dual role of sucrose as both a nutrient and a signal.
- To discuss ongoing debates and new findings in phloem physiology.
Main Methods:
- Analysis of phloem sap composition, including proteins, RNAs, and metabolites.
- Investigation of macromolecular trafficking within sieve elements.
Main Results:
- Sucrose phloem loading is a tightly regulated process with dual nutrient and signaling functions.
- Chaperones and RNA-binding proteins are involved in macromolecular trafficking and ribonucleoprotein complex formation in sieve elements.
- Long-distance signaling integrates electrical waves, calcium bursts, and reactive oxygen species.
- Recent findings challenge the absence of reducing sugars in phloem sap and suggest potential protein synthesis in sieve elements.
Conclusions:
- The phloem plays a central role in plant interorgan nutrient exchange and communication.
- Mechanisms of phloem transport and signaling exhibit species-specific variations.
- Further research is needed to resolve fundamental questions in phloem physiology.