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Phloem and Sugar Transport

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.

Short-distance Transport of Resources

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.

Cellular Membranes and Drug Transport

Cellular Membranes and Drug Transport

Drugs must traverse multiple biological barriers, such as multi-layered skin, single-layered intestinal epithelium, and the plasma membrane, to reach their target sites within the body. The plasma membrane, a highly structured composite of phospholipids, carbohydrates, and proteins, is the cell's protective boundary, facilitating selective substance exchange.
Phospholipids arrange themselves into a bilayer, with hydrophilic heads oriented outward and hydrophobic tails facing inward.

The Apoplast and Symplast

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...

Mechanisms of Drug Absorption: Paracellular, Transcellular, and Vesicular Transport

Mechanisms of Drug Absorption: Paracellular, Transcellular, and Vesicular Transport

Drugs need to permeate cell membranes to reach their target sites after administration. Orally administered drugs must transcend intestinal epithelial membrane barriers to infiltrate the systemic circulation. Drugs with a molecular weight of less than 500 Daltons diffuse through gaps between neighboring cells, called paracellular pathways.
However, most drugs use the transcellular route, traversing directly through the cell membranes via two mechanisms: passive and active transport. Passive...

Transcellular Transport of Solutes

Transcellular 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...

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Image-Based Methods to Study Membrane Trafficking Events in Stomatal Lineage Cells

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Published on: May 12, 2023

Phloem transport: cellular pathways and molecular trafficking.

Robert Turgeon¹, Shmuel Wolf

¹Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA. ert2@cornell.edu

Annual Review of Plant Biology

|November 26, 2008

Summary

Phloem sap sampling is challenging due to sieve tube damage. This review covers sampling methods, transport pathways, and mobile compounds like proteins and RNA in vascular plants.

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Area of Science:

Plant Biology
Plant Physiology
Molecular Biology

Background:

The phloem is crucial for transporting nutrients, defensive compounds, and signals in vascular plants.
Sampling phloem sap is difficult due to the pressurized nature of sieve tubes, often causing damage and artifacts.
Understanding phloem transport is vital for plant communication and development.

Purpose of the Study:

To review current methods for sampling phloem sap.
To discuss artifacts introduced by sampling procedures.
To explore the complex pathways and compounds transported within the phloem, including macromolecules.

Main Methods:

Literature review of phloem sampling techniques.
Analysis of artifacts associated with different sampling methods.
Examination of plasmodesmatal conductivity and transporter roles in phloem loading/unloading.

Main Results:

Phloem sap sampling methods can introduce artifacts.
Phloem transport involves intricate pathways for nutrients, defensive compounds, and signals.
Mobile proteins and RNA are key components of long-distance plant communication.

Conclusions:

Effective phloem sap sampling remains a challenge.
Macromolecular trafficking, including proteins and RNA, plays a significant role in plant signaling.
Future research should focus on dissecting the molecular and cellular mechanisms of long-distance macromolecular transport.