Download Nutrient Uptake, Solute Transport

PLANT PHYSIOLOGY
Az Agrármérnöki MSc szak tananyagfejlesztése
TÁMOP-4.1.2-08/1/A-2009-0010
Nutrient uptake
Solute transport
Overview
1. Ion transport in roots
2. Passive and active transport
3. Membrane transport processes
4. Phloem transport
1. Ion transport in roots
1.1. Solutes move through both apoplast and symplast
1.2. Ions cross both symplast and apoplast
1.3. Xylem parenchima cells participate in xylem loading
Pathways for water and solute uptake by the root
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 89.
Diagram showing electrochemical potentials of K+ and Cl– across a
maize root
Source: Taiz L., Zeiger E. (2002): Plant Physiology. p. 106.
Plasmodesmata connect the cytoplasms of neighbouring cells
facilitating cell-to-cell communication and solute transport
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 154.
2. Passive and active transport
2.1. Concentration gradients and electrical-potential
gradients are integrated by the electrochemical potential
2.2. Movement of solutes across membranes down their
free-energy gradient is called passive transport
mechanisms
2.3. Movement of solutes against their free-energy is
known as active transport and requires energy input
2.4. The Nernst equation distinguishes between active and
passive transport
Relationship between chemical potential and transport (passive, active)
processes
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 133.
Development of a diffusion potential and a charge separation between
two compartments separated by a membrane
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 134.
Diagram of a pair of microelectrodes used to measure membrane
potentials across cell membranes
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 135.
Diagram of the whole-cell and membrane patch configuration
Source: Taiz L., Zeiger E. (2010): Plant Physiology. Web
material, http://5e.plantphys.net
Cyanide (CN-) blocks ATP production that leads to the collapse of the
membrane potential
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 137.
3. Membrane transport processes
3.1. Biological membranes contain specialized proteins
that facilitate solute transport
3.2. Channels enhance diffusion across membranes
3.3. Carriers bind and transport specific substances
3.4. Primary active transport, called pumps, requires direct
energy source
3.5. Secondary active transport uses stored energy
Three classes of membrane transport proteins:
channels, carriers, and pumps
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 138.
Models of K+ channels in plants: (A) top view, and (B) side view of a
channel
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 139.
Carrier transport often shows enzyme kinetics, including saturation
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 143.
Hypothetical model of secondary active transport
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 142.
Two examples of secondary active transport coupled to a primary
proton gradient
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 143.
3. Membrane transport processes
3.6. Cations are transported by both cation channels and
cation carriers
3.7. Anions are transported in the direction of passive
efflux
3.8. Aquaporins forms water channels in membranes
3.9. Plasma membrane H+-ATPases are important for the
regulation of cytoplasmic pH and for the control of cell
turgor
Aquaporin activity is regulated by phosphorilation as well as by pH,
calcium concentration, etc.
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 80.
Hypothetical steps in the transport of a proton against its chemical
gradient by H+-ATPase
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 150.
Ion concentrations in the cytosol and the vacuole are controlled by
passive (dashed arrows) and active (solid arrows) transport
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 136.
Overview of the various transport proteins in the plasma membrane and
tonoplast of plant cell
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 145.
4. Phloem transport
4.1. Pathways of translocation
4.2. Materials translocated in the phloem
4.3. The pressure-flow model, a passive mechanism for
phloem transport
4.4. Photosynthate distribution: allocation and partitioning
4.5. Transport of signaling molecules
Transverse section of a 3-year-old stem of an ash (Fraxinus excelsior)
tree
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 272.
Schematic drawings of mature sieve elements:
(A) external view, (B) longitudinal section
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 273.
ATP-dependent sucrose transport in sieve-element loading
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 287.
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 278.
Pressure-flow model of translocation in the phloem
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 282.
A physical model of the pressure-flow hypothesis for translocation in the
phloem
Source: Hopkins W.G., Hüner N.P.A. (2009): Introduction to
Plant Physiology. p. 162.
A simplified scheme for starch and sucrose synthesis during the day
Source: Taiz L., Zeiger E. (2010): Plant Physiology. p. 295.
Summary
The biological movement of molecules and ions from one
location to another is known as transport. Plants
exchange solutes and water with their environment and
among their tissues and organs. Both local and longdistance transport processes in plants are controlled
largely by cellular membranes. Active and passive
membrane transports are distinguished. Membranes
contain specialized proteins - channels, carriers, and
pumps - that facilitate solute transport.
Translocation in the phloem is the movement of the
products of photosynthesis from mature leaves to areas
of growth and storage. It also transmits chemical signals
and redistributes ions and other substances throughout
the plant body.
Questions
• What is meant by the term "passive transport" and
"active transport"?
• Both membrane channels and carriers show changes in
protein conformation. What is the role of such
conformation changes (a) in channels, and (b) in
carriers?
• In the transport of an ion from the soil solution to the
xylem, what is the minimum number of times it must
cross a cell membrane?
• Describe the pressure-flow model of translocation in the
phloem.
THANK YOU FOR YOUR ATTENTION
Next lecture:
The light reactions of the photosynthesis
Photosynthesis inhibiting herbicides
• Compiled by:
Prof. Vince Ördög
Dr. Zoltán Molnár