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.
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