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Resource Acquisition and Transport in Vascular Plants

Chapter 36. Resource Acquisition and Transport in Vascular Plants. © 2011 Pearson Education, Inc. Overview: Underground Plants. Stone plants ( Lithops ) are adapted to life in the desert Two succulent leaf tips are exposed above ground; the rest of the plant lives below ground. Figure 36.1.

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Resource Acquisition and Transport in Vascular Plants

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  1. Chapter 36 Resource Acquisition and Transport in Vascular Plants

  2. © 2011 Pearson Education, Inc. Overview: Underground Plants • Stone plants (Lithops) are adapted to life in the desert • Two succulent leaf tips are exposed above ground; the rest of the plant lives below ground

  3. Figure 36.1

  4. © 2011 Pearson Education, Inc. • The success of plants depends on their ability to gather and conserve resources from their environment • The transport of materials is central to the integrated functioning of the whole plant

  5. © 2011 Pearson Education, Inc. Concept 36.1: Adaptations for acquiring resources were key steps in the evolution of vascular plants • The algal ancestors of land plants absorbed water, minerals, and CO2 directly from the surrounding water • Early nonvascular land plants lived in shallow water and had aerial shoots • Natural selection favored taller plants with flat appendages, multicellular branching roots, and efficient transport

  6. © 2011 Pearson Education, Inc. • The evolution of xylem and phloem in land plants made possible the long-distance transport of water, minerals, and products of photosynthesis • Xylem transports water and minerals from roots to shoots • Phloem transports photosynthetic products from sources to sinks

  7. Figure 36.2-1 H2O H2Oand minerals

  8. O2 CO2 Figure 36.2-2 H2O O2 H2Oand minerals CO2

  9. O2 CO2 Light Figure 36.2-3 Sugar H2O O2 H2Oand minerals CO2

  10. © 2011 Pearson Education, Inc. • Adaptations in each species represent compromises between enhancing photosynthesis and minimizing water loss

  11. © 2011 Pearson Education, Inc. Shoot Architecture and Light Capture • Stems serve as conduits for water and nutrients and as supporting structures for leaves • There is generally a positive correlation between water availability and leaf size

  12. © 2011 Pearson Education, Inc. • Light absorption is affected by the leaf area index, the ratio of total upper leaf surface of a plant divided by the surface area of land on which it grows • Self-pruning is the shedding of lower shaded leaves when they respire more than photosynthesize

  13. Ground areacovered by plant Figure 36.4 Plant ALeaf area  40%of ground area(leaf area index  0.4) Plant BLeaf area  80%of ground area(leaf area index  0.8)

  14. © 2011 Pearson Education, Inc. Root Architecture and Acquisition of Water and Minerals • Soil is a resource mined by the root system • Taproot systems anchor plants and are characteristic of gymnosperms and eudicots • Root growth can adjust to local conditions • For example, roots branch more in a pocket of high nitrate than low nitrate • Roots are less competitive with other roots from the same plant than with roots from different plants

  15. © 2011 Pearson Education, Inc. • Roots and the hyphae of soil fungi form mutualistic associations called mycorrhizae • Mutualisms with fungi helped plants colonize land • Mycorrhizal fungi increase the surface area for absorbing water and minerals, especially phosphate

  16. Figure 36.5 Roots Fungus

  17. © 2011 Pearson Education, Inc. Concept 36.2: Different mechanisms transport substances over short or long distances • There are two major pathways through plants • The apoplast • The symplast

  18. © 2011 Pearson Education, Inc. The Apoplast and Symplast: Transport Continuums • The apoplast consists of everything external to the plasma membrane • It includes cell walls, extracellular spaces, and the interior of vessel elements and tracheids • The symplast consists of the cytosol of the living cells in a plant, as well as the plasmodesmata

  19. © 2011 Pearson Education, Inc. • Three transport routes for water and solutes are • The apoplastic route, through cell walls and extracellular spaces • The symplastic route, through the cytosol • The transmembrane route, across cell walls

  20. Figure 36.6 Cell wall Apoplastic route Cytosol Symplastic route Transmembrane route Key Plasmodesma Apoplast Plasma membrane Symplast

  21. © 2011 Pearson Education, Inc. Short-Distance Transport of Solutes Across Plasma Membranes • Plasma membrane permeability controls short-distance movement of substances • Both active and passive transport occur in plants • In plants, membrane potential is established through pumping H by proton pumps • In animals, membrane potential is established through pumping Na by sodium-potassium pumps

  22. Figure 36.7a EXTRACELLULAR FLUID CYTOPLASM  + H+ Hydrogen ion  + ATP  + H+ H+ H+ H+ H+ H+  + H+ Proton pump  + (a) H+ and membrane potential

  23. © 2011 Pearson Education, Inc. • Plant cells use the energy of H gradients to cotransport other solutes by active transport

  24. Figure 36.7b  + H+ H+ S  H+ + H+  H+ + H+ H+ S S H+ H+ H+ S S S  + H+  + Sucrose(neutral solute) H+/sucrosecotransporter  + (b) H+ and cotransport of neutral solutes

  25. Figure 36.7c  + H+ H+ NO3  + NO3 H+  + H+ H+ H+ Nitrate H+ H+ NO3 NO3 NO3  + NO3  + H+ H+NO3cotransporter H+ H+  + (c) H+ and cotransport of ions

  26. © 2011 Pearson Education, Inc. • Plant cell membranes have ion channels that allow only certain ions to pass

  27. Figure 36.7d  + Potassium ion K+  + K+  + K+ K+ K+ K+ K+  + Ion channel  + (d) Ion channels

  28. © 2011 Pearson Education, Inc. Short-Distance Transport of Water Across Plasma Membranes • To survive, plants must balance water uptake and loss • Osmosis determines the net uptake or water loss by a cell and is affected by solute concentration and pressure

  29. © 2011 Pearson Education, Inc. • Water potential is a measurement that combines the effects of solute concentration and pressure • Water potential determines the direction of movement of water • Water flows from regions of higher water potential to regions of lower water potential • Potential refers to water’s capacity to perform work

  30. © 2011 Pearson Education, Inc. • Water potential is abbreviated as Ψand measured in a unit of pressure called the megapascal (MPa) • Ψ = 0 MPa for pure water at sea level and at room temperature

  31. © 2011 Pearson Education, Inc. How Solutes and Pressure Affect Water Potential • Both pressure and solute concentration affect water potential • This is expressed by the water potential equation: Ψ  ΨS ΨP • The solute potential (ΨS) of a solution is directly proportional to its molarity • Solute potential is also called osmotic potential

  32. © 2011 Pearson Education, Inc. • Pressure potential (ΨP) is the physical pressure on a solution • Turgor pressure is the pressure exerted by the plasma membrane against the cell wall, and the cell wall against the protoplast • The protoplast is the living part of the cell, which also includes the plasma membrane

  33. © 2011 Pearson Education, Inc. • Considera U-shaped tube where the two arms are separated by a membrane permeable only to water • Water moves in the direction from higher water potential to lower water potential

  34. Figure 36.8a Solutes have a negative effect on  by binding water molecules. Adding solutes to the right arm makes  lower there, resulting in net movement of water to the right arm: Pure water at equilibrium Pure water Solutes Membrane H2O H2O

  35. Positive pressure has a positive effect on  by pushing water. Figure 36.8b Applying positive pressure to the right arm makes  higher there, resulting in net movement of water to the left arm: Positivepressure Pure water at equilibrium H2O H2O

  36. Solutes and positive pressure have opposing effects on watermovement. Figure 36.8c In this example, the effect of adding solutes is offset by positive pressure, resulting in no net movement of water: Positivepressure Pure water at equilibrium Solutes H2O H2O

  37. Negative pressure (tension) has a negative effect on  by pulling water. Figure 36.8d Applying negative pressure to the right arm makes lower there, resulting in net movement of water to the right arm: Negativepressure Pure water at equilibrium H2O H2O

  38. © 2011 Pearson Education, Inc. Water Movement Across Plant Cell Membranes • Water potential affects uptake and loss of water by plant cells • If a flaccid cell is placed in an environment with a higher solute concentration, the cell will lose water and undergo plasmolysis • Plasmolysis occurs when the protoplast shrinks and pulls away from the cell wall Video: Plasmolysis

  39. P 0  S 0.7   0.7 MPa  P 0  S 0.9   0.9 MPa  P 0  S 0.9   0.9 MPa  Figure 36.9 Initial flaccid cell: 0.4 M sucrose solution: Pure water: P 0  S 0   0 MPa Turgid cellat osmoticequilibrium withits surroundings Plasmolyzedcell at osmoticequilibrium withits surroundings  P 0.7  S 0.7   0 MPa  (a) Initial conditions: cellular  environmental  (b) Initial conditions: cellular  environmental 

  40. P 0  0.7 S  0.7 MPa   P 0  0.9 S  0.9 MPa   0 P  0.9 S  0.9 MPa   Figure 36.9a Initial flaccid cell: 0.4 M sucrose solution: Plasmolyzedcell at osmoticequilibrium withits surroundings (a) Initial conditions: cellular  environmental 

  41. P 0  0.7 S  0.7 MPa   P 0  S 0  0 MPa   P 0.7  S 0.7   0 MPa  Figure 36.9b Initial flaccid cell: Pure water: Turgid cellat osmoticequilibrium withits surroundings (b) Initial conditions: cellular  environmental 

  42. © 2011 Pearson Education, Inc. • If a flaccid cell is placed in a solution with a lower solute concentration, the cell will gain water and become turgid • Turgor loss in plants causes wilting, which can be reversed when the plant is watered Video: Turgid Elodea

  43. © 2011 Pearson Education, Inc. Aquaporins: Facilitating Diffusion of Water • Aquaporins are transport proteins in the cell membrane that allow the passage of water • These affect the rate of water movement across the membrane

  44. © 2011 Pearson Education, Inc. Long-Distance Transport: The Role of Bulk Flow • Efficient long distance transport of fluid requires bulk flow, the movement of a fluid driven by pressure • Water and solutes move together through tracheids and vessel elements of xylem, and sieve-tube elements of phloem • Efficient movement is possible because mature tracheids and vessel elements have no cytoplasm, and sieve-tube elements have few organelles in their cytoplasm

  45. © 2011 Pearson Education, Inc. Concept 36.3: Transpiration drives the transport of water and minerals from roots to shoots via the xylem • Plants can move a large volume of water from their roots to shoots

  46. © 2011 Pearson Education, Inc. Absorption of Water and Minerals by Root Cells • Most water and mineral absorption occurs near root tips, where root hairs are located and the epidermis is permeable to water • Root hairs account for much of the surface area of roots • After soil solution enters the roots, the extensive surface area of cortical cell membranes enhances uptake of water and selected minerals Animation: Transport in Roots

  47. © 2011 Pearson Education, Inc. • The concentration of essential minerals is greater in the roots than soil because of active transport

  48. © 2011 Pearson Education, Inc. Transport of Water and Minerals into the Xylem • The endodermis is the innermost layer of cells in the root cortex • It surrounds the vascular cylinder and is the last checkpoint for selective passage of minerals from the cortex into the vascular tissue

  49. © 2011 Pearson Education, Inc. • Water can cross the cortex via the symplast or apoplast • The waxy Casparian strip of the endodermal wall blocks apoplastic transfer of minerals from the cortex to the vascular cylinder • Water and minerals in the apoplast must cross the plasma membrane of an endodermal cell to enter the vascular cylinder

  50. Casparian strip Endodermalcell Pathway alongapoplast Figure 36.10 Pathwaythroughsymplast Plasmamembrane Casparian strip Apoplasticroute Vessels(xylem) Symplasticroute Roothair Endodermis Epidermis Vascular cylinder(stele) Cortex

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