172 CHAPTER 36 2009 TRANSPORT IN PLANTS

Document Sample
172 CHAPTER 36 2009 TRANSPORT IN PLANTS Powered By Docstoc
					 Biology 172

    Chapter 36
Transport in Plants
Figure 36.0x Trees
Figure 36.1 An overview of transport in whole plants (Layer 4)
Concept 36.1: Land plants acquire resources
      both above and below ground

• The algal ancestors of land plants absorbed water,
  minerals, and CO2 directly from the surrounding water
• The evolution of xylem and phloem in land plants made
  possible the long-distance transport of water, minerals,
  and products of photosynthesis
• Adaptations in each species represent compromises
  between enhancing photosynthesis and minimizing
  water loss
     Shoot Architecture and Light
              Capture
• Stems serve as conduits for water and
  nutrients, and as supporting structures for
  leaves
• Phyllotaxy, the arrangement of leaves on a
  stem, is specific to each species
• 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
• Leaf orientation affects light absorption
Fig. 36-4


                                 Ground area
                               covered by plant




                    Plant A                         Plant B
               Leaf area = 40%                 Leaf area = 80%
                of ground area                  of ground area
            (leaf area index = 0.4)         (leaf area index = 0.8)
   Three Levels of Transport
• Uptake and release of water and solutes
  by individual cells.
• Cell to cell transport.
• Long distance transport.
• Water moves from a solution of high water
  potential to one of low water potential.
• Pressure Measured in Megapascals =
  Approx. 10 atmospheres
Transport and Selective
     Premeability
  •Passive Transport
    •Transport Proteins
    •Selective Channels
  •Active transport
  •Proton Pumps
    •K+ Uptake
  •Cotransport
    •NO3-
Figure 36.2 A chemiosmotic model of solute transport in plant cells
Impacts on Water Potential
•Pure Water in Open Container – Zero Water
                                 Potential
•Add Solute, Lower Water Potential
•Increase Pressure – Raise Water Potential
•Negative Pressure of Tension will Move
  Water Across the Membrane
•Water Potential = Pressure Potential +
                    Solute Potential
Figure 36.3 Water potential and water movement: a mechanical model
Water Potential and Plants
     •Plasmolysis
     •Turgor Pressure
     •Aquaporins
     •Tonoplast
     •Symplast
     •Apoplast
     Transport Within Plant
           Tissues
•Transport Within Tissues
   •Symplast
   •Apoplast
•Long Distance Transport by Bulk Flow
   •Movement due to Pressure Differences
     •Transpiration
     •Hydrostatic Pressure - Phloem
Figure 36.4 Water relations of plant cells
Figure 36.5 A watered tomato plant regains its turgor
       Absorption of Water and
              Minerals

Soil     Epidermis   Root Cortex   Xylem

Soil     Epidermis
  •Root Hairs
  •Mycorrhizae
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 most trees
• Roots and the hyphae of soil fungi form
  symbiotic associations called
  mycorrhizae
• Mutualisms with fungi helped plants
  colonize land
Fig. 36-5



            2.5 mm
Absorption of Water and
       Minerals
Epidermis      Root Cortex

  •Apoplastic Route
  •Symplastic Route
  •Active Transport of Minerals
  •K+ Pulled into cell due to
   electrochemical gradient.
Figure 36.6 Compartments of plant cells and tissues and routes for lateral transport
Fig. 36-12a




                                                  Casparian strip

                                    Plasma
                                    membrane
                       Apoplastic
                       route


                                                                                Vessels
                                                                                (xylem)
          Symplastic         Root
          route              hair



                                      Epidermis            Endodermis   Stele
                                                                        (vascular
                                                  Cortex                cylinder)
     Absorption of Water and
            Minerals
Root Cortex      Xylem

•Minerals Must use Symplastic Route
•Endodermis and Casparian Strip
•Minerals in Apoplast are Stopped by Endodermis
•Must Pass Through at Least One Membrane
•Allows Ion Selection
Fig. 36-12b



                         Casparian strip
                        Endodermal cell
        Pathway along
        apoplast


        Pathway
        through
        symplast
   Transport of Xylem Sap

Effective Delivery of Water and Minerals
  •Up To 15m per Hour
  •Xylem in Roots to Leaves
  •Transpiration
  •Upward Flow of Water or Minerals
  •Push or Pull?
  Pushing the Xylem Sap
•Root Pressure
  •Ions Pumped into Stele
  •Osmotic Uptake of Water Creates
    Pressure
  •Guttation – Exudation of Water
  •Hydrathodes
  •Can’t Keep up With Transpiration
  •Can Only Push Water a few Meters
Figure 36.9 Guttation
     Pulling the Xylem Sap
•Transpiration - Cohesion Pull
   •Solar Powered
   •Evaporation of Water From Leaf
   •Creates Negative Water Pressure in
    Leaves
   •Water Film Into Cell Wall Pores
   •Water Pulled Through Symplast and
    Apoplast of Mesophyll
   •Water From Xylem Replaces Lost Water
Figure 36.10 The generation of transpirational pull in a leaf
  Cohesion and Adhesion
H Bonding
•Maintains a Column of Water
•Problem
  •Cavitation – Vapor Pocket
•Solution
  •Can’t be Refilled Except by Root
   Pressure
  •Pits – Detours
  •Secondary Growth
Figure 36.11 Ascent of water in a tree
Fig. 36-15a




                             Water
                             molecule

                             Root
                             hair
                             Soil
                             particle

                             Water
              Water uptake
              from soil
Fig. 36-15b


                             Adhesion
                             by hydrogen
                             bonding
               Xylem                  Cell
               cells                  wall




                             Cohesion
              Cohesion and   by hydrogen
              adhesion in    bonding
              the xylem
Fig. 36-15c




                               Xylem
                               sap
                               Mesophyll
                               cells
                               Stoma

                               Water
                               molecule
              Transpiration
                              Atmosphere
    Control of Transpiration

•Guard Cells
•Photosynthesis-Transpiration Compromise
   •Need for Water
   •Minerals to Leaves
   •Evaporative Cooling
•Transpiration-to-Photosynthesis
 Compromise
   •g H2O lost/g CO2
   •6000:1 for C3 Plants; 300:1 for C4
Figure 36.12 An open (left) and closed (right) stoma of a spider plant (Chlorophytum
                                   colosum) leaf
    Guard Cell Function
•Cells Buckle and Open When Turgid
•Close When Flaccid
•K+ Uptake Lowers Guard Cell Water
 Potential
•Uptake of K+ is countered by Uptake
 of Cl- and Export of H+
Figure 36.13a The mechanism of stomatal opening and closing
Figure 36.13b The mechanism of stomatal opening and closing
       Stomata Regulators
•Opening
  •Light Induces K+ Uptake
     •Blue Light Receptors Stimulate
      Proton Pumps
     •Photosynthesis in Guard Cells
      Produces ATP for H+ Pumps
  •Decrease in Mesophyll CO2
  •Circadian Rhythm
      Stomata Regulators

•Closing
  •K+ Exits the Guard Cells
  •Closing During Day
  •Water Deficiency
  •Mesophyll Production of Abscisic
   Acid
  •High Temp. Increases CO2 in
    Mesophyll due to Respiration
Xerophytes and Transpiration

 •Small Thick Leaves
 •Thick Cuticle
 •Stomata of Underside of Leaf
 •Shed Leaves in Dry Season
 •Store Water in Stems
 •Crassulacean Acid Metabolism (CAM)
Figure 36.15 Structural adaptations of a xerophyte leaf
  Phloem Loading and
       Unloading

•Translocation
•Sieve Tube Member/Sieve Plate
•Directional of Flow
•Sucrose Loading – Source
•Sucrose Unloading – Sink
•Symplast or Symplast/Apoplast
       Phloem Loading and
            Unloading
•Transfer Cells
•H+ Pump – Creates Potential for
 Sucrose Cotransport
•Pressure Flow – 1m per Hour
•Loading End – High Solute Concentration
•Hydrostatic Pressure Greatest at Loading
 End
•Unloading End - High Solute
 Concentration Outside Pholem
Fig. 36-19b




              High H+ concentration           Cotransporter
                    Proton           H+
                    pump                                S




              ATP                                      Sucrose
                              H+         H+
                                                   S
              Low   H+   concentration
Figure 36.16 Loading of sucrose into phloem
Figure 36.17 Pressure flow in a sieve tube
Figure 36.18 Tapping phloem sap with the help of an aphid

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:28
posted:7/27/2012
language:English
pages:49