Transport%20in%20Plants%20II%20Water%20Balance%20of%20Plants

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Transport in Plants IIWater Balance of Plants

• My empty water dish mocks me.
• - Bob the Dog

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Drop-in Tutoring, 206
Sunday Monday Tuesday Weds. Thurs. Friday
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Days 8 5, OM387 Evenings 6 9,
MH220 650-3855
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Rubus spectabilis Salmonberry
Salmonberry bird
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• Local (NW) flora,
• Ethnobotany,
• Fun!

Buy locally, or at Amazon (16.47).
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Transport

• molecular and ionic movement from one location
  to another,
• H2O,
• Sugars and other organics,
• Ions,
• Gases,
• Proteins, RNA, Hormones, etc.

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Today

• Water,
• Water Potential,
• free energy of water,
• Water Relations in Plant Cells,
• The uptake of water by plant roots.

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Water

• Dipole,
• Hydrogen bonding,
• Adhesion,
• Cohesion,
• high Specific Heat,
• high Latent Heat of Vaporization,
• etc.

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Water and Plantsto begin with.

• Up to 80 - 95 FW of Plant Tissues,
• Needed for the proper conformation of all
  macromolecules,
• Constitutes the environment for nearly all
  biochemical reactions in the cell,
• Reagent in many reactions, (e.g. hydrolysis),
• Necessary for tissue mechanics,
• Evaporative cooling,
• Bulk flow

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What Drives the Movement of Water?
Gravity,
Combinations?
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Water Potential (Y)Free Energy Status of Water
in Plants

• The water potential of a sample is the sum of
  three major component potentials gravitational,
  osmotic, and pressure.
• Gravitational potential (YG) depends on the
  position of the water in a gravitational field,
• negligible at the level of the cell. Is
  significant in taller plants and trees.
• Osmotic potential (YS) depends on the
  concentration of dissolved substance in the
  water.
• Pressure potential (YP) depends on the
  hydrostatic pressure on the water.

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Y YS Yp Y (Units)

• Y is the free energy of a water sample per unit
  mass,
• J m-3,
• expressed as units of pressure,
• 1 megapascal (MPa) 10 bars, 10 atmospheres,
  7500 mmHg.
• Standard (Y0) pure water at ambient pressure
  0 MPa.

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Y YS Yp Solute (or) Osmotic Potential

• Represents the effect of dissolved solutes on
  water potential,

YS -RT cs
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YS Solute (or) Osmotic Potential

• of solutions at 25oC,
• 0.1 mol L-1 glucose -0.24 Mpa,
• 0.1 mol L-1 NaCl -0.48 Mpa,
• 0.1 mol L-1 CaCl2 -0.72 Mpa.

Entropy effect the mixing of solutes and water
increases the disorder of the system, thus
lowering the free energy.
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YS Yp Pressure Potential

• Hydrostatic pressure represents the physical
  pressure on a solution, or by the solution,
• Positive pressure raises the pressure potential,
• Negative pressure (tension) reduces pressure
  potential,
• The positive hydrostatic pressure within plant
  cells is referred to as Turgor Pressure.

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Y YS Ypexamples
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Plant Cell Water Relations
Q If a membrane was placed between these
solutions, which way would the water move?
A Water moves toward the compartment with the
lowest Y.
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Practice
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Turgid/Plasmolysis
Turgid Firm. Walled cells become turgid as a
result of the entry of water.
Plasmolysis Shrinking of a cell due to water
leaving the cell.
(Yinside - Youtside DY )
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Pressure Probes
Careful measurement of plant cell membrane
permeability to water suggested that transport
across the membrane was too rapid for simple
diffusion.
...one way to measure water permeability.
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Aquaporins

• 38 different genes code for 38 different
  aquaporin proteins (octimers) in Arabidopsis,
• These genes are expressed in different tissues,
  and expression is partially under environmental
  control,
• Co-ordinated control of aquaporins regulate
  plant cell permeability to water.

integral membrane proteins that form a water
pore across the membrane.
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Class Quiz (2 / -2)?extra credit?
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Transport in Plants IIIWater Balance of Plants II

• Plants suck.
• -   Anonymous 206 Student

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To Do
Transport of Xylem Sap, Transpiration and
control, Evolution of water transport and
adaptations.
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Plant Water Relationsxylem
Process
Driving Force
Diffusion
Dcwv
Bulk Flow
DYp
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Transport of Xylem Sap DRIVING FORCES

• Root pressure,
• sometime DY from the soil/water matrix, but
  usually zero or negative,
• active transport of ions into the root creates
  large gradients, thus - DY.

• Transpiration-Cohesion-Tension,
• water vapor diffuses from leaf-cell surfaces to
  surrounding air,
• a water column extends from the root to this
  interface, and is held together by cohesion,
• the tension that forms, pulls water through the
  plant.

• Transpiration-Cohesion-Tension,
• water vapor diffuses from leaf-cell surfaces to
  surrounding air,
• a water column extends from the root to this
  interface, and is held together by cohesion,
• the tension that forms, pulls water through the
  plant.

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Root Pressure
Solute Accumulation in Xylem

• Absorption and active transport of ions in the
  root create a -Dys and thus a lower Y,
• lower Y provides a driving force for water
  uptake, and a thus DYp,
• Cut stems exude sap (as high as 0.05 - 0.5 MPa),
• Guttation specialized cells release root
  pressure at vein endings in leaf margins,
• hydathodes, specialized cells, (including guard
  cells).

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Transport of Xylem Sap DRIVING FORCES

• Root pressure,
• sometime DY from the soil/water matrix, but
  usually zero or negative,
• active transport of ions into the root creates
  large gradients, thus - DY.

• Transpiration-Cohesion-Tension,
• water vapor diffuses from leaf-cell surfaces to
  surrounding air,
• a water column extends from the root to the leaf
  interface, and is held together by cohesion,
• the tension that forms, pulls water through the
  plant.

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Big Picture
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Evolution of Vasculature
Poisuilles Equation
1. Create a tube, make it bigger. 2. Lower the
viscosity. 3. Create and maintain a pressure
gradient.
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Evolution of Vasculature
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Bryophytes(0.5 mm - 50 cm)
Simple vasculature 500 mya
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Haldrom/Leptom

• Conducting tissues in bryophyte stems with the
  following cell types
• Hydroids elongated cells lacking protoplasts at
  maturity, lack lignification and secondary cell
  walls,
• Leptoids elongate cells with reduced
  cytoplasm....

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Lignin
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Secondary Walls and Lignin

• Secondary Walls provide rigid support for
  conductive tissue,
• maintain higher -Yp,
• Lignin highly branched phenolic polymer, may be
  associated with cellulose and proteins.
  Deposited in secondary walls, adds strength,
• maintain higher -Yp,
• limits leaking,
• add structural potential, facilitating upward
  growth.

Castor Bean Stem
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Xylem Cells
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Big Picture
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Wednesday

• Transport of Xylem Sap,
• Control of Transpirations,
• Evolution of water transport and adaptations,
• Phloem.

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