Bio 226: Cell and Molecular Biology

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1. Biofuels
2. Plant signaling (including neurobiology)
3. Climate/CO2 change
4. Plant movements

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• WATER
• Plants' most important chemical
• most often limits productivity

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Climate change will alter rainfall Overall
prediction is that crops will suffer in many
parts of world
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• WATER
• Plants' most important chemical
• most often limits productivity
• Often gt90 of a plant cells weight
• Gives cells shape
• Dissolves many chem
• most biochem is in water
• Source of e- for PS

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• WATER
• Constantly lose water due to PS
• Water transport is crucial!
• SPAC Soil Plant Air Continuum
• moves from soil-gtplant-gtair

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• Properties of water
• 1) Cohesion water H-bonded to water
• 2) Adhesion water H-bonded to something else
• Cohesion and adhesion are crucial for water
  movement in plants!
• Surface tension adhesion in mesophyll creates
  force that draws water through the plant!

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• Properties of water
• 1) Cohesion water H-bonded to water
• 2) Adhesion water H-bonded to something else
• 3) high specific heat
• absorb heat when break H-bonds
• Release heat when form H-bonds

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Properties of water 1) Cohesion water H-bonded
to water 2) Adhesion water H-bonded to
something else 3) high specific heat 4) Ice floats
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Properties of water 1) Cohesion water H-bonded
to water 2) Adhesion water H-bonded to
something else 3) high specific heat 4) Ice
floats 5) Universal solvent
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• Properties of water
• 1) Cohesion water H-bonded to water
• 2) Adhesion water H-bonded to something else
• 3) high specific heat
• 4) Ice floats
• 5) Universal solvent
• Take up transport
• nutrients dissolved in
• water

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• Properties of water
• 5) Universal solvent
• Take up transport nutrients dissolved in water
• Transport organics dissolved in water

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Properties of water 1) Cohesion water H-bonded
to water 2) Adhesion water H-bonded to
something else 3) high specific heat 4) Ice
floats 5) Universal solvent 6) Hydrophobic
interactions
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Properties of water 1) Cohesion water H-bonded
to water 2) Adhesion water H-bonded to
something else 3) high specific heat 4) Ice
floats 5) Universal solvent 6) Hydrophobic
interactions 7) Water ionizes
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pH H acidity of a solution pH convenient
way to measure acidity pH - log10 H pH 7 is
neutral H OH- -gt at pH 7 H 10-7
moles/l pH of cytoplasm 7.2 pH of stroma
matrix 8 pH of apoplast 5.5 pH of lumen 4.5
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pH Plants vary pH to control many processes!
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Water movement Diffusion movement of single
molecules down ? due to random motion until
is even Driving force?
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Water movement Diffusion movement of single
molecules down ? due to random motion until
is even Driving force lowers free energy ?G
?H- T?S
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Water movement Diffusion movement of single
molecules down ? due to random motion until
is even Bulk Flow movement of groups
of molecules down a pressure gradient
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• Water movement
• Diffusion movement of single molecules down ?
  due to random motion until is even
• Bulk Flow movement of groups of
• molecules down a pressure gradient
• Independent of ? !

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• Water movement
• Diffusion movement of single molecules down ?
  due to random motion until is even
• Bulk Flow movement of groups of molecules down a
  pressure gradient
• Independent of ? !
• How water moves through xylem

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• Water movement
• Diffusion movement of single molecules down
  due to random motion until is even
• Bulk Flow movement of groups of molecules down a
  pressure gradient
• Independent of ? !
• How water moves through xylem
• How water moves through soil and apoplast

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• Water movement
• Bulk Flow movement of groups of molecules down a
  pressure gradient
• Independent of ? !
• How water moves through xylem
• Main way water moves through soil and apoplast
• Very sensitive to radius of vessel increases as
  r4

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• Water movement
• Diffusion movement of single molecules down ?
  due to random motion until is even
• Bulk Flow movement of groups of molecules down a
  pressure gradient
• Independent of ? !
• How water moves through xylem
• Main way water moves through soil and apoplast
• Very sensitive to radius of vessel increases as
  r4
• Osmosis depends on bulk flow and diffusion!

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Water movement Osmosis depends on bulk flow and
diffusion! water crosses membranes but other
solutes do not water tries to even its on
each side
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Water movement Osmosis depends on bulk flow and
diffusion! water crosses membranes but other
solutes do not water tries to even its on
each side other solutes cant result is net
influx of water
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• Water movement
• Osmosis depends on bulk flow and diffusion!
• Moves through aquaporins, so rate depends on
  pressure and gradients!

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• Water movement
• Osmosis depends on bulk flow and diffusion!
• Moves through aquaporins, so rate depends on
  pressure and gradients!
• Driving force water's free energy (J/m3 MPa)

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• Water potential
• Driving force water's free energy
• water potential Yw
• Important for many aspects of
• plant physiology

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• Water potential
• Driving force water's free energy water
  potential Yw
• Water moves to lower its potential

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• Water potential
• Driving force water's free energy water
  potential Yw
• Water moves to lower its potential

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• Water potential
• Driving force water's free energy water
  potential Yw
• Water moves to lower its potential
• Depends on
• H2O Ys (osmotic potential)

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• Water potential
• Water moves to lower its potential
• Depends on
• H2O Ys (osmotic potential)
• Pressure Yp
• Turgor pressure inside cells

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• Water potential
• Water moves to lower its potential
• Depends on
• H2O Ys (osmotic potential)
• Pressure Yp
• Turgor pressure inside cells
• Negative pressure in xylem!

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• Water potential
• Water moves to lower its potential
• Depends on
• H2O Ys (osmotic potential)
• Pressure Yp
• Gravity Yg
• Yw Ys Yp Yg