1. Plan C
We will pick a problem in plant biology and see where it takes us.
Phytoremediation
Plant products
Biofuels
Effects of seed spacing on seed germination
Climate/CO2 change
Stress responses/stress avoidance
Improving food production
Biotechnology
Plant movements
Plant signaling (including neurobiology)
Flowering?
Circadian rhythms
Something else?

2. WATER
Plants' most important chemical
most often limits productivity

3. Climate change will alter rainfall
Overall prediction is that crops will suffer in many parts of world

4. WATER
Plants' most important chemical
most often limits productivity
Often >90%% of a plant cell’s weight
Gives cells shape
Dissolves many chem
most biochem is in water
Source of e- for PS

5. WATER
Constantly lose water due to PS
Water transport is crucial!
SPAC= Soil Plant Air Continuum
moves from soil->plant->air

6. 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

7. Properties of water
5) “Universal” solvent
Take up & transport nutrients dissolved in water
Transport organics dissolved in water

8. 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

9. 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

10. pH
[H+] = acidity of a solution
pH = convenient way
to measure acidity
pH = - log10 [H+]
pH 7 is neutral:
[H+] = [OH-]
-> 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

11. pH
Plants vary pH to control many processes!

12. pH
Plants vary pH to control
many processes!
Plants alter roots to
aid uptake

13. Water movement
Diffusion: movement of single molecules down ∆[ ] due to random motion until [ ] is even
Driving force?

14. Water movement
Diffusion: movement of single molecules down ∆[ ] due to random motion until [ ] is even
Driving force: lowers free energy
∆G = ∆H- T∆S

15. 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

16. 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 ∆ [ ] !

17. 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

18. 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

19. 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

20. 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!

21. 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

22. 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 can’t: result is net influx of water

23. Water movement
Osmosis: depends on bulk flow and diffusion!
Moves through aquaporins, so rate depends on pressure and [ ] gradients!

24. 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)

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

26. Water potential
Driving force = water's free energy = water potential Yw
Water moves to lower its potential

27. Water potential
Driving force = water's free energy = water potential Yw
Water moves to lower its potential

28. Water potential
Driving force = water's free energy = water potential Yw
Water moves to lower its potential
Depends on:
[H2O]: Ys (osmotic potential)

29. Water potential
Water moves to lower its potential
Depends on:
[H2O]: Ys (osmotic potential)
Pressure : Yp
Turgor pressure inside cells

30. Water potential
Water moves to lower its potential
Depends on:
[H2O]: Ys (osmotic potential)
Pressure : Yp
Turgor pressure inside cells
Negative pressure in xylem!

31. Water potential
Water moves to lower its potential
Depends on:
[H2O]: Ys (osmotic potential)
Pressure Yp
Gravity Yg
Yw = Ys +Yp + Yg

32. Water potential
Water moves to lower its potential
Depends on:
[H2O]: Ys (osmotic potential)
Pressure Yp
Gravity Yg
Yw = Ys +Yp + Yg
Yw of pure water at sea level
& 1 atm = 0 MPA

33. Water potential
Yw = Ys +Yp + Yg
Yw of pure water at sea level & 1 atm = 0 MPA
Ys (osmotic potential) is always negative

34. Water potential
Yw = Ys +Yp + Yg
Yw of pure water at sea level & 1 atm = 0 MPA
Ys (osmotic potential) is always negative
If increase [solutes] water will move in

35. Water potential
Yw = Ys +Yp + Yg
Yw of pure water at sea level & 1 atm = 0 MPA
Ys (osmotic potential) is always negative
If increase [solutes] water will move in
Yp (pressure potential) can be positive or negative

36. Water potential
Yw = Ys +Yp + Yg
Yw of pure water at sea level & 1 atm = 0 MPA
Ys (osmotic potential) is always negative
If increase [solutes] water will move in
Yp (pressure potential) can be positive or negative
Usually positive in cells to counteract Ys

37. Water potential
Yp (pressure potential) can be positive or negative
Usually positive in cells to counteract Ys
Helps plants stay same size despite daily fluctuations in Yw

38. Water potential
Yw = Ys +Yp + Yg
Yp (pressure potential) can be positive or negative
Usually positive in cells to counteract Ys
Helps plants stay same size
despite daily fluctuations in Yw
Yp in xylem is negative, draws
water upwards

39. Water potential
Yw = Ys +Yp + Yg
Yp (pressure potential) can be positive or negative
Usually positive in cells to counteract Ys
Helps plants stay same size
despite daily fluctuations in Yw
Yp in xylem is negative, draws
water upwards
Yg can usually be ignored, but
important for tall trees

40. Water potential
Measuring water potential

41. Water potential
Measuring water potential
Ys (osmotic potential) is “easy”
Measure concentration of solution in equilibrium with cells

42. Water potential
Measuring water potential
Ys (osmotic potential) is “easy”
Measure concentration of solution in equilibrium with cells
Yg (gravity potential) is easy: height above ground
-0.01 Mpa/m

43. Water potential
Measuring water potential
Ys (osmotic potential) is “easy”
Measure concentration of solution in equilibrium with cells
Yg (gravity potential) is easy: height above ground
YP (pressure potential) is hard!
Pressure bomb =
most common technique

44. Water potential
Measuring water potential
Ys (osmotic potential) is “easy”
Measure concentration of solution in equilibrium with cells
Yg (gravity potential) is easy: height above ground
YP (pressure potential) is hard!
Pressure bomb =
most common technique
Others include pressure
transducers, xylem probes

45. Measuring water potential
YP (pressure potential) is hard!
Pressure bomb =
most common technique
Others include pressure
transducers, xylem probes
Therefore disagree about H2O
transport in xylem

46. Water transport
Therefore disagree about H2O
transport in xylem
Driving force = evaporation
in leaves (evapotranspiration)
Continuous H2O column
from leaf to root draws up
replacement H2O from soil (SPAC)

47. Water transport
Driving force = evaporation
in leaves (evapotranspiration)
Continuous H2O column
from leaf to root draws up
replacement H2O
Exact mech controversial

48. Water transport
Driving force = evaporation in leaves (evapotranspiration)
Continuous H2O column from leaf to root draws up
replacement H2O
Exact mech controversial
Path starts at root hairs

49. Water transport
Path starts at root hairs
Must take water from soil

50. Water transport
Path starts at root hairs
Must take water from soil
Ease depends on availability
& how tightly it is bound

51. Water transport
Path starts at root hairs
Must take water from soil
Ease depends on availability & how tightly it is bound
Binding depends on particle size & chem

52. Water transport
Must take water from soil
Ease depends on availability & how tightly it is bound
Binding depends on particle size & chem
Availability depends on amount in soil pores

53. Water transport
Availability depends on amount in soil pores
Saturation: completely full

54. Water transport
Availability depends on amount in soil pores
Saturation: completely full
Field capacity: amount left after gravity has drained excess

55. Water transport
Availability depends on amount in soil pores
Saturation: completely full
Field capacity: amount left after gravity has drained excess
Permanent wilting point: amount where soil water potential is too negative for plants to take it up

56. Water movement in plants
Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis

57. Water movement in plants
Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis
Must enter
endodermal cell

58. Water Transport
Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis
Must enter
endodermal cell
Why flooded
plants wilt!

59. Water Transport
Water enters via root hairs mainly through apoplast until hits Casparian strip : hydrophobic barrier in cell walls of endodermis
Must enter
endodermal cell
Why flooded
plants wilt!
Controls solutes

60. Water Transport
Must enter endodermal cell
Controls solutes
Passes water & nutrients to xylem

61. Water Transport
Passes water & nutrients to xylem
Ys of xylem makes root pressure

62. Water Transport
Passes water & nutrients to xylem
Ys of xylem makes root pressure
Causes guttation: pumping water into shoot

63. Water Transport
Passes water & nutrients to xylem
Ys of xylem makes root pressure
Causes guttation: pumping water into shoot
Most water enters near root tips

64. Water Transport
Most water enters near root tips
Xylem is dead! Pipes for moving water from root to shoot

65. Water Transport
Most water enters near root tips
Xylem is dead! Pipes for moving water from root to shoot
Most movement is bulk flow

66. Water Transport
Xylem is dead! Pipes for moving water from root to shoot
Most movement is bulk flow
adhesion to cell wall helps

67. Water Transport
Xylem is dead! Pipes for moving water from root to shoot
Most movement is bulk flow
adhesion to cell wall helps
Especially if column is broken by
cavitation (forms embolisms)

68. Water Transport
Most movement is bulk flow
adhesion to cell wall helps
Especially if column broken by cavitation
In leaf water passes to mesophyll

69. Water Transport
Most movement is bulk flow
adhesion to cell wall helps
Especially if column broken by cavitation
In leaf water passes to mesophyll, then to air via stomates

70. Water Transport
In leaf water passes to mesophyll, then to air via stomates
Driving force = vapor pressure deficit (VPD)
air dryness

71. Water Transport
In leaf water passes to mesophyll, then to air via stomates
Driving force = vapor pressure deficit (VPD)
air dryness
∆ H2O vapor pressure [H2O(g)]
& saturated H2O vapor pressure

72. Water Transport
In leaf water passes to mesophyll, then to air via stomates
Driving force = vapor pressure deficit (VPD)
air dryness
∆ H2O vapor pressure [H2O(g)]
& saturated H2O vapor pressure
saturated H2O vapor pressure
varies with T, so RH depends on T

73. Water Transport
In leaf water passes to mesophyll, then to air via stomates
Driving force = vapor pressure deficit (VPD)
air dryness
∆ H2O vapor pressure [H2O(g)]
& saturated H2O vapor pressure
saturated H2O vapor pressure
varies with T, so RH depends on T
VPD is independent of T: says
how fast plants lose H2O at any T

74. Water Transport
In leaf water passes to mesophyll, then to air via stomates
Driving force = vapor pressure deficit (VPD)
air dryness
Rate depends on pathway resistances

75. Water Transport
Rate depends on pathway resistances
stomatal resistance

76. Water Transport
Rate depends on pathway resistances
stomatal resistance
Controlled by opening/closing

77. Water Transport
Rate depends on pathway resistances
stomatal resistance
boundary layer resistance
Influenced by leaf shape & wind