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

2. WATER Plants' most important chemical most often limits productivity Often >90% of a plant cell’s weight

3. WATER Plants' most important chemical most often limits productivity Often >90% of a plant cell’s weight Gives cells shape

4. WATER Plants' most important chemical most often limits productivity Often >90% of a plant cell’s weight Gives cells shape Dissolves many chem

5. WATER Dissolves many chem most biochem occurs in water Source of e - for PS

6. WATER most biochem occurs in water Source of e - for PS Constantly lose water due to PS (1000 H 2 O/CO 2 )

7. WATER most biochem occurs in water Source of e - for PS Constantly lose water due to PS Water transport is crucial!

8. WATER Water transport is crucial! SPAC= Soil Plant Air Continuum moves from soil->plant->air

9. Plant Water Uptake Water is drawn through plants along the SPAC, using its special properties to draw it from the soil into the air

10. WATER Formula = H 2 O Formula weight = 18 daltons Structure = tetrahedron, bond angle 104.5˚

11. WATER Structure = tetrahedron, bond angle 104.5˚ polar :O is more attractive to electrons than H  + on H  - on O

12. Water Polarity is reason for water’s properties water forms H-bonds with polar molecules

13. Water Polarity is reason for water’s properties water forms H-bonds with polar molecules Hydrophilic = polar molecules Hydrophobic = non-polar molecules

14. Properties of water 1)Cohesion = water H-bonded to water -> reason for surface tension

15. Properties of water 1)Cohesion = water H-bonded to water -> reason for surface tension -> why water can be drawn from roots to leaves

16. Properties of water 1) Cohesion = water H-bonded to water 2) Adhesion = water H-bonded to something else

17. 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!

18. 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!

19. 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: cools leaves

20. 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

21. 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

22. 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

23. 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

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

25. 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 bonds

26. 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 bonds 7) Water ionizes

27. pH [H + ] = acidity of a solution pH = convenient way to measure acidity pH = - log 10 [H + ] pH 7 is neutral: [H+] = [OH-] -> at pH 7 [H+] = 10 -7 moles/l

28. pH Plants vary pH to control many processes!

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

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

31. 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

32. 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 ∆ [ ] !

33. 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

34. 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

35. 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 r 4

36. 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 r 4 Osmosis: depends on bulk flow and diffusion!

37. 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

38. 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

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

40. 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/m 3 = MPa)

41. Water potential Driving force = water's free energy = water potential  w Important for many aspects of plant physiology

42. Water potential Driving force = water's free energy = water potential  w Water moves to lower its potential

43. Water potential Driving force = water's free energy = water potential  w Water moves to lower its potential

44. Water potential Driving force = water's free energy = water potential  w Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential)

45. Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure :  p Turgor pressure inside cells

46. Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure :  p Turgor pressure inside cells Negative pressure in xylem!

47. Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure  p 3.Gravity  g  w =  s +  p +  g

48. Water potential Water moves to lower its potential Depends on: 1.[H 2 O]:  s (osmotic potential) 2.Pressure  p 3.Gravity  g  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA

49. Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative

50. Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative If increase [solutes] water will move in

51. Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative If increase [solutes] water will move in  p (pressure potential) can be positive or negative

52. Water potential  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA  s (osmotic potential) is always negative If increase [solutes] water will move in  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s

53. Water potential  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s Helps plants stay same size despite daily fluctuations in  w

54. Water potential  w =  s +  p +  g  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s Helps plants stay same size despite daily fluctuations in  w  p in xylem is negative, draws water upwards

55. Water potential  w =  s +  p +  g  p (pressure potential) can be positive or negative Usually positive in cells to counteract  s Helps plants stay same size despite daily fluctuations in  w  p in xylem is negative, draws water upwards  g can usually be ignored, but important for tall trees

56. Water potential Measuring water potential

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

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

59. Water potential Measuring water potential  s (osmotic potential) is “easy” Measure concentration of solution in equilibrium with cells  g (gravity potential) is easy: height above ground  P (pressure potential) is hard! Pressure bomb = most common technique

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

61. Measuring water potential  P (pressure potential) is hard! Pressure bomb = most common technique Others include pressure transducers, xylem probes Therefore disagree about H 2 O transport in xylem