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

2. 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

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

4. 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! 3.Gravity  g  w =  s +  p +  g  w of pure water at sea level & 1 atm = 0 MPA

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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. Water potential Measuring water potential

13. Water potential Measuring water potential  s (osmotic potential) is “easy” Measure [solution] in equilibrium with cells

14. Water potential Measuring water potential  s (osmotic potential) is “easy” Measure [solution] in equilibrium with cells  g (gravity potential) is easy = height above ground -0.01 Mpa/m

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

16. Water potential Measuring water potential  s (osmotic potential) is “easy” Measure [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

17. 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

18. Water transport Therefore disagree about H 2 O transport in xylem Driving force = evaporation in leaves (evapotranspiration) Continuous H 2 O column from leaf to root draws up replacement H 2 O from soil (SPAC)

19. Water transport Driving force = evaporation in leaves (evapotranspiration) Continuous H 2 O column from leaf to root draws up replacement H 2 O Exact mech controversial

20. Water transport Driving force = evaporation in leaves (evapotranspiration) Continuous H 2 O column from leaf to root draws up replacement H 2 O Exact mech controversial Path starts at root hairs

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

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

23. 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

24. 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

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

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

27. 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

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

29. 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

30. 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!

31. 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

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

33. Water Transport Passes water & nutrients to xylem  s of xylem makes root pressure

34. Water Transport Passes water & nutrients to xylem  s of xylem makes root pressure Causes guttation: pumping water into shoot

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

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

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

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

39. 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)

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

41. 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

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

43. Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H 2 O vapor pressure [H 2 O (g) ] & saturated H 2 O vapor pressure

44. Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H 2 O vapor pressure [H 2 O (g) ] & saturated H 2 O vapor pressure saturated H 2 O vapor pressure varies with T, so RH depends on T

45. Water Transport In leaf water passes to mesophyll, then to air via stomates Driving force = vapor pressure deficit (VPD) air dryness ∆ H 2 O vapor pressure [H 2 O (g) ] & saturated H 2 O vapor pressure saturated H 2 O vapor pressure varies with T, so RH depends on T VPD is independent of T: says how fast plants lose H 2 O at any T

46. 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

47. Water Transport Rate depends on pathway resistances stomatal resistance

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

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