Water Movement in Plants: The Key to Productivity and Adaptation to Climate Change

1. Biofuels • Plant signaling (including neurobiology) • Climate/CO2 change • Plant movements

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 • Cohesion and adhesion are crucial for water movement in plants! • Surface tension & adhesion in mesophyll creates force that draws water through the plant!

7. 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

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

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

10. 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

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

12. 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

13. 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

14. 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

15. pH • Plants vary pH to control many processes!

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

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

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

19. 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 ∆ [ ] !

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

21. 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

22. 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

23. 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!

24. 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

25. 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

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

27. 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)

28. Water potential • Driving force = water's free energy • = water potential Yw • Important formany aspects of • plant physiology

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

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

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

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

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

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