This document discusses plant water relations and pressure. It covers how plants generate turgor pressure through osmosis, how turgor pressure can be measured in single cells using a pressure probe, and details of the phloem and xylem transport systems. Phloem transports sugars at extremely high pressures of over 30 bars to distances of over 200 meters. Xylem transports water and minerals upwards from the roots but is vulnerable to cavitation if water columns snap due to low pressure.

1. Prof Jeremy Pritchard
@DrJPritchard
Plants & Pressure

2. Prof Jeremy Pritchard
@DrJPritchard
Plants & Pressure
1. Hydraulic machines
2. Measuring turgor
3. Phloem and phloem defence
4. Xylem and climate change

3. What plant do you use for your
water relations?
A. Potato
B. Carrot
C. Apple

4. Plants are hydraulic machines

7. Prof Jeremy Pritchard
@DrJPritchard
Plants & Pressure
1. Hydraulic machines
2. Measuring turgor
3. Phloem
4. Xylem

8. Turgor pressure generation
• Salts and sugars are accumulated
in the cell
• Water follows by osmosis
• Turgor pushes against cell wallwater
P
Solutes

10. The units of pressure ………..
Atmosphere
Bars (millibars)
lb in2 (PSI)
mm Hg
mm H20
Pascal, (KPa, MPa)
Torr

11. Measuring pressure

13. T
C
The pressure probe can measure turgor in single cells

15. Capillary
Pressure
transducer
Plunge
rSilicone oil

16. Cel
l
tur
gor

17. Cel
l
tur
gor

18. (
Cel
l
tur
gor

19. (

20. (
Cel
l
tur
gor

21. (
Cel
l
tur
gor

22. (
Cel
l
tur
gor

24. 20 mm Hg = 0.026 bars
120 mm Hg = 0.16 bars

26. Phloem >30 bars >200 m
Root 6 bars 60 m
Tyre 2 bars 20 m
Bottle 1.5 bars 15 m
Lungs 0.15 bars 1.5

27. Prof Jeremy Pritchard
@DrJPritchard
Plants & Pressure
1. Hydraulic machines
2. Measuring turgor
3. Phloem and phloem defence
4. Xylem and climate change

28. The Human circulation system
Veins Arteries
0.08 0.16 bars

29. The plant circulation system
Xylem phloem
minus 40 plus 40 bars

30. The plant circulation system
Translocation in the high pressure phloem

32. Phloem
The plant circulation system

38. Why does your lawn not bleed to death?

39. 0 min1 min3 min30 min40 min60 min
Plant scabs: Slow tube blockage

46. Nano - technology

47. Prof Jeremy Pritchard
@DrJPritchard
Plants & Pressure
1. Hydraulic machines
2. Measuring turgor
3. Phloem and phloem defence
4. Xylem and climate change

48. Xylem
The plant circulation system

49. A xylem journey

50. CO2
H2O

52. CO2
Carbon
Rhizosphere?
Growth?
Stomata?
Defence?
Reproduction?
Ecology?

53. Water columns can snap

55. Root pressure can flush out cavitation

59. Dr Jeremy Pritchard
@DrJPritchard