Water movement in plants

Biol 121, Fall 2010, Tom Buckley 04 Oct 10

Three functions:

Replace transpired water

(evaporation from leaves)

Deliver nutrients from soil

Supply water for new growth

Osmosissolute molecules (e.g., K+)water molecules

selectively permeable membrane

X

cell

plasmolysis

cell wall

plasmamembrane

cell

Wall stretching creates pressure

Water potential (): relative tendency of water to move by diffusion

Osmotic potential

(always ≤ 0)

Turgor pressure

( ≥ 0 in living cells)

s

p

= s + p

Water potential (): relative tendency of water to move by diffusion

Osmotic potential

(always ≤ 0)

Turgor pressure

( ≥ 0 in living cells)

s

p

= s + p

Osmotic pressures

Water potential (): relative tendency of water to move by diffusion

Osmotic potentials

= s + p

s = -2.5 MPa s = 0

p = 0 p = 0

= -2.5 MPa = 0Water moves fromhigher to lower

s = -RT∙[solutes]

MPa 2.5 mol/L

e.g.:[solutes] = 1 mol/Ls -2.5 MPa

= s + p

s = -2.5 MPa s = 0

p = 0 p = 0

= -2.5 MPa = 0

plasmolysis

finalinitial

s = -0.9 MPa s = 0

p = 0 p = 0

= 0

s = 0

p = +0.9 MPa p = 0

= 0 = 0

turgor

= -0.9 MPa

s = -0.9 MPa

+

+

+

+

+

+

+

+

+

Turgor pressure

Active transport

ATP

ADPprotons (H+)

proton pump

ion channel

+

++

+

++

+

+

+

+ cations (e.g., K+)

ATP

Concentration gradients are a form of energy

ADP

Growth = division + expansion

water uptakeby osmosis

Q: Is the sequence shown at rightan example of osmosis?

(a) yes

(b) no

Q: Which direction will water move?

(a) from left to right

(b) from right to left

s = -2s = -1

p = +1p = +1

= -1 = 0

Cell #1(LEFT)

Cell #2(RIGHT)

Water movement in plants

Three functions:

Replace transpired water

(evaporation from leaves)

Deliver nutrients from soil

Supply water for new growth

Water movement in plants

uptake by fine roots

flow through xylem

evaporation from leaves

water potential:

highest in soil

lowest in leaves

Stoma

Transpiration

CO2H2O

Fig 36.14surface tension = negative pressure

= s + p

stoma

xylemnegativein xylem

Transpiration

= -2 MPa

= water in adrinking straw

holding up2 gallons

Delzon et al (2004) PCE 27:1077-1087

Pinus pinaster

Transpiration

= s + p

negativein xylem

embolisms

vesselelements

tracheids

Fig 35.10

(in angiosperms)

(in most vascular spp.)

bordered pits

perforationplates

Regulation of transpiration:xylem anatomy

Fig 36.14

closed open

ATP

ADP

protons (H+)

potassium (K+)stoma

xylem

Regulation of transpiration: stomatal aperture

pore

Fig 36.14

closed open

stoma

xylem

low lightdry airdry soilhigh CO2

high lighthumid airmoist soillow CO2

Regulation of transpiration: stomatal aperture

Phloem function

companioncells

sieveplate

Fig 35.10

source(e.g., leaf)

sink(e.g., budor root)

Xylem vs Phloem

xylem phloem

conducts: water sugarsconducting cells: dead alivepressure: negative positive

gymnosperms: tracheids seive cellsangiosperms: vessel elements seive tube elements

& tracheids

Root anatomy

apical meristem

root cap

root hairs

cortex

vascular column(stele)

Fig 35.13

uptake

apoplastic

symplastic

Casparian Strip

Fig 36.12

endodermis

root hair