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

Osmosis solute molecules (e.g., K + ) water molecules selectively permeable membrane X

cell

plasmolysis cell wall plasma membrane

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s pp  =  s +  p

Water potential (  ): relative tendency of water to move by diffusion Osmotic potential (always ≤ 0) Turgor pressure ( ≥ 0 in living cells) ss pp  =  s +  p Osmotic pressure  s

Water potential (  ): relative tendency of water to move by diffusion Osmotic potential ss  =  s +  p  s = -2.5 MPa  s = 0  p = 0  = -2.5 MPa  = 0 Water moves from higher  to lower   s = -RT∙[solutes] MPa  2.5 mol/L e.g.: [solutes] = 1 mol/L  s  -2.5 MPa

 =  s +  p  s = -2.5 MPa  s = 0  p = 0  = -2.5 MPa  = 0 plasmolysis

initial  s = -0.9 MPa  s = 0  p = 0  = 0  s = 0  p = +0.9 MPa  p = 0  = 0 turgor  = -0.9 MPa  s = -0.9 MPa

Turgor pressure Active transport ATP ADP protons (H + ) proton pump ion channel cations (e.g., K + )

ATP Concentration gradients are a form of energy ADP

Growth= division+ expansion water uptake by osmosis

Q: Is the sequence shown at right an example of osmosis? (a)yes (b)no

Q: Which direction will water move? (a)from left to right (b)from right to left  s = -2  s = -1  p = +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 CO 2 H2OH2O

Fig surface tension = negative pressure  =  s +  p stoma xylem negative in xylem Transpiration

 = -2 MPa = water in a drinking straw holding up 2 gallons

Delzon et al (2004) PCE 27: Pinus pinaster Transpiration  =  s +  p negative in xylem embolisms

vessel elements tracheids Fig (in angiosperms) (in most vascular spp.)

bordered pits perforation plates Regulation of transpiration: xylem anatomy

Fig closedopen ATP ADP protons (H + ) potassium (K + ) stoma xylem Regulation of transpiration: stomatal aperture pore

Fig closedopen stoma xylem low light dry air dry soil high CO 2 high light humid air moist soil low CO 2 Regulation of transpiration: stomatal aperture

Phloem function companion cells sieve plate Fig source (e.g., leaf) sink (e.g., bud or root)

Xylem vs Phloem xylemphloem conducts:watersugars conducting cells:deadalive pressure:negativepositive gymnosperms:tracheidsseive cells angiosperms:vessel elementsseive tube elements & tracheids

Root anatomy apical meristem root cap root hairs cortex vascular column (stele) Fig 35.13

uptake apoplastic symplastic Casparian Strip Fig endodermis root hair