Transport in Plants IIWater Balance of Plants

My empty water dish mocks me.

- Bob the Dog

Tutoring, 206

• Samantha D’Andrea,

• Mondays, 6 pm, AW 205,

• Will meet MLK Day.

Salmonberry bird…

Rubus spectabilisSalmonberry

Rhizomes

Clones

Leaves Alternet

• Local (NW) flora,• Ethnobotany,• Fun!

Buy locally, or at Amazon ($16.47).

Transport…molecular and ionic movement from one

location to another,

– H2O,

– Sugars and other organics,– Ions,– Gases,– Proteins, RNA, Hormones, etc.

Proteins/RNA/Hormones etc.+ Everything

Today

• Water,

• Water Potential,

– free energy of water,

• Water Relations in Plant Cells,

• The uptake of water by plant roots.

Water

• Dipole,

• Hydrogen bonding,

– Adhesion,

– Cohesion,

– high Specific Heat,

– high Latent Heat of Vaporization,

– etc.

Water and Plants…to begin with.

• Up to 80 - 95% FW of Plant Tissues,

• Needed for the proper conformation of all macromolecules,

• Constitutes the environment for nearly all biochemical reactions in the cell,

• Reagent in many reactions, (e.g. hydrolysis),

• Necessary for tissue mechanics,

• Evaporative cooling,

• Bulk flow…

What Drives the Movement of Water?

Gravity,

Pressure,

Combinations?

Osmosis, (entropy-driven).

Water Potential ()Free Energy Status of Water in Plants

• The water potential of a sample is the sum of three major component potentials: gravitational, osmotic, and pressure.

– Gravitational potential (G) depends on the position of the water in a gravitational field,

• negligible at the level of the cell. Is significant in taller plants and trees.

– Osmotic potential (S) depends on the concentration of dissolved substance in the water.

– Pressure potential (P) depends on the hydrostatic pressure on the water.

Pg + = S

P = S

= S + p (Units)

• is the free energy of a water sample per unit mass,

– J m-3,

…expressed as units of pressure,

• 1 megapascal (MPa) = 10 bars, ~ 10 atmospheres, 7500 mmHg.

• Standard (0) = pure water at ambient pressure = 0 MPa.

= S + p Solute (or) Osmotic Potential

• Represents the effect of dissolved solutes on water potential,

S = -RT cs

R: gas constant (8.32 J mol-1 K-1)

T: absolute temperature (K)

cs: concentration (mol L-1)

S Solute (or) Osmotic Potential

…of solutions at 25oC,

– 0.1 mol L-1 glucose = -0.24 Mpa,– 0.1 mol L-1 NaCl = -0.48 Mpa,– 0.1 mol L-1 CaCl2 = -0.72 Mpa.

Why?

Entropy effect: the mixing of solutes and water increases the disorder of the system, thus lowering the free energy.

= S + p Pressure Potential

• Hydrostatic pressure represents the physical pressure on a solution, or by the solution,

– Positive pressure raises the pressure potential,– Negative pressure (tension) reduces pressure potential,

• The positive hydrostatic pressure within plant cells is referred to as Turgor Pressure.

= S + pexamples

TensionPressure

Plant Cell Water Relations

Q: If a membrane was placed between these solutions, which way would the water move?

A: Water moves toward the compartment with the lowest .

Practice

Turgid/Plasmolysis

Turgid Cell

Turgid: Firm. Walled cells become

turgid as a result of the entry of water.

Plasmolysis: Shrinking of a cell due

to water leaving the cell.

Turgid Plasmolyzed

(inside - outside = )

Pressure Probes

...one way to measure water permeability.

Careful measurement of plant cell membrane permeability to water

suggested that transport across the membrane was too

rapid for simple diffusion.

Aquaporins

…integral membrane proteins that form a water pore across the

membrane.

r4

8

p

xVolume flow rate =

viscosity ( distance

pressure gradient

• 38 different genes code for 38 different aquaporin proteins (octimers) in Arabidopsis,

• These genes are expressed in different tissues, and expression is partially under environmental control,

• Co-ordinated control of aquaporins regulate plant cell permeability to water.

Class Quiz (+2 / -2)?extra credit?

Two good examples as to when an organism might use this protein.

What type of transport?

What drives the transport?

Relatively fast or slow?

What type of transport?

What drives the transport?

Relatively fast or slow?

Transport in Plants IIIWater Balance of Plants II

Plants suck.

-   Anonymous 206 Student

To Do

Transport of Xylem Sap,

Transpiration and control,

Evolution of water transport and adaptations.

Plant Water Relationsxylem

Process Driving Force

Osmosis, etc.

Diffusion cwv

Bulk Flow p

Transport of Xylem Sap DRIVING FORCES

• Root pressure,

– sometime + from the soil/water matrix, but usually zero or negative,

– active transport of ions into the root creates large gradients, thus - .

• Transpiration-Cohesion-Tension,

– water vapor diffuses from leaf-cell surfaces to surrounding air,

– a water column extends from the root to this interface, and is held together by cohesion,

– the tension that forms, “pulls” water through the plant.

• Transpiration-Cohesion-Tension,

– water vapor diffuses from leaf-cell surfaces to surrounding air,

– a water column extends from the root to this interface, and is held together by cohesion,

– the tension that forms, “pulls” water through the plant.

Root Pressure

• Absorption and active transport of ions in the root create a -s and

thus a lower ,

– lower provides a driving force for water uptake, and a thus +p,

• Cut stems exude sap (as high as 0.05 - 0.5 MPa),

• Guttation: specialized cells release root pressure at vein endings in leaf margins,

– hydathodes, specialized cells, (including guard cells).

Guttation

Solute Accumulation in Xylem

Transport of Xylem Sap DRIVING FORCES

• Root pressure,

– sometime + from the soil/water matrix, but usually zero or negative,

– active transport of ions into the root creates large gradients, thus - .

• Transpiration-Cohesion-Tension,

– water vapor diffuses from leaf-cell surfaces to surrounding air,

– a water column extends from the root to the leaf interface, and is held together by cohesion,

– the tension that forms, “pulls” water through the plant.

Big Picture

Evolution of Vasculature

r4

8

p

xVolume flow rate =

viscosity ( distance

pressure gradient

Poisuille’s Equation

1. Create a tube, make it bigger.2. Lower the viscosity.3. Create and maintain a pressure gradient.

Fick’s Law and Organisms

Choleochaete orbicularis

50μm

?TreesBryophytes

50μm

Euglena oxyuris

Evolution of Vasculature

Bryophytes(0.5 mm - 50 cm)

Simple vasculature~ 500 mya

Haldrom/Leptom

Seta w/ Capsules

• Conducting tissues in bryophyte stems with the following cell types;

– Hydroids: elongated cells lacking protoplasts at maturity, lack lignification and secondary cell walls,

– Leptoids: elongate cells with reduced cytoplasm....

Lignin

Secondary Walls and Lignin• Secondary Walls: provide rigid

support for conductive tissue,

– maintain higher -p,

• Lignin: highly branched phenolic polymer, may be associated with cellulose and proteins. Deposited in secondary walls, adds strength,

– maintain higher -p, – limits “leaking”,

…add structural potential, facilitating upward growth.

Castor Bean Stem

Xylem Cells

Bordered Pits

Pits: microscopic regions where the secondary wall of a xylem cell is

absent, and the primary wall is thin and porous.

Big Picture

Wednesday

• Transport of Xylem Sap,

• Control of Transpirations,

• Evolution of water transport and adaptations,

• Phloem.

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