Transport in Plants II Water Balance of Plants

Transport in Plants II Water 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.

Rubus spectabilis Salmonberry üRhizomes üClones üLeaves Alternet Salmonberry bird…

• Local (NW) flora, • Ethnobotany, • Fun! Buy locally, or at Amazon ($16. 47).

Transport …molecular and ionic movement from one location to another, – – – H 2 O, Sugars and other organics, Ions, Gases, Proteins, RNA, Hormones, etc. + Everything Proteins/RNA/Hormones etc.

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, Osmosis, (entropy-driven). Combinations?

Water Potential (Y) 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 (YG) 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 (YS) depends on the concentration of dissolved substance in the water. – Pressure potential (YP) depends on the hydrostatic pressure on the water. Y = Yg + Y = YS + YP

Y = Y S + Y p Y (Units) • Y 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 mm. Hg. • Standard (Y 0) = pure water at ambient pressure = 0 MPa.

Y= YS + Yp Solute (or) Osmotic Potential • Represents the effect of dissolved solutes on water potential, YS = -RT cs R: gas constant (8. 32 J mol-1 K-1) T: absolute temperature (K) cs: concentration (mol L-1)

YS Solute (or) Osmotic Potential …of solutions at 25 o. C, – 0. 1 mol L-1 glucose = -0. 24 Mpa, – 0. 1 mol L-1 Na. Cl = -0. 48 Mpa, – 0. 1 mol L-1 Ca. Cl 2 = -0. 72 Mpa. Why? Entropy effect: the mixing of solutes and water increases the disorder of the system, thus lowering the free energy.

Y= YS + Y 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.

Y = YS + Yp examples Pressure Tension

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 Y.

Practice

Turgid/Plasmolysis 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 Cell -DY + + DY (Yinside - Youtside = DY ) Turgid Plasmolyzed

Pressure Probes Careful measurement of plant cell membrane permeability to water suggested that transport across the membrane was too rapid for simple diffusion. . one way to measure water permeability.

Aquaporins Volume flow rate = viscosity (h) pr 4 DYp 8 h Dx pressure gradient distance • 38 different genes code for 38 different aquaporin proteins (octimers) in Arabidopsis, …integral membrane proteins that form a water pore across the membrane. • 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?

Transport in Plants III Water 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 Relations xylem Process Osmosis, etc. Driving Force DY Diffusion Dcwv Bulk Flow DYp

Transport of Xylem Sap DRIVING FORCES • Root pressure, – sometime +DY from the soil/water matrix, but usually zero or negative, – active transport of ions into the root creates large gradients, thus - DY. • 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 Solute Accumulation in Xylem Guttation • Absorption and active transport of ions in the root create a -Dys and thus a lower Y, – lower Y provides a driving force for water uptake, and a thus +DYp, • 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).

Transport of Xylem Sap DRIVING FORCES • Root pressure, – sometime +DY from the soil/water matrix, but usually zero or negative, – active transport of ions into the root creates large gradients, thus - DY. • 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 Poisuille’s Equation Volume flow rate = viscosity (h) pr 4 DYp 8 h Dx pressure gradient distance 1. Create a tube, make it bigger. 2. Lower the viscosity. 3. Create and maintain a pressure gradient.

Evolution of Vasculature

Bryophytes (0. 5 mm - 50 cm) Simple vasculature ~ 500 mya

Haldrom/Leptom • 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. . Seta w/ Capsules

Lignin

Secondary Walls and Lignin • Secondary Walls: provide rigid support for conductive tissue, – maintain higher -Yp, • Lignin: highly branched phenolic polymer, may be associated with cellulose and proteins. Deposited in secondary walls, adds strength, – maintain higher -Yp, – limits “leaking”, …add structural potential, facilitating upward growth. Castor Bean Stem

Xylem Cells Bordered 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. Start submitting Essay Questions!