Salmonberry bird…
Rubus spectabilisSalmonberry
Rhizomes
Clones
Leaves Alternet
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…
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.
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 .
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?
To Do
Transport of Xylem Sap,
Transpiration and control,
Evolution of water transport and adaptations.
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.
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
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....
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.