1. PLANT-CELL WATER RELATION TERMINOLOGY
HOFLER DIAGRAM

2. WATER Water is the most abaundant constituent of plant cell.
Leaves have 55-80% water
Wood have 30-60% water
Seeds 5-15%

3. Plant - Water Relations Corn yield as a function of water availability
Yield vs Water availability. Number of days with optimum water conditions.
Corn yield as a function of water availability

4. CELL WATER RELATION: TURGOR PRESSURE OSMOSIS IMBIBITION DIFFUSION
STOMATAL MECHANISM
TRANSPIRATION PROCCESS

5. Turgor Pressure
Turgor is a force exerted outward on a plant cell wall by the water contained in the cell.
Plant cell filled
with water 
Wilted plant cell 

6. Diffusion
Movement of molecules from an area of high concentration to an area of lower concentration.
Factors that affect the rate of diffusion: size of molecules, size of pores in membrane, temperature, pressure, and concentration.

7. [High] [Low] Diffusion concentrated, high energy molecules
diffuse, low energy molecules

8. Osmosis
Osmosis is the movement of WATER across a semi-permeable membrane
At first the concentration of solute is very high on the left.
But over time, the water moves across the semi-permeable membrane and dilutes the particles.

9. Osmosis between cells 20
If the concentration of the cell sap is greater in one cell than in its neighbour, water will pass by osmosis from the less concentrated to the more concentrated.
cell sap more
concentrated
cell sap less
concentrated
Osmosis between one cell and the next plays a part in the movement of water throughout the tissues of the plant.

10. Limp and turgid tissue 21
These cells are short of water; the tissue is limp and the plant is wilting
The cells have taken up
water by osmosis; the
cells are turgid and the
tissue is firm

11. Osmosis – A Special kind of Diffusion
Diffusion of water across a selectively permeable membrane (a barrier that allows some substances to pass but not others). The cell membrane is such a barrier.
Small molecules pass through – ex: water
Large molecules can’t pass through – ex: proteins and complex carbohydrates

12. Cell water potential
All living things need a continuous input of free energy to maintain and repair structures, as well as to grow and reproduce
Biochemical reactions, solute accumulation, and long distance transport are all driven by the input of free energy into the plant
This is defined as Water Potential.

13. Osmosis and Tonicity
Tonicity is the osmolarity of a solution--the amount of solute in a solution.
Solute--dissolved substances like sugars and salts.
Tonicity is always in comparison to a cell.
The cell has a specific amount of sugar and salt.
Osmosis is the diffusion of water across a plasma membrane.
Osmosis occurs when there is an unequal concentration of water on either side of the selectively permeable plasma membrane.
Remember, H2O
CAN cross the plasma membrane.

14. Tonic Solutions
A Hypertonic solution has more solute than the cell. A cell placed in this solution will give up water (osmosis) and shrink.
A Hypotonic solution has less solute than the cell. A cell placed in this solution will take up water (osmosis) and blow up.
An Isotonic solution has just the right amount of solute for the cell. A cell placed in this solution will stay the same.

15. Hypotonic – The solution on one side of a membrane where the solute concentration is less than on the other side. Hypotonic Solutions contain a low concentration of solute relative to another solution.
Hypertonic – The solution on one side of a membrane where the solute concentration is greater than on the other side. Hypertonic Solutions contain a high concentration of solute relative to another solution.

16. Over time molecules will move across the membrane until the concentration of solutes is equal on both sides. This type of solution is called ISOTONIC.

17. PLANT CELLS Hypotonic Solution Hypertonic Solution
Turgor Pressure builds in the cell and causes osmosis to stop
because of the rigid cell wall.
Plants will wilt when cells
lose water through osmosis.

18. HOFLER DIAGRAM

19. Hofler diagram uplatnění The roles of individual components:
g - high trees
m - imbibition and germination (till water content about 60 %)
p - veins, apoplast, growth, movements of stomata
s - transport on cell and tissue level, plasmolysis, plasmoptysis, root pressure, osmotic adjustment, growth
uplatnění

20. 3.2.1 The pressure-volume curve
Methodology: first catch your shrub, stem or leaf preferably somewhere in the Mediterranean basin
Place stem or leaf overnight in a beaker of water in a dark cupboard, covered with a plastic bag, to allow complete rehydration to full turgor
Method 1: invert stem in pressure bomb, pressurise to reach balance point, invert pre-weighed tube containing absorbent material over petiole, apply over-pressure of 0.2 to 0.5 MPa for minutes; depressurise, weigh tube, re-measure new balance point; repeat procedure for 10 data points through point of turgor loss
Method 2 : weigh stem/leaf, measure initial balance point, remove, put branch on bench and leave to dehydrate for mins (repeat for replicate 2 and 3); reweigh, re-measure balance point, repeat……
Tabulate data as  and Relative water content and plot as 1/ against RWC…….

21. The curved part of the plot represents approach to loss of turgor; during this period, there is a a progressive decrease in turgor and as water is extruded, increase in osmotic potential/pressure;
Extrapolate linear portion of curve from turgor loss point to 1/ axis to derive 1/s or 1/ since below TLP,  = s (or - )
For a given volume of water extruded, calculate turgor pressure

22. Elasticity of cell walls- the shape of the curve is markedly dependent on the wall rigidity; if the wall is very rigid, the water potential components change very rapidly for a given water loss; more elastic cells allow turgor to be maintained as cells progressively dehydrate, because of the extra “give” in the cell wall
Bulk modulus of elasticity,  (MPa), amount by which a small change in volume (DV) brings about a small change in turgor (DP), such that DP =  . DV/V, and  = dP/dV . V
Modulus of elasticity () can therefore be derived from the slope of the linear portion of the P-V curve; a high value of  corresponds to low cell-wall elasticity in rigid cell, as a large change in P occurs for a small amount of water expressed; a lower value corresponds to an elastic cell
3.2.2 The Höfler diagram