1. Ch:36 Transport in Vascular Plants
By:
Stephanie Tuminello
Patrick Singer
Esther Urena
Melissa Giammarino
Solange Beckles

2. Transport in Vascular Plants Occurs at 3 Levels
1-Transport of water and solutes in individual cells
2- short distance transport at organ and tissue level from cell to cell
3-long distance transport in xylem and phloem at the level of the whole plant

3. Proton Pumps
uses ATP to pump H+ across cell membrane through active transport
Contributes to voltage called membrane potential
Membrane potential is separation of charges across a membrane
Plants use membrane potential and energy in the gradient to transport solutes
Cotransport couples passage of one solute to the passage of another in the opposite direction
In plants sucrose is cotransported with H+

4. Water potential
Osmosis is passive transport of water across a membrane
Water potential(Ψ) is the combination of solute concentration and pressure
Water moves from regions of higher water potential to lower water potential
Solute potential is proportional to the amount of dissolved solute particles
Solute particles bind to water molecules and reduce the amount of free water
Pressure potential is the amount of pressure exerted on the solution

5. Water Potentials Effect on Cells
Cells that have the same water potential as the surrounding solution are flaccid
If the solution has a lower water potential than the cell water will leave the cell and the cell will plasmolyze
When plasmolyed, the protoplast will shrink and pull away from the cell wall
If the solution has a higher water potential than the cell water will enter the cell and it will become turgid, the ideal state for plants
Water often crosses membranes through proteins called aquaporins

6. The Three Compartments of Cells
The plasma membrane is selectively permeable barrier between the cell wall and the cytosol
Most plant cells also have vacuoles
The tonoplast, which is the vacuolar membrane, regules molecular traffic between the cytosol and cell sap
The tonoplasts H+ gradient is used to move ions across the vascular membrane
Plasmodesmata connect the cytosol of neighboring cells the continuum of cytosol of neighboring cell is the symplast
The continuum of cell walls and the extercelluar space is the apoplast

7. 3 Routes of Short-Distance Transport
In the transmembrane route is when substances move out of one cell and across the cell wall to enter the neighboring cell
In the symplastic route solutes and water move from cell to cell via the plasmodesmata after entering one cell
In the apoplastic route solutes and water move along the byways provided by the continuum of cell walls

8. Long-Distance Transport
Bulk Flow, how long distance transport occurs, is the movement of a fluid driven by pressure
Bulk Flow occurs through the tracheids and vessels of the xylem, driven by negative pressure
Transpiration is the evaporation of water from a leaf which reduces pressure and creates tension pulling sap from the roots
Bulk flow occurs in the sieve tubes of the phloem

9. Roots Absorb Water and Minerals From Soil
Most absorption occurs at root tips where the epidermis is permeable to water.
Root hairs are extensions of the epidermal cells.
Soil particles coated with water and minerals attach to root hairs.
This solution then flows along the apoplast into the root cortex.
Here water and certain solutes are taken up into the symplast.
Roots and fungi form mycorrhizae, symbiotic structures consisting of plant roots united with fungal hyphae.
The hyphae absorb minerals and transfers them to the host plant.

10. The Endodermis
The endodermis is the innermost layer of cells in the root cortex and surrounds the vascular cylinder
Last selective barrier for minerals going to the vascular tissue
Casparian strips line the transvverse and radial walls of the vascular cylinder, making it impervious to water
Due to casparian strips minerals must pass through passively selective plasma membranes
The last part of minerals path from the soil to xylem pathway is the trachieds and vessels of the xylem, which lack protoplasts and thereofre are part of the apoplast

11. The Ascent of Xylem Sap
At night when transpiration is really low, root cells continue to pump mineral ions into the xylem of vascular plants.
Because of the accumulation of minerals due to the epidermis, there is a lower water potential within the vascular cylinder.
Root pressure is the upward push of xylem sap.
When more water enters the leaf than is transcribed the result is guttation.

12. Water and Minerals Ascend From Roots to Shoots Through the Xylem
Xylem sap flows upward starting at the roots, then travel throughout the shoot system, into veins that branch out into each leaf.
Transpiration is the loss of water vapor from leaves and other aerial parts.
Plants wilt if the water last through transpiration is not replaced by water traveling up from the roots.

13. Xylem Sap Ascent By Bulk Flow
The movement of fluid in bulk flow is driven by a water potential difference at opposite ends of a conduit.
No energy is expended in lifting xylem sap by bulk flow.
Absorption of sunlight causes water to evaporate from mesophyll cells, driving transpiration, lowering water potential

14. Accent of Xylem Sap
Cohesion and adhesion facillitate the long-distance transport of xylem sap from the leaves to the roots into the soil solution
The cohesion of water due to hydrogen bonding makes it possible to pull a column of sap from above without the water molecules separating
The strong adhesion of water molecules to the hydrophilic walls of xylem cells aids in offsetting the downward pull of gravity
Transpirational pull can extend down to the roots only through an unbroken chain of water molecules.
Cavitation is the formation of a water vapor pocket in a vessel and can cause the chain to break.

15. Transpirational Pull
The air in the airspaces are used to express the mesophyll to the carbon dioxide it needs to perform photosynthesis is saturated with water vapor because it is in contact with the most walls of the cells
Since the air inside the leaf has a lower water potential then the air outside the leaf, water vapor in the air enters the space of leaf diffuses down its water potential gradient and exits the leaf through the stomata. This is called transpiration
The leading hypothesis as to how loss of water vapor from a leaf translates into the pulling force for upward movement of water through a plant is that negative pressure that causes water to move up through the xylem develops at the air water interface in the mesophyl wall
Transpirational pull depends on some of the special properties that water possesses, such as adhesion, cohesion, and surface tension
Negative pressure lowers water potential the negative water potential of leaves provides the pull in transpirational pull

16. Stomata help regulate the rate of transpiration
Leaves have very large surface areas to increase the rate of photosynthesis
Leaves have about 20 to 30 times more internal surface area than outside surface area due to the cells irregular shape

17. Effects Of Transpiration On Wilting And Leaf Temperature
Usually transpiration draws up water from the roots quickly enough to replace the water lost by evaporation
In some extended periods of drought water cannot be drawn up as fast as it evaporates, when this happens wilting occurs
Transpiration also causes evaporative cooling which lowers the temperature of the leaf as much as 10 or 15 degrees compared with the surrounding air to prevent enzyme denaturation

18. Stomata
The amount of water lost by a leaf depends both on the number of stomata and average size of the pores
The stomatal density is under both environmental and genetic controlling factors
Guard cells buckle outward when turgid, increasing the size of the pores between them, thus more water is lost

19. Stomatal Opening and Closing
The active transport of H +out of guard cells creates voltage that drives k + into guard cells
When k + accumulates stomata open, and close when k + leaves the cell
A depletion of CO2 in the air spaces of the leaf occurs during the beginning of photosynthesis in the mesophyll will result in the stomata opening
The stomata will also open due to the internal clock of the guard cells
Cycles with intervals of 24 hours are circadian rhythms
Environmental stresses, such as water deficiency, can cause the stomata to close even during the day
Guard cells regulate photosynthesis and transpiration on a moment-to-moment basis on many different stimuli

20. Xerophyte Adaptations that Reduce Transpiration
Xerophytes are plants adapted to dry climates
Several leaf modifications help reduce the rate of transpiration:
Small, thick leaves reduce surface area relative to leaf volume limiting water loss.
Hairy leaves trap a boundary layer of water.
Stomata are located on the underside of the leaf in clusters protecting them from the wind.
They use CAM, crassulacean acid metabolism, to attain CO2. mesophyll cells transform CO2 into organic acids during the night allowing the stomata to close during the day when its hotter.
During the day, sugars are synthesized by the C3 photosynthetic pathway.

21. Movement of Sugar
Translocation is the movement of organic nutrients in the plants
In angiosperms sieve tube membranes are the conduits for translocation
Phloem sap is much different form xylem sap and contains large amounts of sugar
A sugar source is a plant organ that is a net producer of sugar
A sugar sink is a net consumer of sugar, most notably mature leaves

22. Movement of Sugar (cont’d)
Direction of flow in sugar tubes depends on the surrounding plant parts and external factors such as season
Sometimes sugar travels through cells through the symplastic or apoplastic pathways
Special cells called transfer cells have special ingrown walls that improve solute transfer
Phloem lets sucrose out at the sink end of the seive tube
The concentration of free sugar is always lower in the sink then in the tube because sugar in the sink is either absorbed or converted into insoluble polymers

23. Pressure Flow
In angiosperms sugar moves through sieve tubes through bulk flow called pressure flow
Pressure increases at the source end and decreases at the sink end which causes water to flow from the source to the sink, carrying sugar with it