1. Transport Within Plants
Packet #36
Chapter #36

2. Introduction I Transport
Movement of materials between roots and shoots
Occurs on three levels
Cellular
Uptake and loss of water, and solutes, by individual cells
Tissue/Organ Level
“short distance” transport of substances
Whole Plant Level
Long distance transport of sap within xylem and phloem

3. Cellular Level Most Already Covered Packet #9 “Water”
Packet #12 “Cell Membrane & Movement of Molecules”
Packet #13 “Cell to Cell Communication”

4. Review I Diffusion Proton Pumps Regular Diffusion
Facilitated Diffusion
Active Transport
Proton Pumps
Use of ATP
Formation of the proton gradient

5. Review II Water Potential Also, review
A measure of free energy of water.
Measured in megapascals
Pure water has a water potential of 0 megapascals
Water with dissolved solutes has a negative water potential
Water moves from an area of higher water potential (less negative) to an area of lower water potential (more negative) water potential.
Also, review
Solute potential
Pressure potential
Osmotic Pressure
 = s + p

6. Review III Osmotic Pressure Recall
Determined by the concentration of dissolved substances (solutes) in a solution.
Cells regulate this pressure to prevent shrinking or bursting
Recall
Plant cells withstand high internal hydrostatic pressure because of their cell walls
Prevents the cell from expanding and bursting
When water moves into the cell, via osmosis, the central vacuole is filled
Cell swells
Turgor pressure is built up along the rigid cell walls.

7. Review IV Flaccid describes a limp cell. Plasmolyze Plasmolysis
The shrinking and pulling away of the plasma membrane from the cell wall
Plasmolysis
Process of shrinking and pulling away from the cell wall in a hypertonic environment
Turgor Pressure
Hydrostatic pressure
Describes the swelling of the cell and the associated pressure
Turgid cells are ones in which the solute concentration is greater than their surroundings.
Water flows in to reach an isotonic state.
Cell begins to swell and apply pressure on the cell wall.

8. Review V Facilitated Transport
The movement of a substance, including water, from an area of high concentration to an area of low concentration, using a protein but no ATP
The protein NOW has a name.

9. Aquaporins
Transport proteins that facilitate the passive movement of water across a membrane
Does not effect water potential but increases the rate at which water diffuses.

10. Tissue/Organ Level Lateral Transport
Short Distance along the Radial Axis of Plant Organs.

11. Introduction I Short distances along the radial axis of plant organs
Lateral Transport
Three routes
Cell to cell
Packet #12 & 13
Symplastic Pathway
The symplast is a continuum of living cytoplasm, which is connected from one cell to the next by cytoplasmic bridges called plasmodesmata.
Packet #11
Chapter 34 of Biology by Solomon

12. Introduction II Apoplastic Pathway
The apoplast consists of interconnected pourous cell walls of a plant, along which water and nutrient mineral ions move freely.
Water and minerals diffuse freely without ever entering a living cell.
Chapter 34 of Biology by Solomon

13. Whole Plant Level
Long Distance Transport

14. Introduction Vocabulary
Diffusion
Efficient process for moving solutes over short distances
Bulk Flow
Movement of fluid driven by pressure
Functions in long distance transport
Roots to leaves
Hydrostatic Pressure
Difference in pressure, generated in the phloem, between the top if the tube to the bottom
Transpirational Pull
Tension, or negative pressure, due to the evaporation of water from a leaf

15. Tension Cohesion Model & Transpiration Pull
Explains the rise of water in even the largest plants.
Transpiration pull
Tension or negative pressure due to the evaporation of water from a leaf
Result of the water potential gradient that ranges from the slightly negative water potentials in the soil and roots to the very negative water potentials in the atmosphere.
Rate of flow depend on diameter of the leaf.

16. Functions of Transport

17. Functions of Transport
Absorption of water and minerals by roots
Root hair/epidermis  cortex endodermis  pericycle  root xylem
Transport (ascent) of xylem sap
Xylem sap moves upwards to the veins that branch out each leaf
How?
Root Pressure
Control of transpiration
Guard cells control the size of stomata and help balance the photosynthesis-transpiration compromise
Transport of organic nutrients within phloem
Translocation
Phloem sap moves via bulk flow

18. Root Pressure

19. Root Pressure
Caused by the movement of water into roots from the soil as a result of the active absorption of nutrient mineral ions from the soil
Pushes water up through the xylem.
Causes guttation
HW assignment
Guttation—the exudation of water droplets. More water entering the system than leaving via transpiration so the excess is forced out.

20. Root Pressure II Transpiration low at night
Root cells still pump nutrients into the xylem
Minerals accumulate in the steele
Water potential gets low
Water moves in from the cortex of the root generating a positive pressure
Pressure forces fluid up the xylem

21. Transpiration

22. Transpiration Part II
Loss of water vapor from inside the leaf surfaces.
Transpiration Pull
Negative pressure or tension pulls the water out of the leaf through the mesophyll and ultimately through the stomata.
Pressure is transmitted from leaves, to root tips and even into the soil solution

23. Control of Transpiration
Guard cells control the size of stomata and help balance the photosynthesis- transpiration compromise
Cues for stomata to open at dawn
Light
Depletion of CO2 within air spaces
Circadian rhythms
Environmental stress can cause stomata to close during day

24. Sugar Translocation & Pressure Flow Hypothesis

25. Translocation I
The phloem transports sugars throughout the plant via translocation
Dissolved sugar is translocated upward or downward in phloem
Sucrose is the predominant sugar translocated
Dissolved sugar originates from a source to a sink
Direction of flow may change with the season or the developmental stage of the plant.

26. Translocation II Sugar Source Sugar Sink Storage Organ
Plant organ where sugar is produced by either photosynthesis or the breakdown of starch.
Area of excess sugar
Usually a leaf—mature leaf
Sugar Sink
Plant organ that is a net consumer or storer of sugar
Growing roots
Shoot tips
Apical meristems
Fruits
Seeds
Storage Organ
Can either be a source or sink depending on the season.

27. Bulk (Pressure) Flow Hypothesis
Movement of materials in phloem
Companion cells actively load sugar into the sieve tubes at the source
ATP is required for this process
ATP supplies energy to pump protons out of the sieve tube elements
Proton gradient drives the uptake of sugar by the cotransport of proteins back into the sieve tube elements
Sugar therefore accumulates in the sieve tube element
Causes the movement of water into the sieve tube via osmosis

28. Bulk Flow II
Research suggests that the ability to transport sugars and not photosynthetic rates limits crop production.
A better understanding of the factors that limit bulk flow of sugars may help to improve agricultural technology.