1. TRANSPORT in PLANTS

2. What must be transported in plants?
H2O & minerals
Sugars
Gas Exchange

3. Transport of Water & Minerals
Occurs in the xylem
H2O is moved from root to leaves
Transpiration  loss of H2O from leaves (thru stomata)
Processes
Evaporation
Cohesion
Adhesion
Negative Pressure

4. Transport of Sugar Occurs in the phloem Bulk Flow
Calvin Cycle (Dark Rxns) in leaves loads sugar into the phloem
Positive Pressure Movement
Source (where sugar is made) to Sink (where sugar is stored/consumed)

5. Gas Exchange Photosynthesis Respiration CO2 in O2 out
Transport occurs through stomata
Surrounded by guard cells
Control opening & closing of stomata
Respiration
O2 in
CO2 out
Roots exchange gases w/ air spaces in the soil
Why can over-watering kill a plant?

6. Transport in Plants
Three main physical forces that fuel transport in plants:
Cellular
Gases from the environment into plant cells
H2O & minerals into root hairs
Short-Distance Transport
Cell to cell
Moving sugar from leaves into phloem
Long-Distance Transport
Moving substances through the xylem & phloem of a whole plant

7. Cellular Transport Passive Active
Diffusion down a concentration gradient
Occurs faster w/ proteins
Carrier Proteins (facilitated diffusion)
Active
Requires energy
Proton Pump
Pumps H+ out of a cell
Creates a proton gradient (stored energy)
Generates a membrane potential
Used to transport many solutes

8. Cellular Transport –Active Transport

9. Cellular Transport -Water Potential
Combined effects of solute concentration & physical pressure
Moves from high H2O potential to a low H2O potential
Inversely proportional to solute concentration
Adding solutes – Lowers water potential
Directly proportional to pressure
Raising pressure- Raises water potential
Negative pressure (tension) decreases water potential

10. Cellular Transport- Water Potential
H2O potential =
pressure potential + solute potential
A) adding solutes reduces
H2O potential
B & C) adding pressure,
increases H2O
potential
D) negative pressure
decreases H2O potential

12. Short-Distance Transport
Movement from cell to cell by…
Transmembrane
Crosses membranes & cell walls
Slow, but controlled
Called the apoplastic route
Cytosol (cytoplasm)
Plasmodesmata junctions connect the cytosol of neighboring cells
Called the symplast route

13. Long-Distance Transport
Bulk Flow
Movement of a fluid driven by pressure
Xylem: tracheids & vessel elements
Negative pressure
Transpiration creates negative pressure by pulling xylem up from the roots
Phloem: Sieve tubes
Positive pressure
Loading of sugar at the leaves generates a high positive pressure, which pushes phloem sap thru the sieve tubes

14. Four Basic Transport Functions
Water & Mineral Absorption of Roots
Transport of Xylem Sap
Control of Transpiration
Translocation of Phloem Sap

15. Water & Mineral Absorption
Root Hairs
Increase surface area
Mineral Uptake by Root Hairs
Dilute solution in the soil
Active Transport Pumps
May concentrate solutes up to 100X in the root cells
Water Uptake by Root Hairs
From high H2O potential to low H2O potential
Creates root pressure

16. Water and Mineral Absorption – Root Structure
MONOCOT ROOT
DICOT ROOT

17. Water and Mineral Absorption – Water Transport in Roots
Apoplastic or
symplastic
Until the
endodermis
Is reached!!

18. Water and Mineral Absorption – Control of Water & Minerals in the Root
Endodermis
Surrounds the stele
Selective passage of minerals
Freely enters via the symplastic route
Dead end via the apoplastic route
Casparian Strip
Waxy material
Allows for the preferential transport of certain minerals into the xylem

19. Water & Mineral Absorption & Mycorrhizae
Symbiotic relationship b/w fungi & plant
Symbiotic fungi increase surface area for absorption of water & minerals
Increases volume of soil reached by the plant
Increases transport of water & minerals to host plant

20. Transport of Xylem Sap: Pulling
TRANSPIRATION-COHESION-TENSION MECHANISM
Transpirational Pull
Drying air makes H2O evaporate from the stomata of the leaves
Cohesion
b/w H2O molecules
causes H2O to form a continuous column
Adhesion
H2O molecules adhere to the side of the xylem
Tension
As H2O evaporates from the leaves, it moves into roots by osmosis

21. Transport of Xylem Sap: Pushing
Root Pressure – pushes H2O up xylem
Due to the flow of H2O from soil to root cells at night when transpiration is low
Positive pressure pushes xylem sap into the shoot system
More H2O enters leaves than exits (is transpired) at night
Guttation - H2O on morning leaves

22. Transport of Xylem Sap- Ascent of H2O in Xylem: Bulk Flow
Due to three main
mechanisms:
Transpirational Pull
Adhesion & cohesion
Water potential
High in soil  low in leaves
Root pressure
Upward push of xylem sap
Due to flow of H2 O from soil to root cells

23. Control of Transpiration: Gas Exchange
Stomate Function
Compromise b/w photosynthesis & transpiration
Amount of transpiration (H2O loss) must be balanced with the plant’s need for photosynthesis
Leaf may transpire more than its weight in water every day!
OPEN
STOMATA
CLOSED
STOMATA

24. Control of Transpiration- Leaf Structure

25. Control of Transpiration - Photosynthesis vs. Transpiration
Open stomata allow for CO2 needed for photosynthesis to enter
There is a trade-off…..
Plant is losing water at a rapid rate
Regulation of the stomata allow a plant to balance CO2 uptake with H2O loss
What types of environmental
conditions will increase transpiration?

26. Control of Transpiration – Stomatal Regulation
Microfibril Mechanism
Guard cells attached at tips
Microfibrils elongate & cause cells to arch open
Microfibrils shorten & cause cells to close
Ion Mechanism
Uptake of K+ by guard cells during the day
H2O potential becomes more negative
H2O enters the guard cells by osmosis
Guard cells become turgid & buckle open
Loss of K+ by guard cells
H2O potential becomes more positive
H2O leaves the guard cells by osmosis
Guard cells become flaccid & close the stomata

27. Control of Transpiration- Stomatal Regulation

28. Control of Transpiration – Stomatal Regulation
Three cues that open stomata at sunrise:
Light Trigger
Blue-light receptor in plasma membrane
Turns on proton pumps & takes up K+
Depletion of CO2 in air spaces
CO2 used up at night by the Calvin Cycle
Internal Clock (Circadian Rhythm)
Automatic 24-hour cycle

29. Control of Transpiration- Adaptations that Reduce Transpiration
Small, thick leaves
Reduces surface area-to-volume ratio
Thick cuticle
Stomata on lower leaf side with depressions
Depressions shelter the stomata from wind
May shed leaves during dry months
Fleshy stems for water storage
CAM metabolism
Takes in CO2 at night & can close stomata during the day

30. Translocation of Phloem Sap
Water & sugar (mostly sucrose)
Moved through sieve tube members
Porous cross walls that allow sap to move through
Travels in many directions
From source to sink (where sugar is consumed/stored)
Source: leaf
Sink: roots, shoots, stems,& fruits

31. Translocation of Phloem Sap- Loading of Sugars
Flow through the symplast or apoplast in mesophyll cells into sieve-tube members
Active co-transport of sucrose with H+
Proton pump

32. Translocation of Phloem Sap- Pressure Flow
Bulk Flow Movement
Sugar loaded at the source
Reduces water potential
Causes H2O to move into sieve-tube members
Creates a hydrostatic pressure that pushes sap through the tube
Sucrose is unloaded at the sink
Water moves into xylem & is carried back up the plant

33. Phloem Transport

34. Pressure Flow and Translocation of Sugars