7. Chapter 36: Transport in Vascular Plants
1. Where does transport occur in plants? Start with water….

8. Figure 36.2 An overview of transport in a vascular plant
Minerals
H2O

9. Figure 36.2 An overview of transport in a vascular plant
Minerals
H2O
CO2 O2

10. Figure 36.2 An overview of transport in a vascular plant
CO2 O2
Light
H2O
Sugar
H2O
Minerals

11. Figure 36.2 An overview of transport in a vascular plant
Minerals
H2O
CO2 O2
Sugar
Light

12. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?

13. Figure 36.3 Proton pumps provide energy for solute transport
CYTOPLASM
EXTRACELLULAR FLUID
ATP H+
Proton pump generates
membrane potential
and H+ gradient. – +

14. Figure 36.4 Solute transport in plant cells+
CYTOPLASM
EXTRACELLULAR FLUID
Cations ( for
example) are driven into the cell by the membrane potential.
Transport protein K+ –
(a) Membrane potential and cation uptake H+
NO3–
NO3 –
(b) Cotransport of anions
Plant cells can
also accumulate a
neutral solute,
such as sucrose
( ), by
cotransporting
down the
steep proton
gradient. S
(c) Cotransport of a neutral solute
Cell accumulates
anions (NO3 –, for
example) by
coupling their transport to the inward diffusion of H+ through a
cotransporter.

15. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?
What influences the movement of water?
Ψ = Ψs + Ψp
Water moves from HIGH  low (more  less)

16. Fig. 36.5 Water potential and water movement: an artificial model
Ψ = Ψs + Ψp
Y = –0.23 MPa
(a)
0.1 M
solution
(d)
(c)
(b)
YP = 0
H2O
YS = –0.23
Y= –0.23 MPa
YS = –0.23
Y = 0 MPa
YP =
Y = 0.07 MPa
YP =
YS = 0
Y = –0.30 MPa
YP = –0.30
YP = 0
Y = 0 MPa
Pure water
+ solute decreases Ψs
Water goes from high  low
+ pressure counteracts Ψs
More pressure forces water across membrane
(-) pressure also moves water

17. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?
What influences the movement of water?
What does this mean for plant cells?

18. Figure 36.6 Water relations in plant cells
0.4 M sucrose solution:
p = 0
s = –0.9
 = –0.9 MPa
p = 0
s = –0.7
 = –0.7 MPa
Initial flaccid cell:
p = 0
s = 0
 = 0 MPa
Distilled water:
Plasmolyzed
cell at osmotic
equilibrium
with its
surroundings
p = 0
 = –0.9 MPa
p = 0.7
s = –0.7
 = 0 MPa
Turgid cell
at osmotic
Initial conditions: cellular  > environmental . The cell
loses water and plasmolyzes. After plasmolysis is complete,
the water potentials of the cell and its surroundings are the
same.
Initial conditions: cellular  < environmental . There
is a net uptake of water by osmosis, causing the cell to
become turgid. When this tendency for water to enter is
offset by the back pressure of the elastic wall, water
potentials are equal for the cell and its surroundings.
(The volume change of the cell is exaggerated in this
diagram.)
(b)
Plasmolysis – shrinking of a plant cell away from its cell wall due to water loss
Turgid – plant cell full of water due to its high solute concentration
(turgor pressure)
Aquaporins allow water to move quickly across a membrane

19. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?
What influences the movement of water?
What does this mean for plant cells?
What are the transport routes dissolved substances can take between cells?

20. Fig 36.8 Cell compartments and routes for short-distance transport
Transport proteins in
the plasma membrane
regulate traffic of
molecules between
the cytosol and the
cell wall.
the vacuolar
membrane regulate
traffic of molecules
between the cytosol
and the vacuole.
Plasmodesma
Vacuolar membrane
(tonoplast)
Plasma membrane
Cell compartments. The cell wall, cytosol, and vacuole are the three main
compartments of most mature plant cells.
Key
Symplast
Apoplast
The symplast is the
continuum of
cytosol connected
by plasmodesmata.
The apoplast is
the continuum
of cell walls and
extracellular
spaces.
Transmembrane route
Symplastic route
Apoplastic route
Transport routes between cells. At the tissue level, there are three passages:
the transmembrane, symplastic, and apoplastic routes. Substances may transfer
from one route to another.
Cell wall
Cytosol
Vacuole
(a)
(b)
How does water get into the plant?

21. Figure 36.9 Lateral transport of minerals and water in roots1 2 3
Uptake of soil solution by the
hydrophilic walls of root hairs
provides access to the apoplast.
Water and minerals can then
soak into the cortex along
this matrix of walls.
Minerals and water that cross
the plasma membranes of root
hairs enter the symplast.
As soil solution moves along
the apoplast, some water and
minerals are transported into
the protoplasts of cells of the
epidermis and cortex and then
move inward via the symplast.
Within the transverse and radial walls of each endodermal cell is the
Casparian strip, a belt of waxy material (purple band) that blocks the
passage of water and dissolved minerals. Only minerals already in
the symplast or entering that pathway by crossing the plasma
membrane of an endodermal cell can detour around the Casparian
strip and pass into the vascular cylinder.
Endodermal cells and also parenchyma cells within the
vascular cylinder discharge water and minerals into their
walls (apoplast). The xylem vessels transport the water
and minerals upward into the shoot system.
Casparian strip
Pathway along
apoplast
Pathway
through
symplast
Plasma
membrane
Apoplastic
route
Symplastic
Root
hair
Epidermis
Cortex
Endodermis
Vascular cylinder
Vessels
(xylem) 4 5
Why is the Casparian strip so important?
forces dissolved substances across a selectively permeable membrane
Keeps unwanted & unrecognized substances OUT of the plant

22. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?
What influences the movement of water?
What does this mean for plant cells?
What are the transport routes dissolved substances can take between cells?
What is the mutualistic relationship between plant roots and
another biological organism?

23. Figure 36.10 Mycorrhizae, symbiotic associations of fungi and roots
2.5 mm

24. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?
What influences the movement of water?
What does this mean for plant cells?
What are the transport routes dissolved substances can take between cells?
What is the mutualistic relationship we discussed between plant roots
another biological organism?
How is xylem sap transported? (How can it defy gravity?)
Cohesion – water’s ability to stick to itself via hydrogen bonds
Adhesion – water’s ability to stick to other polar substances via H-bonds
WHY??
electronegative oxygen creates polar covalent bond in water

25. Figure 36.13 Ascent of xylem sap
Outside air Y
= –100.0 MPa
Leaf Y (air spaces)
= –7.0MPa
Leaf Y (cell walls)
= –1.0 MPa
Trunk xylem Y
= – 0.8 MPa
Water potential gradient
Root xylem Y
= – 0.6 MPa
Soil Y
= – 0.3 MPa
Mesophyll
cells
Stoma
Water
molecule
Atmosphere
Transpiration
Adhesion
Cell
wall
Cohesion, by
hydrogen
bonding
Root
hair
Soil
particle
Cohesion
and adhesion
in the xylem
Water uptake
from soil
Transpiration – loss of water vapor through leaves that pulls water up from roots
What controls the loss of water?
Stomata

26. Fig. 36.14 Open stomata (left) and closed stomata (colorized SEM)
What controls the opening & closing of the stomata?
- K+ in the guard cells

27. Figure 36.15 The mechanism of stomatal opening and closing
Cells turgid/Stoma open
H2O
Radially oriented
cellulose microfibrils
Cell
wall
Vacuole
Guard cell K+
Changes in guard cell shape and stomatal opening
and closing (surface view). Guard cells of a typical
angiosperm are illustrated in their turgid (stoma open)
and flaccid (stoma closed) states. The pair of guard
cells buckle outward when turgid. Cellulose microfibrils
in the walls resist stretching and compression in the
direction parallel to the microfibrils. Thus, the radial
orientation of the microfibrils causes the cells to increase
in length more than width when turgor increases.
The two guard cells are attached at their tips, so the
increase in length causes buckling.
(a)
Role of potassium in stomatal opening and closing.
The transport of K+ (potassium ions, symbolized
here as red dots) across the plasma membrane and
vacuolar membrane causes the turgor changes of
guard cells.
(b)
Cells flaccid/Stoma closed

28. Chapter 36: Transport in Vascular Plants
Where does transport occur in plants? Start with water….
How are solutes transported between cells?
What influences the movement of water?
What does this mean for plant cells?
What are the transport routes dissolved substances can take between cells?
What is the mutualistic relationship we discussed between plant roots
another biological organism?
How is xylem sap transported? (How can it defy gravity?)
How is phloem sap transported?

29. Figure 36.17 Loading of sucrose into phloem
Sucrose manufactured in mesophyll cells can
travel via the symplast (blue arrows) to
sieve-tube members. In some species, sucrose
exits the symplast (red arrow) near sieve
tubes and is actively accumulated from the
apoplast by sieve-tube members and their
companion cells.
(a)
Mesophyll cell
Cell walls (apoplast)
Plasma membrane
Plasmodesmata
Companion
(transfer) cell
Sieve-tube
member
Phloem
parenchyma cell
Bundle-
sheath cell
High H+ concentration
Cotransporter
Proton
pump
ATP
Key
Sucrose
Apoplast
Symplast H+
A chemiosmotic mechanism is responsible for
the active transport of sucrose into companion cells
and sieve-tube members. Proton pumps generate
an H+ gradient, which drives sucrose accumulation
with the help of a cotransport protein that couples
sucrose transport to the diffusion of H+ back into the cell.
(b)
Low H+ concentration S

30. Figure 36.18 Pressure flow in a sieve tube
Vessel
(xylem)
H2O
Sieve tube
(phloem)
Source cell
(leaf)
Sucrose
Sink cell
(storage
Root) 1
Loading of sugar (green dots)
into the sieve tube at the
source reduces water
potential inside the
sieve-tube members.
This causes the tube
to take up water
by osmosis. 2 4 3
This uptake of
water generates
a positive pressure
that forces the
sap to flow along
the tube.
The pressure is
relieved by the
unloading of sugar and the consequent
loss of water from the tube
at the sink.
In the case of
leaf-to-root
translocation,
xylem recycles
water from sink
to source.
Transpiration stream
Pressure flow

31. Please put your Ch. 29 & 10 Learning Logs in the blue bin.
Take a Ch. 36 Notes Packet AND the Plant Unit Potential FRQs.
FYI: Animal Unit FRQs are graded…we’ll review them tomorrow in class.