Transcript Slide 1

Chapter 36: Transport in Vascular Plants
1. Where does transport occur in plants? Start with water….
Figure 36.2 An overview of transport in a vascular plant
H2O
H2O
Minerals
Figure 36.2 An overview of transport in a vascular plant
CO2
H2O
H2O
Minerals
O2
Figure 36.2 An overview of transport in a vascular plant
CO2
O2
Light
H2O
H2O
Minerals
Sugar
Figure 36.2 An overview of transport in a vascular plant
CO2
O2
Light
H2O
Sugar
O2
H2O
Minerals
CO2
Chapter 36: Transport in Vascular Plants
1. Where does transport occur in plants? Start with water….
2. How are solutes transported between cells?
Figure 36.3 Proton pumps provide energy for solute transport
CYTOPLASM
ATP
EXTRACELLULAR FLUID
–
+
–
+
–
H+
H+
+
H+
H+
H+
H+
–
–
+
H+
H+
+
Proton pump generates
membrane potential
and H+ gradient.
Figure 36.4 Solute transport in plant cells
CYTOPLASM
K+
K+
–
+
–
–
+
EXTRACELLULAR FLUID
+
Cations ( K+ for
example) are driven
into the cell by the
membrane potential.
K+
K+
K+
K+
K+
–
+
–
+
Transport protein
(a) Membrane potential and cation uptake
–
–
H+
–
H+
+
H+
+
+
+ H
H+
H+
H+
H+
–
–
–
H+
+
+ H+
H+
H+
+
Cell accumulates
anions (NO3 –, for
example) by
coupling their
transport to the
inward diffusion
of H+ through a
cotransporter.
(b) Cotransport of anions
H+
H+
S
–
+
–
+
–
+
H+
H+
H+
H+
H+
H+
H+
–
+
–
+
–
+
(c) Cotransport of a neutral solute
H+
H+
S
H+
Plant cells can
also accumulate a
neutral solute,
such as sucrose
( S ), by
cotransporting
H+ down the
steep proton
gradient.
Chapter 36: Transport in Vascular Plants
1. Where does transport occur in plants? Start with water….
2. How are solutes transported between cells?
3. What influences the movement of water?
Ψ = Ψs + Ψp
Water moves from HIGH  low (more  less)
Fig. 36.5 Water potential and water movement: an artificial model
Ψ = Ψs + Ψp
(b)
(a)
(c)
(d)
0.1 M
solution
Pure
water
H2O
H2O
H2O
H2O
YP = 0
Y = 0 MPa
Y = –0.23 MPa
YP = 0.30
YP = 0.23
YS = –0.23
YS = –0.23
Y = 0 MPa
Y = 0 MPa
YS = –0.23
Y = 0 MPa
Y = 0.07 MPa
YP = –0.30
YP =
YS =
YS = –0.23
0
Y = –0.30 MPa
0
Y = –0.23 MPa
+ solute decreases Ψs
Water goes from high  low
+ pressure counteracts Ψs
More pressure forces water across membrane
(-) pressure also moves water
Chapter 36: Transport in Vascular Plants
1.
2.
3.
4.
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?
Figure 36.6 Water relations in plant cells
Plasmolyzed
cell at osmotic
equilibrium
with its
surroundings
p = 0
s = –0.9
0.4 M sucrose solution:
p = 0
s = –0.9
Initial flaccid cell:
p = 0
s = –0.7
 = –0.7 MPa
 = –0.9 MPa
 = –0.9 MPa
(a) 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.
Distilled water:
p = 0
Turgid cell
s = 0
at osmotic
 = 0 MPa
equilibrium
with its
surroundings
p = 0.7
s = –0.7
 = 0 MPa
(b) 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.)
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
Chapter 36: Transport in Vascular Plants
1.
2.
3.
4.
5.
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?
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.
Cell wall
Cytosol
Vacuole
Transport proteins in
the vacuolar
membrane regulate
traffic of molecules
between the cytosol
and the vacuole.
Vacuolar membrane
Plasmodesma
Plasma membrane (tonoplast)
(a) Cell compartments. The cell wall, cytosol, and vacuole are the three main
compartments of most mature plant cells.
Key
Symplast
Apoplast
Transmembrane route
Apoplast
The symplast is the
continuum of
cytosol connected
by plasmodesmata.
Symplast
Symplastic route
The apoplast is
the continuum
of cell walls and
extracellular
spaces.
Apoplastic route
(b) 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.
How does water get into the plant?
Figure 36.9 Lateral transport of minerals and water
in roots
Casparian strip
Pathway along
apoplast
Endodermis
Pathway
through
symplast
1
2
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.
Casparian strip
Minerals and water that cross
the plasma membranes of root
hairs enter the symplast.
1
Plasma
membrane
Apoplastic
route
3
2
3
4
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.
Symplastic
route
4
5
Vessels
(xylem)
Root
hair
Epidermis
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.
5
Cortex
Endodermis 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.
Why is the Casparian strip so important?
-forces dissolved substances across a selectively permeable membrane
-Keeps unwanted & unrecognized substances OUT of the plant
Chapter 36: Transport in Vascular Plants
1.
2.
3.
4.
5.
6.
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?
Figure 36.10 Mycorrhizae, symbiotic associations of fungi and roots
2.5 mm
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?
7. 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
1.
2.
3.
4.
5.
6.
Figure 36.13 Ascent of xylem sap
Xylem
sap
Outside air Y
= –100.0 MPa
Leaf Y (air spaces)
= –7.0MPa
Transpiration
Leaf Y (cell walls)
= –1.0 MPa
Root xylem Y
= – 0.6 MPa
Soil Y
= – 0.3 MPa
Water potential gradient
Trunk xylem Y
= – 0.8 MPa
Xylem
cells
Mesophyll
cells
Stoma
Water
molecule
Atmosphere
Adhesion
Cell
wall
Cohesion,
by
Cohesion
and adhesion hydrogen
bonding
in the xylem
Water
molecule
Root
hair
Water uptake
from soil
Soil
particle
Water
Transpiration – loss of water vapor through leaves that pulls water up from roots
What controls the loss of water?
Stomata
Fig. 36.14 Open stomata (left) and closed stomata (colorized SEM)
20 µm
What controls the opening & closing of the stomata?
- K+ in the guard cells
Figure 36.15 The mechanism of stomatal opening and closing
(a) 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.
Cells turgid/Stoma open Cells flaccid/Stoma closed
Cell
wall
Radially oriented
cellulose microfibrils
Vacuole
Guard cell
(b) 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.
H2O
K+
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
H2O
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?
7. How is xylem sap transported? (How can it defy gravity?)
8. How is phloem sap transported?
1.
2.
3.
4.
5.
6.
Figure 36.17 Loading of sucrose into phloem
High H+ concentration
Mesophyll cell
Cell walls (apoplast)
Plasma membrane
Plasmodesmata
Companion
(transfer) cell
Sieve-tube
member
Cotransporter
H+
Proton
pump
S
Key
ATP
Mesophyll cell
Bundlesheath cell
Phloem
parenchyma cell
(a) 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.
H+
Low H+ concentration
H+
Sucrose
S
Apoplast
Symplast
(b) 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.
Figure 36.18 Pressure flow in a sieve tube
Vessel
(xylem)
Sieve tube
(phloem)
H2O
Source cell
(leaf)
Sucrose
1
H2O
2
4
Sink cell
(storage
Root)
3
H2O
This uptake of
water generates
a positive pressure
that forces the
sap to flow along
the tube.
3 The pressure is
relieved by the
unloading of sugar and the consequent
loss of water from the tube
at the sink.
Pressure flow
Transpiration stream
2
4
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.
Sucrose
In the case of
leaf-to-root
translocation,
xylem recycles
water from sink
to source.
• 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.