Figure 36.1 An overview of transport in whole plants (Layer 1)
3) Transpiration
creates a force
that pulls water
upward in
xylem
Transport in plants
2) Water and
minerals
transported
upward form
roots to
shoots in
xylem
1) Roots
absorb water
and dissolved
minerals from
soil
Figure 36.1 An overview of transport in whole plants (Layer 2)
4. Gas exchange
occurs through the
stomata
Figure 36.1 An overview of transport in whole plants (Layer 3)
5. Sugar is produced
in the leaves
6. Sugar is
transported
to other
parts of
plant in
phloem
Figure 36.1 An overview of transport in whole plants (Layer 4)
There are three levels of transport in
plants:
► the
individual cell level (membrane
transport)
uptake and export of materials in root cells
► short
distance - cell to cell
sugar loading from mesophyll to phloem
► long
distance transport – tissue to tissue or
organ to organ
7. Respiration
in the roots
leads to gas
exchange
xylem and phloem
1
Uniport
COTRANSPORT
Uniport
Water movement in plants is driven
by three processes
► Diffusion
► Osmosis
► Bulk
Water potential (Ψ)
► term
used to characterize the energy state
of water
► free energy of water (that which is available
to do work~ potential energy of water).
► differences in water potential drive water
transport in plants
► water potential is measure in MPa
Flow
Water potential
► In
plants water potential has two parts
Ψ S = osmotic potential
Ψ p = hydrostatic potential (pressure potential)
►Ψ= Ψs
+ Ψp
2
Water potential
► Water
moves from regions where the water
potential is relatively positive to areas where
it is relatively negative.
► The addition of solutes will lower the water
potential (water will form a shell around a
solute and will move less freely than if only
in water).
► There are three assumptions of these
statements:
► water
moves whenever there is a difference in
water potential within the mass of water.
► if
water potentials of two regions are equal, the
regions are in equilibrium and there will be no net
movement of water.
► water
potentials must always be considered in
pairs or groups because the movement of water is
due to the relative differences between areas.
Figure 36.3 Water potential and water movement: a mechanical model
model
Location
Water potential is
higher on the left
side and lower on
the left side.
The application of
pressure increases
the water potential
on the right side so
that now the two
sides are equal
0 MPa vs. -.023MPa
When the
application of
pressure is negative
relative to the right
side, water will
move to the left
When the
application of
pressure is more
than the osmotic
potential, water will
move in the
opposite direction
(to the left)
Ψ
A
-253
(inside
cell)
B
0
(outside
cell)
s
+
Ψ
p
Ψ
=
-100
- 353
-100
-100
Q: Which way will the water move?
A: from B to A (to inside the cell)
Figure 36.4 Water relations of plant cells
Turgor Pressure
► fully
supplied with water, plant cells exhibit
a positive hydrostatic pressure
► caused by the flow of water into the plant
cell and its pushing back onto the cell wall
Water relations of plant cells –
cellular Ψ > environmental Ψ
Cell plasmolyzes
Water relations of plant cells –
cellular Ψ < environmental Ψ
−0.7 MPa vs O MPa
3
Figure 36.5 A watered tomato plant regains its turgor
There are three levels of transport in
plants:
► the
individual cell level (membrane
transport)
uptake and export of materials in root cells
► short
distance - cell to cell
sugar loading from mesophyll to phloem
► long
distance transport – tissue to tissue or
organ to organ
xylem and phloem
Figure 36.6 Compartments of plant cells and tissues and routes for lateral transport
There are three levels of transport in
plants:
Figure 36.7 Lateral transport of minerals and water in roots
Figure 36.8 Mycorrhizae, symbiotic associations of fungi and roots
roots
► the
individual cell level (membrane
transport)
uptake and export of materials in root cells
► short
distance - cell to cell
sugar loading from mesophyll to phloem
► long
distance transport – tissue to tissue or
organ to organ
xylem and phloem
4
TRANSPIRATION
► is
driving force for movement of water in
the plant
► Defined as the loss of water vapor from
leaves, which must be replaced continuously
► Q. What three forces are working to move
water up the stems?
► A. Partially driven by cohesion, adhesion,
surface tension
S – soil
P – plant
A – air
C- continuum
(hydrogen bonding OH MY ☺!)
The SPAC
Guttation
► driving
force in the SPAC is the continuously
decreasing value of Ψ.
► No one point in space is isolated, movement
always depends on what is behind it and
ahead of it.
► Atmosphere has a very low Ψ
Figure 36.10 The generation of transpirational pull in a leaf
Figure 36.11 Ascent of water in a tree
5
Figure 36.13a The mechanism of stomatal opening and closing
► DAWN:
Ψ guard cell ≠ Ψ adjacent cell
Ψ in guard cell is < than adjacent cell
Guard cells pump in K+, osmotic potential (Ψs);
water the guard cell
► DAY
Ψ guard cell = Ψ adjacent cell
as Ψs so does the Ψp until cell is in equilibrium
with adjacent cells (net water movement stops)
cell is turgid, stomata are open
► NIGHT
DAY
Ψ guard cell ≠ Ψ adjacent cell
Ψ is lower than adjacent cell
So water moves into the cell
NIGHT
Ψ guard cell = Ψ adjacent cell
Figure 36.13b The mechanism of stomatal opening and closing
Ψ guard cell ≠ Ψ adjacent cell
K+ is pumped back into adjacent cells
Equilibrium is reached and the guard cells are
flaccid and the stoma is closed.
Figure 36.12 An open (left) and closed (right) stoma of a spider
spider plant (Chlorophytum
colosum)
colosum) leaf
Which of the following conditions
would increase transpiration? Which
would decrease transpiration?
►A
► Transpiration
rates are affected by environmental
factors
windy day?
►A rainy day?
►A hot day?
Wind, humidity, temperature, soil moisture, brightness
of light
6
Figure 36.17 Pressure flow in a sieve tube
Figure 36.16 Loading of sucrose into phloem
Figure 36.18 Tapping phloem sap with the help of an aphid
7