chapter 36: transport in vascular plants

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

Minerals

H2O

H2O


Minerals

H2O

CO2 O2

H2O


Minerals

H2O

CO2 O2

H2O Sugar

Light


Minerals

H2O CO2

O2

CO2 O2

H2O Sugar

Light


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 EXTRACELLULAR FLUID

ATP

H+

H+ H+

H+

H+

H+

H+

H+

Proton pump generates membrane potentialand H+ gradient.

–

–

–

–

– +

+

+

+

+

Figure 36.4 Solute transport in plant cells+

CYTOPLASMEXTRACELLULAR FLUID

Cations ( for example) are driven into the cell by themembrane potential.

Transport protein

K+

K+

K+

K+

K+ K+

K+

K+

–

–

– +

+

(a) Membrane potential and cation uptake

H+

H+

H+

H+

–

–

+

+

H+

H+

H+

H+

H+

H+

H+

H+

NO3–

NO 3 –

NO3–

NO 3

–

NO3

–

NO 3 – –

–

– +

+

+

(b) Cotransport of anions

H+

H+

H+

H+

H+

H+

H+H+

H+ H+

H+

H+

Plant cells canalso accumulate a neutral solute,such as sucrose( ), bycotransporting down thesteep protongradient.

S

S

S

SS

S

S

H+

(c) Cotransport of a neutral solute

–

–

– +

+

+

–

–

–

+

+

+

–

–

–

+

+

+

Cell accumulates anions (NO3

–, for example) by coupling their transport to theinward diffusion of H+ through acotransporter.


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

= –0.23 MPa

(a)

0.1 Msolution

(d)(c)(b)

P = 0

H2O

H2O

H2O H2O

S = –0.23

= –0.23 MPa

S = –0.23

= 0 MPa

P = 0.23S = –0.23

= 0.07 MPa

P = 0.30

S = 0

= –0.30 MPa

P = –0.30

S = –0.23

P = 0

= 0 MPa = 0 MPa = 0 MPa

Purewater

+ solute decreases Ψs Water goes from high low

+ pressure counteracts Ψs

More pressure forces water across membrane

Ψ = Ψs + Ψp

(-) pressure also moves water


1. Where does transport occur in plants? Start with water…. 2. How are solutes transported between cells?3. What influences the movement of water?4. What does this mean for plant cells?

Figure 36.6 Water relations in plant cells

s = –0.9

(a)

0.4 M sucrose solution:p = 0s = –0.9

= –0.9 MPa

p = 0s = –0.7

= –0.7 MPa

Initial flaccid cell:

p = 0s = 0

= 0 MPa

Distilled water:

Plasmolyzed cell at osmotic equilibriumwith its surroundingsp = 0

= –0.9 MPa

p = 0.7s = –0.7

= 0 MPa

Turgid cellat osmotic equilibriumwith its surroundings

Initial conditions: cellular > environmental . The cellloses 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 tobecome 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 lossTurgid – plant cell full of water due to its high solute concentration

(turgor pressure)Aquaporins allow water to move quickly across a membrane


1. Where does transport occur in plants? Start with water…. 2. How are solutes transported between cells?3. What influences the movement of water?4. What does this mean for plant cells?5. What are the transport routes dissolved substances can take between cells?

Fig 36.8 Cell compartments and routes for short-distance transportTransport proteins in

the plasma membraneregulate traffic of

molecules betweenthe cytosol and the

cell wall.

Transport proteins inthe vacuolarmembrane regulatetraffic of moleculesbetween the cytosoland the vacuole.

Plasmodesma Vacuolar membrane(tonoplast)Plasma membrane

Cell compartments. The cell wall, cytosol, and vacuole are the three maincompartments of most mature plant cells.

Key

Symplast

Apoplast

The symplast is thecontinuum of

cytosol connectedby plasmodesmata.

The apoplast isthe continuumof cell walls andextracellularspaces.

Apoplast

Transmembrane route

Symplastic route Apoplastic route

Symplast

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 wallCytosol

Vacuole

(a)

(b)

How does water get into the plant?

Figure 36.9 Lateral transport of minerals and water in roots

1

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 crossthe plasma membranes of roothairs enter the symplast.

As soil solution moves alongthe apoplast, some water andminerals are transported intothe protoplasts of cells of theepidermis and cortex and thenmove 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 thepassage 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 thevascular cylinder discharge water and minerals into theirwalls (apoplast). The xylem vessels transport the waterand minerals upward into the shoot system.

Casparian strip

Pathway alongapoplast

Pathwaythroughsymplast

Plasmamembrane

Apoplasticroute

Symplasticroute

Root hair

Epidermis Cortex Endodermis Vascular cylinder

Vessels(xylem)

Casparian strip

Endodermis

4 5

2

1

34 5

Why is the Casparian strip so important?-forces dissolved substances across a selectively permeable membrane-Keeps unwanted & unrecognized substances OUT of the plant


1. Where does transport occur in plants? Start with water…. 2. How are solutes transported between cells?3. What influences the movement of water?4. What does this mean for plant cells?5. What are the transport routes dissolved substances can take between cells? 6. 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


1. Where does transport occur in plants? Start with water…. 2. How are solutes transported between cells?3. What influences the movement of water?4. What does this mean for plant cells?5. What are the transport routes dissolved substances can take between cells? 6. 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

Figure 36.13 Ascent of xylem sap

XylemsapOutside air

= –100.0 MPa

Leaf (air spaces) = –7.0MPa

Leaf (cell walls) = –1.0 MPa

Trunk xylem = – 0.8 MPa

Wat

er p

ote

nti

al g

rad

ien

t

Root xylem = – 0.6 MPa

Soil = – 0.3 MPa

MesophyllcellsStoma

Watermolecule

Atmosphere

Transpiration

Xylemcells Adhesion Cell

wall

Cohesion,byhydrogenbonding

Watermolecule

Roothair

Soilparticle

Water

Cohesion and adhesionin the xylem

Water uptakefrom soil

Transpiration – loss of water vapor through leaves that pulls water up from rootsWhat 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

Cells flaccid/Stoma closedCells turgid/Stoma open

H2O

Radially oriented cellulose microfibrils

Cellwall

VacuoleGuard cell

H2O

H2OH2O

H2O

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 increasein 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 andvacuolar membrane causes the turgor changes of guard cells.

(b) H2O H2O

H2O

H2O

H2O


1. Where does transport occur in plants? Start with water…. 2. How are solutes transported between cells?3. What influences the movement of water?4. What does this mean for plant cells?5. What are the transport routes dissolved substances can take between cells? 6. 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?

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 cellCell walls (apoplast)

Plasma membranePlasmodesmata

Companion(transfer) cell

Sieve-tubemember

Mesophyll cellPhloem parenchyma cell

Bundle-sheath cell

High H+ concentration Cotransporter

Protonpump

ATPKey

SucroseApoplast

Symplast

H+

A chemiosmotic mechanism is responsible forthe 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)

H+

Low H+ concentration

H+

S

S

Figure 36.18 Pressure flow in a sieve tube

Vessel(xylem)

H2O

H2O

Sieve tube(phloem)

Source cell(leaf)

Sucrose

H2O

Sink cell(storageRoot)

1

Sucrose

Loading of sugar (green dots) into the sieve tube at thesource reduces water potential inside the sieve-tube members. This causes the tube to take up waterby osmosis.

2

4 3

1

2 This uptake ofwater generates a positive pressurethat forces the sap to flow along the tube.

The pressure isrelieved by theunloading of sugar and the consequentloss of water from the tubeat the sink.

3

4 In the case of leaf-to-roottranslocation,xylem recycleswater from sinkto source.

Tra

ns

pir

ati

on

str

ea

m

Pre

ss

ure

flo

w

• 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.

chapter 36: transport in vascular plants

Documents