Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint TextEdit Art Slides for Biology, Seventh Edition Neil Campbell and.

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

PowerPoint TextEdit Art Slides forBiology, Seventh Edition

Neil Campbell and Jane Reece

Chapter 36Chapter 36

Transport in Vascular Plants


Figure 36.1 Coast redwoods (Sequoia sempervirens)


Figure 36.2 An overview of transport in a vascular plant (layer 1)

Minerals

H2O

H2O



Minerals

H2O

CO2 O2

H2O



Minerals

H2O

CO2 O2

H2O Sugar

Light



Minerals

H2O CO2

O2

CO2 O2

H2O Sugar

Light


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.


Figure 36.5 Water potential and water movement: an artificial model

= –0.23 MPa

(a)

0.1 Msolution

(d)(c)(b)

P = 0

H2OH2O

H2O H2O

S = –0.23

= –0.23 MPa

S = –0.23

= 0 MPa

P = 0.23S = –0.23

= –0.07 MPa

P = 0.30S = 0

= –0.30 MPa

P = –0.30S = –0.23P = 0

= 0 MPa = 0 MPa = 0 MPa

Purewater


Figure 36.6 Water relations in plant cells

s = –0.9

(a)

0.4 M sucrose solution: = 0s = –0.9

= –0.9 MPa

= 0s = –0.7

= –0.7 MPa

Initial flaccid cell:

= 0s = 0

= 0 MPa

Distilled water:

Plasmolyzed cell at osmotic equilibriumwith its surroundings = 0

= –0.9 MPa

= 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)


Figure 36.7 A watered Impatiens plant regains its turgor


Figure 36.8 Cell compartments and routes for short-distance transport

Transport proteins inthe plasma membrane

regulate traffic ofmolecules 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)


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


Figure 36.10 Mycorrhizae, symbiotic associations of fungi and roots

2.5 mm


Figure 36.11 Guttation


Figure 36.12 The generation of transpirational pull in a leaf

Evaporation causes the air-water interface to retreat farther into the cell wall and become more curved as the rate of transpiration increases. As the interface becomes more curved, the water film’s pressure becomes more negative. This negative pressure, or tension, pulls water from the xylem, where the pressure is greater.

CuticleUpperepidermis

Mesophyll

Lowerepidermis

CuticleWater vapor

CO2 O2 Xylem CO2 O2

Water vapor

Stoma

Evaporation

At first, the water vapor lost bytranspiration is replaced by evaporation from the water film that coats mesophyll cells.

In transpiration, water vapor (shown as blue dots) diffuses from the moist air spaces of the leaf to the drier air outside via stomata.

Airspace

Cytoplasm

Cell wall

Vacuole

EvaporationWater film

Low rate oftranspiration

High rate oftranspiration

Air-waterinterface

Cell wall

Airspace

= –0.15 MPa = –10.00 MPa

Vacuole

3

1 2


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


Figure 36.14 Open stomata (left) and closed stomata (colorized SEM)

20 µm


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


Figure 36.16 Structural adaptations of a xerophyte leaf

Lower epidermaltissue

Trichomes(“hairs”)

Cuticle Upper epidermal tissue

Stomata 100m


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 tubeVessel(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


Figure 36.19 What causes phloem sap to flow from source to sink?

Aphid feeding Stylet in sieve-tube member

Severed styletexuding sap

Sieve-Tubemember

To test the pressure flow hypothesis, researchers used aphids that feed on phloem sap. An aphid probes with a hypodermic-like mouthpart called a stylet that penetrates a sieve-tube member. As sieve-tube pressure force-feeds aphids, they can be severed from their stylets, which serve as taps exuding sap for hours. Researchers measured the flow and sugar concentration of sap from stylets at different points between a source and sink.

EXPERIMENT

The closer the stylet was to a sugar source, the faster the sap flowed and the higher was its sugar concentration.

RESULTS

The results of such experiments support the pressure flow hypothesis.

CONCLUSION

Sap dropletStylet

Sapdroplet

25 m

Sieve-tubemember

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint TextEdit Art Slides for Biology, Seventh Edition Neil Campbell and.

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