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© 2014 Pearson Education, Inc.

Light

H2O and minerals

H2O Sugar

O2

CO2

O2 CO2

2

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Shoot apical meristem Buds

34 21

42 29 16 11 19

27

32 24 40

28

15

10

23 31

18

13 26

22

12 17

25 20

1

2

3

4

5

6

7

8

9

14

1 mm

3

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Apoplastic route

Cell wall

Symplastic route

Transmembrane route

Cytosol

Key Plasmodesma

Plasma membrane Apoplast

Symplast

4

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CYTOPLASM EXTRACELLULAR FLUID

Proton pump

Hydrogen ion

Sucrose (neutral solute)

Potassium ion

Ion channel

Nitrate

(d) Ion channels (c) H+ and cotransport of ions

(b) H+ and cotransport of neutral solutes (a) H+ and membrane potential

H+/sucrose cotransporter

H+/NO3−

cotransporter

S

NO3−

K+ K+

K+

K+ K+ K+

K+

H+ H+ H+ H+

H+ H+

H+

H+

H+

H+

H+

H+

S

S

S

S

S

H+

H+

H+

H+

H+ H+

H+

H+

H+ H+

H+

H+

H+ H+

H+

H+ H+

H+

NO3−

NO3−

5

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Plasmolyzed cell at osmotic equilibrium with its surroundings

Turgid cell at osmotic equilibrium with its surroundings

0.4 M sucrose solution:

(a) Initial conditions: cellular ψ > environmental ψ

−0.9 MPa = ψ 0 MPa = ψ

Initial flaccid cell:

0 MPa = ψ

0 0

= =

ψP ψS

Pure water:

(b) Initial conditions: cellular ψ < environmental ψ

−0.7 MPa = ψ

−0.7

= =

ψP ψS

−0.9

= =

ψP ψS

0

−0.9 MPa = ψ

−0.9

= =

ψP ψS

0

0

0.7 = =

ψP ψS −0.7

6

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Turgid

Wilted

7

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Technique

Control: Solution containing all minerals

Experimental: Solution without potassium

8

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Nitrogen-deficient

Potassium-deficient

Phosphate-deficient

Healthy

10

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Soil particle K+

Root hair

Cell wall

Mg2+ K+

H+ H+

K+

Ca2+ Ca2+

H2O + CO2 H2CO3 HCO3− +

11

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ATMOSPHERE

ATMOSPHERE

SOIL

SOIL

Nitrogen-fixing bacteria

N2

N2 N2

NH3 (ammonia)

H+ (from soil)

Ammonifying bacteria

Amino acids

NH4+

(ammonium) NO2

− (nitrite) Nitrifying

bacteria

NO3−

(nitrate) Nitrifying bacteria

Denitrifying bacteria

Microbial decomposition

Nitrate and nitrogenous

organic compounds exported in

xylem to shoot system

NH4+

Root

Proteins from humus (dead organic material)

12

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Roots

Nodules

13

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Epidermis Cortex

Epidermal cell

Endodermis

Mantle (fungal sheath)

Mantle (fungal sheath)

Fungal hyphae between cortical cells (LM) 50 µm

1.5 mm (C

olor

ized

SEM

)

Epidermis Cortex

Fungal vesicle

Endodermis

Cortical cell

Casparian strip

Plasma membrane

Arbuscules

(LM)

10 µ

m

Root hair

Fungal hyphae

(a) Ectomycorrhizae

(b) Arbuscular mycorrhizae (endomycorrhizae) 14

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Experiment Results

Invaded Uninvaded Sterilized invaded

Sterilized uninvaded

Soil type

Invaded Uninvaded Soil type White ash

Sugar maple Seedlings

Red maple

Myc

orrh

izal

co

loni

zatio

n (%

) In

crea

se in

pl

ant b

iom

ass

(%) 300

200

100

0

30 20 10 0

40

15

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Staghorn fern, an epiphyte 16

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Parasitic plants

Mistletoe, a photosynthetic parasite

Dodder, a nonphoto- synthetic parasite (orange)

Indian pipe, a nonphoto- synthetic parasite of mycorrhizae

17

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Carnivorous plants

Pitcher plants

Venus flytraps

Sundew

18

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Apoplastic route

Symplastic route

Transmembrane route

The endodermis: controlled entry to the vascular cylinder (stele)

Apoplastic route

Symplastic route

Root hair

Plasma membrane

Epidermis

Casparian strip

Vascular cylinder (stele)

Vessels (xylem)

Cortex

Endodermis

Pathway along apoplast

Transport in the xylem

Casparian strip

Pathway through symplast

Endodermal cell

1

1 2

2

4

5

3

3 4

5

5 4

19

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Xylem

Microfibrils in cell wall of

mesophyll cell

Microfibril (cross section) Air-water

interface Water film

Cuticle

Mesophyll

Cuticle Stoma

Air space

Upper epidermis

Lower epidermis

20

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Cohesion by hydrogen bonding

Water molecule

Cohesion and adhesion in the xylem

Water uptake from soil Water Soil particle

Root hair

Cell wall

Transpiration

Xylem cells

Water molecule

Adhesion by hydrogen bonding

Xylem sap

Mesophyll cells

Stoma

Atmosphere

Outside air ψ

Wat

er p

oten

tial g

radi

ent

Leaf ψ (air spaces)

Trunk xylem ψ

Leaf ψ (cell walls)

Trunk xylem ψ

Soil ψ

−7.0 MPa

−100.0 MPa =

=

−1.0 MPa =

−0.8 MPa =

−0.6 MPa =

−0.3 MPa = 21

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Guard cells turgid/Stoma open

K+

Guard cells flaccid/Stoma closed

H2O

Radially oriented cellulose microfibrils

Cell wall

Vacuole

(a) Changes in guard cell shape and stomatal opening and closing (surface view)

Guard cell

(b) Role of potassium ions (K+) in stomatal opening and closing

H2O H2O

H2O

H2O H2O

H2O

H2O

H2O H2O

22

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Old man cactus (Cephalocereus senilis)

Ocotillo (Fouquieria splendens)

Oleander (Nerium oleander) Thick cuticle Upper epidermal tissue

Stoma Lower epidermal tissue

Crypt Trichomes (“hairs”)

100 µ

m

23

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Apoplast Symplast

Cell walls (apoplast)

Plasmodesmata

Mesophyll cell

Plasma membrane

Companion (transfer) cell

Sieve-tube element

Mesophyll cell

Bundle- sheath cell

Phloem parenchyma cell

(a) Sucrose manufactured in mesophyll cells can travel via the symplast (blue arrows) to sieve-tube elements.

(b) A chemiosmotic mechanism is responsible for the active transport of sucrose.

High H+ concentration

Low H+ concentration

Proton pump

Cotransporter

Sucrose S

S H+

H+ H+

24

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Loading of sugar

H2O

Vessel (xylem)

Source cell (leaf)

Sieve tube

(phloem)

H2O Sucrose

Uptake of water

Unloading of sugar

Recycling of water

Sink cell (storage root)

H2O Sucrose

Bul

k flo

w b

y ne

gativ

e pr

essu

re

Bul

k flo

w b

y po

sitiv

e pr

essu

re

1

1

2

2

3

4 3 4

25