resource acquisition and transport in vascular plants...concept 36.1: adaptations for acquiring...

CAMPBELL

BIOLOGY Reece • Urry • Cain • Wasserman • Minorsky • Jackson

© 2014 Pearson Education, Inc.

TENTH

EDITION

36 Resource Acquisition and

Transport in Vascular Plants

Lecture Presentation by

Nicole Tunbridge and

Kathleen Fitzpatrick


A Whole Lot of Shaking Going On

Plants have various adaptations that aid in the

acquisition of resources, including water, minerals,

carbon dioxide, and light

For example, Aspen leaves have a peculiar

adaption that causes their leaves to tremble even

in light wind


Evolution of Plants, Cladogram


Figure 36.1


Figure 36.1a


The success of plants depends on their ability to

gather resources from their environment and

transport them to where they are needed


Concept 36.1: Adaptations for acquiring resources were key steps in the evolution of vascular plants

The algal ancestors of land plants absorbed water,

minerals, and CO2 directly from the surrounding

water

Early nonvascular land plants lived in shallow

water and had aerial shoots

Natural selection favored taller plants with flat

appendages, multicellular branching roots, and

efficient transport


The evolution of xylem and phloem in land plants

made possible the long-distance transport of

water, minerals, and products of photosynthesis

Xylem transports water and minerals from roots to

shoots

Phloem transports photosynthetic products from

sources to sinks


Figure 36.2-1

H2O

H2O and

minerals


Figure 36.2-2

H2O

H2O and

minerals

CO2

O2

O2

CO2


Figure 36.2-3

H2O

H2O and

minerals

CO2

O2

O2

CO2

Light Sugar


Adaptations in each species represent

compromises between enhancing photosynthesis

and minimizing water loss


Shoot Architecture and Light Capture

Stems serve as conduits for water and nutrients

and as supporting structures for leaves

Shoot length and branching pattern affect light

capture

There is a trade-off between growing tall and

branching


There is generally a positive correlation between

water availability and leaf size

Phyllotaxy, the arrangement of leaves on a stem,

is a species-specific trait important for light capture

Most angiosperms have alternate phyllotaxy with

leaves arranged in a spiral

The angle between leaves is 137.5 and likely

minimizes shading of lower leaves


Figure 36.3

Buds

1 mm

Shoot apical meristem

42 29

34 21

8

26 13

18

5

16

3

24

11

32

19

6

40

27

14

1 22

9

4 17

12

25 20

7

2

15

28

10

23

31


Figure 36.3a


Figure 36.3b

1 mm

Shoot apical meristem

42 29

34 21

8

26 13

18

5

16

3

24

11

32

19

6

40

27

14

1 22

9

4 17

12

25 20

7

2

15

28

10

23

31


The depth of the canopy, the leafy portion of all

the plants in a community, affects the productivity

of each plant

Self-pruning, the shedding of lower shaded leaves,

occurs when they respire more than

photosynthesize


Light absorption is affected by the leaf area index,

the ratio of total upper leaf surface of a plant

divided by the surface area of land on which it

grows


Figure 36.4

Ground area

covered by plant

Plant A

Leaf area = 40%

of ground area

(leaf area index = 0.4)

Plant B

Leaf area = 80%

of ground area

(leaf area index = 0.8)


Leaf orientation affects light absorption

In low-light conditions, horizontal leaves capture

more sunlight

In sunny conditions, vertical leaves are less

damaged by sun and allow light to reach lower

leaves


Manzanita Leaves


Root Architecture and Acquisition of Water and Minerals

Soil contains resources mined by the root system

Root growth can adjust to local conditions

For example, roots branch more in a pocket of high

nitrate than low nitrate

Roots are less competitive with other roots from

the same plant than with roots from different plants


Roots and the hyphae of soil fungi form mutualistic

associations called mycorrhizae

Mutualisms with fungi helped plants colonize land

Mycorrhizal fungi increase the surface area for

absorbing water and minerals, especially

phosphate


Mycorrhizae


Concept 36.2: Different mechanisms transport substances over short or long distances

There are two major pathways through plants

The apoplast

The symplast


The Apoplast and Symplast: Transport Continuums

The apoplast consists of everything external to

the plasma membrane

It includes cell walls, extracellular spaces, and the

interior of vessel elements and tracheids

The symplast consists of the cytosol of all the

living cells in a plant, as well as the

plasmodesmata


Three transport routes for water and solutes are

The apoplastic route, through cell walls and

extracellular spaces

The symplastic route, through the cytosol

The transmembrane route, across cell walls


Figure 36.5

Cell wall

Cytosol

Apoplastic route

Symplastic route

Transmembrane route

Plasmodesma

Plasma membrane

Key

Apoplast

Symplast


Short-Distance Transport of Solutes Across Plasma Membranes

Plasma membrane permeability controls short-

distance movement of substances

Both active and passive transport occur in plants

In plants, membrane potential is established

through pumping H by proton pumps

In animals, membrane potential is established

through pumping Na by sodium-potassium pumps


Figure 36.6

CYTOPLASM EXTRACELLULAR FLUID

Proton pump

Hydrogen ion

H+/sucrose cotransporter

H+/NO3−

cotransporter

Sucrose (neutral solute)

Potassium ion

Ion channel

(b) H+ and cotransport of neutral solutes

(a) H+ and membrane potential

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

H+

H+

H+

H+ H+

H+ H+

H+

ATP

H+

+

+

+

+

−

−

−

−

+

+

+

+

−

−

−

−

−

+

+

−

+

+

+

+

+

−

−

−

−

− +

−

+

+

+

+

+

−

−

−

− +

−

H+

H+

H+

H+ H+

H+

H+ H+

H+ H+

H+

H+ H+

H+ H+

H+

H+

H+ H+

H+

H+

S

S

S

K+

K+

K+

K+ K+

K+

K+

Nitrate

−


Figure 36.6a

CYTOPLASM EXTRACELLULAR FLUID

Proton pump

Hydrogen ion

(a) H+ and membrane potential

H+

H+

H+

H+

H+

H+

H+

H+

ATP

+

+

+

+

−

−

−

−

−

+


Figure 36.6b

H+/sucrose cotransporter

Sucrose (neutral solute)

+

+

+

+

−

−

−

−

− +

−

+

H+

H+

H+

H+ H+

H+

H+ H+

H+ H+

H+ S

S

S

(b) H+ and cotransport of neutral solutes


Figure 36.6c

H+/NO3−

cotransporter

(c) H+ and cotransport of ions

H+

+

+

+

+

−

−

−

−

− +

−

+ H+

H+

H+ H+

H+

H+

H+

H+

H+

H+

Nitrate


Figure 36.6d

Potassium ion

Ion channel

(d) Ion channels

+

+

+

+

−

−

−

− +

−

K+

K+

K+

K+

K+

K+

K+


Plant cells use the energy of H gradients to

cotransport other solutes by active transport

Plant cell membranes have ion channels that allow

only certain ions to pass


Short-Distance Transport of Water Across Plasma Membranes

To survive, plants must balance water uptake and

loss

Osmosis is the diffusion of water into or out of a

cell that is affected by solute concentration and

pressure


Water potential is a measurement that combines

the effects of solute concentration and pressure

Water potential determines the direction of

movement of water

Water flows from regions of higher water potential

to regions of lower water potential

Potential refers to water’s capacity to perform work


Water potential is abbreviated as and measured

in a unit of pressure called the megapascal (MPa)

0 MPa for pure water at sea level and at room

temperature


How Solutes and Pressure Affect Water Potential

Both solute concentration and pressure affect

water potential

This is expressed by the water potential equation:

S P

The solute potential (S) of a solution is directly

proportional to its molarity

Solute potential is also called osmotic potential


Pressure potential (P) is the physical pressure

on a solution

Turgor pressure is the pressure exerted by the

plasma membrane against the cell wall, and the

cell wall against the protoplast

The protoplast is the living part of the cell, which

also includes the plasma membrane


Water Movement Across Plant Cell Membranes

Water potential affects uptake and loss of water by

plant cells

If a flaccid (limp) cell is placed in an environment

with a higher solute concentration, the cell will lose

water and undergo plasmolysis

Plasmolysis occurs when the protoplast shrinks

and pulls away from the cell wall


Figure 36.7

Initial flaccid cell:


Final plasmolyzed cell at osmotic

equilibrium with its surroundings:

Final turgid cell at osmotic


(a) Initial conditions: cellular ψ > environmental ψ

(b) Initial conditions: cellular ψ < environmental ψ

ψP = 0

ψS = −0.7

ψ = −0.7 MPa

ψP = 0

ψS = −0.9

ψ = −0.9 MPa

ψP = 0

ψS = −0.7

ψ = −0.7 MPa

ψP = 0

ψS = −0.7

ψ = 0 MPa

ψP = 0

ψS = −0.9

ψ = −0.9 MPa

ψP = 0

ψS = 0

ψ = 0 MPa

Environment

0.4 M sucrose solution:

Environment

Pure water:


Figure 36.7a


Final plasmolyzed cell at osmotic


(a) Initial conditions: cellular ψ > environmental ψ

ψP = 0

ψS = −0.7

ψ = −0.7 MPa

ψP = 0

ψS = −0.9

ψ = −0.9 MPa

ψP = 0

ψS = −0.9

ψ = −0.9 MPa

Environment

0.4 M sucrose solution:


Video: Plasmolysis


Figure 36.7b


Final turgid cell at osmotic


(b) Initial conditions: cellular ψ < environmental ψ

ψP = 0

ψS = −0.7

ψ = −0.7 MPa

ψP = 0.7

ψS = −0.7

ψ = 0 MPa

ψP = 0

ψS = 0

ψ = 0 MPa

Environment

Pure water:


Video: Turgid Elodea


If a flaccid cell is placed in a solution with a lower

solute concentration, the cell will gain water and

become turgid

Turgor loss in plants causes wilting, which can be

reversed when the plant is watered


Figure 36.UN02

Turgid


Figure 36.UN03

Wilted


Aquaporins: Facilitating Diffusion of Water

Aquaporins are transport proteins in the cell

membrane that facilitate the passage of water

These affect the rate of water movement across

the membrane


Long-Distance Transport: The Role of Bulk Flow

Efficient long-distance transport of fluid requires

bulk flow, the movement of a fluid driven by

pressure

Water and solutes move together through

tracheids and vessel elements of xylem, and

sieve-tube elements of phloem

Efficient movement is possible because mature

tracheids and vessel elements have no cytoplasm,

and sieve-tube elements have few organelles in

their cytoplasm


Concept 36.3: Transpiration drives the transport of water and minerals from roots to shoots via the xylem

Plants can move a large volume of water from

their roots to shoots


Absorption of Water and Minerals by Root Cells

Most water and mineral absorption occurs near

root tips, where root hairs are located and the

epidermis is permeable to water

Root hairs account for much of the surface area of

roots

After soil solution enters the roots, the extensive

surface area of cortical cell membranes enhances

uptake of water and selected minerals


The concentration of essential minerals is greater

in the roots than soil because of active transport


Transport of Water and Minerals into the Xylem

The endodermis is the innermost layer of cells in

the root cortex

It surrounds the vascular cylinder and is the last

checkpoint for selective passage of minerals from

the cortex into the vascular tissue


Water can cross the cortex via the symplast or

apoplast

The waxy Casparian strip of the endodermal wall

blocks apoplastic transfer of minerals from the

cortex to the vascular cylinder

Water and minerals in the apoplast must cross the

plasma membrane of an endodermal cell to enter

the vascular cylinder


Figure 36.8 Casparian strip

Pathway along

apoplast

Endodermal cell

Pathway

through

symplast

Water

moves

upward

in vascular

cylinder Plasmodesmata

Plasma

membrane

Casparian strip

Vessels

(xylem)

Apoplastic

route

Symplastic

route

Root

hair

Endodermis Vascular

cylinder

(stele)

Epidermis

Cortex

Apoplastic

route

Symplastic

route

Transmembrane

route

The endodermis: controlled entry

to the vascular cylinder (stele) Transport in the xylem

1

1

2

3

2 3

4

4

4

5

5

5


Figure 36.8a

Plasma

membrane

Casparian strip

Vessels

(xylem)

Apoplastic

route

Symplastic

route Root

hair

Endodermis Vascular

cylinder

(stele)

Epidermis

Cortex

Apoplastic

route

Symplastic

route

Transmembrane

route

The endodermis: controlled

entry to the vascular cylinder

(stele)

Transport in the xylem

3

1

1

2

4

3

4

5

5

2


Figure 36.8b

5

5

4

4

Casparian strip

Pathway along

apoplast

Endodermal cell

Pathway

through

symplast

Water

moves

upward

in vascular

cylinder Plasmodesmata

The endodermis: controlled entry

to the vascular cylinder (stele)

Transport in the xylem


Animation: Transport in Roots


The endodermis regulates and transports needed

minerals from the soil into the xylem

Water and minerals move from the protoplasts of

endodermal cells into their own cell walls

Diffusion and active transport are involved in this

movement from symplast to apoplast

Water and minerals now enter the tracheids and

vessel elements


Bulk Flow Transport via the Xylem

Xylem sap, water and dissolved minerals, is

transported from roots to leaves by bulk flow

The transport of xylem sap involves transpiration,

the evaporation of water from a plant’s surface

Transpired water is replaced as water travels up

from the roots

Is sap pushed up from the roots, or pulled up by

the leaves?


Pushing Xylem Sap: Root Pressure

At night root cells continue pumping mineral ions

into the xylem of the vascular cylinder, lowering

the water potential

Water flows in from the root cortex, generating

root pressure, a push of xylem sap

Root pressure sometimes results in guttation, the

exudation of water droplets on tips or edges of

leaves


Figure 36.9


Positive root pressure is relatively weak and is a

minor mechanism of xylem bulk flow


Pulling Xylem Sap: The Cohesion-Tension Hypothesis

According to the cohesion-tension hypothesis,

transpiration and water cohesion pull water from

shoots to roots

Xylem sap is normally under negative pressure, or

tension


Transpirational Pull

Water vapor in the airspaces of a leaf diffuses

down its water potential gradient and exits the leaf

via stomata

As water evaporates, the air-water interface

retreats further into the mesophyll cell walls

The surface tension of water creates a negative

pressure potential


This negative pressure pulls water in the xylem

into the leaf

The transpirational pull on xylem sap is

transmitted from leaves to roots


Figure 36.10

Cuticle

Upper

epidermis

Mesophyll

Lower

epidermis

Cuticle

Xylem

Air space

Stoma

Water from xylem pulled

into cells and air spaces.

Microfibrils

in cell wall of

mesophyll cell

Microfibril

(cross section) Water

film

Air-water

interface

Increased surface

tension pulls

water from cells

and air spaces.

Air-water

interface

retreats.

Water vapor

replaced

from water

film.

Water vapor diffuses outside

via stomata. 1

2

3

4

5


Figure 36.11

Xylem

cells

Xylem sap

Mesophyll cells

Stoma

Water molecule

Atmosphere

Transpiration

Adhesion by

hydrogen bonding

Cell

wall

Cohesion

by hydrogen

bonding Cohesion and

adhesion in

the xylem

Water molecule

Root hair

Soil particle

Water

Water uptake from soil

Wate

r p

ote

nti

al

gra

die

nt

Outside air ψ

= −100.0 MPa

Leaf ψ (air spaces)

= −7.0 MPa

Leaf ψ (cell walls)

= −1.0 MPa

Trunk xylem ψ

= −0.8 MPa

Trunk xylem ψ

= −0.6 MPa

Soil ψ

= −0.3 MPa


Figure 36.11a

Water molecule

Root hair

Soil particle

Water

Water uptake from soil


Figure 36.11b

Xylem

cells Adhesion by

hydrogen bonding

Cell

wall

Cohesion

by hydrogen

bonding Cohesion and

adhesion in

the xylem


Figure 36.11c

Xylem sap

Mesophyll cells

Stoma

Water molecule

Atmosphere

Transpiration


BioFlix: Water Transport in Plants


Animation: Transpiration


Animation: Water Transport


Adhesion and Cohesion in the Ascent of

Xylem Sap

Water molecules are attracted to cellulose in

xylem cell walls through adhesion

Adhesion of water molecules to xylem cell walls

helps offset the force of gravity


Water molecules are attracted to each other

through cohesion

Cohesion makes it possible to pull a column of

xylem sap

Thick secondary walls prevent vessel elements

and tracheids from collapsing under negative

pressure

Drought stress or freezing can cause a break in

the chain of water molecules through cavitation,

the formation of a water vapor pocket


Xylem Sap Ascent by Bulk Flow: A Review

The movement of xylem sap against gravity is

maintained by the cohesion-tension mechanism

Bulk flow is driven by a water potential difference

at opposite ends of xylem tissue

Bulk flow is driven by transpiration and does not

require energy from the plant; like photosynthesis

it is solar powered


Bulk flow differs from diffusion

It is driven by differences in pressure potential, not

solute potential

It occurs in hollow dead cells, not across the

membranes of living cells

It moves the entire solution, not just water or

solutes

It is much faster


Concept 36.4: The rate of transpiration is regulated by stomata

Leaves generally have large surface areas and

high surface-to-volume ratios

These characteristics increase photosynthesis, but

also increase water loss through stomata

Guard cells help balance water conservation with

gas exchange for photosynthesis


Figure 36.12


Figure 36.12a


Figure 36.12b


Stomata: Major Pathways for Water Loss

About 95% of the water a plant loses escapes

through stomata

Each stoma is flanked by a pair of guard cells,

which control the diameter of the stoma by

changing shape

Stomatal density is under genetic and

environmental control


Mechanisms of Stomatal Opening and Closing

Changes in turgor pressure open and close

stomata

When turgid, guard cells bow outward and the pore

between them opens

When flaccid, guard cells become less bowed and

the pore closes


Figure 36.13 Guard cells turgid/

Stoma open

Guard cells flaccid/

Stoma closed

Guard cell Vacuole

Radially oriented

cellulose microfibrils

Cell

wall

(a) Changes in guard cell shape and stomatal

opening and closing (surface view)

(b) Role of potassium ions (K+) in stomatal

opening and closing

K+

H2O H2O

H2O

H2O

H2O

H2O H2O

H2O

H2O

H2O


Figure 36.13a

Guard cells turgid/

Stoma open


Stoma closed

Guard cell Vacuole

Radially oriented

cellulose microfibrils

Cell

wall

(a) Changes in guard cell shape and stomatal

opening and closing (surface view)


Figure 36.13b

(b) Role of potassium ions (K+) in stomatal

opening and closing

K+

H2O H2O

H2O H2O

H2O

H2O

H2O

H2O

H2O

H2O

Guard cells turgid/

Stoma open


Stoma closed


This results primarily from the reversible uptake

and loss of potassium ions (K) by the guard cells


Stimuli for Stomatal Opening and Closing

Generally, stomata open during the day and close

at night to minimize water loss

Stomatal opening at dawn is triggered by

Light

CO2 depletion

An internal “clock” in guard cells

All eukaryotic organisms have internal clocks;

circadian rhythms are 24-hour cycles


Drought, high temperature, and wind can cause

stomata to close during the daytime

The hormone abscisic acid (ABA) is produced in

response to water deficiency and causes the

closure of stomata


Effects of Transpiration on Wilting and Leaf Temperature Plants lose a large amount of water by

transpiration

If the lost water is not replaced by sufficient

transport of water, the plant will lose water and wilt

Transpiration also results in evaporative cooling,

which can lower the temperature of a leaf and

prevent denaturation of various enzymes involved

in photosynthesis and other metabolic processes


Adaptations That Reduce Evaporative Water Loss

Xerophytes are plants adapted to arid climates

Some desert plants complete their life cycle during

the rainy season

Others have fleshy stems that store water or leaf

modifications that reduce the rate of transpiration

Some plants use a specialized form of

photosynthesis called crassulacean acid

metabolism (CAM) where stomatal gas exchange

occurs at night


Figure 36.14

▶ Ocotillo

(Fouquieria

splendens)

100 µ

m

▼ Oleander (Nerium oleander)

▼ Oleander (Nerium oleander)

► Old man cactus

(Cephalocereus

senilis)

Thick cuticle Upper

epidermal tissue

Trichomes

(“hairs”) Crypt

Stoma Lower epidermal

tissue


Figure 36.14a

Ocotillo (leafless)


Figure 36.14b

Ocotillo after heavy rain


Figure 36.14c

Ocotillo leaves


Figure 36.14d

10

0 µ

m

Thick cuticle

Upper

epidermal tissue

Trichomes

(“hairs”) Crypt

Stoma Lower epidermal

tissue

Oleander leaf cross section


Figure 36.14e

Oleander flowers


Figure 36.14f

Old man cactus


Concept 36.5: Sugars are transported from sources to sinks via the phloem

The products of photosynthesis are transported

through phloem by the process of translocation


Movement from Sugar Sources to Sugar Sinks

In angiosperms, sieve-tube elements are the

conduits for translocation

Phloem sap is an aqueous solution that is high in

sucrose

It travels from a sugar source to a sugar sink

A sugar source is an organ that is a net producer

of sugar, such as mature leaves

A sugar sink is an organ that is a net consumer or

storer of sugar, such as a tuber or bulb


A storage organ can be both a sugar sink in

summer and sugar source in winter

Sugar must be loaded into sieve-tube elements

before being exported to sinks

Depending on the species, sugar may move by

symplastic or both symplastic and apoplastic

pathways

Companion cells enhance solute movement

between the apoplast and symplast


Figure 36.15

Apoplast

Symplast

Mesophyll cell

Cell walls (apoplast)

Plasma

membrane

Plasmodesmata

Companion

(transfer) cell

Sieve-tube

element

Mesophyll cell Bundle-

sheath cell

Phloem

parenchyma cell

High H+ concentration

Proton

pump

Low H+ concentration

Cotransporter

Sucrose

H+

H+ H+

S

S

ATP

(b) A chemiosmotic mechanism is

responsible for the active transport

of sucrose.

(a) Sucrose manufactured in mesophyll cells

can travel via the symplast (blue arrows)

to sieve-tube elements.


Figure 36.15a

Apoplast

Symplast

Mesophyll cell

Cell walls (apoplast)

Plasma

membrane

Plasmodesmata

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.


Figure 36.15b

High H+ concentration

Proton

pump

Low H+ concentration

Cotransporter

Sucrose

H+

H+ H+

S

S

ATP

(b) A chemiosmotic mechanism is

responsible for the active transport

of sucrose.


In many plants, phloem loading requires active

transport

Proton pumping and cotransport of sucrose and

H enable the cells to accumulate sucrose

At the sink, sugar molecules diffuse from the

phloem to sink tissues and are followed by water


Bulk Flow by Positive Pressure: The Mechanism of Translocation in Angiosperms

Phloem sap moves through a sieve tube by bulk

flow driven by positive pressure called pressure

flow


Figure 36.16

Vessel

(xylem)

Sieve

tube

(phloem)

Source cell

(leaf) Loading of sugar

Sucrose

Sink cell

(storage

root)

Sucrose

Uptake of water

Unloading of sugar

Recycling of water

H2O

H2O

H2O

Bu

lk f

low

by n

eg

ati

ve

pre

ss

ure

Bu

lk f

low

by p

os

itiv

e p

res

su

re

1

1

2

2

3

3 4

4


Animation: Translocation of Phloem Sap in Spring


Animation: Translocation of Phloem Sap in Summer


The pressure flow hypothesis explains why

phloem sap always flows from source to sink

Experiments have built a strong case for pressure

flow as the mechanism of translocation in

angiosperms

Self-thinning, the dropping of sugar sinks such as

flowers, seeds, or fruits, occurs when there are

more sugar sinks than the sources can support


Figure 36.17

Sap

droplet

25 µm

Sap droplet

Sieve-

tube

element

Stylet

Aphid feeding Stylet in sieve-

tube element

Separated stylet

exuding sap


Figure 36.17a

Sap

droplet

Aphid feeding


Figure 36.17b

25 µm

Sieve-

tube

element

Stylet

Stylet in sieve-

tube element


Figure 36.17c

Sap droplet

Separated stylet

exuding sap


Concept 36.6: The symplast is highly dynamic

The symplast is a living tissue and is responsible

for dynamic changes in plant transport processes


Changes in Plasmodesmatal Number and Pore Size

Plasmodesmata can open or close in response to

turgor pressure, cytoplasmic calcium levels, or

cytoplasmic pH

Plant viruses can cause plasmodesmata to dilate,

allowing viral RNA to pass between cells


Figure 36.18

Plasmodesma

100 nm

Cytoplasm

of cell 1

Cytoplasm

of cell 2

Virus

particles

Cell walls


Phloem: An Information Superhighway

Phloem is a “superhighway” for systemic transport

of macromolecules and viruses

Systemic communication through the phloem

helps integrate functions of the whole plant


Electrical Signaling in the Phloem

The phloem allows for rapid electrical

communication between widely separated organs

For example, rapid leaf movements in the sensitive

plant (Mimosa pudica)


Figure 36.UN01


Figure 36.UN04

Minerals H2O

H2O CO2

CO2

O2

O2


Figure 36.UN05

resource acquisition and transport in vascular plants...concept 36.1: adaptations for acquiring...

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