Plant

Transport

Plants

Plant: terrestrial (mostly), multicellular,

photoautotrophic, eukaryote, true tissues

and organs

Plant Structure

Tissue Basic Tissue Types: pg 717

- give rise to specialized cells

o Dermal - outer coat

o Vascular – transport tubes

o Ground – between Dermal and Vascular

Basic Tissue Layout

Dermal

Ground

Vascular

Dermal

tissue

Ground

tissue Vascular

tissue

Dermal Tissue

Epidermis

Function: protection: secretes the cuticle,

forms prickles and root hairs

Thorns, Spines and Prickles

Based on where they originate

Thorns – modified stems

Spines – modified leaves

Prickles – modified epidermal cells

Thorn

Spine

Prickle

Rose “thorns” are prickles “A rose between two prickles.”

Vascular TissueXylem: Water conducting –

unidirectional (up) Dead at maturity – pg 719

Phloem: Sugar conduction –bidirectional Sieve Tube Members: alive and functional –

lack many organelles

Companion Cells: connected to Sieve Tube Members by plasmodesmata – supports the STM with its organelle function

Xylem

Phloem

Figure. 35.9

WATER-CONDUCTING CELLS OF THE XYLEM

Vessel Tracheids 100 m

Tracheids and vessels

Vessel

element

Vessel elements with

partially perforated

end walls

Pits

Tracheids

SUGAR-CONDUCTING CELLS OF THE PHLOEM

Companion cell

Sieve-tube

member

Sieve-tube members:

longitudinal view

Sieve

plate

Nucleus

Cytoplasm

Companion

cell

30 m

15 m

Ground Tissue

Occupies the space between the

vascular tissue and the dermal tissue

Functions:

Storage – roots and stems

Support – stems

Photosynthesis – leaves and some stems

Types of Ground Tissue1.Parenchyma: undifferentiated, thin cell walls (still

flexible) – used for metabolism and photosynthesis

Ex: Pallisade and Spongy Mesophyll of leafPotato, Fruit pulp

2. Collenchyma: unevenly thickened cell walls – support young parts of plants – no lignin, but stronger than parenchyma

Ex: “Strings” in celery3. Sclerenchyma: highly thickened cell walls

– lignified – support mature tissue – hard and deadTwo types: Fibers and Sclerids

Ex: Walnut Shell, Stone Cells in Pears

Parenchyma cells60 m

PARENCHYMA CELLS

80 m Cortical parenchyma cells

COLLENCHYMA CELLS

Collenchyma cells

SCLERENCHYMA CELLS

Cell wall

Sclereid cells

in pear25 m

Fiber cells

5 m

Plant Parts: Roots, Stems and

Leaves

Roots:

Functions:

- absorb water, nutrients and minerals

- anchor plant in soil

- store food and water

- support the plant

(a) Prop roots (b) Storage roots (c) “Strangling” aerial

roots

(d) Buttress roots (e) Pneumatophores

Increasing Absorption

- Root hairs – extensions of the epidermis

- Branching roots – lateral roots

- Mycorrhizae

Root Structure

Outside In

Epidermis (D)

Cortex (G) – storage and nutrient transfer

Endodermis (G) – separates ground and

vascular tissue – important for water transfer

Pericycle (V) – forms the lateral roots

Stele (Xylem and Phloem) (V)

Cortex

Vascular

cylinder

Endodermis

Pericycle

Core of

parenchyma

cells

Xylem

Endodermis

Pericycle

Xylem

Phloem

Key

100 m

Vascular

Ground

Dermal

Phloem

Transverse section of a root with parenchyma

in the center. The stele of many monocot roots

is a vascular cylinder with a core of parenchyma

surrounded by a ring of alternating xylem and phloem.

(b)Transverse section of a typical root. In the

roots of typical gymnosperms and eudicots, as

well as some monocots, the stele is a vascular

cylinder consisting of a lobed core of xylem

with phloem between the lobes.

(a)

100 m

Epidermis

Eudicot Root – Cross Section

From: http://www.inclinehs.org/smb/Sungirls/images/dicot_stem.JPG

Monocot Root Cross Section From: http://www.inclinehs.org/smb/Sungirls/images/monocot_stem.JPG

Monocot Root Vascular

Cylinder

Monocot Stele

From:

http://www.botany.hawaii.edu/faculty/webb/BOT201/Angiosperm/MagnoliophytaLab99/SmilaxRotM

aturePhloemXylem300Lab.jpg

Growth of Lateral Roots

Cortex

Vascular

cylinder

Epidermis

Lateral root

100 m

1 2

3 4

Emerging

lateral

root

Eudicot & Monocot Roots - External Eudicot – tap root Monocot – fibrous roots

Stems

Function:

- support leaves and flowers

- photosynthesis (non-woody plants –

herbaceous)

- storage: food (tubers – potato) and

water (cactus)

Stem Structure Nodes: points where leaves are/were attached Internodes: area of growth between the nodes Bud: Developing leaves

Terminal/Apical Bud: end of a branch Lateral/Axillary Bud: lateral growth – between leaf

petiole (“stem” of leaf) and main stem Bud Scale Scars: Sites of old bud scales (protective

layers around the buds) - # of bud scale scars indicates the age of the stem

Leaf Scars: Sites where leaves were attached to the stem

Lenticles: “bumps” of cork lined pores that allow for oxygen exchange in the stem

This year’s

growth

(one year old)

Last year’s growth

(two years old)

Growth of two

years ago (three

years old)

One-year-old side

branch formed

from axillary bud

near shoot apex

Scars left by terminal

bud scales of previous

winters

Leaf scar

Leaf scar

Stem

Leaf scar

Bud scale

Axillary buds

Internode

Node

Terminal bud

Stem: Internal Anatomy

Epidermis

Ground Tissue

Pith

Vascular Bundles

Contain Xylem and Phloem

May contain: Vascular Cambium, Cork Cambium, Sclerenchyma

Monocot Stem StructureGround

tissue

Epidermis

Vascular

bundles

1 mm

(b) A monocot stem. A monocot stem (maize) with vascular

bundles scattered throughout the ground tissue. In such an

arrangement, ground tissue is not partitioned into pith and

cortex. (LM of transverse section)

Monocot Stem Vascular

Bundles

Xylem

Phleom

Monocot Stem Vascular

Bundle From: http://iweb.tntech.edu/mcaprio/stem_dicot_400X_cs_E.jpg

Eudicot Stem StructureXylemPhloem

Sclerenchyma

(fiber cells)Ground tissue

connecting

pith to cortex

Pith

Epidermis

Vascular

bundle

Cortex

Key

Dermal

Ground

Vascular1 mm

(a) A eudicot stem. A eudicot stem (sunflower), with

vascular bundles forming a ring. Ground tissue toward

the inside is called pith, and ground tissue toward the

outside is called cortex. (LM of transverse section)

Eudicot Stem Cross Section From: http://plantphys.info/plant_physiology/images/stemcs.jpg

Eudicot Stem Vascular Bundle

XylemPhloem

Vascular Cambium

Sclerenchyma

Leaves

Functions:

- photosynthesis

- storage (succulent leaves, Aloe)

- protection: spines, toxins, trichomes

- reproduction: flowers (modified leaves)

Leaves

Functions:

- photosynthesis

- storage (succulent leaves, Aloe)

- protection: spines, toxins, trichomes

- reproduction: flowers (modified leaves)

Leaves: External Structure

- Blade

- Petiole

- Stipule

- Axillary Bud

- Veins

Stipule – growth at the base of

petiole

Leaves: Internal Structure

- Cuticle- Upper Epidermis (Adaxil)- Mesophyll:

- Palisade Layer- Spongy Layer - Air Spaces

- Vascular Bundle- Bundle Sheath Cells- Xylem and Phloem

-Lower Epidermis (Abaxil)- Stomata- Guard Cells

- Cuticle

Key

to labels

Dermal

Ground

Vascular

Guard

cells

Stomatal pore

Epidermal

cell

50 µm

Surface view of a spiderwort

(Tradescantia) leaf (LM)

(b)Cuticle

Sclerenchyma

fibers

Stoma

Upper

epidermis

Palisade

mesophyll

Spongy

mesophyll

Lower

epidermis

Cuticle

Vein

Guard

cells

Xylem

Phloem

Guard

cells

Bundle-

sheath

cell

Cutaway drawing of leaf tissues(a)

Vein Air spaces Guard cells

100 µmTransverse section of a lilac

(Syringa) leaf (LM)(c)

Figure 35.17a–c

Leaf Mesophyll

Leaf Stomata

Plant Transport

Turgor loss in plants causes wilting

Which can be reversed when the plant is watered

Figure 36.7

Plant Transport of Solutes Proton Pumps: Active transport of H+ out of

the cell

Builds proton gradient

Functions: provides potential for the COTRANSPORT of materials across the membrane with the H+

CYTOPLASM EXTRACELLULAR FLUID

ATP

H+

H+ H+

H+

H+

H+H+

H+Proton pump generates

membrane potential

and H+ gradient.

–––

–– +

+

+

++

Figure 36.4b

H+

H+

H+

H+

H+

H+H+

H+

H+

H+

H+

H+

–

–

– +

+

+

––– +

+

+

NO3–

(b) Cotransport of anions

H+of through a

cotransporter.

Cell accumulates anions ( , for example) by coupling their transport to theinward diffusion

H+

H+

H+

H+

H+H+

H+

H+ H+

H+S

Plant cells can

also accumulate a

neutral solute,

such as sucrose

( ), by

cotransporting

down the

steep proton

gradient.

S

H+

–

–

–

+

+

+

–

–

++–

Figure 36.4c

H+ H+S+

–(c) Contransport of a neutral solute

Water Flow from Cell to Cell Water moves between three major

compartments of the plant cell.

1. Vacuole – surrounded by Tonoplast

2. Cytosol – surrounded by the Cell

Membrane

3. Cell Wall – hydrophilic cellulose – absorbs

water

Vacuole

Tonoplast

Cytosol

Cell Membrane

Cell Wall

Three compartments make up three major

pathways of transport of water from cell to cell.

1. Apoplastic Route: movement of water and

solutes through the cell walls

2. Symplastic Route: transfer of materials from

cytosol to cytosol via plasmodesmata

3. Transmembrane Route: movement of water

through the walls and cell membranes

Key

Symplast

Apoplast

The symplast is the

continuum of

cytosol connected

by plasmodesmata.

The apoplast is

the continuum

of cell walls and

extracellular

spaces.

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.

(b)

Figure 36.8b

Importance of Symplast and

Apoplast

- provides the route for lateral movement of water from the root epidermis to the vascular cylinder

- Water Pathway:

- Soil to root epidermis

- In the epidermis water can pass through the cell membrane, enter the symplastic route and travel to the xylem

- OR it can stay in the cell wall and follow the apoplastic route to the endodermis.

Apoplastic Barrier: Endodermis

Endodermal walls are infused with suberin(wax) that prevents the water from entering the vascular cylinder

The water must enter the cell through the cell membrane and then into the xylem

IMPORTANCE: This ensures that all the water and dissolved materials pass through at least one cell membrane before entering the xylem.

Figure 36.9

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 cross

the plasma membranes of root

hairs enter the symplast.

As soil solution moves along

the apoplast, some water and

minerals are transported into

the protoplasts of cells of the

epidermis and cortex and then

move 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 the

passage 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 the

vascular cylinder discharge water and minerals into their

walls (apoplast). The xylem vessels transport the water

and minerals upward into the shoot system.

Casparian strip

Pathway along

apoplast

Pathway

through

symplast

Plasma

membraneApoplastic

route

Symplastic

route

Root

hair

Epidermis Cortex Endodermis Vascular cylinder

Vessels

(xylem)

Casparian strip

Endodermal cell

4 5

2

1

Neither the apoplastic nor symplastic

route is continuous to the xylem

Apoplastic stops at the endodermis

Symplastic stops at the xylem

Since xylem cells are dead, the

plasmodesmata from the symplastic route will

not work so the water must exit the cells via the apoplastic route to go into the xylem walls

Vertical Movement Water – Xylem – Pushing and Pulling

Hydrostatic Pushing – Root Pressure Roots pump ions and solutes into the roots

increasing the solute concentration

Lowers the water potential resulting in an influx of water which builds pressure

The pressure pushes water up the xylem

Only good for short distances and may result in GUTTATION – forcible expulsion of water out of special structures called hydathodes (can be used as a salt gland for plants that live in high saline environments)

Transpirational Pull Pulling water up the xylem

Transpiration: regulation of the photosynthesis/transpiration compromise by the guard cells and stomata

Proper gas exchange causes the loss of water from the air spaces in the spongy mesophyll

The drier air space pulls water our of the mesophyll which gets the water from the xylem

Water loss from the xylem pulls on the water molecules down the xylem

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.

Cuticle

Upper

epidermis

Mesophyll

Lower

epidermis

Cuticle

Water vapor

CO2 O2 Xylem CO2 O2

Water vapor

Stoma

Evaporation

At first, the water vapor lost by

transpiration 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

VacuoleEvaporation

Water film

Low rate of

transpiration

High rate of

transpiration

Air-water

interface

Cell wall

Airspace

Y = –0.15 MPa Y = –10.00 MPa

3

1 2

Air-

space

Transpirational pull results from the properties

of cohesion and adhesion

As one water molecule moves out of the xylem

it tugs on the water molecule behind it because

they are bound by cohesion forces of the

hydrogen bonds between the molecules.

Water does not move down the xylem because

it is held in place by the adhesive forces

between the water and the cellulose of the

xylem walls.

Xylem

sap

Outside air Y

= –100.0 MPa

Leaf Y (air spaces)

= –7.0 MPa

Leaf Y (cell walls)

= –1.0 MPa

Trunk xylem Y

= – 0.8 MPa Wa

ter

po

ten

tia

l g

rad

ien

t

Root xylem Y

= – 0.6 MPa

Soil Y

= – 0.3 MPa

Mesophyll

cells

Stoma

Water

molecule

Atmosphere

Transpiration

Xylem

cellsAdhesion

Cell

wall

Cohesion,

by

hydrogen

bonding

Water

molecule

Root

hair

Soil

particle

Water

Cohesion

and adhesion

in the xylem

Water uptake

from soil

Other Roles of Transpiration:

Evaporative Cooling – helps keep leaves cooler

during hot days

Factors Affecting Transpiration:

Temperature: Hotter = more

Humidity: Higher = less

Air flow (wind): Higher = more

Hormone Signals (Abscisic Acid) – response to dry

conditions: Release of hormone closes stomata

Regulation of Transpiration:

Guard Cells

Regulate the size of stomatal openings for

gas exchange – responsible for the

photosynthesis/transpiration compromise

Anatomy of Guard Cell:

Eudicots: Kidney shaped

Monocots: Dumbbell shaped

Both: unevenly thickened cell walls

(stomatal side is thicker)

20 µm

Figure 36.14

Cells flaccid/Stoma closedCells turgid/Stoma open

Radially oriented

cellulose microfibrils

Cell

wall

VacuoleGuard cell

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 increase

in length more than width when turgor increases.

The two guard cells are attached at their tips, so the

increase in length causes buckling.

(a)

Figure 36.15a

Physiology Of the Guard Cell

Potassium ions are pumped into the vacuole of the guard cell from surrounding cells

Higher concentration of K+ reduces the water potential causing an influx of water

More water causes the cell to swell

Uneven thickness of the cell wall causes the cell to curve and open

Loss of water causes the cell to become flaccid and close

H2O

H2O

H2OH2O

H2O

K+

Role of potassium in stomatal opening and closing.

The transport of K+ (potassium ions, symbolized

here as red dots) across the plasma membrane and

vacuolar membrane causes the turgor changes of

guard cells.

(b)H2O H2O

H2O

H2OH2O

Figure 36.15b

Control of Guard Cells

1. Light stimulation gives energy for H+

pumps

Results in the co-transport of K+

2. CO2 depletion in air space opens

stomata

3. Circadian rhythm: internal “clock” –

plants kept in the dark still open their

stomata when it should be day

Stomatal Modifications Xerophytic Plants (dry)

Lower epidermal

tissue

Trichomes

(“hairs”)

Cuticle Upper epidermal tissue

Stomata 100 m

Cavitation: Air bubble in the xylem –

equivalent of an embolism in an artery –

blocks the flow of water – plant reroutes

through other xylem

Translocation of Phloem

Hydrostatic Push from Source to Sink

Source: Location of Sugar Production

Photosynthesis: Leaves (summer and fall)

Starch Metabolism: Roots (spring)

Sink: Location of Sugar Consumption or

Storage

Fall (Roots)

Spring (buds for leaf and stem growth)

A chemiosmotic mechanism is responsible for

the 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)

High H+ concentration Cotransporter

Proton

pump

ATP

Key

SucroseApoplast

Symplast

H+ H+

Low H+ concentration

H+

S

S

Figure 36.17b

Movement of Phloem Solution

Sugar is produced

Sugar is cotransported into the cell with

H+ ions

Water potential in the cell is lowered

Osmotic influx of water into the cell

Builds pressure inside of the cell and pushes the

solution through the cells to the sink.

Vessel

(xylem)

H2O

H2O

Sieve tube

(phloem)

Source cell

(leaf)

Sucrose

H2O

Sink cell

(storage

root)

1

Sucrose

Loading of sugar (green

dots) into the sieve tube

at the source reduces

water potential inside the

sieve-tube members. This

causes the tube to take

up water by osmosis.

2

4 3

1

2 This uptake of water

generates a positive

pressure that forces

the sap to flow along

the tube.

The pressure is relieved

by the unloading of sugar

and the consequent loss

of water from the tube

at the sink.

3

4 In the case of leaf-to-root

translocation, xylem

recycles water from sink

to source.

Tra

ns

pir

ati

on

str

ea

m

Pre

ss

ure

flo

w

CRASH COURSE