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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 Tissue
Xylem: 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
WATER-CONDUCTING CELLS OF THE XYLEM
Vessel Tracheids
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Sieve-tube members:
longitudinal view
100 m
Pits
Companion cell
Sieve-tube
member
Sieve
plate
Tracheids and vessels
Vessel
element
Vessel elements with
partially perforated
end walls
Nucleus
30 m
15 m
Tracheids
Cytoplasm
Figure. 35.9
Companion
cell
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 Tissue
1.Parenchyma: undifferentiated, thin cell walls (still
flexible)
– used for metabolism and photosynthesis
Ex: Pallisade and Spongy Mesophyll of leaf
Potato, Fruit pulp
2. Collenchyma: unevenly thickened cell walls
– support young parts of plants – no lignin, but
stronger than parenchyma
Ex: “Strings” in celery
3. Sclerenchyma: highly thickened cell walls
– lignified – support mature tissue – hard and dead
Two types: Fibers and Sclerids
Ex: Walnut Shell, Stone Cells in Pears
PARENCHYMA CELLS
COLLENCHYMA CELLS
80 m
Cortical parenchyma cells
SCLERENCHYMA CELLS
5 m
Sclereid cells
in pear
25 m
Cell wall
Parenchyma cells
60 m
Collenchyma cells
Fiber cells
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
(d) Buttress roots
(b) Storage roots
(c) “Strangling” aerial
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)
Epidermis
Cortex
Vascular
cylinder
Endodermis
Pericycle
Core of
parenchyma
cells
Xylem
100 m
Phloem
100 m
(a)
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.
(b)
Endodermis
Key
Dermal
Pericycle
Ground
Vascular
Xylem
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.
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
100 m
Emerging
lateral
root
Cortex
Vascular
cylinder
1
2
Epidermis
Lateral root
3
4
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
Terminal bud
Bud scale
Axillary buds
Leaf scar
This year’s
growth
(one year old)
Node
Stem
Internode
One-year-old side
branch formed
from axillary bud
near shoot apex
Leaf scar
Last year’s growth
(two years old)
Growth of two
years ago (three
years old)
Scars left by terminal
bud scales of previous
winters
Leaf scar
Stem: Internal Anatomy
Epidermis
Ground Tissue
Pith
Vascular Bundles
Contain Xylem and Phloem
May contain: Vascular Cambium, Cork
Cambium, Sclerenchyma
Monocot Stem Structure
Ground
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 Structure
Phloem
Xylem
Sclerenchyma
(fiber cells)
Ground tissue
connecting
pith to cortex
Pith
Key
Cortex
Epidermis
Vascular
bundle
Dermal
Ground
Vascular
1 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
Sclerenchyma
Phloem
Xylem
Vascular Cambium
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
Guard
cells
Key
to labels
Dermal
Ground
Stomatal pore
Vascular
Cuticle
Epidermal
cell
Sclerenchyma
fibers
50 µm
(b) Surface view of a spiderwort
(Tradescantia) leaf (LM)
Stoma
Upper
epidermis
Palisade
mesophyll
Bundlesheath
cell
Spongy
mesophyll
Lower
epidermis
Guard
cells
Cuticle
Vein
Xylem
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Figure 35.17a–c
Vein
Air spaces
Guard cells
(c) Transverse section of a lilac 100 µm
(Syringa) leaf (LM)
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
CYTOPLASM
–
–
ATP
–
EXTRACELLULAR FLUID
gradient
+
H+
+
+ H+
H+
H+
H+

H+
–
–
+
+
H+
Proton pump generates
membrane potential
and H+ gradient.
H+
Functions: provides potential for the
COTRANSPORT of materials across the
membrane with the H+
–
–
–
H+
+
+
+
H+
H+
H+
H+
H+
H+
–
–
–
H+
+
+
+
Cell accumulates
anions (
, for
–
NO
example)
by3
coupling their
transport to the
inward
diffusion
of
H+ through a
cotransporter.
H+
H+
H+
H+
(b) Cotransport of anions
Figure 36.4b
H+
H+
S
–
–
+
+
–
+
H+
H+
–
–
H+
–
(c) Contransport of a neutral solute
Figure 36.4c
+
+
+
Plant cells can
also accumulate a
neutral solute,
such as sucrose
H+
H+
H+
–+
H
H+
S
H+
H+
( S ), by
cotransporting
H+ down the
steep proton
gradient.
Water Flow from Cell to Cell

Water moves between three major
compartments of the plant cell.
1.
2.
3.
Vacuole – surrounded by Tonoplast
Cytosol – surrounded by the Cell
Membrane
Cell Wall – hydrophilic cellulose – absorbs
water
Cytosol
Tonoplast
Vacuole
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
Transmembrane route
Apoplast
The symplast is the
continuum of
cytosol connected
by plasmodesmata.
The apoplast is
the continuum
of cell walls and
extracellular
spaces.
Symplast
Symplastic route
Apoplastic route
(b) 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.
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.
Casparian strip
Endodermal cell
Pathway along
apoplast
Pathway
through
symplast
1 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.
Casparian strip
2 Minerals and water that cross
the plasma membranes of root
hairs enter the symplast.
1
Plasma
membrane
Apoplastic
route
Vessels
(xylem)
2
3 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.
Symplastic
route
Root
hair
4 Within the transverse and radial walls of each endodermal cell is the
Figure 36.9
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.
Epidermis
Cortex Endodermis Vascular cylinder
5 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.
 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
3
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.
Y = –0.15 MPa
Y = –10.00 MPa
Cell wall
Air-water
interface
Airspace
Low rate of
transpiration
Cuticle
High rate of
transpiration
Upper
epidermis
Cytoplasm
Evaporation
Mesophyll
Airspace
Airspace
Cell wall
Lower
epidermis
Evaporation
Water film
Cuticle
CO2
O2
Xylem
Water vapor
1
In transpiration, water vapor (shown as
blue dots) diffuses from the moist air spaces of the
leaf to the drier air outside via stomata.
CO2
O2
Stoma
Water vapor
2
At first, the water vapor lost by
transpiration is replaced by
evaporation from the water film
that coats mesophyll cells.
Vacuole

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
Mesophyll
cells
Stoma
Water
molecule
Leaf Y (air spaces)
= –7.0 MPa
Transpiration
Atmosphere
Leaf Y (cell walls)
= –1.0 MPa
Water potential gradient
Trunk xylem Y
= – 0.8 MPa
Xylem
cells
Cohesion
and adhesion
in the xylem
Adhesion
Cell
wall
Cohesion,
by
hydrogen
bonding
Water
molecule
Root xylem Y
= – 0.6 MPa
Root
hair
Soil Y
= – 0.3 MPa
Soil
particle
Water uptake
from soil
Water
 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
(a) 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.
Cells turgid/Stoma open Cells flaccid/Stoma closed
Radially oriented
cellulose microfibrils
Cell
wall
Vacuole
Guard cell
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
(b) 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.
H2O
K+
H2O
H2O
H2O
H2O
H2O
H2O
H2O
Figure 36.15b
H2O
H2O
Control of Guard Cells
1.
Light stimulation gives energy for H+
pumps

2.
3.
Results in the co-transport of K+
CO2 depletion in air space opens
stomata
Circadian rhythm: internal “clock” –
plants kept in the dark still open their
stomata when it should be day
Stomatal Modifications
 Xerophytic
Plants (dry)
Cuticle
Lower epidermal
tissue
Upper epidermal tissue
Trichomes
(“hairs”)
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)
Movement of Phloem Solution
 Sugar
is produced
 Sugar is cotransported into the cell with
H+ ions
High H+ concentration
H+
Proton
pump
Figure
(b) 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
36.17b sucrose transport to the diffusion of H+ back into the cell.
Cotransporter
S
Key
ATP
H+
Low H+ concentration
H+
Sucrose
S
Apoplast
Symplast
 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)
Sieve tube
(phloem)
H2O
Source cell
(leaf)
1
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
This uptake of water
generates a positive
pressure that forces
the sap to flow along
the tube.
3
The pressure is relieved
by the unloading of sugar
and the consequent loss
of water from the tube
at the sink.
4
In the case of leaf-to-root
translocation, xylem
recycles water from sink
to source.
Sucrose
1
H2O
2
Pressure flow
Transpiration stream

4
Sink cell
(storage
root)
3
Sucrose
H2O