Plant Transport

PlantsPlant: terrestrial (mostly), multicellular,

photoautotrophic, eukaryote, true tissues and organs

Plant StructureTissue Basic Tissue Types: pg 717

- give rise to specialized cellso Dermal - outer coato Vascular – transport tubeso Ground – between Dermal and Vascular

Basic Tissue Layout

Dermal

Ground

Vascular

Dermaltissue

Groundtissue Vascular

tissue

Dermal Tissue Epidermis Function: protection: secretes the

cuticle, forms prickles and root hairs

Thorns, Spines and PricklesBased 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

Vesselelement

Vessel elements withpartially perforated end walls

Pits

Tracheids

SUGAR-CONDUCTING CELLS OF THE PHLOEM

Companion cell

Sieve-tubemember

Sieve-tube members:longitudinal view

Sieveplate

Nucleus

CytoplasmCompanioncell

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 photosynthesisEx: 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 parenchymaEx: “Strings” in celery

3. Sclerenchyma: highly thickened cell walls – lignified – support mature tissue – hard and deadTwo types: Fibers and ScleridsEx: Walnut Shell, Stone Cells in Pears

Parenchyma cells 60 m

PARENCHYMA CELLS

80 m Cortical parenchyma cells

COLLENCHYMA CELLS

Collenchyma cells

SCLERENCHYMA CELLS

Cell wall

Sclereid cells in pear

25 m

Fiber cells

5 m

Plant Parts: Roots, Stems and LeavesRoots:

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” aerialroots

(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

Vascularcylinder

Endodermis

Pericycle

Core ofparenchymacells

Xylem

Endodermis

Pericycle

Xylem

Phloem

Key

100 m

Vascular

Ground

Dermal

Phloem

Transverse section of a root with parenchymain the center. The stele of many monocot roots is a vascular cylinder with a core of parenchymasurrounded by a ring of alternating xylem and phloem.

(b)Transverse section of a typical root. In theroots of typical gymnosperms and eudicots, aswell as some monocots, the stele is a vascularcylinder consisting of a lobed core of xylemwith 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/

SmilaxRotMaturePhloemXylem300Lab.jpg

Growth of Lateral Roots

Cortex

Vascularcylinder

Epidermis

Lateral root

100 m

1 2

3 4

Emerginglateralroot

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

StemsFunction:

- 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 twoyears ago (threeyears old)

One-year-old sidebranch formedfrom axillary budnear shoot apex

Scars left by terminalbud scales of previouswinters

Leaf scar

Leaf scar

Stem

Leaf scar

Bud scale

Axillary buds

Internode

Node

Terminal bud

Stem: Internal AnatomyEpidermisGround TissuePithVascular Bundles

Contain Xylem and PhloemMay contain: Vascular Cambium, Cork Cambium, Sclerenchyma

Monocot Stem StructureGroundtissue

Epidermis

Vascularbundles

1 mm

(b) A monocot stem. A monocot stem (maize) with vascularbundles scattered throughout the ground tissue. In such anarrangement, ground tissue is not partitioned into pith andcortex. (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 tissueconnecting pith to cortex

Pith

Epidermis

Vascularbundle

Cortex

Key

Dermal

Ground

Vascular1 mm

(a) A eudicot stem. A eudicot stem (sunflower), withvascular bundles forming a ring. Ground tissue towardthe inside is called pith, and ground tissue toward theoutside 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

LeavesFunctions:

- photosynthesis- storage (succulent leaves, Aloe)- protection: spines, toxins, trichomes- reproduction: flowers (modified leaves)

LeavesFunctions:

- 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

Keyto labels

DermalGroundVascular

Guardcells

Stomatal pore

Epidermalcell

50 µmSurface view of a spiderwort(Tradescantia) leaf (LM)

(b)Cuticle

Sclerenchymafibers

Stoma

Upperepidermis

Palisademesophyll

Spongymesophyll

Lowerepidermis

CuticleVein

Guard cells

XylemPhloem

Guard cells

Bundle-sheathcell

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 potentialand H+ gradient.

–––

–– +

+

+

++

Figure 36.4b

H+

H+

H+

H+

H+

H+H+H+

H+

H+

H+

H+

NO3–

NO 3 –

NO3

–

NO 3–

NO3

–

NO3 – –

–– +

++

––– +

++

NO3–

(b) Cotransport of anions

H+of through acotransporter.

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

H+

H+

H+

H+

H+H+

H+

H+ H+

H+

SSS

S

SPlant cells canalso accumulate a neutral solute,such as sucrose

( ), bycotransporting down thesteep protongradient.

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 Tonoplast2. Cytosol – surrounded by the Cell

Membrane3. Cell Wall – hydrophilic cellulose –

absorbs water

VacuoleTonoplastCytosol

Cell MembraneCell 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 thecontinuum of

cytosol connectedby plasmodesmata.

The apoplast isthe continuumof cell walls andextracellularspaces.

Apoplast

Transmembrane route

Symplastic routeApoplastic 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 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

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

Upperepidermis

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 theleaf to the drier air outside via stomata.

Airspace

Cytoplasm

Cell wall

VacuoleEvaporation

Water film

Low rate oftranspiration

High rate oftranspiration

Air-waterinterface

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.

Xylemsap

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 W

ater

pot

entia

l gra

dien

t

Root xylem Y = – 0.6 MPa

Soil Y = – 0.3 MPa

Mesophyllcells

Stoma

Watermolecule

Atmosphere

Transpiration

Xylemcells Adhesion Cell

wall

Cohesion,byhydrogenbonding

Watermolecule

Roothair

Soilparticle

Water

Cohesion and adhesionin the xylem

Water uptakefrom 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 36.14Cells flaccid/Stoma closedCells turgid/Stoma open

Radially oriented cellulose microfibrils

Cellwall

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 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)

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 andvacuolar membrane causes the turgor changes of guard cells.

(b) H2O H2O

H2O

H2OH2O

Figure 36.15b

Control of Guard Cells1. 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 epidermaltissue

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 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)

High H+ concentration Cotransporter

Protonpump

ATPKey

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(storageroot)

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 tubeat the sink.

3

4 In the case of leaf-to-roottranslocation, xylem recycles water from sinkto source.

Tran

spira

tion

stre

am

Pres

sure

flow