*photosynthetic, multicellular, terrestrial

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© 2013 American Society of Plant Biologists How to be a *plant *photosynthetic, multicellular, terrestrial

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Page 1: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

How to be a *plant

*photosynthetic, multicellular,

terrestrial

Page 2: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants are multicellular, terrestrial

and photosynthetic

Multicellular: Different cells can

have various functions, but they

must integrate their activities

Terrestrial: Plant ancestors were

aquatic, but terrestrial plants

have to cope with very dry air

Photosynthetic: Plants and many

other organisms can convert solar

energy to chemical energy

Leaf cross section image from Bouton, J.H., et al., (1986). Photosynthesis, leaf anatomy, and morphology of progeny from hybrids between C3 and C3/C4 Panicum Species. Plant Physiol. 80: 487-492.

Page 3: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Human physiology centers on

systems Respiratory

system Gas exchange

Digestive

system Water and

Nutrient uptake

Circulatory

system Nutrient

transport

Nervous

system

Perception,

control

Skeletal

system

Support

Page 4: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plant physiology: Same functions,

more broadly distributed Gas exchange

takes place

through

thousands of

stomata

Nutrients are

transported

from cell to cell

and through

vascular tissues

Water and nutrient uptake

take place across the root

(and sometimes shoot)

surfaces

Energy assimilation

takes place

throughout

photosynthetic

tissues

Signals to control and

coordinate plant functions

move from cell to cell and

through vascular tissues

Perception (of light,

pathogens etc.) occurs

through receptors and

other sensors found in

most cells

Support comes

from cell walls and

hydrostatic

pressure

Page 5: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

What are plants? Plants are

photosynthetic eukaryotes

ALL LIFE PHOTOSYNTHETIC

ORGANISMS

CYANOBACTERIA +

“DESCENDANTS”

EUKARYOTES WITH

CYANOBACTERIA-DERIVED

CHLOROPLASTS

Non-

photosynthetic

bacteria

Archaea

Fungi

Animals

You are here

Green

sulfur

bacteria

Purple

sulfur

bacteria

Other

bacteria

Cyanobacteria

Diatoms Red algae

Brown

algae

PLANTS

GREEN ALGAE AND

DESCEDANTS

(Circles not

drawn to

scale)

Page 6: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants descended from a eukaryotic

ancestor + a cyanobacteria

ORIGIN OF LIFE

Bacteria Archaea Eukarya

Mitochondrial

endosymbiosis

Plastid

endo-

symbiosis

PL

AN

TS

AL

GA

E

FU

NG

I

AN

IMA

LS

>3.5 BYA

>1.5 BYA

>0.5 BYA

Photosynthesis evolved

in bacteria. All

photosynthetic

eukaryotes acquired this

ability through

endosymbiosis of

photosynthetic bacteria

Therefore, some “plant” genes

(those derived from the

ancestral bacteria) are more like

bacterial genes than the genes

of other eukaryotes

Adapted from Govindjee and Shevela, D. (2011). Adventures with cyanobacteria: a personal perspective. Frontiers in Plant Science. 2: 28.

Page 7: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Two endosymbiotic organelles –

mitochondria and plastids

Cyanobacteria Proteobacteria

The host that acquired

mitochondria

Early diversification of eukarya

Ancient

proteobacterium

PLANTS

EUKARYOTES

Ancient cyanobacterium

Adapted from Timmis, J.N., Ayliffe, M.A., Huang, C.Y. and Martin, W. (2004). Endosymbiotic gene transfer: organelle genomes forge eukaryotic chromosomes. Nat Rev Genet. 5: 123-135.

Page 8: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Family tree: Plants and green algae

Adapted from Hay, A. and Tsiantis, M. (2010). KNOX genes: versatile regulators of plant development and diversity. Development. 137: 3153-3165 and Prigge,

M.J. and Bezanilla, M. (2010). Evolutionary crossroads in developmental biology: Physcomitrella patens. Development. 137: 3535-3543.

1200?

450

400

360

300

Ch

loro

ph

yte

s

Ch

aro

ph

yte

s

Bry

op

hyte

s

Lyco

ph

yte

s

Fern

s

Gym

no

sp

erm

s

An

gio

sp

erm

s

Green algae Plants

Terrestrialization

Stomata

Vascular tissues

Seeds

Flowers

Page 9: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Green algae are photosynthetic

eukaryotes, but not all plants

Image credits: JGI; Spike Walker Wellcome Images; Jaspser Nance; Show_ryu

Chlamydomonas reinhardtii

10 μm

Ostreococcus

tauri

Volvox spp

Chlorophytes Spirogyra spp

Charophytes

Chara braunii

Page 10: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Bryophytes are “non-vascular”

plants

Adapted from Chang, Y. and Graham, S.W. (2011). Inferring the higher-order phylogeny of mosses (Bryophyta) and relatives using a large, multigene plastid data set. Am. J. Bot. 98: 839-849 and Ligrone, R., Duckett, J.G. and

Renzaglia, K.S. (2012). Major transitions in the evolution of early land plants: a bryological perspective. Ann. Bot. 109: 851-871. Photo credits Tom Donald, Mary Williams and gjshepherd_br / Foter.com / CC BY-NC-SA

Green algae

Land plants

Liverworts (~7000

– 8500 species)

Mosses (~10,000 –

17,000 species)

Hornworts (~200 species)

Vascular

plants

Page 11: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Tracheophytes are vascular plants

Bryophytes

Vascular tissue

Lycophytes

(~ 1200 species)

Ferns

(~ 13,000 species)

Gymnosperms

(~ 1000 species) Angiosperms

(~ 350,000 species)

Seeds

Photos by Tom Donald

Page 12: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Introduction to bioenergetics

Photo credit: Tom Donald

Page 13: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Energy is never gained or lost,

just transferred to other forms H

igher

energ

y

Chemical energy

transferred to

potential energy by

muscles

Potential energy

transferred to

kinetic energy

Kinetic

energy

transferred

to heat

Page 14: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Energy exists in many forms and

can be interconverted between them

Chemical

energy

Kinetic

energy

Electromagnetic

(solar) energy

Po

ten

tial

Kin

eti

c

Chemical

energy

Image credit: NOAA

Page 15: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Chemical energy can be stored in

bonds and as reducing power

Energy released

sugar sugar sugar sugar sugar

sugar sugar

sugar

sugar

sugar

Starch – a polymer made of sugar

A carbohydrate like

starch has energy

stored in its bonds

Energy is released

when the bonds

are broken

More energy is

released when the

carbon in the sugar

is oxidized

O2

CO2

Energy released

Page 16: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Energy can be stored or released via

the redox state of an element

Higher

energy,

reduced

form

Carbohydrates

C6H12O6

CH2O

Ammonium

NH4+

Iron (II)

Lower

energy,

oxidized

form

Carbon Dioxide

CO2

Nitrate, nitrite

NO3-, NO2

-

Iron (III)

Oxidation involves

the removal of

electrons, and

requires an

electron acceptor

Reduction O

xid

atio

n

Energy

input

required

Energy

released

Page 17: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Campfire: Oxidation of carbon with

energy released as heat and light High-

energy

reduced

carbon in

wood

C6H12O6 + 6 O2 6 CO2 + 6 H2O

Low energy

oxidized carbon

in carbon

dioxide

The non-carbon elements

in wood contribute to ash

Energy is released

as heat and light

Oxygen is required

for a fire to burn.

Oxygen is the

electron acceptor in

the oxidation

reaction

Page 18: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Biological metabolism: Controlled

release and recapture of energy High-

energy

reduced

carbon in

food

C6H12O6 + 6 O2 6 CO2 + 6 H2O

Low energy

oxidized carbon

in carbon

dioxide

Energy is captured

for later use

Oxygen is required to

efficiently extract energy

from carbohydrates. (Oxygen is the electron

acceptor in the oxidation

reaction)

Metabolism

(Specifically,

oxidative

phosphorylation)

ATP (adenosine

triphosphate)

Page 19: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Adapted from TXU Corp; Poco a poco

Analogy: Hydroelectricity is produced by the

controlled release and capture of kinetic

energy from falling water

Reserv

oir

Dam Power Plant

Generator

Turbine

Electricity Kinetic energy in the moving

water turns the turbine to

generate electricity

(electromagnetic energy)

The energy of a

natural waterfall is

transferred to the

rocks below it

Page 20: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Cellular energy currencies, ATP and

NAD(P)H

H2O

-

-

ATP (Adenosine

triphosphate)

ADP (Adenosine

diphosphate)

H+

energy

NADP+ (nicotinamide

adenine dinucleotide

phosphate)

NADPH

H+ + 2e-

ATP stores energy in a

high-energy bond

NADPH stores reducing

power and electrons

Page 21: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Introduction to photosynthesis

Daum, B., Nicastro, D., Austin, J., McIntosh, J.R. and Kühlbrandt, W. (2010). Arrangement of photosystem II and ATP synthase in chloroplast membranes of spinach and

pea. Plant Cell. 22: 1299-1312 Chuartzman, S.G., et al., (2008). Thylakoid membrane remodeling during state transitions in Arabidopsis. Plant Cell. 20: 1029-1039..

ATP synthase (yellow) embedded in

thylakoid membranes (green)

PSII supercomplexes in thylakoid membranes

lumen

Ultrastructure of a chloroplast

showing thylakoid membrane stacks

Page 22: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Energy enters the biosphere mainly

through photosynthesis by plants

TERRESTRIAL

BIOSPHERE

MARINE

BIOSPHERE

Some energy is

introduced by the

action of

chemotrophs COAL, OIL

AND GAS

RESERVES

Field, C.B., Behrenfeld, M.J., Randerson, J.T. and Falkowski, P. (1998). Primary production of the biosphere: Integrating terrestrial and oceanic components. Science. 281: 237-240.

Page 23: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Burning buried sunshine*

*Title credit from Dukes, J. (2003). Burning buried sunshine: Human consumption of ancient solar energy. Climatic Change. 61: 31-44.

COAL, OIL

AND GAS

RESERVES

One gallon of gasoline comes

from ~89 metric tons (~180,000

pounds) of ancient lycophytes and

ferns that dominated the earth 300

million years ago, but mostly have

been supplanted by seed plants

Fossil fuel reserves are

estimated to be about

5,000 gigatons (Gt) of

carbon, accumulated

over millions of years

89 metric tons

of gold is worth

$4 billion

($4 x 109)

89 metric tons is

about 89 elephants

“I get 500

meters per ton”

Page 24: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

In plants, photosynthesis captures

light energy as reduced carbon

Low energy,

oxidized carbon

in carbon

dioxide

Energy input

from sunlight

High

energy,

reduced

carbon

Oxygen is

released as

a byproduct

6 CO2 + 6 H2O C6H12O6 + 6 O2

The first step is the capture of

light energy as ATP and

reducing power, NADPH

The second step is the transfer of

energy and reducing power from

ATP and NADPH to CO2, to produce

high-energy, reduced sugars

ATP NADPH

Page 25: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Photosynthesis is two sets of

connected reactions

Chloroplast 2 H2O O2 + 2 H+

ADP H+

ATP

The LIGHT-HARVESTING reactions take

place in the chloroplast membranes

The CARBON-FIXING

reactions take place in

the chloroplast stroma

Adapted from Kramer, D.M., and Evans, J. R. (2010). The importance of energy balance in improving photosynthetic productivity. Plant Physiol.155: 70–78.

Page 26: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Light harvesting reactions produce

O2, ATP and NADPH

2 H2O O2 + 2 H+

ADP

H+

ATP

ATP synthase Photosystem II (PSII)

Photosystem I

(PSI)

Cytochrome

b6f complex The reactions

require several

large multi-protein

complexes: two

light harvesting

photosystems (PSI

and PSII), a

cytochromome b6f

complex, and an

ATP synthase

Adapted from Kramer, D.M., and Evans, J. R. (2010). The importance of energy balance in improving photosynthetic productivity. Plant Physiol.155: 70–78.

Page 27: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Chlorophyll captures light energy to

initiate the light harvesting reactions

Hydrophobic

tail anchors

chlorophyll in

membrane

Porphyrin ring

captures photons

Photon capture by

chlorophyll excites the

chlorophyll (Chl*). Chl*

loses an electron (e-)

and relaxes back to its

unexcited state

Chl

Chl* e-

Photon

Chl

2 H2O

e-

4 H+

O2

Oxidized Chl is

reduced by stripping

an electron from

water, releasing

oxygen and protons

Buchanan, B.B., Gruissem, W. and Jones, R.L. (2000) Biochemistry and Molecular Biology of Plants. American Society of Plant Physiologists.

Page 28: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants have two photosystems that

work together

Adapted from Govindjee and Shevela, D. (2011). Adventures with cyanobacteria: a personal perspective. Frontiers in Plant Science. 2: 28.

2 H2O e-

4 H+

O2

H+

Thylakoid

Membrane

PSII PSI

e-

e-

e-

e-

2 NADP+

2 NADPH

2 H+ e-

In photosystem II,

water is split to

release oxygen

Electrons are passed from

PSII to PSI and eventually to

NADP+, producing NADPH

Cytochrome

b6f complex

Protons accumulate in

the thylakoid lumen

Thylakoid lumen

Page 29: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

[H+]

Thylakoid

Membrane

Thylakoid lumen

ADP + Pi

H+

ATP

H+

Proton gradient from

high (in) to low (out)

2 H2O e-

4 H+

O2

H+

ATP

Synthase

H+

H+

H+ H+

H+

H+

H+

H+

H+

A proton gradient drives ATP

synthesis

Adapted from Kramer, D.M., and Evans, J. R. (2010). The importance of energy balance in improving photosynthetic productivity. Plant Physiol.

155: 70–78 and Hohmann-Marriott, M.F. and Blankenship, R.E. (2011). Evolution of photosynthesis. Annu. Rev. Plant Biol. 62: 515-548.

Page 30: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Through the Calvin-Benson cycle,

ATP and NADPH are used to fix CO2

Adapted from: Buchanan, B.B., Gruissem, W. and Jones, R.L. (2000) Biochemistry and Molecular Biology of Plants. American Society of Plant Physiologists.

Carboxylation

Reduction

Rubisco 3 x CO2 3 x Ribulose-1,5-

bisphosphate

6 x 3-phosphogylcerate

6 ATP

6 ADP + 6 Pi

6 NADP+ + 6 H+

6 NADPH

Energy input

Reducing

power input

6 x glyceraldehyde

3-phosphate (GAP)

Regeneration

For every 3 CO2 fixed, one

GAP is produced for

biosynthesis and energy

5 x GAP

1 x GAP

6 ATP

6 ADP + 6 Pi

Each CO2 fixed

requires 3 ATP

and 2 NADPH

Page 31: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Some plants have additional,

CO2-concentrating steps

Because Rubisco has

an oxygenase as well

as a carboxylase

activity, some plants

concentrate CO2 to

promote the

carboxylation reaction

PEP

carboxylase

Rubisco

CCC CO2

CCCC

CCC

CCCCC Calvin-

Benson

cycle

C4 cycle Energy input

Regeneration CO2

Ribulose-1,5-

bisphosphate

Phosphoenolpyruvate

This cycle produces a

four-carbon compound,

so it is called the C4 cycle

The result of the C4 cycle

is to elevate the

concentration of CO2 at

the site of Rubisco action

Page 32: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Fixed carbon has many fates

Some is used for

biosynthesis of other

compounds

CO2

CO2

CO2

Some of the fixed carbon is

oxidized in the

mitochondria to produce

ATP, and released as CO2

Some is

transported to

growing tissues,

or stored as

starch or oil in

seeds

Some is transported to the roots

and used for growth, stored, used

to support nutrient uptake, or

exuded into the soil

Page 33: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Summary: Plants are photosynthetic

eukaryotes

• Plants convert light energy to

chemical energy

• Photosynthesis evolved in

bacteria, and takes place in the

descendants of endosymbiotic

photosynthetic bacteria

• Through photosynthesis, plants

and algae are responsible for the

transfer of most of the energy that

enters the biosphere

Low energy,

oxidized carbon

in carbon

dioxide

Energy input

from sunlight

High

energy,

reduced

carbon

Oxygen is

released as

a byproduct

6 CO2 + 6 H2O C6H12O6 + 6 O2

Page 34: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants are assembled from cells

VACUOLE

NUCLEUS CHLOROPLASTS

MIT

OC

HO

ND

RIA

Vacuolar membrane

Plasma membrane

Cell wall

A “typical” plant cell

The plasma membrane

is a barrier that lets cells

maintain a different

internal environment

from their surroundings

Plasma membrane

Page 35: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Systems move towards uniformity,

unless energy is expended

Energy

Dispersed,

equally

distributed

Nonuniform

distribution,

Equilibrium Disequilibrium –

stored energy

Energy

Cells expend energy to maintain an

internal environment that is distinct

from the external environment

Page 36: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Cells are surrounded by a semi-

permeable plasma membrane

Na+

Na+

K+

K+

H2O OUT

IN

CO2

The membrane is

permeable to water and

gases, but impermeable to

ions and larger molecules

Photo credit: Wenche Eikrem and Jahn Throndsen, University of Oslo

Page 37: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Proteins in the plasma and vacuolar

membranes move molecules

Adapted from Hedrich, R. (2012). Ion channels in plants. Physiol. Rev. 92: 1777-1811.

These transporters bring

in needed ions and other

compounds, and export

unwanted molecules.

The transporters are also

needed to regulate the

cell’s osmotic potential

VACUOLE

Vacuolar membrane

Plasma membrane

Cell wall

ADP

H+

ATP

H+ X

H+

ADP

ATP

Page 38: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Membrane proteins form pores,

channels or pumps for ion transport

K+

K+

K+

K+

The complex protein

structures are usually draw

in simplified forms

Ion transport across a

membrane usually directly

or indirectly requires energy

Page 39: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plant cells move water by osmosis

and pressure

Buer, C.S., Weathers, P.J. and Swartzlander, G.A. (2000). Changes in Hechtian strands in cold-hardened cells measured by optical microsurgery. Plant Physiol. 122: 1365-1378.

Cell wall

WATER

WATER

WATER

WATER

Cell showing the cytoplasm pull

away from the cell wall as it

loses volume (plasmolysis)

Page 40: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Water moves down osmotic

gradients

Water moves across a

semipermeable membrane

into a compartment

containing salt

The water flows inwards

until the force of the

pressure inside balances

the osmotic driving force

The osmotic potential of pure water is 0. The addition

of solutes lowers the water potential. Water moves

towards a region with a lower water potential.

Page 41: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Osmotic forces drive the movement

of water into and out of cells

Salt water

Fresh water Fresh water

Salt water

An animal cell might burst Plant cell walls prevent them

from bursting

Cells have a lower osmotic

potential than pure water,

(because of the salts and

proteins in them), so water

moves into them

Salt water has a lower

osmotic potential than

cells, so water flows

outwards

Osmotic potential is written as Ψπ and measured in MegaPascals (MPa)

For seawater, Ψπ is about -2.5 MPa, and for a typical cell, Ψπ is about -0.8 MPa

Page 42: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Water can be moved by tension

(pulling) or pressure (pushing)

Pulling up the

plunger causes

the pressure

inside the barrel

to be lower than

atmospheric.

Water from the

beaker moves

towards the

region of lower

pressure, into the

barrel.

Pushing down the

plunger causes

the pressure

inside the barrel

to be higher than

atmospheric.

Water from the

barrel moves out,

towards the

region of lower

pressure.

Page 43: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Pressure can be positive or negative

Mschel; Image 14869 CDC/ Nasheka Powell

Household

water

pressure

0.3 MPa

Car tire

pressure

0.25 MPa

Pressure

required to

blow up a

balloon

0.01 MPa

Vacuum cleaner

-0.02 MPa

(household)

-0.1 MPa

(commercial)

Laboratory

vacuum

-0.01 MPa

Human blood

pressure

< 0.02 MPa

Inside typical plant cell

0.5 – 1.5 MPa

Pressure

washer

15 MPa

Inside xylem:

From +1 MPa to

-3 MPa or lower

Page 44: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

The water potential equation

incorporates osmotic and pressure

potentials

Ψw = Ψp + Ψπ

The water potential (Ψw) is the sum of the pressure

potential (Ψp) and the osmotic potential (Ψw) The water

potential

equation

Water flows

from higher to

lower water

potential

Page 45: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Water moves towards lower water

potential

Initial conditions: Final conditions:

Ψπ = 0

Ψp = 0

Ψw = 0

+

Ψπ = -2

Ψp = 0

Ψw = -2

+

Water moves

towards lower

water potential

Ψπ = 0

Ψp = 0

Ψw = 0

+

Ψπ = -2

Ψp = 2

Ψw = 0

+

Water is at

equilibrium

Page 46: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plant cell walls are flexible, strong,

and complex The primary cell

wall is thin and

somewhat

flexible

Cytoplasm

Vacuole

Plasma membrane

The cell wall is synthesized

outside of the plasma

membrane from materials

transported outward through

the plasma membrane

Secondary cell walls form

inside of the primary cell wall.

Secondary walls are usually

rigid and contain lignin, a

complex, insoluble polymer

Primary cell wall

Secondary cell wall

Vanholme, R., Demedts, B., Morreel, K., Ralph, J. and Boerjan, W. (2010). Lignin biosynthesis and structure. Plant Physiol. 153: 895-905.

Page 47: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Primary cell wall: cellulose, proteins

and other components

Reprinted from McCann, M.C., Bush, M., Milioni, D., Sado, P., Stacey, N.J., Catchpole, G., Defernez, M., Carpita, N.C., Hofte, H., Ulvskov, P., Wilson, R.H. and Roberts, K. (2001). Approaches to

understanding the functional architecture of the plant cell wall. Phytochemistry. 57: 811-821, with permission from Elsevier; Drawing credit LadyofHats.

Page 48: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants are multicellular

Advantages:

• Bigger means better

able to compete for light,

nutrients

• Cells can specialize

Disadvantages:

• Need to move resources

and information,

coordinate actions

Photo credit: Tom Donald

Page 49: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Multicellular organisms need to

transmit materials and information

Metabolic products

have to be distributed

throughout the body

Information has to be

transmitted to

integrate activities

Raw materials

have to be

distributed –

diffusion is

inadequate for

larger organisms

Page 50: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

(Most) plant cells are connected by

plasmodesmata

Reprinted from Lee, J.-Y. and Lu, H. (2011). Plasmodesmata: the battleground against intruders. Trends Plant Sci. 16: 201-210 with permission from Elsevier.

Plasmodesmata are

plasma-membrane

lined, regulated

cytoplasmic bridges

between plant cells

Signals, nutrients,

ions and water

can move to

adjacent cells, or

longer distances

via the phloem

Pathogens can

spread through

the plant through

plasmodesmata

Guard cells are

isolated, without

functional

plasmodesmata

Page 51: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Transport in bryophytes – some

specialized transport cells

Hydroids (h) in

cross section

Water moves along

external surfaces,

within cells, between

cells, and through

specialized water-

conducting cells or

hydroids (h)

Bryophytes take up water from the air and substrate

Some bryophytes

have food-

conducting cells

or leptoids (l)

The end walls

between food-

conducting cells can

have enlarged

plasmodesmata-

Micrographs from Ligrone, R., Duckett, J.G. and Renzaglia, K.S. (2000). Conducting tissues and phyletic relationships of bryophytes. Philosophical

Transactions of the Royal Society of London. Series B: Biological Sciences. 355: 795-813 by permission of the Royal Society.

Page 52: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Vascular plants have long-distance

transport systems

XYLEM Water moves from

the soil to the

atmosphere

through the hollow

dead cells of the

xylem

PHLOEM Photosynthetically-

produced sugars (and

other molecules) move

from their source to

sinks (non-

photosynthetic tissues)

through the phloem

Page 53: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Water moves from the soil, into the

outer layers of the root , then into the

vascular cylinder and xylem

Water is pulled through the

hollow xylem by tension

developed at evaporative

sites in the leaves

In the leaf, water evaporates out of

the xylem into the intracellular

spaces, and then through the

stomata into the atmosphere

Stomate

Outer root

layer

Endodermis

Vascular

cylinder

Water uptake and movement in

vascular plants

Page 54: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Water movement in the xylem is

driven by evaporation

Ψw= -0.2 MPa

Water moves

from moist soil to

the dry

atmosphere. The

plant simply taps

into this force to

draw water

through its body

Ψw= -15 to

-100 MPa

Page 55: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Water movement in the xylem is

driven by evaporation

Adapted from Lucas, W.J. et al. (2013). The plant vascular system: Evolution, development and functions. J. Integr. Plant Biol. 55: 294-388.

Ψw= -0.2 MPa

Simple model:

Hollow tube

that water

evaporates

through

Better model:

Hollow tube

with a

selectivity

filter in the

roots and a

flow regulator

at the top

Guard

cells

Casparian

strip of the

endodermis

Ψw= -15 to

-100 MPa

Page 56: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Xylem cells are highly specialized

water-conducting cells

Oda, Y., Mimura, T. and Hasezawa, S. (2005). Regulation of secondary cell wall development by cortical microtubules during tracheary element differentiation in Arabidopsis cell

suspensions. Plant Physiol. 137: 1027-1036. Reprinted from Höfte, H. (2010). Plant cell biology: How to pattern a wall. Curr. Biol. 20: R450-R452 with permission from Elsevier.

Secondary

wall

deposition

Elongation

Programmed

cell death

The cells form

thickened rings

of secondary wall

tissue and then

die, leaving

behind a hollow,

reinforced vessel

Page 57: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

The structure of xylem cell walls

prevents embolisms from spreading

Reprinted from Li, H.-F., et al. (2011). Vessel elements present in the secondary xylem of Trochodendron

and Tetracentron (Trochodendraceae). Flora. 206: 595-600 with permission from Elsevier.

Because water

moves under

tension, air

bubbles or

embolisms can

form. The small

gaps in the xylem

walls permit

water but not air

bubbles to move

through them

Air bubble

Page 58: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Bryophotes

produce

monolignols:

UV protection?

Defense?

Tracheophytes produce

lignin polymer:

Structure for xylem,

support and strength for

size

Lignin-strengthened

cell walls are one of

the major features

that let plants get big

The secondary walls are reinforced by

lignin, a water-impermeable polymer

Reprinted from Höfte, H. (2010). Plant cell biology: How to pattern a wall. Curr. Biol. 20: R450-R452 with permission from Elsevier.

Weng, J.-K. and Chapple, C. (2010). The origin and evolution of lignin biosynthesis. New Phytol. 187: 273-285.

Page 59: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Lignified xylem provides structural

support for vascular plants

11

5 m

Seq

uo

ia s

em

perv

iren

s

Sydney Opera House 65 m Taj Mahal 65 m

Statue of Liberty 93 m

St. Paul’s Cathedral 111 m

The tallest living trees

tower over many

familiar monuments

Page 60: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

The root endodermis acts as a

selectivity filter Na+

Na+

Na+

Na+

Na+ Na+

Na+

The endodermis produces a

water-impermeable layer,

the Casparian strip, that

provides selectivity Photo credit Michael Clayton

Page 61: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

The Casparian strip forces water to

cross a plasma membrane

Photo credit Michael Clayton; Adapted from Grebe, M. (2011). Plant biology: Unveiling the Casparian strip. Nature. 473: 294-295.

Na+

Na+

OUT IN

Water can enter

the root through

the apoplast (cell

wall spaces) until

it reaches the

Casparian strip,

which blocks

apoplastic water

flow

Water forced to

cross a plasma

membrane is

effectively filtered

Page 62: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Waxy cuticles prevent water loss;

regulated pores allow it OPEN

CLOSED

Most plant aerial surfaces are

covered by a waxy cuticle. Pores

called stomata, usually covered by

pairs of guard cells, permit

transpiration

Guard cells change

their volume to

open and close the

pore. Guard cells

are sensitive to the

atmospheric

conditions and the

plant’s needs for

gas exchange and

water conservation

Page 63: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Functional unit of the phloem: sieve

element – companion cell complex

Oparka, K.J. and Turgeon, R. (1999). Sieve elements and companion cells—Traffic control centers of the phloem. Plant Cell. 11: 739-750;

Mullendore, D.L., Windt, C.W., Van As, H. and Knoblauch, M. (2010). Sieve tube geometry in relation to phloem flow. Plant Cell. 22: 579-593.

Companion

cell The companion cell loads

the sieve element and

provides it with genetic

materials, through

extensive plasmodesmatal

connections

Functional sieve

elements lack nuclei

and central vacuoles,

facilitating flow

The ends of

adjoining sieve

elements are

connected by pores

derived from

enlarged

plasmodesmata

Page 64: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Transport in the phloem

Sugars

1. Sugars are loaded into the

phloem by active transport

2. Water moves

in by osmosis

3. The fluid

moves

through the

sieve

elements

under

pressure, by

bulk flow (like

water in a

hose) 4. Sugars are released

into the sink tissues

5. Water

follows by

osmosis

From source

to sink

CC SE

Adapted from Lucas, W.J. et al. (2013). The plant vascular system: Evolution, development and functions. J. Integr. Plant Biol. 55: 294-388.

Page 65: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Vascular tissues are essential

conduits for information flow

Reprinted from Schachtman, D.P. and Goodger, J.Q.D. (2008). Chemical root to shoot signaling under drought. Trends Plant Sci. 13: 281-287 with permission from

Elsevier; see also Christmann, A., Grill, E. and Huang, J. (2013). Hydraulic signals in long-distance signaling. Curr. Opin. Plant Biol. 16: 293-300.

In animals, signals

moving through the

nervous and

circulatory systems

convey information

Some signals

move in the

xylem. Signals

from drought-

stressed roots

cause guard

cells to close

Other xylem-borne

signals convey

information about

nutrient availability

and soil-microbes

Page 66: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

The phloem is also responsible for

long-distance signaling

Time to reproduce:

Under appropriate day-

length conditions (i.e.

seasons) the protein

FLOWERING LOCUS T

(FT) and its orthologs

move from leaves to the

shoot apex, to promote

the transition to

reproductive growth

Coordination of root and

shoot functions:

When leaves are

phosphate-limited, a

microRNA (miR399)

moves through the phloem

to the root and promotes

phosphate uptake

FT

miR399

See for example Chiou, T.-J., et al. (2006). Regulation of phosphate homeostasis by microRNA in Arabidopsis. Plant Cell. 18: 412-421; McGarry, R.C. and Kragler, F. (2013). Phloem-mobile signals affecting

flowers: applications for crop breeding. Trends Plant Sci. 18: 198-206; Lucas, W.J. et al. (2013). The plant vascular system: Evolution, development and functions. J. Integr. Plant Biol. 55: 294-388.

Page 67: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Opportunities and challenges of the

terrestrial environment

>450 million years ago, plants moved onto dry land

However, plants had to

overcome significant challenges

to adapt to dry land

The aquatic environment

was competitive and filled

with herbivores

Initially, land offered

less competition and

fewer herbivores

Page 68: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

The terrestrial environment is

challenging

Aquatic environment:

Buoyancy

Abundant water

Moderate temperatures

Filtered light

Terresrial environment:

No buoyancy

Scarce water

Extreme temperatures

Excess light including UV

Too heavy, dry, hot and cold and bright

Page 69: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

As sessile organisms, plants have to

respond and adjust to stress

Like animals,

plants sense and

respond to the

physical conditions

of their

environment:

temperature,

humidity, light

intensity

Page 70: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Obtaining and retaining water is a

challenge for terrestrial plants

Freshwater green

algae easily take up

water from their

aquatic environment

The water potential of air

and soil is usually lower

than that of the plant

cells. How do terrestrial

plants survive?

Page 71: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Desiccation tolerance or avoidance,

drought evasion or tolerance Most bryophytes can tolerate

desiccation (drying out extensively)

Some desert plants evade

drought. They survive the

dry season as seeds,

sprouting and flowering in

a brief period of rain

Some desert plants

tolerate dry conditions

through adaptations such

as deep roots, C4

photosynthesis, and tiny or

absent leaves

Most

tracheophytes

cannot tolerate

desiccation –

they die

Photo credits: Mary Williams; Amrum; Scott Bauer; James Henderson, Golden Delight Honey, Bugwood.org

Page 72: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Desiccation tolerance or desiccation

avoidance

Photo credits: Mel Oliver, IRRI, IRRI

Most bryophytes (and a few

angiosperms) can tolerate

desiccation

The vegetative tissues of

most angiosperms cannot

tolerate desiccation, but the

seeds can

Desiccated

and alive

Desiccated

but DEAD

The cells adjust with external water

availability, and can survive desiccation

Cuticle

The cells do not really adjust with external water availability,

and die if totally desiccated

Decreasing water availability

Page 73: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Strategies for desiccation tolerance

include stabilization and repair

Reprinted from Hoekstra, F.A., Golovina, E.A. and Buitink, J. (2001). Mechanisms of plant desiccation tolerance. Trends Plant Sci. 6: 431-438 with permission from Elsevier; Vander

Willigen, C., Pammenter, N.W., Mundree, S.G. and Farrant, J.M. (2004). Mechanical stabilization of desiccated vegetative tissues of the resurrection grass Eragrostis nindensis: does a

TIP 3;1 and/or compartmentalization of subcellular components and metabolites play a role? Journal Exp. Bot. 55: 651-661 by permission of Oxford University Press.

Craterostigma

pumilumI, an

angiosperm

desiccation tolerant

“resurrection plant”

Upon desiccation, the

leaves curl in, purple

anthocyanin

photoprotective pigments

accumulate, and small

molecules that stabilize

cell integrity accumulate

Desiccation affects

membranes and walls,

which must be rapidly

repaired on rehydration

Page 74: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

By contrast, most tracheophytes

avoid desiccation

Vascular

tissue

Roots

Tracheophytes have:

• A waxy cuticle that covers their aerial

tissues

• Regulated pores (stomata) for water

and gas exchange

• Lignified vascular tissues that

conduct water

• Roots specialized for water and

nutrient uptake

Cuticle Stomata

Image sources:B.W. Wells lantern slides, (UA023.039) NCSU Libraries, Yvan Lindekens; Girard, A.-L., et al., (2012). Tomato GDSL1 is required for cutin deposition in the fruit cuticle. Plant Cell. 24: 3119-3134;

Reprinted from Li, H.-F., et al. (2011). Vessel elements present in the secondary xylem of Trochodendron and Tetracentron (Trochodendraceae). Flora. 206: 595-600 with permission from Elsevier.

Page 75: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants can survive across most of

the earth Mountain Arctic

Desert Antarctic

Photo credits: Hannes Grobe, AWI; Gnomefilliere; Liam Quinn; Florence Devouard

Page 76: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants can adapt and acclimate to

temperature extremes

Adapted from Berry, J., and Björkman, O. (1980). Photosynthetic response and adaptation to temperature in higher plants. Annu. Rev. Plant Physiol. 31: 491 – 543. Photo credit Sue in Az

Leaf temperature (°C)

Photo

synth

etic r

ate

10 20 30 40 50

Desert

species

Coastal

species

Leaf temperature (°C)

Photo

synth

etic r

ate

10 20 30 40 50

Desert species acclimated

to high temperatures

Acclimated to

cool

temperatures

To a certain extent, most

plants can acclimate to

higher or lower

temperatures, by sensing

and responding to a

change in temperature

Some plants have

evolved to tolerate high

temperatures

Larrea tridentata, an

extremely thermotolerant

desert plant

Page 77: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

How long can bryophytes tolerate

extreme cold? 400 years!

Behind a retreating glacier,

scientists found viable

bryophytes that laid dormant

under the ice for ~400 years

La Farge, C., Williams, K.H. and England, J.H. (2013). Regeneration of Little Ice Age bryophytes emerging from a polar glacier

with implications of totipotency in extreme environments. Proc. Natl. Acad. Sci. 110: 9839-9844.

Page 78: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Light is good, but too much light is

damaging

Image credits: Dennis Haugen, Bugwood.org; Tomas Sobek; Reprinted by permission from Macmillan Publishers Ltd from Kasahara, M., Kagawa, T.,

Oikawa, K., Suetsugu, N., Miyao, M. and Wada, M. (2002). Chloroplast avoidance movement reduces photodamage in plants. Nature. 420: 829-832.

When light is too

bright, chloroplasts

can move to reduce

light incidence Photoprotective

pigments can

protect delicate

light-harvesting

machinery

Vertical orientation

minimizes light

absorption at midday

Page 79: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Image credit: Forest & Kim Starr, Starr Environmental, Bugwood.org

SUMMARY

Like animals, plants need

energy, water, and the ability to

tolerate environmental

challenges

Plants have endosymbiotic

photosynthetic organelles that

let them produce chemical

energy from light

The two groups of plants,

bryophytes and tracheophytes,

differ in size, how they move

materials, and how they deal

with desiccation

Page 80: *photosynthetic, multicellular, terrestrial

© 2013 American Society of Plant Biologists

Plants are green, but they aren’t

aliens. (They were here first!)

Photo credits: Tom Donald