The Greening of Earth

• Looking at a lush landscape it is difficult to imagine the land without plants

For first 3 billion years of Earth’s history

-terrestrial surface was lifeless

• Land plants evolved f/ green algae

• The potato’s response to light• Is an example of cell-signal processing

Figure 39.3

CELLWALL

CYTOPLASM

  1 Reception 2 Transduction 3 Response

Receptor

Relay molecules

Activationof cellularresponses

Hormone orenvironmentalstimulus

Plasma membrane

Figure 39.4

1 Reception   2 Transduction 3 Response

CYTOPLASM

Plasmamembrane

Phytochromeactivatedby light

Cellwall

Light

cGMP

Second messengerproduced

Specificproteinkinase 1activated

Transcriptionfactor 1 NUCLEUS

P

P

Transcription

Translation

De-etiolation(greening)responseproteins

Ca2+

Ca2+ channelopened

Specificproteinkinase 2activated

Transcriptionfactor 2

• Signal transduction in plants

1 The light signal isdetected by thephytochrome receptor,which then activatesat least two signaltransduction pathways.

2 One pathway uses cGMP as asecond messenger that activatesa specific protein kinase.The otherpathway involves an increase incytoplasmic Ca2+ that activatesanother specific protein kinase.

3 Both pathwayslead to expressionof genes for proteinsthat function in thede-etiolation(greening) response.

Adaptations for life on land

*

Alternation of generations*

Haploid multicellularorganism (gametophyte)

Mitosis Mitosis

Gametes

Zygote

Diploid multicellularorganism (sporophyte)

MEIOSIS FERTILIZATION

2n

2n

n

n

nn

nSpores

Mitosis

ALTERNATION OF GENERATIONS

Cuticle* (a waxy covering of the leaves) evolved in many plant species

Fossil evidence indicates that plants were on land at least 475 million years ago

• Land plants grouped• Based on the presence or absence of vascular tissue*

• Life cycles of bryophytes (e.g. moss) dominated by the gametophyte stage

Bryophyte Sporophytes• Dependant on gametophytes

Ferns and other seedless vascular plants* formed the first forests, evolved during Carboniferous period

Figure 29.15

• The growth of these early forests• May have helped produce the major global cooling that

characterized the end of the Carboniferous period• Decayed and eventually became coal

life cycle of a fern – alternation of generations

Fern sperm use flagellato swim from the antheridia to eggs in the archegonia.

4

Sporangia release spores.Most fern species produce a singletype of spore that gives rise to abisexual gametophyte.

1 The fern sporedevelops into a small,photosynthetic gametophyte.

2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanismspromote cross-fertilizationbetween gametophytes.

3

On the undersideof the sporophyte‘sreproductive leavesare spots called sori.Each sorus is acluster of sporangia.

6

A zygote develops into a newsporophyte, and the young plantgrows out from an archegoniumof its parent, the gametophyte.

5

MEIOSIS

Sporangium

Sporangium

Maturesporophyte

Newsporophyte Zygote

FERTILIZATION

ArchegoniumEgg

Haploid (n)Diploid (2n)

Spore Younggametophyte

Fiddlehead

Antheridium

Sperm

Gametophyte

Key

Sorus

Figure 29.12

Transport*

• Vascular plants have two types of vascular tissue*• Xylem* and phloem*

• Xylem*• Conducts water and minerals

• Phloem*• Distributes sugars, amino acids, and other organic products• Living cells

• Ascent of xylem sap - TranspirationXylemsapOutside 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

Wat

er p

oten

tial g

radi

ent

Root xylem Y = – 0.6 MPa

Soil Y = – 0.3 MPa

MesophyllcellsStomaWatermolecule

Atmosphere

Transpiration

Xylemcells Adhesion Cell

wall

Cohesion,byhydrogenbonding

Watermolecule

Roothair

Soilparticle

Water

Cohesion and adhesionin the xylem

Water uptakefrom soil Figure 36.13

Vessel

(xylem)

H2OH2O

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

Figure 36.18

Pressure Flow - Translocation• Sap moves through a sieve tube by bulk flow driven by

positive pressure

Evolution of Leaves• Increase the surface area of vascular plants, thereby

capturing more solar energy for photosynthesis

Keyto labels

DermalGroundVascular

Guardcells

Stomatal pore

Epidermalcell

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

(b)Cuticle

Sclerenchymafibers

Stoma

Upperepidermis

Palisademesophyll

Spongymesophyll

Lowerepidermis

Cuticle

VeinGuard 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 anatomy

• Absorption spectra of 3 types of pigments

Three different experiments helped reveal which wavelengths of light are photosynthetically important. The results are shown below.

EXPERIMENT

RESULTS

Abs

orpt

ion

of li

ght b

ych

loro

plas

t pig

men

ts

Chlorophyll a

(a) Absorption spectra. The three curves show the wavelengths of light best absorbed by three types of chloroplast pigments.

Wavelength of light (nm)

Chlorophyll b

Carotenoids

Figure 10.9

E Transformations Thermodynamics• E flows into ecosystem as sunlight, leaves as heat

Light energy

ECOSYSTEM

CO2 + H2O

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

Organicmolecules + O2

ATP

powers most cellular work

HeatenergyFigure 9.2

• Review

Light reactions:• Are carried out by molecules in the thylakoid membranes• Convert light energy to the chemical energy of ATP and NADPH• Split H2O and release O2 to the atmosphere

Calvin cycle reactions:• Take place in the stroma• Use ATP and NADPH to convert CO2 to the sugar G3P• Return ADP, inorganic phosphate, and NADP+ to the light reactions

O2

CO2H2O

Light

Light reaction Calvin cycle

NADP+

ADP

ATP

NADPH

+ P 1

RuBP 3-Phosphoglycerate

Amino acidsFatty acids

Starch(storage)

Sucrose (export)

G3P

Photosystem IIElectron transport chain

Photosystem I

Chloroplast

Figure 10.21

Seeds* changed the course of plant evolution• Enabling their bearers to become the dominant* producers

in most terrestrial ecosystems

Figure 30.1

Pollen*, (dispersed by air or animals *)• Eliminated the water requirement for fertilization

The Evolutionary Advantage of Seeds*** • A seed ***

• Develops from the whole ovule• Embryo, + food supply, packaged in a protective coat*

Figure 30.3c

Gymnosperm seed. Fertilization initiatesthe transformation of the ovule into a seed,which consists of a sporophyte embryo, a food supply, and a protective seed coat derived from the integument.

(c)

Seed coat(derived fromIntegument)

Food supply(femalegametophytetissue) (n)

Embryo (2n)(new sporophyte)

Angiosperm Evolution• Originated at least 140 mya during the late Mesozoic

Fungi

Symbionts• Symbiotic relationships w/

• Plants, algae, and animals

Lichens• Symbiotic association of millions of photosynthetic

microorganisms held in a mass of fungal hyphae

(a) A fruticose (shrub-like) lichen

(b) A foliose (leaf-like) lichen (c) Crustose (crust-like) lichensFigure 31.23a–c

• Fungi plus algae or cyanobacteria

Ascocarp of fungus

Fungalhyphae

Algallayer

Soredia

Algal cell

Fungal hyphae

10

m

Figure 31.24

Mycorrhizae• Enormously important in natural ecosystems and

agriculture

RESULTS

Researchers grew soybean plants in soil treated with fungicide (poison that kills fungi) to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants’ roots.

EXPERIMENT

The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to a phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae.

CONCLUSION These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant’s ability to take up phosphate and other needed minerals.Figure 31.21

RESULTS