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ChlorophytaI. Characteristics of Eukaryotic AlgaeII. CharacteristicsIII. Classes• Prasinophyceae• Chlorophyceae

Evolutionary LinesFlagellated SpeciesNon-flagellated SpeciesColoniesFilaments

• Ulvophyceae• Charophyceae

Division Chlorophyta

General Characteristics:• chlorophylls a&b• storage product is starch• cellulose cell walls; (organic scales)• 2 (4)smooth flagella (whiplash)• 2 chloroplast membranes• marine, freshwater, aerial, symbiotic• unicell to parenchymatous

Four Classes

1.

Prasinophyceae

Chlorophyceae2.

Ulvophyceae3.

4.

Charophyceae

• least advanced (ancestral ?)• unicellular• organic scales for cell coverings• Scales on smooth flagella (1 - 4)• haplontic life history (zygotic meiosis)• marine and freshwater• e.g Micromonas

Class Prasinophyceae

Pyramimonas• organic scales• 4 flagella• fibrous root

Micromonas• < 2µM• 1 flagellum• naked cell

Four Classes

1.

Prasinophyceae

Chlorophyceae2.

Ulvophyceae3.

4.

Charophyceae

2

• large group• single cells to colonies to

filaments• cellulose cell wall• freshwater and terrestrial

(mostly)• haplontic (zygotic meiosis)• zygote is overwintering (harsh

times) structure

Class Chlorophyceae

Three evolutionary lines (from flagellated ancestor)

Class Chlorophyceae cont.

Flagellated ancestor

Flagellated colonies

Non-flagellated cellsand colonies

Filamentous species

Flagellated Chlorophytes

Volvocine series:• increasing colony complexity• increasing reproductive complexity• evolutionary model for multicellularity?

single cell Chlamydomonas

4 - 32flat

Gonium

4 - 32Sphere

PandorinaIsogamousno polarity

Anisogamouspolarity

16 - 64Eudorina

50- 50,000Volvox

Palmelloid Chlorophytes (Tetrasporales)• vegetative cells loose flagella• retain flagellar apparatus

e.g. basal bodies and microtubule roots

Tetraspora

Flagellated Chlorophytes cont. Class Chlorophyceae

Flagellated ancestor

Flagellated colonies

Non-flagellated cellsand colonies

Filamentous species

Pediastrum

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2. Non-flagellated Chlorophytes(Chlorococcales)

•mostly freshwater group• unicells to colonies• no flagella (or remnants of flagellar

apparatus)• however, zoospores are produced

for asexual reproduction

colony form is Pediastrum(Coenobium - reproductive colony inside mother colony - cell number fixed)

Non-flagellated Chlorophytes cont.

coenocytes - colonies formed by mitosis without cell division i.e. multinucleated.eg. Hydrodictyon

Non-flagellated Chlorophytes cont.

Colony form cont.

Flagellated ancestor

Flagellated colonies

Non-flagellated cellsand colonies

Filamentous species

Oedogonium

Class Chlorophyceae

• filamentous algae occur in several Orders :

Microsporales - simple, ancestralChaetophorales - heterotrichousOedogonales - specialized branches

• Growth is by cell division and enlargement

Filamemtous Chlorophytes

Class Chlorophyceae cont.

Unbranched Filaments (simplest)

Order Microsporales

• uninucleate cells• single chloroplasts• no intercellular connections• less advanced cell wall (H-pieces)• growth by interpolation

Filamemtous Chlorophytes cont.

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Growthvia turgorpressure

Filament growth by interpolatione.g. Microspora (Microsporales)

some are heterotrichouse.g. Fritscheilla

Filamemtous Chlorophytes cont.

Branched filaments

Order Chaetophorales

Filament differentiationtwo branching systems

Compactprostrate

filamentouserect

1

2

heterotrichy filamentouserect

Compactprostrate

e.g. Chaetophora

Specialized Branches(Order Oedogoniales)

• specialized cell division (forms distinctive “cap”)• stephanokontous zoospores

(flagellar crown)

Filamemtous Chlorophytes cont.

• oogamous (advanced)

• sexual reproduction

Filamemtous ChlorophytesOedogoniales cont.

antheridiaegg

oogonia

me

zygote(2n)

macandrous

nannandrous

dwarfmale

androspore

macandrous nannandrous

d.m.

an.

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Four Classes

1.

Prasinophyceae

Chlorophyceae2.

Ulvophyceae3.

4.

Charophyceae

Class Ulvophyceae•most are macrophytes (can be

seen with naked eye)•most are marine (a few are

freshwater)•morphology is variable:

parenchymatous, filamentous, siphonous, unicellular (coenocytic)

Chlorophyta cont..

Ulva fasciata

Codium reedii

Siphonous (coenocytic)• Codium•mass of thread-like tubes

(siphons)•multinucleate - mitosis and cell

division occurs but no crosswallare formed• forms spongy thallus

(Psedoparenchmyatous)

Siphons

• movement required to maintain pseudoparenchymatous thallus

• in still culture filaments form• shake the culture the more complex thallus forms

Siphons cont.• siphons form loose inner

medulla and outer cortex• cortex is primarily swollen

Utricle • utricle are site of

photosynthesis•medulla often without

chloroplasts

Siphons cont.

medulla cortex

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Ulva fasciata

Codium reedii

Parenchymatousforms

Ulva sp. & Enteromorpha sp.

• cellulose cell wall• marine diplohaplonic• isomorphic Ulva

n

2nme

zygote

gametophyte

sporophyte

• isomorphic

• isogamous

gametes

zoospores

Ulva life history: isomorphic

zoosporeformation

Four Classes

1.

Prasinophyceae

Chlorophyceae2.

Ulvophyceae3.

4.

Charophyceae

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Class Charophyceae• cellulose cell walls• freshwater• haplontic life history•most closely related to

Bryophytes and vascular plants?

Chlorophytes cont..

• molecular evidence• similar introns• tufA gene in nucleus (not chloroplast)

• biochemical• lignin in cell walls

• developmental• retaining egg + zygote on gametophyte• cells covering zygote• more than 4 spores from zygote• similar flagellated sperm (Bryophytes)

Charophyceae cont.

Class Charophyceae

4 Orders

1. Klebsormidiales (unbranched)2. Coleochaetales (heterotrichous)3. Zygnemetales• Spirogyra, Zygnema, Mougeotia• Desmids

4. Charales• Chara• Nitella

ZygnemaSpirogyraDesmids

filamentous, unicellularno flagellar stages

Spirogyra spiral chloroplastZygnema - stellate chloroplastMougeotia - plate chloroplasts

Charophyceae cont.Order Zygnemateles

Plate-likeMougeotia

SpiralSpirogyra

StellateZygnema

Sexual reproduction -conjugation

Reproduction

• no zoospores• fragmentation

Spirogyraholdfast

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Scalariform conjugation• filaments line up• mucilage is excreted• protoplast balls and becomes

amoeboid gamete• papillae form towards each

other• meet, cell wall degrades and

conjugation tube forms• gametes fuse into dormant

Zygote• Zygote germinates - one cell

becomes new filament

zygo

te2n

me

Scalariform Lateral

Desmids

Two groups1. Saccoderm Desmids• simple• unicellular• resemble filamentous forms

2. Placoderm Desmids• eloborate cells• usually two halve (semi-cells)• contain two chloroplasts

Placoderm DesmidSaccoderm Desmid

Netrium Closterium

Desmid reproduction

asexual

Charophyceae cont.Order Charales• large• oogamous• corticated• CaCO3 encrusted• enclosed egg• no zoospores