Division: – Very important from an evolutionary point of view Some formed complex multicellular bodies Moved onto land – later to become “true” plants • Body Construction in the Green Algae – simplest is a motile unicellular organism – from this simple plan several paths were taken

– Motile colonies

• Cells adhere to one another • All cells are similar

17 Division: Chlorophyta – Green Algae – Nonmotile Colonies

• Cells either never develop flagella or flagella is lost • Flagella considered the ancestral trait

– Filamentous Body

• Cells held together via middle lamella • division transverse; if longitudinal results in filament branching • Parts can be specialized

» Holdfast » Gamete production

18 Division: Chlorophyta – Green Algae • Membranous Body – Cell division occurs in only two planes • Forms a thin sheet of cells • Easily torn by wave action

• Parenchymatous Body

– Cell division occurs in three planes

• Cells connected by plasmodesmata • True parenchyma tissue is formed

19 Division: Chlorophyta – Green Algae • Coenocytic or Siphonous Body – Karyokinesis without cytokinesis; results in a giant multinucleate cell

20 Life Cycles of the Green Algae • Asexual Reproduction – ex. Euglenoids – Cell cycle – mitosis and cytokinesis • – Requires meiosis – Requires syngamy – Simplest form • Dipoloid cell undergoes meiosis – Haploid individuals produced that can reproduce via mitosis – Some cells act as gametes and fuse » Produces a diploid cell that can reproduce via mitosis

• Very little difference between diploid and haploid individuals • Referred to as being DIBIONTIC (alternation of generations between haploid and diploid) 21 Life Cycles of the Green Algae

– Monobiontic Species - Only one free-living generation

• Example #1

– Haploid phase only represented by the individual

» Can be either uni or multicellular » Carries out photosynthesis and growth

– Only diploid cell is the zygote

22 Life Cycles of the Green Algae

• Example #2

– Diploid phase represents the individual - undergoes vegetative growth

– Haploid cells are gametes which undergo syngamy

23 Life Cycles of the Green Algae • Isomorphic vs Heteromorphic Generations

24 Life Cycles of the Green Algae

• Gamete Development

– Early on gametes were identical, isogamous

– Later anisogamy developed (slight difference)

– Ultimately oogamy evolved

25 Representative Genera of the Green Algae • Unicellular Species – ex. Chlamydomonas

– Chlorophylls a and b, carotenoids, xanthophylls – Starch produced in – Two anterior flagella (common to most motile green algae) – Reproduces via mitosis, meiosis + syngamy

• Haploid resorbs flagella • Divides mitotically producing either 2, 4, 8, or 16 cells • Each new cell grows a two flagella • These cells swim and eventually meet another cell

– Plasmogamy and karyogamy produce a single large zygote (only diploid cell) – Becomes dormant – Germinates via meiosis, producing four haploid individuals

26 Representative Genera of the Green Algae • Motile Colonial Species – cell closely resemble Chlamydomonas – after zygote divides individuals are held together by a gelatinous mass

27 Representative Genera of the Green Algae – Based upon advances

• Gonium

– Colonies small (4 – 32 cells) – Simple organization, flagella beat in synchrony

28 Representative Genera of the Green Algae

•

– Similar in size to Gonium – Some differentiation, anterior cells slightly different than posterior cells, causes colony to swim in one direction

29 Representative Genera of the Green Algae

•

– up to 50,000 cells (can see colony without a microscope) – Group of anterior cells, about 50, modified for reproduction

30 Representative Genera of the Green Algae

• Filamentous Species – Ulothrix • Monobiontic • A single row of cells, with terminal cell modified to a holdfast • Zoospores can be produced mitotically – Possess four flagella – Settle to bottom – Germinate into new filaments • Some cells produce gametes – isogamous – Two flagella, resemble Chlamydomonas – Fuse producing a zygote which germinates via meiosis producing haploid zoospores – Settle to the bottom and germinate into a filament

31 Representative Genera of the Green Algae – Syrogyra

• Very common if freshwater environments • spirally arranged • No swimming gametes; rather a conjugation tube • Each filament is haploid (+ or -) • Zygote becomes dormant and thick walled • Germinates into a new filament from haploid spores

32 Representative Genera of the Green Algae

• Laminar Species – Ulva

• Similar to Ulothrix • Cell germinate in two planes • Dibiontic life cycle (alternation of isomorphic generations) • Separate individuals producing different gametes, dioecy

33 Representative Genera of the Green Algae

• Coenocytic Species

– Dibiontic life cycle – Heteromorphic generations (initially caused real problems)

34 Representative Genera of the Green Algae • Parcnchmatous Species – some types divide via a phragmoplast (plants do this) possibly ancestral

– Chara – has multicellular gametangia (plant or not)

35 Division Phaeophyta: Brown Algae • Major Characteristics – Mostly marine, in littoral zone (between high and low tides) – Very complex anatomically and morphologically – Similar to plants but very different

• Possess chlorophylls a and c, fucoxanthin, violaxanthin, diatoxanthin and carotenes (implications?) • Storage product is laminarin (glucose polymer), mannitol and fat (no starch) • Have a holdfast, stipe (stalk) and a blade

36 Division Phaeophyta: Brown Algae

• Cell walls contain cellulose and alginic acid (used in paint an food industry) • Can be very large, and have developed specialized regions

– Holdfast, anchoring – Epidermis to prevent damage from waves – With an epidermis diffusion is impaired, need a conducting system

» Have trumpet cells that resemble phloem (convergence)

37 Division Phaeophyta Brown Algae – Ectocarpus

• Isomorphic generations • Diploid sporophytes possess unilocular sporangia at the ends of small terminal branches – First nuclear division is via meiosis (haploid) – Zoospores germinate into gametophyte

» Ends of branches are gametangia » Plurilocular gametangia » Gametes anisogamous » Settle to the bottom secrete ectocarpene, attracts opposite, syngamy ensues

38 Division Phaeophyta Brown Algae

– Fucus

• Common on rocks of intertidal zone • Diploid individuals seen at low tide • Dichotomously branched blades • Ends of branches posses receptacles that contain concepticles

39 40 Division Rhodophyta: Red Algae • Major Characteristics – Large group – 3,900 sp. – Very different from other algae and true plants • Like cyanobacteria have phycobilin (accessory pigment) • Typically red (phycoerythrin) can be purple, brown or black (phycocyanin), chlorophyll a and carotenoids • Storage product floridean starch, similar to glycogen • Different sugars formed • Cell wall contains cellulose and sulfated galactans (slimy mucilages) – used to produce agar • No plasmodesmata • Mostly multicellular • Life cycles poorly known – Unique, lack any motile cells – Lack centrioles but have polar rings for this function – Polysiphonia – three phases to its life history

» Haploid gametophyte » Diploid carposporophyte » Diploid tetrasporophyte

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