Archaeplastida Notes

Supergroup Archaeplastida

Monophyletic group.
Chloroplasts originated from primary endosymbiosis with a cyanobacterium.
Cells typically lack centrioles.
Cell walls are composed of cellulose.
Food is stored as starch (of various types).

Kingdom Rhodoplantae (Red Algae)

Phylum Rhodophyta
Phylum Glaucophyta

Phylum Rhodophyta: Red Algae

Ranges from unicellular to complex filamentous and parenchymatous thalloid plants.
Mainly found in warm marine habitats.
Contains phycobilin pigments.
Possesses Chlorophyll a (absence of b or c).
No flagellate stages.
Food stored as floridean starch (alpha 1,4 glucan), similar to cyanophycean starch of Cyanobacteria.

Class Florideophyceae

Order Ceramiales

Family Rhodomelaceae

Polysiphonia

Mostly branched, filamentous.
Attached by rhizoids or haptera.
Thallus consists of fine branched filaments.
Central axial filament.
Supporting pericentral cells = 4–24.

Reproduction in Rhodophyta

Typically diplohaplontic, with alternation of haploid and diploid stages; some are haplontic.
Oogamous – female gametophyte with carpogonium containing the egg with a receptive surface called trichogyne.
Male gametophyte produces spermatia, which are non-motile cells that function as male gametes.
Triphasic life cycle – with gametangial, carposporangial, and tetrasporangial phases.

Triphasic Life Cycle

Gametangial Phase

Gametophyte phase (n).
Male gametophyte produces spermatia that function as male gametes.
Female gametophyte produces the carpogonium, which contains the female gamete (ovum/egg).
After fertilization of gametes, the zygote migrates and fuses with a supporting cell in the carpogonium.
Zygote grows and develops into carposporophyte (2n).

Carposporophyte Phase

Diploid phase of the life-cycle.
Originates from the zygote.
Entirely parasitic on the parent female gametophyte.
Non-motile diploid carpospores are produced in the carposporangium by mitosis.
Carpospores are released from the carposporangium, settle, and grow to form a diploid tetrasporophyte.

Tetrasporophyte Phase

Develops tetrasporangium.
Produces tetraspores after meiosis.
Spores settle and grow to become the male and female gametophyte plants, completing the cycle.

Ecology of Red Algae

Mostly marine, a few freshwater.
Typically live attached to surfaces.
Light harvesting is very efficient, and red algae can live at tremendous depths.
Phycoerythrin accessory pigments allow absorption of blue and green lights, which penetrates relatively far into the water.
Coralline red algae build up calcium carbonate in their cell walls and can be reef-building organisms.

Economic Importance of Red Algae

Agar-agar is a jelly-like food delicacy in Japan.
Agar is used as a culture medium in microbiology because it cannot be digested by most microorganisms.
Agarose, purified from agar, is used in molecular biology for gel electrophoresis.

Ecological Importance of Red Algae

Corallines (calcified red algae) help build and maintain coral reefs, which harbor diverse organisms.
They form hard, flat sheets that consolidate and stabilize reef crests, protecting reefs from wave damage.
Regarded as keystone organisms – species whose decline could cause the collapse or loss of entire biotic communities.

Phylum Glaucophyta

Freshwater habitat.
Coccoid and occur in loose colonies formed by the persistent cell wall of the parent cell following division.
Have mitochondria with flat cristae.
The chloroplasts are known as 'cyanelles‘.
With a peptidoglycan layer (relic of the endosymbiotic origin of plastids from cyanobacteria).
Plastids contain chlorophyll a and phycobilins organized into phycobilisomes
Class Glaucocystophyceae; Order Glaucocystales; Family Glaucocystaceae.

Viridiplantae

CH = Chlorobiont Clade
ST = Streptobiont Clade
EM = Embryophytes
VP = Vascular Plants
SP = Seed Plants

Kingdom Viridiplantae

Comprises the green algae and land plants.
Common synapomorphies include:
- Cell walls containing cellulose.
- Chloroplasts containing chlorophylls a and b.
- Food stored in the form of starch.
- Typically have mitochondria with flat cristae.

Two Lineage Subgroups:

Chlorophyta (chlorobiont clade)
Streptophyta (Streptobiont clade)
- Charophyta
- Embryophyta

Differences Between Chlorobionts and Streptobionts

CHARACTER	CHLOROBIONTS	STREPTOBIONTS
MITOSIS	GENERALLY WITH CENTRIOLES (CENTRIC) AND CLOSED (THE NUCLEAR ENVELOPE REMAINS INTACT)	NO CENTRIOLES (ACENTRIC) AND OPEN (THE NUCLEAR ENVELOPE BREAKS DOWN)
CYTOKINESIS	PHYCOPLAST	PHRAGMOPLAST
FLAGELLAR INSERTION	AT THE APEX OF MOTILE CELLS	SUBAPICAL ON MOTILE CELLS

Phycoplast: (Chlorophyceans) set of microtubules arranged parallel to the plane of cell division.
Phragmoplasts: (Charophyceae) microtubules arranged perpendicular to the plane of division.
Closed mitosis: nuclear envelope remains intact (Ulvophyceans).
Open Mitosis: nuclear envelope breaks down early in mitosis (Charophyceans and in higher plants).

Phylum Chlorophyta

Includes most of the green algae.
May grow as colonies, unicells, filaments, and large seaweeds.
Occur in almost all types of water and often are dominants in freshwater environments.
Some are terrestrial species.

Ulva (Sea Lettuce)

Flat expanded sheet.
Asexual reproduction via biflagellated zoospores.
Sexual reproduction is isogamous.
Alternation of diploid and haploid isomorphic generations.

Chlamydomonas (Sea Cockroach)

Motile unicellular algae; oval in shape.
Cell wall of glycoprotein and non-cellulosic polysaccharides.
With prominent cup or bowl-shaped chloroplast.
Pyrenoid contains a starch sheath.
2 anterior flagella (whiplash; 9+2 arrangement).

Volvox

Composed of numerous flagellate cells similar to Chlamydomonas, up to 50,000 in total.
Haploid adult cells.
Cells are embedded in the surface of a hollow sphere or coenobium containing an extracellular matrix made of a gelatinous glycoprotein.

Asexual Reproduction

Occurs by repeated mitotic division of one of the cells (zooids) to form a hollow sphere of cells, with the flagellated ends of the cells inside.
The sphere then turns itself inside out to form a daughter colony similar to the parent colony.
Several daughter colonies are formed inside the parent colony before they escape by rupture of the parent.

Sexual Reproduction

Some of the zooids differentiate into macrogametes or microgametes.
Macrogametes are fewer and larger and are loaded with food for nourishment of the young organism.
Microgametes, by repeated division, form flagellated sperm that leave the mother organism and swim about to find a mature ovum.
After fertilization, the zygote secretes a hard, spiny, protective shell around itself. When released by the breaking up of a parent, a zygote remains dormant during the winter. Within its shell, the zygote undergoes repeated division, producing a small organism that breaks out in the spring.

Pandorina

Composed of 8, 16, or sometimes 32 cells, held together at their bases surrounded by mucilage.

Eudorina

Composed of 16 or 32 spherical biflagellate cells loosely aggregated into a globular shape within a mucilage envelope.

Family Hydrodictyaceae: Pediastrum

Members are organized as coenobium colonies and occur in quite or slow-moving waters.
Free-floating with 2 to 128 polygonal cells.
Cells are arranged in a stellate plate, one cell in thickness.
Each cell has a single parietal plate-like chloroplast.

Asexual and Sexual Reproduction in Pediastrum

Haplontic life cycle.
A parent colony produces a number of biflagellate zoospores kept within a vesicle.
Aggregation and arrangement of motile spherical spores transform into "butterfly-shaped cells".
The cells organize into a new complete daughter colony drifting and floating along the water current.
The cell forms two bi-flagellate gametes (isogamy).
The gametes fuse into a zygote and develop further through the asexual lifecycle as described above.

Oedogonium

Filamentous; cells uninucleate.
Sexual reproduction is oogamous; with flagellated zoospores
Oedogonium is an unbranched filament with only certain cells that can divide. Those that do divide have stacks of old cell walls (called apical caps) at the cell apex.

Phylum Charophyta

Group of green algae that had characters in common with the land plants.
Phragmoplast and cell plate formation during cell division.
Sexual reproduction.
Do not involve flagellated gametes except in the stoneworts (Charales) where flagellated sperm cells are found.

Chara (Muskgrass/Stoneworts)

Multicellular.
Superficially resemble land plants because of stem-like and leaf-like structures.
With nodes and internodes.
Typically anchored to the substrate by means of branching underground rhizoids.
Rough to the touch because of deposited calcium salts on the cell wall.

Reproduction in Chara

Asexual reproduction takes place by tubers and secondary protonema.
Sexual reproduction involves:
- Globule or antheridium (male) producing biflagellated antherozoids.
- Nucule or archegonium (female) with oogonium.

Life Cycle of Chara

Alternation of generations is present.
The thallus produces both oogonium and antheridium.
Meiosis occurs in the diploid zygote.

Class Zygnematophyceae

Filamentous or unicellular.
Reproduction involving conjugation between 2 cells.
No flagellated stages.
All freshwater.

Order Desmidiales (Cosmariales)

Variously shaped unicells; usually 2 chloroplasts with nucleus sited between them; often with a narrow isthmus.
Mobility by mucilage secretion.
"Desmids."

Order Zygnematales

Unbranched, filamentous.
Varied forms of chloroplasts.
Cell wall usually slimy.
Conjugation results in resistant zygospore.

Zygnema

Freshwater filamentous, free-floating, or anchored with a holdfast.
Composed of elongate barrel-shaped cells with two star-shaped chloroplasts arrayed one after the other along the axis of the cell.

Spirogyra

Unbranched with cells connected end to end in long green filaments.
With spiral-arranged chloroplasts.
Cell wall layers:
- Outer wall = pectin
- Inner wall = cellulose
Pyrenoids = centers for starch production.

Reproduction in Spirogyra

Asexual reproduction: fragmentation and mitosis to form new filaments.
Sexual Reproduction: Conjugation and formation of zygospore.
- Scalariform conjugation: occurs between two filaments.
- Lateral conjugation: occurs between two adjacent cells on the same filament.

Classification of the Supergroup Archaeplastida

Kingdom – Rhodoplantae (Red algae)
- Phylum Glaucophyta
- Phylum Rhodophyta
Viridiplantae (land plants and green algae)
- Subkingdom Chlorobionta (Chlorobiont clade)
- Subkingdom Streptobionta (Streptobiont clade)

Kingdom Viridiplantae: Subkingdom Chlorobionta

Phylum Chlorophyta
- CLASS Ulvophyceae
  - ORDER Ulvales
    - Family Ulvaceae
      - Parenchymatous; flat expanded sheet
      - Asexual reproduction by flagellated zoospores
      - Sexual life history isomorphic alternation of generation with biflagellate gametes.
      - Ulva
- CLASS Chlorophyceae
  - ORDER Chlamydomonadales
    - FAMILY Volvocaceae
      - Vegetative stages flagellated or coenobia
      - Gametes and zoospores normally biflagellate
      - Volvox, Chlamydomonas, Pandorina, Eudorina
  - ORDER Sphaeropleales
    - FAMILY Hydrodictiaceae
      - The coenobia are orderly arranged in a flat disk
      - Cells are dimorphic, consisting of interior cells and peripheral cells
      - Peripheral cells usually possess bristles, V-like cutting edges, or wavy projections.
      - Pediastrum
  - CLASS Chlorophyceae cont.
    - ORDER Oedogoniales
      - Filamentous
      - Cells have a complex method of cell division (cell cap formation)
      - Haploid with zygotic meiosis
      - Oogamous; flagellated zoospores and sperm bear a ring of numerous flagella.
      - Oedogonium

Kingdom Viridiplantae: Subkingdom Streptobionta (Basal Streptobiont Clade)

PHYLUM Charophyta
- CLASS Zygnematophyceae
  - Reproduction by conjugation
  - No flagellated stages
  - Haploid, with zygotic meiosis
  - All freshwater
  - ORDER Cosmariales (Desmidiales)
    - Micrasterias (FAMILY Desmidiaceae)
    - Closterium (FAMILY Closteriaceae)
  - ORDER Zygnematales
    - FAMILY Zygnemataceae
      - Zygnema, Spirogyra
- CLASS Charophyceae
  - Macroscopic
  - Rhizoids and stems with whorls of branches at nodes
  - Growth from apical cell
  - Cell walls heavily calcified
  - Sexual reproduction by flagellated antherozoids in antheridia (globule) and oogonia in complex oogonium (nucule)
  - No zoospores
  - Zygotes produce small protonema that develops into the upright gametophyte.
  - ORDER Charales
    - FAMILY Characeae
      - Chara