Thylakoids in stacks of 2-6 membranes
Flagella usually smooth and of equal length
Cell walls of cellulse (or glycoprotein)
A Single Class
9 Orders: Separated by vegetative cell form
Volvocales: vegetative cells actively motile, unicells and colonies, glycoprotein (sporopollenin?) walls
Tetrasporales: non-flagellated palmelloid colonies (pseudoflagella) in a gelatinous matrix
Chlorococcales: nonmotile vegetative cells solitary -colonial, asexual reproduction by spores
Ulotrichales: filamentous plants with uninucleate cells, branching or not.
Ulvales: growth as hollow filaments or sheets
Oedogoniales: branched or unbranched filaments, sperm & zoospores with numerous
flagella, prominent cell division scars remain
Cladophorales: filamentous plants with multinucleate cells
Caulerpales: a single coenocytic cell makes up filament (no cross walls)
Dasycladales: single cell with radial symmetry
The ancestral green alga probably similar to members of this order.
Chlamydomonas is representative.
Chlamydomonas: small biflagellate unicell with cup-shaped plastid, pyrenoid, eyespot. ~400 species
Chlamy Life Cycle
Asexual fission common. 1 cell forms 2.
Sex. Induced by stress (ie. low N) Heterothallic (+,-) or Homothallic species exist.
Gametes look like vegetative cells but with "sticky" flagella
Sex in Chlamy...!
Gametes initially clump together (chemical attractant?)
Individuals next pair off by flagellar contact (glycoproteins on tip)
Flagella join along their length
Cells brought together and fuse
Motile zygote(2N) results (4 flagella)
Germination and meiosis brings back 1N vegetative cells
Points of Note
Vegetative cells are haploid (1N), only zygote is diploid (2N)
Sex is in response to stress and results in a dormant zygote stage
Colony of hundreds of cells.
Some asexual "gonidia" present which undergo division to form new asexual colonies.
Colonies are male & female
Sex brought on by stress!!
Sex in Volvox
Heat shock (42*C) asexual colonies will induce sexuality
Male colonies release a 30Kd glycoprotein inducer.
Inducer works at 6x10-17 M. One converted male will affect all Volvox in 1000 L.
Males release sperm, females with eggs!!
Chlamy-like cells in a mucilaginous sheath
Cells non-motile with pseudoflagella (9+0)
Botryococcus braunii, free-floating colony found in oil deposits (?) and possible source of hydrocarbon fuel.
From single cells to colonies to coenocytes (single cell, many nuclei)
non-motile vegetative cells
Trebouxia. Common phycobiont (algal partner) with fungi to form a lichen.
Fungi secretes a protein that will bind only with Trebouxia.
Free-Living vs. Phycobiont
Free-living cells produce less sugar
Free-living cells form more polysccharides
Free-living cells develop a cell sheath
Free-living cells release less photosynthate into medium
Chlorella. Possible new food source.
Produces little cellulose, 50% protein, lots of vitamins Prototheca.
Colorless Chlorella lives in soil. Cause of human & animal disease. Often misdiagnosed as yeast infection.
Alga common to freshwater lakes. Unbranched filament with modified basal cell forming a holdfast
Lifecycle is H,h.
Asexual reproduction involves 1N vegetative cell producing quadriflagellate 1N zoospores
Sex in Ulothrix
Gametes formed as in zoospores but are biflagellate.
Isogamous gametes from separate plants fuse to form 2N zygote
Meiosis occurs after dormancy (overwinter) produces germling 1N plant
Sheet-like or hollow cylinder 1-2 cells thick
Marine intertidal plant. Sheet-like growth lost if plant grows without bacteria (or bacterial extracts).
Ulva life cycle is an alteration of generations.
Alternating between identical sporophyte & gametophyte stages
Unique cell division forming distinctive scar along cell.
Multinucleate filaments which develop from cell mitosis without cell division to form a "siphonous" thallus.
Alternation of Generations
Example: Cladophora. A branching marine form.
Siphonous forms- No cross walls.
Tropical species Derbesia with a life cycle comprising two completely different generations.
A filamentous sporophyte with a bulbous gametophyte.
1N plant termed Halicystis. Thought to be different alga.
Halicystis: Gametophyte of Derbesia
Gamete formation independent of temperature or light. Appears to be an endogenous rhythm.
tropical plants, calcified, radial symmetry
Acetabularia "Mermaids wineglass". Single-celled plant
Classic studies on nucleus-cytoplasmic interactions
Showed that nucleus produces certain morphogenic factors which influence development.
What are these factors?
Shows circadian rhythms in photosynthesis, chloroplast shape, polysaccharide content...