biology 3404f evolution of plants fall 2008 lecture 7 october 9 chapter 15, algae &...
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BIOLOGY 3404FEVOLUTION OF PLANTS
Fall 2008Lecture 7October 9
Chapter 15, Algae & Heterotrophic Protists,
Part I
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Algae are not monophyletic!
• What they share is a lack of the following characters that distinguish plants (= embryophytes):
1) presence of protective layer of cells surrounding the male and female gametangia,
2) retention of zygote and developing sporophyte within female gametophyte (= archegonium),
3) presence of a multicellular diploid sporophyte (multiple meioses per mating event),
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Shared missing features, II
4) multicellular sporangia (capsules) with protective layer of sterile cells,
5) drying-resistant spores with walls containing sporopollenin (a cyclic alcohol), which is also highly decay resistant [sporopollenin is also found in walls of zygotes in Charophyceae of Chlorophyta].
• These are all adaptive characters for life on dry land (and the vascular plants have a few more distinguishing them from bryophytes).
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Generalities about “Algae”
• Some are planktonic – usually unicellular forms that move with water currents, and some are multicellular and often anchored in some way.
• Big ones (red, brown and green) are called seaweeds.
• Most of what we need to know about these groups is summarized in Table 15-1.
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850 MYA acritarchs from Grand Canyon, Arizona. Others are as old as 1.8 BYA, the oldest fossil eukaryotes.
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Marine phytoplankton, including dinoflagellates and filamentous (multicellular) and unicellular diatoms
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4* Branches of Eukaryotic Life
* Or 3 - “Plantae” + “SAR” are monophyletic (Burki et al. 2008)
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Dinophyta
Chrysophyta,Phaeophyta,Bacillariophyta
Chlorachniophyta,Paulinella (Cercozoa) Plantae
Chlorophyta
GlaucophytaRhodophyta
Euglenophyta
Purple = Chl aGreen = Chl a+bRed = Chl a+c
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Most Photoautotrophs are Monophyletic
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Euglena is Distantly Related
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Dinophyta (dinoflagellates):
• Unique unicellular organisms with 2 flagella that beat within grooves
• Cellulose plates forming the theca (armour) are inside cell membrane
• Many are heterotrophs, at least in part of their (often complex) life cycles; many produce toxic blooms; others are the endosymbionts of corals (= zooxanthellae) that make coral reefs the most productive ecosystem on Earth
• Life cycles may be quite complex (not discussed in detail)
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Ceratium tripos
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Noctiluca scintillans, a bioluminescent marine dinophyte
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Gonyaulax, a Red Tide dinophyte
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Fish killed by Pfiesteria piscicida, a dinoflagellate
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Zooxanthellae endosymbiotic within tentacles of a coral animal
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Euglenophyta:
• wall-less (with protein strips beneath plasma membrane)
• photosynthetic or (more often) not: may be photoautotrophs, photoheterotrophs, or heterotrophs, and may switch during life of a single cell
• chloroplasts derived from endosymbiotic green algae?
• hypothesized to be primitively asexual (?).
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Euglena (note, photo on left misidentified in text as an electron micrograph, but is a light micrograph)
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Trachelomonas, a euglenoid
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Cryptophyta:• In this group, chloroplasts have four membranes (you’ve always learned that chloroplasts, like nuclei and mitochondria, have two membranes), suggesting endosymbiosis of a photosynthetic eukaryote (as opposed to endosymbiosis of a cyanobacterium, for instance) = secondary endosymbiosis, most likely of a red alga
• Important phytoplankton in both freshwater and marine habitats
• Asexual and ??• As with euglenoids, often photoheterotrophs, with phagocytosis and photosynthesis
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Cryptomonas
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Haptophyta:• Tiny both in size and numbers of species• Perhaps most important in combating global warming – they form natural carbon sinks by carrying organic carbon and calcium carbonate to the deep ocean sediments; others form atmospheric sulfur compounds (dimethylsulfide = DMS and methane sulfonic acids) that increase cloud cover and may act to cool the atmosphere and combat global warming to some degree
• Others form toxic blooms• Some have a heteromorphic alternation of generations, in which a diploid flagellate stage alternates with a haploid filament stage (i.e., sporic meiosis); life cycle of others is unclear.
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The Haptophyte Prymnesium: note haptonema between flagella
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Two haptophytes: Emiliania and Phaeocystis
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Bacillariophyta (diatoms):
• Cell walls, made of silica, are in two overlapping parts, called frustules
• Most are phototrophs, at least in part of their life cycle, and estimated to contribute 25% of all primary production on Earth; a few are heterotrophs, or phototrophic endosymbionts (without frustules); some cause shellfish poisoning
• Most reproduction is mitotic; sexual reproduction via gametic meiosis (like us).
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Representative diatoms – they’re beautiful
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SEM of ½ of a frustule from Entogonia
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Pennate diatoms, with bilateral symmetry (Licomophora)
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A centric diatom, with radial symmetry (Cyclotella)
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Chrysophyta (golden algae):
• Important as phytoplankton in freshwater and marine habitats (also, some are multicellular)
• Both hetero and photoautotrophs; some cause harmful blooms (e.g., one of Dr. Trick’s pet organisms, Heterosigma)
• Asexual, or with zygotic meiosis (cysts)• Golden colour from fucoxanthin
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Cyst of Dinobryon, a chrysophyte; an amoeboid cell emerges
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The colonial chrysophyte Synura
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Phaeophyta (brown algae):
• The biggest seaweeds – kelps and rockweeds – are in this group (some others are unicellular or multicellular but microscopic)
• Abundant and important in tidal regions, habitat for many animals and even some epiphytes
• Source of alginates, used in foods and many industries, including the coatings on paper (to prevent bleeding of ink)
• Life cycles may have sporic meiosis (Laminaria) or gametic meisosis (Fucus)
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Kelp on a Vancouver beach
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Bull kelp, Durvillea, on a New Zealand shore
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Holdfasts of Laminaria
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Rockweed, Fucus, with midrib on blade, and air-filled flotation bladders
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Giant kelp forest, home to sea otters, abalones, etc.
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Ectocarpus, which we saw in lab, has simple branched filaments
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Life cycle of Laminaria and most brown algae involves sporic meiosis
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Life cycle of Fucus is an example of gametic meiosis