BIOLOGY 3404FEVOLUTION OF PLANTS

Fall 2008Lecture 7October 9

Chapter 15, Algae & Heterotrophic Protists,

Part I

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),

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).

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.

850 MYA acritarchs from Grand Canyon, Arizona. Others are as old as 1.8 BYA, the oldest fossil eukaryotes.

Marine phytoplankton, including dinoflagellates and filamentous (multicellular) and unicellular diatoms

4* Branches of Eukaryotic Life

* Or 3 - “Plantae” + “SAR” are monophyletic (Burki et al. 2008)

Dinophyta

Chrysophyta,Phaeophyta,Bacillariophyta

Chlorachniophyta,Paulinella (Cercozoa) Plantae

Chlorophyta

GlaucophytaRhodophyta

Euglenophyta

Purple = Chl aGreen = Chl a+bRed = Chl a+c

Most Photoautotrophs are Monophyletic

Euglena is Distantly Related

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)

Ceratium tripos

Noctiluca scintillans, a bioluminescent marine dinophyte

Gonyaulax, a Red Tide dinophyte

Fish killed by Pfiesteria piscicida, a dinoflagellate

Zooxanthellae endosymbiotic within tentacles of a coral animal

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 (?).

Euglena (note, photo on left misidentified in text as an electron micrograph, but is a light micrograph)

Trachelomonas, a euglenoid

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

Cryptomonas

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.

The Haptophyte Prymnesium: note haptonema between flagella

Two haptophytes: Emiliania and Phaeocystis

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).

Representative diatoms – they’re beautiful

SEM of ½ of a frustule from Entogonia

Pennate diatoms, with bilateral symmetry (Licomophora)

A centric diatom, with radial symmetry (Cyclotella)

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

Cyst of Dinobryon, a chrysophyte; an amoeboid cell emerges

The colonial chrysophyte Synura

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)

Kelp on a Vancouver beach

Bull kelp, Durvillea, on a New Zealand shore

Holdfasts of Laminaria

Rockweed, Fucus, with midrib on blade, and air-filled flotation bladders

Giant kelp forest, home to sea otters, abalones, etc.

Ectocarpus, which we saw in lab, has simple branched filaments

Life cycle of Laminaria and most brown algae involves sporic meiosis

Life cycle of Fucus is an example of gametic meiosis