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Phaeophyta (Brown algae)
  • Prominent macrophytic algae in freshwater and marine benthic systems with high diversity (1500 species)
  • Annual and perennial forms, some up to 15 years old
  • Cell walls contain three components: cellulose (structural support), alginic acid, sulfated polysaccharids
  • Alginates are located in intercellular matrix and provide flexibility of the thallus and prevent desiccation
  • Pigments: Chl. a, c, b-carotene, violaxanthin, fucoxanthin
  • Storage product: laminaran, mannitol, glycerol
  • Anti-freeze effect of mannitol and glycerol important for kelps in temperate and polar regions
  • Cell division involves centrioles, which determine the plane of division; nucelar envelope remains intact until late division stage, when envelope disintegrates completely
  • Plasmodesmata: plasma connections between adjacent cells, formed during cell division; cell-to-cell transport of photosynthetic producs and cell communication
Growth of Brown Algae: Meristems
  • Thalli of brown algae may be filaments or complex tissues analogous to land plants
  • Aggregated filaments produce thalli termed pseudoparenchymatous; true tissue thalli are called parenchymatous
  • Parenchymatous thalli form by cell division in variuous planes; origin polyphyletic
  • Diffuse growth: cell division throughout the thallus
  • Meristem: localized regions of cell division
    • Single apical cell: growth of a filament of one cell‘s width
    • Apical meristem: several cells that divide in different directions, form mutlilayered thalli
    • Intercalary meristem: found in large kelps between stipe and blade to increase length of thallus
    • Surface meristem: thickens the thallus (blade)
  • Three types of reproductive cells: meiospores, asexual zoospores, gametes with typical ochrophyte structure and eye-spot
  • Flagella origin at the side of the cells rather apically
  • Gametes can be isogamous, anisogamous, oogamous
  • Isogamous gametes: one type of gametes settles very soon onto substrate, the other type (male) remains swimming longer
  • Pheromons are produced by female gametes to attrackt male gametes
  • Gametophytes produce gametes in plurilocular gametangia
  • Plurilocula gametangia („sporangia“) sometimes also produce asexual zoospores, which into thalli similar to parent thalli
  • Unfused gametes sometimes can also develop into a thallus (parthenogenesis); result in female and male thalli at a rate of 19:1
  • Unilocular sporangia only occur on sporophytes

  • unilocular (left); plurilocular (right)
  • Life Cycle of Ectocarpus: Sporophyte and gemetophyte appear morphologically similar; only the sporophyte carries both pluri- and unilocular sporangia, the gametophyte carries only plurilocular gametangia

  • Life Cycle of Laminaria: sporophye is prominent sea kelp, but gametophyte is microscopically small; unilocular sporangia occur on the surface of the sporophyte's blade

  • Sporophyte; unilocular sporangia on sporophyte; gametophyte
  • Life Cycle of Fucus: A gametophyte is  lacking; the sporophyte produces gametangia in conceptacles on its blades, which release eggs and sperms; the zygote develops into a new sporophyte. No asexual reproduction in Fucus.

    Development of Fucus zygotes
The Giant Kelp Macrocystis
  • Kelp forrests on the Pacific coast (California)
  • Pneumatocysts provide bouyancy; up to 10% carbon monoxide
  • Meristoderm: pigmented, photosynthetic cells
  • Cortex: colorless cells
  • Sieve elements: elongated cells with perforated end walls, forming transportation ducts through the thallus at rates of 50 cm per day

Sieve cell