Basic characteristics

Дата канвертавання26.04.2016
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Large group of primarily marine macrophytes (over 5000 species), important economically as sources of gums and agar and of food, and ecologically in the intertidal, shallow and deep benthos; many are obligate epiphytes with specific hosts or obligate parasites

  1. Basic characteristics

    1. plastids

      1. primary plastids with only two envelope membranes, probable source of plastids incorporated into ochrophytes, haptophytes, and cryptophytes

      2. pigments include chlorophylls a and d and phycobilins arranged into phycobilisomes indicating that they are derived from cyanobacteria; xanthophylls and carotenoids are found as accessory pigments

      3. storage product is floridean starch, found in the cytoplasm

    1. flagella and centrioles are completely absent in all red algae

    1. walls formed from cellulosic microfibrils in a mucilaginous matrix of sulfated polygalactans (agars and carrageenans), glucose-, xylose-, and glucourinic-acid-based mucilages; many of the matrix polysaccharides are of commercial and taxonomic value

      1. in coralline algae the wall is impregnated with calcite (crystalline calcium carbonate)

      2. many species are covered with a proteinaceous cuticle

    1. mitosis -- centrioles appear to be replaced by a nuclear associated organelle (sometimes called a polar ring), which may be associated with or contain a microtubule organizing center and is associated with a spindle

    1. pit-plugs

      1. primary pit-plugs -- cytokinesis is incomplete in most red algae, leaving a membrane-lined pore in the center of the new wall; this is filled with a homogenous proteinaceous matrix called a primary pit-plug

        1. in some genera, the plug develops a cap of some sort (that may be continuous with the cell membrane); the structure of which may have phylogenetic significance

        2. cells joined by a primary pit-plug are said to linked by a primary pit connection; because the plugs may end up as extracellular structures, they are not equivalent to plasmodesmata

      2. secondary pit plugs can develop when two cells come into contact; the smaller cell undergoes mitosis, forms a primary pit plug between the two daughter cells, then one of the daughters fuses with the other cell

    1. reproduction and life-histories

      1. asexual reproduction via monospores produced singly in monosporangia by mitosis

      2. sexual reproduction typically involves three stages

        1. gametophytes

          1. non-flagellate spermatia are produced singly or in groups in spermatangia

          2. carpogonia (oogonia, female gametes) are produced at the tips of carpogonial branches; these typically are flask-shaped with a narrow extension called a trichogyne

        2. fertilization occurs when a spermatium adheres to the trichogyne and the spermatial nucleus enters the carpogonium

        3. after fertilization

          1. in Bangiophycean reds, the zygote undergoes mitosis to form carpospores; these are released and develop into diploid plant; the diploid produces spores (conchospores) by mitosis that germinate and then undergo meiosis to produce a patchwork haploid gametophyte

          2. in Floridophycean reds, the zygote develops into a multicellular, diploid carposporophyte, which remains attached to the female gametophyte; the carposporophyte produces carpospores by mitosis; carpospores develop into tetrasporophytes, which produce tetraspores by either mitosis or meiosis--mitotic tetraspores undergo meiosis upon germination--that develop into haploid gametophytes

            1. complications exist with respect to the development of the carposporophyte

              1. in some cases copies of the diploid zygote nucleus are passed to cells outside of the carpogonial branch (auxiliary cells) where they divide separately from the cell's nucleus; each of these transformed cells may develop into a separate carposporophyte or gonimoblast (any filament that produces carpospores)

              2. in advanced cases, the gametophyte/carposporophyte forms a cystocarp: pericarp of photosynthetic gametophyte tissue; interior colorless gametophyte filaments acting as nutritional cells; and a carposporophyte whose cell have secondary pit connections with gametophytic cells

  1. Diversity

    1. Bangiophyceae

      1. unicellular, filamentous, and membranous forms, usually with a single plastid, and simple life-cycles

      2. examples

        1. Cyanidium -- spherical unicells from hot springs; reproduces by means of autospores

        2. Porphyridium -- unicellular form common in soils; with a stellate plastid

        3. Porphyra -- intertidal organism with membranous frond

    1. Floridophyceae

      1. diverse group with multiple orders; characterized by a triphasic life-cycle with carposporophytes

      2. selected orders

        1. Corallinales -- calcite-impregnated walls and reproductive structures in conceptacles

          1. genicullate corallines -- with jointed, erect thallus

            1. Corallina

          2. non-geniculate or crustose corallines -- without unimpregnated joints

            1. Lithothamnion

        2. Palmeriales -- carposporophyte generation absent

          1. Palmeria -- large, frond-like genus

        3. Batrachospermales -- freshwater, filamentous forms; sporophytes do not form tetrasporangia, instead meiospores formed in apical cells

          1. Batrachospermum -- fairly common in the Okefenokee

        4. Gigartinales -- large order of uniaxial and multiaxial algae with economic (carrageenan) value

          1. Eucheuma

          2. Hypnea

          3. Chondrus

        5. Gracilariales -- economically important agar-producing algae

          1. Gracilaria

        6. Ceramiales -- multiaxial group which forms auxiliary cells after fertilization

          1. Ceramium -- jointed appearance

          2. Polysiphonia

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