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Plasmodial Slime Molds. Pl P 421/521. http://www.ucmp.berkeley.edu/chromista/chromistasy.html. Ribosomal RNA phylogenies place slime molds as unrelated, early branching eurkaryote lineages . Baldauf and Doolittle, 1997. PNAS 94 (22): 12007-12012.

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Plasmodial Slime Molds

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Plasmodial Slime Molds

Pl P 421/521


http://www.ucmp.berkeley.edu/chromista/chromistasy.html

Ribosomal RNA phylogenies place slime molds as unrelated, early branching eurkaryote lineages


Baldauf and Doolittle, 1997. PNAS 94 (22): 12007-12012

Actin, elongation factor, and β-tubulin phylogenies place the plasmodial and cellular slime molds as a monophyletic group close to Animal + FungI


Classification

  • Mycetozoa = cellular, plasmodial slime molds plus protostelids

  • Cellular slime molds and protostelids now placed in phylum Myxomycota

  • Names imply a fungal-like affinity


Myxomycota

  • Myxomycetes--5 orders, 13 families, 62 genera, 800 species

  • Characterized by plasmodium

    • Engulfs bacteria, fungal spores, small pieces of organic matter


Physarum life cycle

meiosis

karyogamy

microcyst

Synchronous mitotic divisions

macrocyst


Stages in Life Cycle

  • Spores (2nn)

    • 4-20 µm, pigmented ornamented; meiosis in spore = 4 nuclei; 3 degenerate


Stages in Life Cycle

  • Myxamoebae (n)

    • feed, divide, convert to swarm cells, function as gametes; form microcysts under adverse conditions

www.uoguelph.ca/~gbarron/ MISCE2002/myxamo2.jpg


Stages in Life Cycle

  • Swarm cells (n)

    • 1-4 anterior whiplash flagella, amoeboid posterior; feed (absorption and engulfment), function as gametes

    • can’t undergo cell division

http://www.botany.hawaii.edu/faculty/wong/Bot201/Myxomycota/Swarm_Cells2.jpg


Stages in Life Cycle

  • Zygote (2n)

    • Formed by fusion of myxamoebae or swarm cells; enlarges through synchronous nuclear division

  • Plasmodium (2n)

    • Multinucleate, wall-less protoplasm

Photo by Stephen Sharnoff

http://www.plant.uga.edu/mycology-herbarium/myxogal/Physros3.jpg


Stages in Life Cycle

  • Sporophore (2n)

    • Entire plasmodium is converted into sporophore(s)

  • Sclerotium or macrocyst (2n)

    • Resistant stage formed by plasmodium


Types of plasmodia

  • Phaneroplasmodium

    • Conspicuous, often colored, with protoplasm forming veins with reversible streaming

  • Aphanoplasmodium

    • With a network of fine, transparent threads and homogenous protoplasm

  • Protoplasmodium

    • Microscopic, with homogenous protoplasm, giving rise to one sporophore


Sporophores

  • Mass of spores formed inside peridium, spores intermingled with:

    • Capillitium

      • threadlike, often ornamented

    • Elaters

      • Threadlike, ornamented, not connected at ends

    • Pseudocapillitium

      • Threads, bristles, membrane or platelike network

  • Lime may be present on peridium, stalk, columella or capillitium, or nodes of pseudocapillitum


Capillitium (top left; photo by David Geiser)

Pseudocapillium (top right; photo from Fifth Kingdom)

Elaters (bottom left)

www.botany.hawaii.edu/.../Bot201/ Myxomycota/elaters.jpg


Sporocarp—stalked or sessile

May have columella 


Aethalium

  • Large, cushion-shaped sporophore, one per plasmodium


Pseudoaethalium

  • Cluster of sporophores grouped tightly together

Photo by David Geiser


Plasmodiocarp

  • Sporophore developing along veins of phaneroplasmodium; takes on reticulate shape of veins


Photo by Stephen Sharnoff


Liceales-- Pale or brown spores, capillitium and lime absent, pseudocapillitium may be present

Dictydium

Lycogala

Photo by Stephen Sharnoff


Trichiales--Pale spores (yellow, orange or red) and abundant, conspicuous capillitium

Trichia

Arcyria


Physarales--Purplish-brown spores, usually with abundant and conspicuous lime on or in sporophore

Badhamia

Leocarpus

Fuligo


Stemonitales--Violet-brown spores, lime absent

Lamproderma

Diachea


Photo by Stephen Sharnoff

Stemonitis


Ceratiomyxales--Exosporous sporophores; probably belongs in protostelids (one genus, Ceratiomyxa)

Photo by Stephen Sharnoff

Photo by David Geiser


Protostelids

  • Simplest known slime molds

  • Discovered in 1970

    • Easily mistaken for mucoraceous fungi or deuteromycetes

  • In dead, attached plant parts, herbivore dung or soil; feed on bacteria, yeast and fungal spores

  • 14 genera and 32 species


Protostelid Life Cycle

  • Amoeboid cells (filose pseudopodia) become one or more prespore cells that rise on stalk and encyst to form one to four spores

  • Plasmodium and flagellated cells present in “complex” life cycles

  • Sexual reproduction not known


Life cycle of simple protostelid

http://comp.uark.edu/~fspiegel/protist.html#sporocarp%20morphology


Life cycle of complex protostelid

http://comp.uark.edu/~fspiegel/protist.html#sporocarp%20morphology


Images courtesy of Fred Spiegal, Univ. of Arkansas


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