Lecture #19

Acrasiomycota: the cellular slime molds


Acrasiomycetes
Dictyosteliomycetes

Myxomycota: true or plasmodial slime molds

Myxomycetes

Anton de Bary (1858, 1859, 1887) - first detailed life history studies that characterize slime molds; distinguished the true slime molds from the cellular slime molds on the basis of plasmodium formation by myxomycetes.

Acrasiomycota

Dictyosteliomycetes

Acrasin, now known to be cyclic AMP, a pheromone responsible for aggregation in some species of Dictyostelium

Life cycle of Dictyostelium discoideum

(IMAGE)

Myxomycota: The true slime molds, or plasmodial slime molds

Myxomycetes exhibit two types of mitotic divisions, one that is centric with a nonpersistent nuclear envelope that breaks down in prophase and another that is acentric with a nuclear envelope remaining more or less intact until late anaphase or early telophase.

Fuligo septica, actually has several common names, "flowers of tan" and, more recently, "the blob."


Phylum Myxomycota

Orders are distinguished on the basis of

Endosporous Myxomycetes- Physarales, Stemonitales

Spores

Spore Dispersal


Spore Germination, Myxamoeba, and Swarm Cells.


Formation of Zygotes and Plasmodia

"Ever changing, ever flowing, the plasmodium creeps over the surface of the substratum, engulfing particles of food in its path."

Three basic types of plasmodia

protoplasmodium - microscopic throughout its existence; gives rise to only a single sporangium when it fruits.

aphanoplasmodium - resembles a protoplasmodium in its initial stages, but soon elongates, branches, and becomes a network of very fine, transparent strands; Stemonitales.

phaneroplasmodium - characteristic of Physarales, also resembles a protoplasmodium at first; it grows larger and becomes more massive. Its protoplasm is very granular, and the plasmodium is visible even at an early stage of development. The gelified and fluid portions of the veins are easily distinguishable and the rhythmic, reversible streaming is very conspicuous.

Sclerotia

In the normal course of events, the plasmodium gives rise to sporophores. Under certain conditions, however, a phaneroplasmodium becomes converted into an irregular, hardened mass, the sclerotium, that can remain dormant for a long time, but grows out into a plasmodium again when conditions favorable for growth return.


Sporulation and Sporophores