Encyclopedia
| Slime mold
Encyclopedia
|
| Tutorials | Encyclopedia | Dictionary | Directory |
|
Slime mold
Slime Mold (or Gymnomycota) is a broad term often referring to roughly four groups of Eukaryotes. The taxonomy is still in flux. Originally, slime molds were considered Fungi, but now they have been split into various groups:
The Myxogastria, Protosteli, and Dictyosteliida make up the modern phylum Mycetozoa. The mycetozoan groups all fit into the unikont supergroup Amoebozoa, whereas the others fit into various bikont groups. Slime molds feed on microorganisms in decaying vegetable matter. They can be found in the soil, on lawns, and in the forest commonly on deciduous logs. They are also common on mulch or even in leaf mold which collects in gutters. They begin life as amoeba-like cells. These unicellular amoebae are commonly haploid and multiply if they encounter their favorite food, bacteria. These amoebae can mate if they encounter the correct mating type and form zygotes which then grow into plasmodia which contain many nuclei without cell membranes between them, which can grow to be meters in size. One variety is often seen as a slimy yellow network in and on rotting logs. The amoebae and the plasmodia engulf microorganisms. The plasmodium grows into an interconnected network of protoplasmic strands (Ling, 1999). Within each protoplasmic strand the cytoplasmic contents rapidly stream. If one strand is carefully watched for about 50 seconds the cytoplasm can be seen to slow, stop, and then reverse direction. The streaming protoplasm within a plasmodial strand can reach speeds of up to 1.35 mm per second which is the fastest rate recorded for any organism (Alexopoulos, 1962). Migration of the plasmodium is accomplished when more protoplasm streams to advancing areas and protoplasm is withdrawn from rear areas. When the food supply wanes, the plasmodium will migrate to the surface of its substrate and transform into rigid fruiting bodies. The fruiting bodies or sporangia are what we commonly see, superficially look like fungi or molds but they are not related to the true fungi. These sporangia will then release spores which hatch into amoebae to begin the life cycle again (Ling, 1999).
Types of slime mold
Mycetozoa from Ernst Haeckel's 1904 Kunstformen der Natur (Artforms of Nature) Slime molds can generally be divided into two main groups. A cellular slime mold involves numerous individual cells attached to each other, forming one large membrane. This "supercell" is essentially a bag of cytoplasm containing thousands of individual nuclei. By contrast, plasmodial slime molds (Dictyosteliida) spend most of their lives as individual unicellular protists, but when a chemical signal is secreted, they assemble into a cluster that acts as one organism. A common slime mold which forms tiny brown tufts on rotting logs is Stemonitis. Another form which lives in rotting logs and is often used in research is Physarum polycephalum. In logs it has the appearance of a slimy webwork of yellow threads, up to a few feet in size. Fuligo forms yellow crusts in mulch. The Protostelids life cycle is very similar to the above descriptions, but are much smaller, the fruiting bodies only forming one to a few spores. The Dictyosteliida, cellular slime molds, are distantly related to the plasmodial slime molds and have a very different life style. Their amoebae do not form huge coenocytes, and remain individual. They live in similar habitats and feed on microorganisms. When food runs out and they are ready to form sporangia, they do something radically different. They release signal molecules into their environment, by which they find each other and create swarms. These amoeba then join up into a tiny multicellular slug-like coordinated creature, which crawls to an open lit place and grows into a fruiting body. Some of the amoebae become spores to begin the next generation, but some of the amoebae sacrifice themselves to become a dead stalk, lifting the spores up into the air. The Acrasidae, have a life style similar to Dictyostelids, but their amoebae behave differently and are of uncertain taxonomic position. The Plasmodiophorids also form coenocytes but are internal parasites of plants (e.g., club root disease of cabbages). Finally the Labyrinthulomycetes are marine and form labyrinthine networks of tubes in which amoebae without pseudopods can travel. Utility in research
Slime mold on lawn, USA. Trail of movement can be seen. Slime molds like Physarum polycephalum are useful for studying cytoplasmic streaming. They have also been used to study the biochemical events that surround mitosis, since all the nuclei in a medium-sized plasmodium divide in synchrony. It has been observed that they can find their way through mazes by spreading out and choosing the shortest path, an interesting example of information processing without a nervous system. Myxomycete plasmodia have also been used to study the genetics of asexual cell fusion. The giant size of the plasmodial cells allows for easy evaluation of complete or partial cell fusion. In 2006, researchers at the University of Southampton and the University of Kobe reported that they had built a six-legged robot whose movement was remotely controlled by a Physarum slime mold. The mold directed the robot into a dark corner most similar to its natural habitat. Slime molds are sometimes studied in advanced mathematics courses. Slime mold aggregation is a natural process that can be approximated with partial differential equations. Slime molds in culture
Slime mold from Olympic National Park, USA (Possibly Physarum) References
Dog Vomit slime mold
External links
ca:Mixomicet cs:Hlenky da:Slimdyr de:Schleimpilze es:Myxomycota eo:Mukofungoj fr:Mycetozoa he:?????? ka:????????????? lt:Gleivainis nl:Slijmzwammen ja:??? no:Slimsopper pl:?luzowce pt:Mycetozoa sr:Eumycetozoa fi:Limasienet sv:Slemsvampar th:??????? zh:?? Source: Wikipedia | The above article is available under the GNU FDL. | Edit this article
|
|
top
©2008-2009 TutorGig.com. All Rights Reserved. Privacy Statement
