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A petri dish of Dictyostelium.. When food (normally bacteria) is readily available dictyostelids behave as individual amoebae, which feed and divide normally. However, when the food supply is exhausted, they aggregate to form a multicellular assembly, called a pseudoplasmodium, grex, or slug (not to be confused with the gastropod mollusc called a slug).
Most of its life, this haploid social amoeba undergoes a vegetative cycle, preying upon bacteria in the soil, and periodically dividing mitotically. When food is scarce, either the sexual cycle or the social cycle begins. Under the social cycle, amoebae aggregate in response to cAMP by the thousands, and form a motile slug, which moves towards ...
Clockwise from top right: Amoeba proteus, Actinophrys sol, Acanthamoeba sp., Nuclearia thermophila., Euglypha acanthophora, neutrophil ingesting bacteria. An amoeba (/ ə ˈ m iː b ə /; less commonly spelled ameba or amœba; pl.: amoebas (less commonly, amebas) or amoebae (amebae) / ə ˈ m iː b i /), [1] often called an amoeboid, is a type of cell or unicellular organism with the ability ...
In D. discoideum, the amoeba secretes the signal, cAMP, out of the cell, attracting other amoebae to migrate toward the source. Every amoeba moves toward a central amoeba, the one dispensing the greatest amount of cAMP secretions. The secretion of the cAMP is then exhibited by all amoebae and is a call for them to begin aggregation.
During the aggregation phase of their life cycle, Dictyostelium discoideum amoebae communicate with each other using traveling waves of cyclic AMP. [51] [52] [53] There is an amplification of cyclic AMP when they aggregate. [54] Pre-stalk cells move toward cyclic AMP, but pre-spore cells ignore the signal. [55]
All species of animals, land plants and most fungi are multicellular, as are many algae, whereas a few organisms are partially uni- and partially multicellular, like slime molds and social amoebae such as the genus Dictyostelium. [2] [3] Multicellular organisms arise in various ways, for example by cell division or by aggregation of many single ...
When starving, the usually solitary single-celled amoebae aggregate and form a multicellullar slug that can contain 10 4 –10 6 cells. This slug migrates to the soil surface, where it transforms into a fruiting body composed of a spherical tip of spores and a stalk consisting of nonviable stalk cells that hold the spores aloft (Figure 2).
When the amoebae are stressed, typically by a shortage of food, they form a grex. According to species and circumstances, details of the shape of the grex and how it may form will vary but typically the stressed amoebae first produce pheromones that stimulate the flock to vertically assemble in a column. When the column of aggregated cells ...