ISSN:
1432-072X
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary The axenic culture of two unusual, zoosporic Phycomycetes, Oedogoniomyces and Harpochytrium, is reported for the first time. Cultural studies have made it possible to clarify and document many developmental and morphological characteristics of the two genera thus revealing their fundamental similarity to each other and necessitating their taxonomic grouping in a new order of Chytridiomycetes, the Harpochytriales. For Oedogoniomyces it has been shown that the genus occurs outside Japan in tropical and temperate regions of the western hemisphere; that it has the capacity, probably by means of gemmae, to withstand drying for as long as 7 years; that some isolates form gemmae in culture whereas others under identical conditions do not; and that the extent to which the thallus becomes septated into reproductive structures also varies in different isolates. The thick-walled, pitted chlamydocysts, originally considered to represent a resistant stage of O. lymanaeae, were never developed in any of the present isolates, and it is concluded that they have no genetic relation to Oedogoniomyces but are, on the contrary, resistant sporangia of Allomyces. For Harpochytrium it has been shown that zoospore release occurs, not by gelatinization of the sporangial apex, but as a result of circumscissile weakening of the sporangial wall followed by displacement of a cap-like terminal portion; that the zoospores, only rarely seen before, are in fact posteriorly uniflagellate and have a central globule with associated smaller globules; and that, whereas a thallus very occasionally becomes entirely cleaved up into zoospores, a sterile, vegetative, nucleated portion almost always remains and provides the basis for internal sporangial proliferation. Histochemical studies have verified the presence of chitin in the walls of both genera but revealed no cellulose. The new order Harpochytriales, with the single family Harpochytriaceae Wille, amended to include Oedogoniomyces, is distinguished from all other Chytridiomycetes by the uniaxial thallus with its extracellular basal holdfast and the sporangium that opens by circumscissile weakening and rupture of the wall near its apex releasing a cap-like terminal portion.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00446606
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