Egg mushrooms
| Egg mushrooms | ||||||||||||
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Achlya sp. (Saprolegniales) on a hemp seed |
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| Peronosporomycetes | ||||||||||||
| Dick , 2001 |
The oomycete called (Peronosporomycetes, formerly Oomycota or Oomycetes), algae fungi, cellulose fungi or sham fungi, form a taxon within the Stramenopilen and thus with greater detail brown algae , gold algae (in the broad sense, that is golden algae , diatoms and yellow-green algae ), Netzschlimpilzen and Hyphochytriales (only order of the Hyphochytriomycota ) related than with the real mushrooms or the slime molds . The egg fungi live mainly in fresh water, in aquatic animals, in the soil or in land plants asSaprophytes or parasites .
The egg fungi also include the causative agents of some dreaded plant diseases, such as the causative agent of late blight in potatoes and tomatoes Phytophthora infestans and downy mildew (Peronosporales).
construction
Like the real mushrooms, the egg mushrooms consist of a network of cell threads ( hyphae ), the mycelium . The cell walls of the egg fungi consist of glucans , hydroxyproline and cellulose ; Chitin rarely occurs. Inside the hyphae there are cell nuclei and cytoplasm as well as large vacuoles . The hyphae are usually not divided by septa (partitions); only gametangia and sporangia are each sealed off from the hypha carrying them by a septum.
In many species flagellated swarming cells, so-called zoospores, develop in the sporangia . These are heterocontact flagellated, that is, on their surface directly next to each other arise a trailing flagellated with fine hairs pointing in the swimming direction and a backward pointing, featherless dragging flagellum. The possession of such heterocontact swarming cells identifies the egg fungi as stramenopiles .
For most of their life cycle, egg fungi are diploid . Haploid cell nuclei occur only during sexual reproduction.
nutrition
Among the egg fungi there are both saprophytes , which feed on dead plant and animal material, and parasites , which attack plants, aquatic animals or even other egg fungi. The egg mushrooms digest dead or living organic matter by secreting enzymes that break it down. The fungus then absorbs the dissolved nutrients through its cell membrane.
Reproduction
Egg fungi can reproduce asexually as well as sexually.
Asexual reproduction
The most widespread and probably most primitive type of asexual reproduction in egg fungi is reproduction through zoospores. A hyphae tip is separated from the rest of the hyphae by a septum ; it becomes the sporangium . By mitosis , the sporangium filled with a more or less large number of cores. Each nucleus is surrounded by a portion of the plasma and a cell membrane; the mononuclear cells thus created form the typical two flagella and leave the sporangium.
After a while, the pear-shaped or kidney-shaped swarming cells take on a spherical shape and draw in the flagella. The resulting spherical cell is called a cyst . Depending on the type at hand, a hypha can germinate from the cyst, with which the fungus can take possession of a new source of food, or another flagellated swarming cell. This second generation of zoospore forms a cyst again after a while. Some species now germinate with a hypha; Others can repeat the interplay between the swarmer and the cyst until a suitable substrate is found or the cell starves to death.
Egg species, which live as parasites on land plants, have often modified this reproductive principle. With them, the sporangium detaches itself from the hypha as a whole and is spread by the wind (it functions as a conidia ). The condition for the survival of the sporangium is usually high humidity. After a while, the sporangium releases zoospores or it germinates with a hypha. For some species there is only the latter possibility.
Sexual reproduction
The female gametangium is called the oogonium . It is usually an approximately spherical vesicle and sits on the tip of a hypha, from which it is sealed off by a septum. Meiosis takes place inside ; one or more haploid , spherical egg cells, the oospheres (Greek for “egg balls”) are formed.
The male gametangium is called the antheridium . It can have different shapes and is usually smaller than the oogonium. It is sealed off by a septum from the tip of a hypha that extends towards the oogonium. Then meiosis takes place in the antheridium. Fertilization takes place when haploid nuclei move from the antheridium through plasma tubes into the oospheres and fuse with their haploid nuclei. This type of sexual reproduction is called cytogamy and is a form of gametangiogamy (gametes are not released, but the gametangia fuse).
Egg fungus species in which oogonium and antheridium have to come from different mycelia in order to carry out fertilization are called heterothallic . In most species, oogonia can be fertilized by antheridia from the same mycelium; these types are called homothallic .
After fertilization, the now diploid oospheres form a stable wall and are now called oospores. After a resting phase, they germinate into a new mycelium. In some species they sometimes only form a sporangium instead, as in asexual reproduction.
Egg mushrooms and humans
Parasitic egg fungi can cause great damage if they penetrate new habitats with the unintentional help of humans.
The cancer plague
The crab plague Aphanomyces astaci originally lived on freshwater crabs in America. They have developed defense mechanisms against the fungus so that it is relatively harmless to them. But when American crabs were introduced into European waters, the crayfish plague jumped over to the European crayfish ( Astacus astacus ) and almost wiped it out.
The Great Famine in Ireland 1845–1846
The late blight of the potato Phytophthora infestans is probably the most notorious of all plant diseases. Originally it probably lived on the wild nightshade family in Mexico . In the 1840s, she jumped over to cultivated potatoes and subsequently ate her way across the potato fields of the world, as the potatoes had little resistance to the new disease. In 1845 it first appeared in the west of the European continent, where it was described by Jean Pierre François Camille Montagne as Botrytis infestans . It reached Ireland in the fall of 1845 and caused the Great Famine of 1845 .
P. infestans needs moisture and not too high temperatures for effective reproduction (sporangia germination with several zoospores instead of a single hypha). These conditions were met very well in Ireland in 1845 and 1846. The rot infected the entire potato crop. Since P. infestans also produces toxins, the tubers were not only unsavory but also harmful to health. Since potatoes were practically the only source of food for many Irish people, about a million people on the island died of starvation. In the following years 1.5 million Irish emigrated, mainly to the USA. Ireland has not yet returned to the population it had before the potato blight.
Systematics
As members of the stramenopils, the egg fungi come from autotrophic organisms ( algae ) and have lost the plastids . They are divided into several orders, numerous basal egg fungi have hardly been investigated so far, so that it is to be expected that more will be added to the six known orders given below.
- The water mold ( Saprolegniales ) live in fresh water, some species also in moist soils. Most are saprophytes ; some are parasites on plants and aquatic animals. An example of the latter is the cancer plague Aphanomyces astaci .
- The Lagenidiales live parasitically on aquatic animals, algae or Saprolegniales.
- The sewage fungus-like (Leptomitales) live saprophytically in the water. They resemble the Saprolegniales; however, in contrast to these, they often have constrictions in their hyphae, which are closed by chitin plugs and thus act like septa. There are only seven species in three genera.
- The Rhipidiales live as saprophytes in polluted fresh water. They live by fermentation . They cannot breathe oxygen , but it is also not toxic to them.
- The Peronosporales mainly contain pathogens of plant diseases. The largest group of the Peronosporales are the downy mildew fungi , another important genus is Phytophthora . In many species, the sporangia become detached from their carrier hyphae and are spread by the wind before they release their zoospores or germinate with a hypha. Important plant diseases belong to this order, for example the late blight of the potato Phytophthora infestans and the downy mildew from the family Peronosporaceae.
- The white rust pathogens ( Albuginales ), which sporulate under the epidermis of their host plants and thereby cause white pustules on leaves, sprouts and in the inflorescences. Like the false powdery mildew, the white rust pathogens are also dependent on living host plants for their nutrition.
literature
- Sina M. Adl, Alastair GB Simpson, Christopher E. Lane, Julius Lukeš, David Bass, Samuel S. Bowser, Matthew W. Brown, Fabien Burki, Micah Dunthorn, Vladimir Hampl, Aaron Heiss, Mona Hoppenrath, Enrique Lara, Line le Gall, Denis H. Lynn, Hilary McManus, Edward AD Mitchell, Sharon E. Mozley-Stanridge, Laura W. Parfrey, Jan Pawlowski, Sonja Rueckert, Laura Shadwick, Conrad L. Schoch, Alexey Smirnov, Frederick W. Spiegel: The Revised Classification of Eukaryotes . In: The Journal of Eukaryotic Microbiology . Volume 59, No. 5, September 28, 2012, doi: 10.1111 / j.1550-7408.2012.00644.x , ISSN 1550-7408 , ISSN 1066-5234 , pp. 429-493 (English; PDF file , 828, 83 KiB, in the Wiley Online Library by John Wiley & Sons, Inc. ).
- Constantine John Alexopoulos, Charles W. Mims, Meredith Blackwell: Introductory mycology . 4th edition. Wiley-VCH, New York 1996, ISBN 0-471-52229-5 .
- Peter Sitte , Elmar Weiler , Joachim W. Kadereit , Andreas Bresinsky , Christian Körner : Textbook of botany for universities . Founded by Eduard Strasburger . 35th edition. Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1010-X .
- Emil Müller, Wolfgang Loeffler: Mykologie , 4th ed., Stuttgart and New York (Georg Thieme) 1982, pp. 177-187
Web links
- Introduction to the Oomycota - University of California Museum of Paleontology (UCMP)
supporting documents
- ↑ a b Sina M. Adl, Alastair GB Simpson, Christopher E. Lane, Julius Lukeš, David Bass, Samuel S. Bowser, Matthew W. Brown, Fabien Burki, Micah Dunthorn, Vladimir Hampl, Aaron Heiss, Mona Hoppenrath, Enrique Lara , Line le Gall, Denis H. Lynn, Hilary McManus, Edward AD Mitchell, Sharon E. Mozley-Stanridge, Laura W. Parfrey, Jan Pawlowski, Sonja Rueckert, Laura Shadwick, Conrad L. Schoch, Alexey Smirnov, Frederick W. Spiegel : The Revised Classification of Eukaryotes . In: The Journal of Eukaryotic Microbiology . Volume 59, No. 5, September 28, 2012, doi: 10.1111 / j.1550-7408.2012.00644.x , ISSN 1550-7408 , ISSN 1066-5234 , pp. 429-493 (English; PDF file , 828, 83 KiB, accessed from the Wiley Online Library by John Wiley & Sons, Inc. , and received on March 21, 2017).
- ↑ Dubey Manish Kumar, Upadhyay RS: Isolation and Characterization of Some Indian Hyphochytriomycetes . In: International Research Journal of Biological Sciences . Volume 2, No. 6, 2013, ISSN 2278-3202 , pp. 31–34, here: 31 (English; PDF file , 2.51 MiB, summary , first page at scribd.com ( Memento from March 22, 2017 in the Internet Archive ), accessed and received on March 22, 2017).