Characteristic zoospores, life cycle, nutrition

3122
Jonah Lester

The zoospores They are mobile spores that use flagella for their locomotion. Protists, bacteria and fungi of various species use them as a means of propagation. The flagella can be of two types.

Stramopile flagella (estramopiles) that have lateral filaments, called mastigonemes. These are located perpendicular to the main axis of the flagellum. Whip-shaped flagella lack mastigonemes.

Zoospore of the fungus Phytophthora infestans. Taken and edited from siafemor.inifap.gob.mx/tizon-tardio.php

The number and distribution of flagella in zoospores will differ depending on the taxonomic group to which the zoospore belongs. There are four main forms of zoospores: opisthoconta, anisoconta, heteroconta, and zoospora with a single stramopile flagellum..

Article index

  • 1 Features
    • 1.1 Zoospore opistoconta
    • 1.2 Zoospore anisoconta
    • 1.3 Zoospora heteroconta
    • 1.4 Zoospore with a single stramopile flagellum
  • 2 Life cycle
    • 2.1 Zoospora opistoconta
    • 2.2 Zoospore anisoconta
    • 2.3 Zoospora heteroconta
    • 2.4 Zoospore with a single stramopile flagellum
  • 3 Nutrition
  • 4 Playback
  • 5 Diseases
    • 5.1 Zoospora opistoconta
    • 5.2 Zoospore anisoconta
    • 5.3 Zoospora heteroconta
    • 5.4 Zoospore with a single stramopile flagellum
  • 6 References

Characteristics

Zoospore opistoconta

They generally have only one posterior flagellum, except in the neocallimastigales, which present up to 16 flagella. It is characteristic of opisthokonta organisms.

Opisthtocons are a clade of eukaryotic organisms that contain choanozoa, along with fungi and animals. In these the flagellum, when present, occupies a posterior position, pushing the cell to advance, as occurs in the sperm of animals..

Zoospore anisoconta

It has two whip-shaped flagella of different lengths. Both flagella insert laterally. The longest is directed posteriorly, while the shortest is directed anteriorly. It occurs in some myxomycota and plasmodiophoromycota.

Zoospore heteroconta

These zoospores have two anterior flagella of different shape and length. This type of spore is typical of heteronkonta organisms. Heterocons are a superphylum of eukaryotic organisms.

It contains from unicellular algae, such as diatoms, to multicellular brown algae. It also includes oomycetes, formerly considered mushrooms. In these, the longest flagellum is covered with mastigonemes.

The other flagellum is whip-shaped and generally shorter or greatly reduced. The flagella insert anteriorly near the apex (subapical) or laterally and are generally supported by four microtubular roots with a distinctive pattern. The flagella draw the cell towards each other during the movement.

Zoospore with a single stramopile flagellum

The zoospore has a single flagellum located above. The flagellum is relatively short and covered with mastigonemas. This zoospore is characteristic of the hyphochytridiomycetes.

Lifecycle

Zoospore opistoconta

Chytridiomycetes, for example, have alternating haploid gametotali and diploid sporothali. Gametotali produce mobile gametes that fuse in the middle to form a biflagellate zygote that encysts. When germinating it produces a sporotalus. It will develop zoosporangia of two types: mitosporangia and meiosporangia..

Mitosporangia produce diploid zoospores by mitotic division and zoospores originate new diploid sporothals.

Meiosporangia produce haploid zoospores by meiosis. Spores germinate to form haploid gametotali.

Zoospore anisoconta

The life cycle of plasmodiophorida, for example, alternates the soil and the interior of the root of the host plant. These present mobile secondary zoospores thanks to the presence of two flagella.

These zoospores act as isogametes. When the zygote is formed, it infects a root hair of the host. This initial cell divides repeatedly and forms a very small intracellular plasmodia..

In plasmodium, due to meiosis, a multitude of cysts are formed inside the cells. The cells end up lysing and releasing the cysts to the ground.

Each of the cysts germinates and gives rise to a monadic state, a primary zoospore, which actively swims looking for other root hairs. Once introduced into these, it forms a plasmodia that becomes a sporocyst.

The sporocyst ends up giving rise to many spores, which are again released to the ground. The new primary spores give rise to secondary zoospores that can already fuse.

Zoospore heteroconta

An example of the life cycle where heterochant zoospores participate is that of the oomycetes. These organisms exhibit both sexual and asexual reproduction. Diploid mycelial phases alternate with haploid sexual reproduction phases.

During asexual reproduction they present heterocontaus zoospores. These have the mastigonematous flagellum directed forward and the naked one directed backward..

The sexual reproduction phase is by oogamy. Sex spores, called oospores, are used to survive in harsh environmental conditions.

Zoospore with a single stramopile flagellum

The zoospores of the hyphochytridiomycetes are distinguished by presenting an anterior flagellum with mastigonemes. These become encyst when their movement ceases. Later they germinate giving a place to a thallus. This thallus will produce new zoospores.

Nutrition

Zoospores do not feed, they obtain their energy from reserve substances supplied by the parent during their formation. The substances used in reserve are of different nature depending on the taxonomic group.

Reproduction

Zoospores do not reproduce themselves. Depending on the taxonomic group, they can be produced by meiosis or by mitosis. Zoospores can be haploid or diploid, sexual or asexual.

Asexual spores germinate directly. Sex spores act as sex gametes and must fuse to produce diploid zygotes.

Sporangium and zoospore formation in a Plasmopara halstedii sporangium. Photograph by Aranka Kormany. Taken and edited from herbariofitopatologia.agro.uba.ar/?page_id=499

Diseases

Zoospores are not infective stages but rather a means of dispersal of organisms that can be pathogens. Among the diseases that can be produced by organisms that have zoospores, the following could be noted:

Zoospore opistoconta

Chitidromycetes possess opisthoconta spores. These organisms cause diseases such as potato black wart and corn brown spot in plants.. 

In animals, chytridiomycosis that affects amphibians has even caused species extinctions. This disease is caused by Batrachochytrium dendrobatidi and the zoospores of these pathogens are produced in sporangia during asexual reproduction.

Zoospore anisoconta

Several species of plasmodiophoromycota are economically important plant pathogens. Among the diseases they cause are cabbage root disease and powdery scab on potatoes. These are caused by Plasmodiophora brassicae, Y Underground spongospora respectively.

Zoospore heteroconta

Diseases caused by oomycetes include potato late blight, grape downy mildew, and sudden oak death in plants..

In animals it produces aphanomycosis in river crabs, saprolegniosis in fish, pythiosis in horses, cats, dogs and occasionally in humans. Zoospores are attracted by chemical signals from the hosts, where they encyst and then germinate.

Zoospore with a single stramopile flagellum

The hyphochytridiomycetes are a small group of saprobic pseudo-fungi or parasites. About fifty species contained in this class are known.

Pseudo-fungi are fungal-like protists. There are very few references to the diseases caused by the parasitic species of this group to their hosts..

References

  1. G.W. Beakes, S. Sekimoto (2009). The evolutionary phylogeny of oomycetes-insights gained from studies of holocarpic parasites of algae and invertebrates. In: K. Lamour, S. Kamoun (Eds.), Oomycete genetics and genomics: diversity, interactions, and research tools. John Wiley & Sons, Inc.
  2. F.H. Gleason, O. Lilje (2009). Structure and function of fungal zoospores: ecological implications. Fungal Ecology.
  3. J. Guarro, J. Gene, A.M. Stchigel (1999). Developments in Fungal Taxonomy. Clinical Microbiology Reviews.
  4. E.P. Hill (I 969). The Fine Structure of the Zoospores and Cysts of Allomyces macrogynus. Journal of general Microbiology.
  5. P.M. Letcher, J.P. Powell (2005). Phylogenetic position of Phlyctochytrium planicorne (Chytridiales, Chytridiomycota) based on zoospore ultrastructure and partial nuclear LSU rRNA gene sequence analysis. - Nova Hedwigia 80: 135-146.
  6. Zoospores. On Wikipedia. Retrieved on October 9, 2018 from en.wikipedia.org.

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