Zygnematophyceae

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Zygnematophyceae
Conjugation in Spirogyra.
Scientific classification Edit this classification
(unranked): Viridiplantae
(unranked): Charophyta
Class: Zygnematophyceae
Round, 1971
Subclasses
Synonyms[1]
  • Akontae Blackman & Tansley, 1902
  • Conjugatophyceae Engler, 1892
  • 'Conjugatae' Engler, 1892
  • Gamophyceae
  • Saccodermae Pascher ex Kossinskaja, 1952
  • Zygnemaphyceae Round 1971
  • Zygophyceae Widder, 1960

Zygnematophyceae (or Conjugatophyceae) is a class of

Embryophyta (land plants).[4][5][6]

Common members of the Zygnematophyceae include the filamentous algae

desmids, which are microscopic algae characterized by symmetrical and elaborately ornate cells.[7]

Morphology

The body plan of Zygnematophyceae is simple, and the group appears to have gone through a secondary loss of morphological complexity.[8] The most basal members are unicellular, but filamentous species have evolved at least five times,[9] and a few species form colonies.[7] Each cell contains a single nucleus.[7]

The chloroplasts of the Zygnematophyceae are large, typically axile but sometimes parietally located, and contain one or several pyrenoids. One or several chloroplasts may be present in a single cell. The shape of the chloroplast may be star-shaped (in Zygnema), ribbon-shaped (in Spirogyra), or elaborately lobed and dissected. In some taxa, particularly Mougeotia, the chloroplast is able to move in response to different light conditions.[7]

In the Zygnematophyceae, cell walls are composed of three layers: one outer layer consisting of mucus, a primary wall consisting of

microfibrils. Some species shed their primary wall and retain only the innermost layer. The cell wall may be variously decorated with striations, granules, or spines. In the Desmidiales, there are pores in the cell wall which allow the cell to extrude a layer of mucilage for protection.[7]

Several Zygnematophyceae contain genes involved in protection from desiccation that appear to have been derived by horizontal gene transfer from bacteria; the genes are found in plants, Zygnematophyceae, and bacteria, but no other organisms. The genes may have helped to enable plants to make the transition to life on land.[10][11]

A new subclass called Spirogloeophycidae, represented by the species Spirogloea muscicola, was established after the unicellular subaerial algae, resembling a "gelatinous blob", was rediscovered on a rock close to a river bank near Cologne in 2006, after first being discovered in France in 1845.[12]

Reproduction

The Zygnematophyceae are able to reproduce both asexually and sexually. Asexual reproduction takes place via fragmentation, cell division, akinete formation, or parthenospores.[7]

flagella,[7] and they also lack centrioles which suggest that flagella were not secondarily lost. This lack of flagella sets the Zygnematophyceae apart from nearly all groups of algae, except for red algae and cyanobacteria (also known as blue-green algae, if they are classified as such).[1] The gametes are scarcely differentiated from vegetative cells.[7]

In conjugation, cells or filaments of opposite sex line up, and tubes form between corresponding cells. The male cells then become amoeboid and crawl across the female, or sometimes both cells crawl into the connecting tube. The cells then meet and fuse to form a zygote, which later undergoes meiosis to produce new cells or filaments. As in land plants, only the female passes its chloroplasts on to the offspring.[14]

Taxonomy

The Zygnematophyceae is

paraphyletic with respect to the Desmidiales, and so it was split up. As of 2023, five orders and two subclasses are recognized: the Spirogloeales in Spirogloeophycidae, and the Serritaeniales, the Zygnematales, the Spirogyrales, and the Desmidiales in Zygnematophycidae.[9]

Class Zygnematophyceae[15]

Phylogeny

A phylogeny of the families of Zygnematophyceae is presented below:[16][11]

Zygnematophyceae

Habitat

Members of the Zygnematophyceae are common in nearly all freshwater habitats, particularly filamentous genera such as Spirogyra and Mougeotia. Some Spirogyra species can tolerate disturbed habitats. On the other hand, desmids (the Desmidiales) often prefer bogs, peatlands, and lakes.[17]

Fossil record

Vegetative cells of the Zygnematophyceae are fragile and usually not preserved, but the zygospores are resistant to decay and can become fossilized. The Zygnematophyceae have been recorded from at least the middle Devonian period, and before the Carboniferous period, all the major groups had diverged. Fossils of zygospores are indicators of warming spring conditions and shallow, stagnant mesotrophic habitats.[7]

Genomes

The first genomes published for Zygnematophyceae were Mesotaenium endlicherianum and Spirogloea muscicola.[11] Since then, genomes have been published on Penium margaritaceum,[18] Zygnema spp.,[19] and the Closterium peracerosum–strigosum–littorale complex.[20] Furthermore, the gene models of Mesotaenium endlicherianum have been updated.[21]

References

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    ISBN 978-3-319-28149-0
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  8. S2CID 206569169
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  9. ^
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  10. ^ Zimmer, Carl (14 November 2019). "How Did Plants Conquer Land? These Humble Algae Hold Clues". The New York Times.
  11. ^
    PMID 31730849
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  12. ^ Ancient plants learned to survive on land by stealing other species' DNA
  13. PMID 17272304
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  14. PMID 37616005
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  15. ^ Guiry, M.D.; Guiry, G.M. "Zygnematophyceae". AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. Retrieved 2023-04-30.
  16. PMID 25810560
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  17. ISBN 978-0-12-385876-4
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  18. S2CID 218763002
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  19. PMID 36778228
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  20. S2CID 254918679
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  21. PMID 37640935
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