Coleochaete

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Coleochaete
Coleochaete orbicularis (top picture)

Coleochaete orbicularis (top picture)

Systematics
without rank: Charophyta
without rank: Phragmoplastophyta
without rank: Coleochaetophyceae
Order : Coleochaetales
Family : Coleochaetaceae
Genre : Coleochaete
Scientific name
Coleochaete
Brébisson , 1844

Coleochaete is a genus of green algae from the Charophyta group . They grow epiphytically in fresh water on aquatic plants , less often on inorganic hard substrates such as cans or plastic thrown into the water.

description

Species of the genus form (haploid) thalli from cell threads, which are variable in shape depending on the species. Most species form beds of densely packed threads that are reminiscent of tissue and are therefore called pseudoparenchyma , but in some species the threads are also loosely branched. Three basic types can be distinguished: Some types consist of two types of filaments (heterotrich), with one type of filament that crawls on the substrate surface and extending upright filaments that form pillow-shaped beds ( e.g. Coleochaete pulvinata ). In other species the upright (prostrate) threads are missing, their thalli consist only of loosely growing creeping cell threads (for example Coleochaete divergens ). In other species only the prostrate threads are present, but these form a dense, mutually fused pseudoparenchymal bed of disk-shaped form (for example Coleochaete scutata ).

In all species, the cell threads are single-row (uniseriat) and forked (densely) or branched irregularly. In the prostrate cell filaments the individual cells are hexagonal (hexagonal) or polygonal, in the upright elongated cells. Each cell has a nucleus and only one, plate-shaped wall-mounted (parietal) chloroplast , each with a conspicuous pyrenoid (rarely several). Vegetative cells are noticeable by the cell hairs called setae that protrude at right angles and are anchored in the cell wall in a structure called blepharoplast. The base of the seta is usually enclosed in a gelatinous sheath. The setae are used as defense mechanisms against herbivores, broken setae release a deterrent substance. The characteristic setae, which are covered by a sheath, gave the genus its name (from Greek koleon: sheath, quiver and chaetos: hair).

Multiplication and life cycle

Coleochaete reproduces both asexually and sexually. During asexual reproduction, a double flagellated zoospore is formed from each cell , which has no eye spot. Zoospores are released through a special pore in the cell wall through which they emerge with amoeboid movements. After a swimming phase, they settle on a suitable substrate, absorb the flagella and secrete a cell wall; from this a thallus grows like the parent organism. Zoospores can occur year round, but are most common in early summer. Alternatively, under unfavorable environmental conditions, very thick-walled, non-chiseled spores, so-called aplanospores, are formed.

During sexual reproduction, depending on the species, there are thalli in which both sexes are formed on one individual (monoecious or homothallic) and those in which they sit on different individuals, i.e. these are male or female (dioecious or heterothallic). As in the case of vascular plants, the male plants, called antheridia , are several at the tip of the cell threads. Each antheridium produces only a single spermatozoid , flagellated by two flagella , which can be colorless or green. The terminal or marginal female systems or oogonia remain on the mother organism, they are not released. They are usually bottle-shaped and develop a neck-shaped extension of the cell wall, which is called trichogyne. In ripe oogonia, the tip of the appendage opens, substances are released into the water that attract the spermatozoids. After the penetration of a spermatozoid and fertilization, the trichogyne is separated by a septum. After fertilization, the oogonia of Coleochaete become very large (up to 150 micrometers) due to the storage of reserve substances from the maternal organism. They form a massive cell wall, which is also enveloped by cell threads growing out of the maternal organism, which form a closed pseudoparenchymal shell or cortex. This structure later turns brown and is then called the spermocarp. It remains after the mother organism dies and hibernates. Under favorable environmental conditions, meiosis and then mitotic divisions occur until about 8 to 32 daughter cells are formed. Each of these cells eventually transforms into a flagellated meiozoospore, which is released after the shell is torn open, from which a new thallus is formed after it has settled.

ecology

The species of the genus live in fresh water in stagnant waters such as lakes, growing up on hard substrates, mostly epiphytic on aquatic plants or the submerged shoots of reed plants such as cattails . They also colonize chandelier algae , especially of the genera Chara and Nitella , where they rarely penetrate inside, i.e. grow endophytically. They are less common on other hard substrates of all kinds, in aquariums they often grow on the glass panes. The European and North American species clearly prefer nutrient-poor (oligotrophic) waters and disappear with eutrophication . Little is known about the biology of tropical species.

Phylogeny and Systematics

The genus is led, with three other, species-poor and little-known genera in a family Coleochaetaceae, which is the only family that makes up the order Coleochaetales. With the order of the Chaetosphaeridiales (with the best known genus Chaetosphaeridium ) this forms the class Coleochaetophyceae.

The peculiar sexual reproduction of the Coleochaete species and other similarities such as the formation of a phragmoplast and other biochemical and ultrastructural characteristics have given botanists theories since the beginning of the 20th century that the genus could be a model for the origin of land plants . After phylogenomic investigations, in which the relationship is determined by comparing the sequences of homologous genes, these together with the chandelier algae (Charales) and the land plants form a clade called Charophyta . However, there is still no agreement between different studies about the position within the Charophyta. Some see them as a sister group of the ornamental algae (Zygnematophyceae), but this is not always confirmed in other analyzes. Possibly they are actually more closely related to the land plants than the candelabrum algae, which would confirm earlier speculations about sexual reproduction.

species

In the database Algaebase about 25 species names described so far are listed for the genus. Depending on the investigator, about 10 to 12 species are recognized as valid. In the better known algae flora of Europe and North America, seven more common species are given.

swell

  • M. Arora and D. Sahoo: Growth Forms and Life Histories in Green Algae. In: Dinabandhu Sahoo, Joseph Seckbach (editors): The Algae World. Springer Verlag, Dordrecht etc., 2015. ISBN 978-94-017-7320-1 . on pages 162–166.
  • Linda E. Graham (1984): Coleochaete and the Origin of Land Plants. American Journal of Botany 71 (4): 603-608. JSTOR 2443336
  • John D. Wehr & Robert G. Sheath: Freshwater Algae of North America. Ecology and Classification. Elsevier (Academic Press), Amsterdam etc. 2003. ISBN 978-0-12-741550-5 .
  • CF Delwiche, KG Karol, MT Cimino, KJ ​​Sytsma: Phylogeny of the genus Coleochaete (Coleochaetales, Charophyta) and related taxa inferred by analysis of the chloroplast gene rbc {L}. Journal of Phycology 38, 2002: pp. 394-403.

Individual evidence

  1. ↑ Cedric Finet, Ruth E. Timme, Charles F. Delwiche, Ferdinand Marletaz (2012): Multigene Phylogeny of the Green Lineage Reveals the Origin and Diversification of Land Plants. Current Biology 22: 1456-1457. doi: 10.1016 / j.cub.2012.07.021
  2. ↑ Charles Francis Delwiche & Endymion Dante Cooper (2015): The Evolutionary Origin of a Terrestrial flora. Current Biology 25: R899-R910. doi: 10.1016 / j.cub.2015.08.029
  3. ↑ Frederik Leliaert, Heroen Verbruggen, Frederick W. Zechman (2011): Into the deep: New discoveries at the base of the green plant phylogeny. Bioessays 33: 683-692. doi: 10.1002 / bies.201100035
  4. ↑ Mark N. Puttick, Jennifer L. Morris, Tom A. Williams, 2 Cymon J. Cox, 5 Dianne Edwards, 4 Paul Kenrick, Silvia Pressel, Charles H. Wellman, Harald Schneider, Davide Pisani, Philip CJ Donoghue (2018) : The Interrelationships of Land Plants and the Nature of the Ancestral Embryophyte. Current Biology 28: 733-745. doi: 10.1016 / j.cub.2018.01.063
  5. ↑ Guiry, MD & Guiry, GM 2018. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. www.algaebase.org, accessed March 7, 2018

Web links

Commons : Coleochaete  - collection of images, videos and audio files