Chlorophyceae

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Chlorophyceae
Pediastrum.jpg
Light micrograph of Pediastrum sp.
Scientific classification OOjs UI icon edit-ltr.svg
Clade: Viridiplantae
Division: Chlorophyta
Clade: UTC clade
Class: Chlorophyceae
Wille in Warming, 1884 [1]
Orders

See text.

The Chlorophyceae are one of the classes of green algae, distinguished mainly on the basis of ultrastructural morphology. [2] They are usually green due to the dominance of pigments chlorophyll a and chlorophyll b. The chloroplast may be discoid, plate-like, reticulate, cup-shaped, spiral- or ribbon-shaped in different species. Most of the members have one or more storage bodies called pyrenoids located in the chloroplast. Pyrenoids contain protein besides starch. Some green algae may store food in the form of oil droplets. They usually have a cell wall made up of an inner layer of cellulose and outer layer of pectose.

Contents

General characteristics

Depending on the species, Chlorophyceae can grow unicellular (e.g. Chlamydomonas), colonial (e.g. Volvox ), filamentous (e.g. Ulothrix ), or multicellular.[ example needed ] They are usually green due to the presence of chlorophyll a and chlorophyll b; they can also contain the pigment beta-carotene. There are two clades of Chlorophyceae as defined by the arrangement of their flagella, called CW and DO. Members of the CW clade have flagella that are displaced in a "clockwise" (CW, 1–7 o'clock) direction e.g. Chlamydomonadales. Members of the DO clade have flagella that are "directly opposed" (DO, 12–6 o'clock) e.g. Sphaeropleales. [3]

The chloroplast may be discoid, cup-shaped (e.g. Chlamydomonas), spiral or ribbon shaped.[ example needed ] Most chlorophytes have one or more storage bodies called pyrenoids (central proteinaceous body covered with a starch sheath) that are localised around the chloroplast. Some algae may also store food in the form of oil droplets. The inner cell wall layer is made of cellulose and the outer layer of pectose.

Reproduction

Chlorophyceae can reproduce both asexually and sexually. Vegetative reproduction usually takes place by fragmentation. Asexual reproduction is by flagellated zoospores. And haplospore, perennation (akinate and palmella stage). Asexual reproduction by mitospore absent in spyrogyra. Also by aplanospores, hypnospores, Palmella stage, etc.

Sexual reproduction shows considerable variation in the type and formation of sex cells and it may be isogamous e.g. Chlamydomonas, Ulothrix, anisogamous e.g. Chlamydomonas, Eudorina or Oogamous e.g. Chlamydomonas, Volvox. Chlamydomonas has all three types of sexual reproduction.

They share many similarities with the higher plants, including the presence of asymmetrical flagellated cells, the breakdown of the nuclear envelope at mitosis, and the presence of phytochromes, flavonoids, and the chemical precursors to the cuticle. [4]

The sole method of reproduction in Chlorella is asexual and azoosporic. The content of the cell divides into 2,4 (B), 8(C) sometimes daughter protoplasts. Each daughter protoplast rounds off to form a non-motile spore. These autospores (spores having the same distinctive shape as the parent cell) are liberated by the rupture of the parent cell wall (D). On release each autospore grows to become a new individual. The presence of sulphur in the culture medium is considered essential for cell division. It takes place even in the dark with sulphur alone as the source material but under light conditions nitrogen also required in addition. Pearsall and Loose (1937) [5] reported the occurrence of motile cells in Chlorella. Bendix (1964) [6] also observed that Chlorella produces motile cells which might be gametes. These observations have an important bearing on the concept of the life cycle of Chlorella, which at present is considered to be strictly asexual in character.

Asexual reproduction in Chlorella ellipsoides has been studied in detail and the following four phases have been observed during the asexual reproduction.

  1. Growth phase - During this phase the cells grow in size by utilizing the photosynthetic products.
  2. Ripening phase - In this phase the cells mature and prepare themselves for division.
  3. Post ripening phase - During this phase, each mature cell divides twice either in dark or in light. The cells formed in dark are known as dark to light phase, cells again grow in size.
  4. Division phase - During this phase the parent cell wall ruptures and unicells are released.

Orders

As of May 2023, AlgaeBase accepted the following orders in the class Chlorophyceae:

Along with these genera, AlgaeBase recognizes several taxa that are incertae sedis (i.e. unplaced to an order):

Other orders that have been recognized include:

In older classifications, the term Chlorophyceae is sometimes used to apply to all the green algae except the Charales, and the internal division is considerably different.[ citation needed ]

See also

Related Research Articles

<span class="mw-page-title-main">Chlorophyta</span> Phylum of green algae

Chlorophyta is a division of green algae informally called chlorophytes.

<i>Chlamydomonas</i> Genus of algae

Chlamydomonas is a genus of green algae consisting of about 150 species of unicellular flagellates, found in stagnant water and on damp soil, in freshwater, seawater, and even in snow as "snow algae". Chlamydomonas is used as a model organism for molecular biology, especially studies of flagellar motility and chloroplast dynamics, biogenesis, and genetics. One of the many striking features of Chlamydomonas is that it contains ion channels (channelrhodopsins) that are directly activated by light. Some regulatory systems of Chlamydomonas are more complex than their homologs in Gymnosperms, with evolutionarily related regulatory proteins being larger and containing additional domains.

<span class="mw-page-title-main">Chlamydomonadales</span> Order of green algae

Chlamydomonadales, also known as Volvocales, are an order of flagellated or pseudociliated green algae, specifically of the Chlorophyceae. Chlamydomonadales can form planar or spherical colonies. These vary from Gonium up to Volvox. Each cell has two flagella, and is similar in appearance to Chlamydomonas, with the flagella throughout the colony moving in coordination.

<span class="mw-page-title-main">Sphaeropleales</span> Order of algae

Sphaeropleales is an order of green algae that used to be called Chlorococcales. The order includes some of the most common freshwater planktonic algae such as Scenedesmus and Pediastrum. The Sphaeropleales includes vegetatively non-motile unicellular, colonial, or filamentous taxa. They have biflagellate zoospores with flagella that are directly opposed in direction : Sphaeroplea, Atractomorpha, Neochloris, Hydrodictyon, and Pediastrum. All of these taxa have basal body core connections. Motile cells generally lack cell walls or have only a very fine layer surrounding the cell membrane. Other common characteristics include a robust vegetative cell wall, cup-shaped chloroplasts with large pyrenoids, and relatively large nuclei.

<span class="mw-page-title-main">Chlamydomonadaceae</span> Family of algae

Chlamydomonadaceae is a family of algae within the order Chlamydomonadales. Traditionally, it has been defined as containing single-celled flagellates with a cell wall.

The Palmellaceae are a family of green algae, specifically of the Chlamydomonadales. Members of this group are typically found in atmophytic or terrestrial habitats, or as phycobionts associated with lichens; a few are found in fresh water.

<span class="mw-page-title-main">Selenastraceae</span> Family of algae

Selenastraceae is a family of green algae in the order Sphaeropleales. Members of this family are common components of the phytoplankton in freshwater habitats worldwide. A few species have been found in brackish and marine habitats, such as in the Baltic Sea.

<i>Ankistrodesmus</i> Genus of algae

Ankistrodesmus is a genus of green algae in the family Selenastraceae. It is one of the most common types of phytoplankton in freshwater habitats around the world.

Asteromonas is a genus of green algae in the family Asteromonadaceae. It has been described from saline, marine, and brackish environments. It is closely related to the genus Dunaliella, another genus common in saline waters.

<i>Carteria</i> Genus of algae

Carteria is a genus of green algae in the family Chlamydomonadaceae. Carteria are similar in morphology to the common genus Chlamydomonas and differ by having four, rather than two, flagella at the vegetative stage.

<i>Chlamydocapsa</i> Genus of algae

Chlamydocapsa is a genus of green algae, specifically of the Chlorophyceae.

<i>Chloromonas</i> Genus of algae

Chloromonas is a genus of green algae in the family Chlamydomonadaceae. It is closely related to the model green algae, Chlamydomonas, and traditionally has been distinguished mainly through the absence of a pyrenoid.

Planktosphaeria is a genus of Chlorophyceae of the green algae. It was first described by the phycologist Gilbert Morgan Smith in 1918, with Planktosphaeria gelatinosa as its type species. Species of Planktosphaeria are commonly found in freshwater plankton around the world.

Treubaria is a genus of green algae, the sole genus in the family Treubariaceae. Treubaria is found in freshwater habitats and has a cosmopolitan distribution.

<span class="mw-page-title-main">Actinochloridaceae</span> Family of algae

Actinochloridaceae is a family of green algae, in the order Chlamydomonadales.

Deuterocharacium is a genus of green algae in the family Characiaceae. It is found in freshwater habitats, attached to algae or detritus. It is rare and has only been recorded from Europe.

Chlorotetraedron is a genus of green algae, in the family Neochloridaceae. The name may also be written as Chlorotetraëdon. It is found as freshwater plankton or in soil.

Follicularia is a genus of green algae, in the family Schizochlamydaceae. It is found in terrestrial habitats, mainly soil.

<i>Chlorokybus</i> Genus of basal green algae

Chlorokybus is a multicellular (sarcinoid) genus of basal green algae or charophyte. It has been classified as the sole member of the family Chlorokybaceae, which is the sole member of the order Chlorokybales, in turn the sole member of the class Chlorokybophyceae. It grows on soil and rock surfaces, and is rare.

Bracteamorpha is a genus of green algae in the order Sphaeropleales, and is the only genus in the family Bracteamorphaceae. It contains a single species, Bracteamorpha trainorii.

References

  1. ↑ Warming, E., 1884. Haandbog i den systematiske botanik. Anden gjennemsete udgave. 2nd ed. Kjøbenhavn, 434 pp. German translation (1890) of the 2nd Danish edition available at archive.org: . English translation (1895) of the 3rd Danish edition (1892) available at archive.org: .
  2. ↑ Štenclová, Lenka, Karolina Fučíková, Jan Kaštovský, and Marie Pažoutová (December 2017). "Molecular and morphological delimitation and generic classification of the family Oocystaceae (Trebouxiophyceae, Chlorophyta)". Journal of Phycology. 53 (6): 1263–1282. Bibcode:2017JPcgy..53.1263S. doi:10.1111/jpy.12581. PMID   28833138. S2CID   21278460 – via PubMed.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  3. ↑ Lewis, Louise A. and Richard M. McCourt (2004-10-01). "Green algae and the origin of land plants". American Journal of Botany. 91 (10): 1535–1556. doi:10.3732/ajb.91.10.1535. PMID   21652308 – via onlinelibrary.wiley.com.
  4. ↑ Raven, Evert and Eichhorn. The Biology of Plants 7th edition, pg. 335. W. H. Freeman and Company, New York, 2005.
  5. ↑ Pearsall WH, Loose L (1937). "The Growth of Chlorella Vulgaris in Pure Culture". Proc Roy Soc B. 121 (824): 451–501. doi:10.1098/rspb.1936.0075 . Retrieved 2024-08-13.
  6. ↑ Bendix S (1964-01-22). "Phenotypic Variability in Certain Chlorella pyrenoidosa Strains". Phycologia. 4 (2): 84–92. Bibcode:1964Phyco...4...84B. doi:10.2216/i0031-8884-4-2-84.1.
  7. ↑ Guiry, M.D.; Guiry, G.M. "Dunaliella". AlgaeBase . World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
  8. ↑ Guiry, M.D.; Guiry, G.M. "Chlorococcum". AlgaeBase . World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
  9. ↑ Guiry, M.D.; Guiry, G.M. "Microspora". AlgaeBase . World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
  10. ↑ Guiry, M.D.; Guiry, G.M. "Tetraspora". AlgaeBase . World-wide electronic publication, National University of Ireland, Galway. Retrieved 2022-02-25.
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