''Closterium'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of desmid, a group of

charophyte Charophyta () is a paraphyletic group of freshwater green algae, called charophytes (), sometimes treated as a division, yet also as a superdivision. The terrestrial plants, the Embryophyta emerged deep within Charophyta, possibly from terres ...

green algae The green algae (: green alga) are a group of chlorophyll-containing autotrophic eukaryotes consisting of the phylum Prasinodermophyta and its unnamed sister group that contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ...

.See the

NCBI The National Center for Biotechnology Information (NCBI) is part of the National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The NCBI is loca ...

br>webpage on Closterium
Data extracted from the It is placed in the family Closteriaceae. Species of ''Closterium'' are a common component of freshwater

microalgae Microalgae or microphytes are microscopic scale, microscopic algae invisible to the naked eye. They are phytoplankton typically found in freshwater and marine life, marine systems, living in both the water column and sediment. They are unicellul ...

flora worldwide.

Description

''Closterium'' is a diverse genus consisting of solitary cells, each made of two identical halves called semicells. Usually they are microscopic, but the largest can become easily visible to the naked eye. Cells are many times longer than broad, and are variously elongate to lunate (crescent-shaped). The poles are rounded, truncated, or pointed. The surface of the cell may be smooth or decorated with various features, such as striations or punctae. The cell wall is transparent, but with age it may become dark brown due to accumulated

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

and

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

compounds. The

cell nucleus The cell nucleus (; : nuclei) is a membrane-bound organelle found in eukaryote, eukaryotic cell (biology), cells. Eukaryotic cells usually have a single nucleus, but a few cell types, such as mammalian red blood cells, have #Anucleated_cells, ...

is located in the middle of the cell. Each semicell contains a single axial

chloroplast A chloroplast () is a type of membrane-bound organelle, organelle known as a plastid that conducts photosynthesis mostly in plant cell, plant and algae, algal cells. Chloroplasts have a high concentration of chlorophyll pigments which captur ...

dotted with several

pyrenoid Pyrenoids are sub-cellular phase-separated micro-compartments found in chloroplasts of many algae,Giordano, M., Beardall, J., & Raven, J. A. (2005). CO2 concentrating mechanisms in algae: mechanisms, environmental modulation, and evolution. ''An ...

s. At either end of the cell, there is a generally a polar

vacuole A vacuole () is a membrane-bound organelle which is present in Plant cell, plant and Fungus, fungal Cell (biology), cells and some protist, animal, and bacterial cells. Vacuoles are essentially enclosed compartments which are filled with water ...

. The vacuoles often contain conspicuous

barium sulfate Barium sulfate (or sulphate) is the inorganic compound with the chemical formula Ba SO4. It is a white crystalline solid that is odorless and insoluble in water. It occurs in nature as the mineral barite, which is the main commercial source of ...

crystals.

Taxonomy

''Closterium regulare'' was first described from Lower Normandy by Brebisson.Carter, C.F. and Williamson, D.B. (2008) A rediscovered UK desmid: ''Closterium regulare'' Breb ''The Phycologist.'' Autumn 2008 No.75:24 The name comes from the Greek word ''klosterion'', meaning a small spindle.

Species

''Closterium'' includes the following species (incomplete): * '' C. abruptum'' * '' C. acerosum'' * '' C. aciculare'' * '' C. acutum'' * '' C. angustum'' * '' C. archerianum'' * '' C. baillyanum'' * '' C. braunii'' * '' C. calosporum'' * '' C. closterioides'' * '' C. cornu'' * '' C. costatum'' * '' C. delpontei'' * '' C. dianae'' * '' C. didymotocum'' * '' C. directum'' * '' C. ehrenbergii'' * '' C. elongatum'' * '' C. exile'' * '' C. gracile'' * '' C. idiosporum'' * '' C. incurvum'' * '' C. intermedium'' * '' C. jenneri'' * '' C. juncidum'' * '' C. karnakense'' * '' C. kuetzingii'' * '' C. leibleinii'' * '' C. limneticum'' * '' C. lineatum'' * '' C. littorale'' * '' C. lunula'' * '' C. moniliferum'' * '' C. navicula'' * '' C. nematodes'' * '' C. parvulum'' * '' C. peracerosum'' * '' C. peracerosum-strigosum-littorale complex'' * '' C. praelongum'' * '' C. pritchardianum'' * '' C. pronum'' * '' C. pseudolunula'' * '' C. pusillum'' * '' C. ralfsii'' * '' C. rectimarginatum'' * '' C. rostratum'' * '' C. selenaeum'' * '' C. setaceum'' * '' C. strigosum'' * '' C. striolatum'' * '' C. submoniliferum'' * '' C. subulatum'' * '' C. tumidulum'' * '' C. tumidum'' * '' C. turgidum'' * '' C. venus'' * '' C. wallichii''

Reproduction

Asexual: binary fission from a partitioned parent cell. Sexual: Conjugation to form a hypnozygote. The ''Closterium peracerosum-strigosum-littorale (C. psl)'' complex is a

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

isogamous Isogamy is a form of sexual reproduction that involves gametes of the same morphology (indistinguishable in shape and size), and is found in most unicellular eukaryotes. Because both gametes look alike, they generally cannot be classified as ma ...

charophycean

alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...

cells that is the closest unicellular relative to land plants. These algae are capable of forming two types of dormant

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

zygospore A zygospore is a diploid reproductive stage in the life cycle of many fungi and protists. Zygospores are created by the nuclear fusion of haploid cells. In fungi, zygospores are formed in zygosporangia after the fusion of specialized budding stru ...

s. Some populations form zygospores within single clones of cells ( homothallic), whereas others form zygospores between different clones of cells ( heterothallic). The heterothallic strains have two mating types, mt(-) and mt(+). When cells of opposite mating types are mixed in a nitrogen-deficient mating medium, mt(-) and mt(+) cells pair with each other and release protoplasts. This release is then followed by protoplast fusion (conjugation) leading to formation of a diploid zygospore. Sex

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

s termed protoplast-release inducing proteins produced by mt(-) and mt(+) cells facilitate this process. A homothallic strain of Closterium forms selfing zygospores via the conjugation of two sister gametangial cells derived from one vegetative cell. Conjugation in the homothallic strain occurs mainly at low cell density and is regulated by an

ortholog Sequence homology is the biological homology between DNA, RNA, or protein sequences, defined in terms of shared ancestry in the evolutionary history of life. Two segments of DNA can have shared ancestry because of three phenomena: either a speci ...

of a heterothallic sex-specific pheromone. Although self-fertilization employs

meiosis Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

, it produces minimal genetic variability. Homothallism is thus a form of sex that is unlikely to be adaptively maintained by a benefit related to producing variability. However, homothallic meiosis may be maintained in ''Closterium peracerosum'' as an adaptation for surviving under stressful conditions such as growth in nitrogen depleted media at low cell density. A proposed adaptive benefit of meiosis is the promotion of

homologous recombination Homologous recombination is a type of genetic recombination in which genetic information is exchanged between two similar or identical molecules of double-stranded or single-stranded nucleic acids (usually DNA as in Cell (biology), cellular organi ...

al repair of DNA damages that can be caused by a stressful environment

Habitats

Like other desmids, ''Closterium'' is found in

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

habitats. ''Closterium'' is usually attached to sediments or aquatic plants, but may sometimes be

planktonic Plankton are the diverse collection of organisms that drift in water (or air) but are unable to actively propel themselves against currents (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they pro ...

, i.e. free-floating in the water column, or found in wet soils. Most species prefer oligotrophic and slightly acidic waters, but a few species (for example '' Closterium aciculare'') prefer eutrophic, slightly alkaline lakes.

References

External links

AlgaTerra database

Index Nominum Genericorum
{{Taxonbar, from=Q141751 Desmidiales Charophyta genera