''Closterium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of unicellular

charophyte Charophyta () is a group of freshwater green algae, called charophytes (), sometimes treated as a division, yet also as a superdivision or an unranked clade. The terrestrial plants, the Embryophyta emerged within Charophyta, possibly from terr ...

green algae The green algae (singular: green alga) are a group consisting of the Prasinodermophyta and its unnamed sister which contains the Chlorophyta and Charophyta/ Streptophyta. The land plants ( Embryophytes) have emerged deep in the Charophyte alg ...

in the family Closteriaceae.See the NCBIbr>webpage on Closterium
Data extracted from the

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

Species

''Closterium'' includes the following species: * '' C. acerosum'' * '' C. calosporum'' ** '' C. calosporum var. himalayense'' * '' C. cornu'' * '' C. ehrenbergii'' * '' C. gracile'' * '' C. incurvum'' * '' C. littorale'' * '' C. lunula'' * '' C. moniliferum'' * '' C. navicula'' * '' C. peracerosum'' * '' C. peracerosum-strigosum-littorale complex'' * '' C. pleurodermatum'' * '' C. pusillum'' * '' C. selenastrum'' * '' C. setaceum'' * '' C. spinosporum'' * '' C. tumidum'' * '' 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 charophycean

alga Algae ( , ; : alga ) are any of a large and diverse group of photosynthetic, eukaryotic organisms. The name is an informal term for a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from u ...

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. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respecti ...

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

clone Clone or Clones or Cloning or Cloned or The Clone may refer to: Places * Clones, County Fermanagh * Clones, County Monaghan, a town in Ireland Biology * Clone (B-cell), a lymphocyte clone, the massive presence of which may indicate a pathologi ...

s of cells ( homothallic), whereas others form zygospores between different clones of cells ( heterothallic). The heterothallic strains have two

mating type Mating types are the microorganism equivalent to sexes in multicellular lifeforms and are thought to be the ancestor to distinct sexes. They also occur in macro-organisms such as fungi. Definition Mating types are the microorganism equivalent to s ...

s, 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 spe ...

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

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately ...

, it produces minimal genetic variability.

Homothallism Homothallic refers to the possession, within a single organism, of the resources to reproduce sexually; i.e., having male and female reproductive structures on the same thallus. The opposite sexual functions are performed by different cells of a si ...

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 cellular organisms but may be ...

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

Fun facts

# The ends of the closterium are called polar vacuoles. # Inside the vacuoles are crystals called "gypsum crystals"

References

External links

Scientific references

Scientific databases

*
AlgaTerra database

Index Nominum Genericorum
Desmidiales Charophyta genera {{green algae-stub