| Closterium | |
|---|---|
 | |
| Closterium sp. | |
Scientific classification  | |
| (unranked): | Viridiplantae |
| (unranked): | Charophyta |
| Class: | Zygnematophyceae |
| Order: | Desmidiales |
| Family: | Closteriaceae |
| Genus: | Closterium Nitzsch ex Ralfs, 1848 |
| Species | |
See text. | |
Closterium is a genus of desmid, a group of charophyte green algae. [1] It is placed in the family Closteriaceae. [2] Species of Closterium are a common component of freshwater microalgae flora worldwide. [3]
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 and manganese compounds. [2] The cell nucleus is located in the middle of the cell. Each semicell contains a single axial chloroplast dotted with several pyrenoids. [4]
At either end of the cell, there is a generally a polar vacuole. The vacuoles often contain conspicuous barium sulfate crystals. [4]
Closterium regulare was first described from Lower Normandy by Brebisson. [5]
Closterium includes the following species:
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, isogamous charophycean alga cells that is the closest unicellular relative to land plants. These algae are capable of forming two types of dormant diploid zygospores. 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 pheromones termed protoplast-release inducing proteins produced by mt(-) and mt(+) cells facilitate this process. [6]
A homothallic strain of Closterium forms selfing zygospores via the conjugation of two sister gametangial cells derived from one vegetative cell. [7] Conjugation in the homothallic strain occurs mainly at low cell density and is regulated by an ortholog of a heterothallic sex-specific pheromone.
Although self-fertilization employs meiosis, 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 recombinational repair of DNA damages that can be caused by a stressful environment [8]
Like other desmids, Closterium is found in freshwater habitats. Closterium is usually attached to sediments or aquatic plants, but may sometimes be planktonic, i.e. free-floating in the water column, or found in wet soils. [4] Most species prefer oligotrophic and slightly acidic waters, but a few species (for example Closterium aciculare ) prefer eutrophic, slightly alkaline lakes. [3]
Volvox is a polyphyletic genus of chlorophyte green algae in the family Volvocaceae. Volvox species form spherical colonies of up to 50,000 cells, and for this reason they are sometimes called globe algae. They live in a variety of freshwater habitats, and were first reported by Antonie van Leeuwenhoek in 1700. Volvox diverged from unicellular ancestors approximately 200 million years ago.
Paramecium is a genus of eukaryotic, unicellular ciliates, commonly studied as a model organism of the ciliate group. Paramecium are widespread in freshwater, brackish, and marine environments and are often abundant in stagnant basins and ponds. Because some species are readily cultivated and easily induced to conjugate and divide, they have been widely used in classrooms and laboratories to study biological processes. The usefulness of Paramecium as a model organism has caused one ciliate researcher to characterize it as the "white rat" of the phylum Ciliophora.
Dictyostelium is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores. Though they are Protista and in no way fungal, they traditionally are known as "slime molds". They are present in most terrestrial ecosystems as a normal and often abundant component of the soil microflora, and play an important role in the maintenance of balanced bacterial populations in soils.
Desmidiales, commonly called the desmids, are an order in the Charophyta, a division of green algae in which the land plants (Embryophyta) emerged. Desmids consist of single-celled microscopic green algae. Because desmids are highly symmetrical, attractive, and come in a diversity of forms, they are popular subjects for microscopists, both amateur and professional.
The green algae 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 alga as a sister of the Zygnematophyceae. Since the realization that the Embryophytes emerged within the green algae, some authors are starting to include them. The completed clade that includes both green algae and embryophytes is monophyletic and is referred to as the clade Viridiplantae and as the kingdom Plantae. The green algae include unicellular and colonial flagellates, most with two flagella per cell, as well as various colonial, coccoid and filamentous forms, and macroscopic, multicellular seaweeds. There are about 22,000 species of green algae. Many species live most of their lives as single cells, while other species form coenobia (colonies), long filaments, or highly differentiated macroscopic seaweeds.
Heterothallic species have sexes that reside in different individuals. The term is applied particularly to distinguish heterothallic fungi, which require two compatible partners to produce sexual spores, from homothallic ones, which are capable of sexual reproduction from a single organism.
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 structures, from mycelia of the same or different mating types, and may be chlamydospores. In many eukaryotic algae, including many species of the Chlorophyta, zygospores are formed by the fusion of unicellular gametes of different mating types.
Micrasterias is a unicellular green alga of the order Desmidiales. Its species vary in size reaching up to hundreds of microns.
Characiosiphon is a genus of green algae in the family Characiosiphonaceae. It contains a single species, Characiosiphon rivularis.
Cosmarium is a genus of freshwater organisms belonging to the Charophyta, a division of green algae from which the land plants (Embryophyta) emerged.
Desmidium is a genus of green algae, specifically of the Desmidiaceae.
Pleurotaenium is a genus of green algae, specifically of the desmids (Desmidiaceae).
Spinoclosterium is a genus of green algae, specifically of the Closteriaceae. It is rare, but widely distributed in freshwater regions throughout the world.
Staurodesmus is a genus of green algae, specifically of the Desmidiaceae.
Triploceras is a genus of desmid in the family Desmidiaceae.
Xanthidium is a genus of green algae, specifically of the Desmidiaceae.
Zygnematophyceae is a class of green algae in the paraphylum streptophyte algae, also referred to as Charophyta, consisting of more than 4000 described species. The Zygnematophyceae are the sister clade of the Embryophyta.
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 single mycelium.
Cosmarium botrytis is a species of green algae in the family Desmidiaceae. It is a freshwater species with a worldwide distribution, and has been recorded from all continents.
Prescottiella is a genus of green algae in the family Desmidiaceae, containing the single species Prescottiella sudanensis. Originally classified as Micrasterias sudanensis in 1958, it was moved into its own genus by Carlos E. M. Bicudo in 1976, due to its asymmetric character. It is named after Gerald Webber Prescott, an American phycologist.
