Polytomella

Polytomella
Polytomella agilis
Scientific classification
Clade:	Viridiplantae
Division:	Chlorophyta
Class:	Chlorophyceae
Order:	Chlamydomonadales
Family:	Dunaliellaceae
Genus:	Polytomella Aragão
Species
Polytomella agilis Polytomella caeca Polytomella capuana Polytomella magna Polytomella papillata Polytomella parva

Polytomella is a genus of green algae in the family Dunaliellaceae. It is widespread in freshwater habitats worldwide. ^[1]

Polytomella consists of single, cells that lack cell walls. Cells are ellipsoid, pyriform, or globose, and slightly metabolic (flexible). Cells have four anterior flagella arising from a central papilla. The posterior of the cell is usually rounded, rarely pointed or with spine-like extensions. Although classified as an alga, chloroplasts and pyrenoids are absent and cells instead have vestigial leucoplasts. The cell accumulates starch in its cytoplasm. A single stigma and two to four apical contractile vacuoles are typically present. The single nucleus is located in the central or anterior half of the cell. ^{[2] [1]}

Asexual reproduction occurs by longitudinal, binary division; sexual reproduction is isogamous with the zygotes giving rise to four motile cells. ^[1]

Polytomella is somewhat similar to Tetrablepharis , another colorless alga with four flagella, but Tetrablepharis has cell walls. Species are distinguished based on morphological characters such as the presence or absence of a papilla, shape of the cells, and position of intracellular features like starch granules. ^[3]

Evolution

Polytomella is a free-living, flagellated, nonphotosynthetic green alga with a highly reduced, linear fragmented mitochondrial genome. ^{[4] [5]} Polytomella, as it exists today, bears evidence of once having a functional photosynthetic plastid which has over evolutionary time changed such that it would appear now to have no genome or gene expressing mechanisms remaining to it. ^[6] Having transitioned completely to heterotrophy, Polytomella uses organic acids, alcohols and monosaccharides as its carbon source. ^{[5] [7] [8]} Despite being an evolutionary descendant of the green algae, Polytomella is a colourless organism because it has lost its photosynthetic ability. ^[8]

References

1. Guiry, M.D.; Guiry, G.M. "Polytomella". AlgaeBase . University of Galway.
2. Nakada, Takashi; Nozaki, Hisayoshi (2014). "Chapter 6. Flagellate Green Algae". In Wehr, John D.; Sheath, Robert G.; Kociolek, J. Patrick (eds.). Freshwater Algae of North America: Ecology and Classification (2 ed.). Elsevier Inc. pp. 265–313. ISBN   978-0-12-385876-4.
3. Ettl, H. (1983). Ettl, H.; Gerloff, J.; Heynig, H.; Mollenhauer, D. (eds.). Chlorophyta. 1. Teil / Part 1: Phytomonadina. Süßwasserflora von Mitteleuropa. Vol. 9. VEB Gustav Fischer Verlag. pp. XIV + 808. ISBN   978-3-8274-2659-8.
4. Smith, DR; Lee, RW (2011). "Nucleotide diversity of the colorless green alga Polytomella parva (Chlorophyceae, Chlorophyta): high for the mitochondrial telomeres, surprisingly low everywhere else". The Journal of Eukaryotic Microbiology. 58 (5): 471–3. doi:10.1111/j.1550-7408.2011.00569.x. PMID   21762422.
5. Inwood, W; Yoshihara, C; Zalpuri, R; Kim, KS; Kustu, S (November 2008). "The ultrastructure of a Chlamydomonas reinhardtii mutant strain lacking phytoene synthase resembles that of a colorless alga". Molecular Plant. 1 (6): 925–37. doi:10.1093/mp/ssn046. PMC   2902904 . PMID   19825593.
6. "Plant Phys". m.plantphysiol.org. Retrieved 2015-09-28.
7. Links, J.; Verloop, A.; Havinga, E. (December 1961). "Some growth experiments withPolytoma uvella on synthetic media". Antonie van Leeuwenhoek. 27 (1): 76–80. doi:10.1007/BF02538425.
8. Cruz, Vidal; Gittleson, Stephen (1981). "The genus Polytomella: A review of classification, morphology, life cycle, metabolism, and motility" . Archiv für Protistenkunde. 124 (1–2): 1–28. doi:10.1016/s0003-9365(81)80001-2 . Retrieved 25 September 2015.