Mesostigma

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Mesostigma
Systematics
Domain : Eukaryotes (eukaryota)
without rank: Diaphoreticks
without rank: Archaeplastida
without rank: Chloroplastida
without rank: Charophyta
Genre : Mesostigma
Scientific name
Mesostigma
Lauterborn , 1894

Mesostigma is a genus of green algae that is at the base of the entire group of chloroplastida . There are two types in fresh water.

features

The alga is a unicellular organism with two flagella of approximately the same length . The diameter is 11 to 25 micrometers. The cells are very flattened and saddle-shaped. The flattening is along the longitudinal axis. The two flagella start in the middle of the flat cell, the scourge pit is difficult to see. The basal body or its transition region is similar to that of the streptophytina . The eye spot is pale and sits at the rear end.

The cell wall consists of cellulose . Scales of different sizes sit on the surface and on the flagella. They grow up to a micrometer in size. They cover the cell evenly and completely. Each cell has a disc-shaped chloroplast with two pyrenoids on the edge . In Mesostigma grande the pyrenoids missing. The chloroplast is usually bulging at the edges and appears ring-shaped in the apical view. Chlorophyll a and b occur in photosynthetic pigments . The chloroplast is surrounded by a double membrane, there is no periplastidic endoplasmic reticulum . Starch is made within the chloroplast. There are several contractile vacuoles near the scourge pit .

Mesostigma swims sideways with rotational movements. The two flagella beat unevenly.

Reproduction occurs through asexual cell division. Sexual reproduction is unknown.

Occurrence

Mesostigma occurs in fresh water in stagnant waters, mostly in rather small numbers.

Systematics

The systematic position of the genus is not entirely clear. The flagellum structure is similar to the Charophyta. Phylogenetic studies based on rbcL sequences and four-gene analyzes (rbcL, atpB, nad5 and 18S rDNA) saw Mesostigma as a sister group of the Charophyta . Several other studies saw them as the sister group of all other chloroplastida , i.e. the most basic group. This view is supported by the presence of the dye 9'-cis- neoxanthin , while all other chloroplastida have trans-neoxanthin. In any case, mesostigma is very close to the base of all green algae (chloroplastida).

There are two kinds:

literature

  • Sina M. Adl, Alastair GB Simpson, Mark A. Farmer, Robert A. Andersen, O. Roger Anderson, John A. Barta, Samual S. Bowser, Guy Bragerolle, Robert A. Fensome, Suzanne Fredericq, Timothy Y. James, Sergei Karpov, Paul Kugrens, John Krug, Christopher E. Lane, Louise A. Lewis, Jean Lodge, Denis H. Lynn, David G. Mann, Richard M. McCourt, Leonel Mendoza, Øjvind Moestrup, Sharon E. Mozley-Standridge, Thomas A. Nerad, Carol A. Shearer, Alexey V. Smirnov, Frederick W. Spiegel, Max FJR Taylor: The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists. The Journal of Eukaryotic Microbiology 52 (5), 2005; Pages 399-451. doi : 10.1111 / j.1550-7408.2005.00053.x .
  • Louise A. Lewis, Richard M. McCourt: Green Algae and the origin of land plants : American Journal of Botany 91 (10), 2004, pages 1535-1556. Abstract and full text
  • Karl-Heinz Linne von Berg, Michael Melkonian u. a .: The Kosmos algae guide. The most important freshwater algae under the microscope. Kosmos, Stuttgart 2004, ISBN 3-440-09719-6 , p. 58.

Individual evidence

  1. ↑ summarized in Lewis and McCourt: Green Algae and the origin of land plants , 2004.

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