Eye animals
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| Bütschli , 1884 |
Eye animals ( Euglena ) form a genus of flagellated eukaryotic unicellular organisms from the class of the Euglenoida . It is named after the eye spot (stigma), which is not a primitive eye, but a pigment spot that shadows a photoreceptor and thus enables the eye animal to move depending on the direction of the light - a phenomenon called phototaxis .
features
Representatives of the genus Euglena have longitudinally ovoid or elongated cells that can appear in cylindrical, flattened or corkscrew-like twisted shape. Photosynthetically active Euglena species are colored green by the chlorophylls a and b contained in the chloroplasts . They can move forward in the water by means of a single flagellum that is inserted at the front pole and arises from a flagellum sac. The eye animals move around a central axis on a spiral curve. A second flagella is greatly shortened and does not protrude from the flagellum sac. On it is the para-flagellar body, a light-sensitive organelle that is functionally related to the eye-spot or stigma. During the rotation of Euglena around the longitudinal axis, the eye spot, a lipid vesicle filled with carotenoids , periodically shadows the light receptor of the paraflagellar body. This enables Euglena to register the direction of incidence of the light and show a corresponding phototaxis . One cytostome is missing. Since Euglena shows both plant and animal characteristics, a clear assignment to the plant or animal kingdom was not previously possible.
Way of life
Most eye animals contain chloroplasts with the green pigments chlorophyll a and b. With their help, they carry out photosynthesis (phototrophic nutrition). The representatives of the genus Euglena , however, are not completely autotrophic, since they also depend on the uptake of organic substances from the surrounding medium. Under certain circumstances, some species adopt a heterotrophic diet: They then temporarily reduce their chlorophyll and live on organic substances that are ingested by pinocytosis . Almost all Euglena species (with the exception of some marine forms) live in freshwater.
The reproduction of Euglena takes place - as with all Euglenoida - exclusively asexually by longitudinal division. Observations of sexual processes could never be confirmed.
Phototaxis (light orientation)
Euglena is able to perceive the direction and intensity of the light and react to it. This ability is known as phototaxis. With moderate to high light intensities, Euglena swims towards the light source (positive phototaxis). The point of this behavior is to be seen in the fact that Euglena visits places that allow the best possible photosynthesis. At very high light intensities, Euglena swims away from the light source (negative phototaxis). Very high light intensities could damage the photosynthetic system of Euglena . The basis of the phototaxis of Euglena is the interaction of the paraflagellar body and the eye spot (stigma). Due to the rotating movement, the eye-spot shadows the paraflagellar body at regular intervals. Depending on the relationship between the direction of swimming and the direction of the incident light, this shading pattern changes and Euglena can deduce the direction of the light from it.
Systematics and evolution
The systematics of the genus Euglena was thoroughly revised on the basis of molecular biological findings. The genus Euglena therefore only includes phototrophic or secondary osmotrophic Euglenidae with a flexible pellicle . Also new is that the species Astasia longa and Khawkinea quartana are now integrated into the genus Euglena as Euglena longa and Euglena quartana . The basis for this is the knowledge that these two organisms descend from green, Euglena- like ancestors and have lost the ability to photosynthesize again in the course of evolution. Euglena longa still has plastids, but these are greatly reduced and no longer photosynthesize. These heterotrophic species, which can be proven to have descended from phototrophic ancestors, are known as secondary osmotrophs.
Some species of the genus Euglena
- Euglena Carterae
- Euglena deses
- Euglena ehrenbergii
- Euglena gracilis
- Euglena haematoda
- Euglena intermedia
- Euglena longa (formerly Astasia longa )
- Euglena pisciformis
- Euglena quartana (formerly Khawkinea quartana )
- Euglena sanguinea
- Euglena terricola
- Euglena texta
- Euglena variabilis
- Euglena viridis
Former Euglena species, which are now grouped into other genera
- Lepocinclis acus (formerly Euglena acus )
- Lepocinclis oxyuris (formerly Euglena oxyuris )
- Lepocinclis platydesma (formerly Euglena platydesma )
- Lepocinclis spirogyroides (formerly Euglena spirogyra )
- Lepocinclis tripteris (formerly Euglena tripteris )
use
The phototrophic species Euglena gracilis is of particular importance as a model organism in research . For example, researchers are interested in the basic functioning of phototaxis and gravitaxis .
The Japanese company euglena Co., Ltd. would like to use eye animals as animal feed , components of cosmetics, food or nutritional supplements as well as fuels in order to create a sustainable carbon cycle .
Individual evidence
- ↑ a b c Gordon F. Leedale, Keith Vickerman : Euglenozoa , In: John J. Lee, GF Leedale, P. Bradbury (Eds.): An Illustrated Guide to the Protozoa . tape 2 . Allen, Lawrence 2000, ISBN 1-891276-23-9 , pp. 1141-1143 .
- ↑ schulbiologiezentrum.info: Working aid 3:20 p.m. “Euglena / Augentierchen” (PDF; 469 kB) , accessed on January 7, 2011
- ↑ B. Marin, A. Palm, M. Klingberg, M. Melkonian: Phylogeny and taxonomic revision of plastid-containing euglenophytes based on ssu rDNA sequence comparisons and synapomorphic signatures in the ssu rRNA secondary structure . In: Protist . tape 154 , 2003, p. 99-145 (English).
- ^ W. Hachtel: A plastid genome in the heterotrophic flagellate Astasia longa . In: Endocytobiosis and Cell Research . tape 12 , 1998, pp. 191-193 (English).
- ^ V. Daiker, DP Häder, PR Richter, M. Lebert: The involvement of a protein kinase in phototaxis and gravitaxis of Euglena gracilis . In: Planta . tape 233 , no. 5 , May 2011, p. 1055-62 , PMID 21286747 .
- ↑ Company Vision. (No longer available online.) Euglena Co., archived from the original on August 8, 2012 ; accessed on August 13, 2012 . Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
Web links
- Tree of Life Web Project : Euglena
- Euglena Ehrenberg 1838. Retrieved August 20, 2012 (English).
- The eye animal Euglena: A unicellular flagellum carrier of fresh water
Paramecium (2007) | Tetrahymena (2009) | Eye animals (2010) | Dictyostelium (2011) | Acanthamoeba (2012) | Actinophrys (2013) | Trumpet Animals (2014) | Vampire Amoeba (2015) | Trichomonas (2016) | Diaphanoeca grandis (2017) | Dictyocysta mitra (2018) | Nuclearia (2019)