Golden algae

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The division of living beings into systematics is a continuous subject of research. Different systematic classifications exist side by side and one after the other. The taxon treated here has become obsolete due to new research or is not part of the group systematics presented in the German-language Wikipedia.

Drawing of Ochromonas sp.

The golden algae (Chrysophyta) are in some systematic classifications a division within the realm of the protists (Protista), they are assigned to the sub- realm of the stramenopiles (Stramenopila). However, the taxonomic rank of the golden algae is not generally recognized. The groups of golden-brown algae (Chrysophyceae), diatoms (Bacillariophyceae) and golden-green algae are classified as separate groups within the stramenopile.

Mark

The characteristics of the golden algae are mainly of an electron microscopic nature. A fold of the endoplasmic reticulum that surrounds the plastids is common to all species . Another feature is the arrangement of the thylakoids in stacks of three.

Most species are monadal protozoa without a cell wall, some of them are also grouped in colonies. Almost all morphological levels of organization except parenchymatic thalli occur in the department. Amoeboid ( Rhizochysis ), capsale ( Chrysocapsa ), coccal ( Chrysosphaera ), trichal ( Phaeothamnion ) forms or tissue thalli ( Thallochrysis ) are rare . Most species have the heteroconous flagellation typical of the stramenopiles . They have a long draw scourge and a shorter drag scourge . The scourge is directed forward and covered with two rows of stiff side hairs, the mastigonemen .

Structural formula of fucoxanthin , which gives the golden algae their typical color.

As a rule, gold algae have two chloroplasts with the chlorophylls a and c and, in terms of quantity, predominantly the carotenes α- and β-carotene, which cover the green chlorophyll color. Many species form the dye fucoxanthin , a xanthophyll that gives the plastids a golden brown to brown color. Other xanthophylls that occur in the golden algae are diatoxanthin , diadinoxanthin and neoxanthin . In some species you can also find zeaxanthin , antheraxanthin , violaxanthin and α-cryptoxanthin .

The majority of golden algae have no cell walls. However, some species (for example in the genus Dinobryon ) form a cellulose-containing casing. Some golden algae are covered on their cell surface by finely structured silica scales (genera Synura and Mallomonas ). These scales are formed in vesicles close to the chloroplast and deposited in finished form on the cell surface. Some species (for example in the genus Dictyocha ) also have an inner pebble shell .

Another typical feature is the eye spot (stigma). It is located within the chloroplast under a thickened plasma layer at the beginning of the dragging whip, the flagellum swelling. They are tiny droplets of lipids with red colored carotenoids . In addition, there is a photoreceptor directly on the swelling of the flagella . Depending on the incidence of light, the eye spot casts a shadow on this receptor. This enables the cell to perceive the direction of the incidence of light ( phototaxy ). The golden algae react positively phototactically to a weak light source, that is, they move towards it. They react negatively phototactically to a strong light source.

Way of life and occurrence

Different diets can be found in the golden algae. Most golden algae are photoautotrophic and have one or two chloroplasts. Numerous golden algae are mixotrophic . You can use both organic carbon in dissolved form and inorganic carbon through photosynthesis. For example, the species Ochromonas granularis can live in a sucrose solution without any light .

There are also species that live phagotrophically . They actively absorb carbon and other organic substances in the form of larger particles up to small living bacteria with the help of pseudopodia and can also do without photosynthesis. Other species have a completely heterotrophic diet and have no chloroplasts, so photosynthesis is not possible.

The typical reserve product of the golden algae is chrysolaminarin , a 1,3-β-linked glucan ( polysaccharide ). Fat droplets stored in vacuoles often serve as reserve substances.

Golden algae are found mainly in fresh water (especially in light and cool water), less often in brackish or salt water. In the oceans, they probably play an important role as primary producers of nanoplankton . The phagotrophic golden algae are also of great importance in the food competition in lakes , since they can use bacteria as a source of food.

Propagation and Stages of Persistence

Golden algae reproduce mainly asexually through cell division. Sexual reproduction in the form of isogamy has only been observed in a few species .

Many species form permanent stages ( cysts ) in order to survive unfavorable living conditions. They are endogenous cysts, the walls of which are made of silica . Endogenous cysts are formed inside the cell by a vesicle filled with silica , which attaches itself under the plasma lemma. When the cyst formation is complete, the plasma that is now on the outside is broken down. When the environmental conditions improve, the algae are released again. The cysts have a shape typical of the golden algae and can easily be preserved as fossils .

Systematics

The following groups are counted among the golden algae:

According to the system of Adl et al. (2005), however, these groups are classified directly in the stramenopile, the Chrysophyta does not exist in this systematics.

See also

literature

  • Christian van den Hoek, Hans M. Jahns, David G. Mann: Algae . 3. Edition. Georg Thieme Verlag, Stuttgart 1993, ISBN 3-13-551103-0 .

Individual evidence

  1. ↑ 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 .

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