Umbrella algae
| Umbrella algae | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
Acetabularia , drawing by Ernst Haeckel 1904 |
||||||||||||
| Systematics | ||||||||||||
|
||||||||||||
| Scientific name | ||||||||||||
| Acetabularia | ||||||||||||
| JVLamour. |
The umbrella algae (Latin Acetabularia ) are a genus of marine unicellular algae , the species of which can be between 0.5 and 10 centimeters in size. The genus includes 12 species, which are differentiated based on the shape of their umbrella.
Occurrence
The genus is common in tropical and subtropical seas. A. mediterranea lives in the Mediterranean Sea and in the adjacent Eastern Atlantic. The umbrella algae had their heyday in the Triassic and Jura .
description
The unicellular thallus of a umbrella alga consists of a root-like rhizoid with which the alga is stuck on a substrate, a thin (approx. 1 mm thick) stem and the umbrella that gives it its name. The size varies, depending on the species, between one and six centimeters, the diameter of the umbrella between 0.5 and 1.5 cm. Whorls of lateral outgrowths sit on the stalk and are thrown off after a while like the leaves of trees. The screen consists of 30–75 radial chambers. The wall of the thallus is more or less heavily calcified. The interior is occupied by a large vacuole , around which numerous chloroplasts circulate in the peripheral cytoplasm ( plasma flow ).
Development and reproduction
The duration of the life cycle of the umbrella algae varies depending on the species and within the range (degree of latitude) of a species. For a long time the alga only has a very large diploid cell nucleus (primary nucleus ) located in the rhizoid. After the formation of the screen, meiosis takes place , i.e. the transition to the haploid phase, and the subsequent mitoses result in numerous haploid secondary nuclei that migrate into the chambers of the screen. With the formation of thick cell walls, mononuclear cysts initially develop there , in which, however, further mitoses take place until finally there are 20–50 two-flagellated gametes in each cyst . When the umbrella breaks down at the end of the growing season, the cysts become free as a permanent stage. At a later time, they release the gametes by opening a lid. The union of gametes of different sexes - which do not differ externally (isogamy) - creates the diploid zygote , which attaches itself to a suitable substrate and grows into a new alga.
meaning
The genus Acetabularia is of great importance in various areas. On the one hand in geology , as the already mentioned heavy calcium deposits resulted in a great number of fossils . Ten of the species that still exist today can already be identified in the Cretaceous period. In nature it takes on a position as a reef builder . Acetabularia also has an outstanding position in science . In 1932 it was able to prove the importance of the cell nucleus. At that time a molecular biological investigation was impossible. Evidence was provided at the microscopic level . Various grafting and division experiments were used for this purpose . Some of them are presented below. In general, this type of algae has an enormous regenerative capacity. After the loss of the cell nucleus, it is able to remain viable for 3 to 7 months, to produce cellulose and protein and to undergo form formation.
Division experiments
- Amputation of the rhizoid
When the rhizoid is removed, a new rhizoid is formed from the stem, but it has no nucleus. The cell can survive for a few more months under favorable conditions, but is no longer capable of reproduction.
- Amputation of the hat
After the amputation, the cell nucleus gives the command to release morphogenic substances, which after a short time initiate a new formation of the hat.
- Amputation of the rhizoid and hat
The stem regenerates differently depending on the location of the division. The larger the piece, the easier it is to recreate the missing piece. A distinction is made between 3 scenarios:
- The stalk is separated just above the rhizoid. This leads to the formation of two seedless rhizoids.
- A piece of stalk is taken approximately from the middle between the rhizoid and the hat. As a result, a seedless rhizoid and a hat are formed.
- Remove a piece of the stem from below the hat and remove the rhizoid as well. As a result, a normal hat and a "worried hat" are formed instead of the rhizoid.
From this one can see a polar distribution of at least 2 morphogenic regeneration substances, which are in the opposite substance gradient. The development of the regenerate depends on the amount of these substances. In the seedless section, these substances are no longer regenerated.
- Double regeneration attempt
In this experiment it was proven that the substances responsible for regeneration are produced from the nucleated piece. It is carried out in two steps. First a piece of the stem tip is removed and later the rhizoid too. The tip of the handle was reproduced because the educational substances were already produced and then transported into the tip. It follows that the cell nucleus is responsible for training.
Grafting tests
- Rhizoid of Parvocaulis parvulus and stalk of A. acetabulum
A nucleated rhizoid of the species Parvocaulis parvulus is separated from its stalk and cap, and the stalk of A. acetabulum is grafted onto this rhizoid. A. acetabulum whorls develop first , but the expression of the cap is clearly Parvocaulis parvulus .
- A. acetabulum rhizoid and A. crenulata stalk
In this experiment, a stalk of the A. crenulata is grafted onto the rhizoid of the A. acetabulum . The result differs from that of the previous experiment. An intermediate hat is created. If this is separated, only a cap of the acetabulum artery develops .
- Rhizoid of the A. crenulata and rhizoid of the A. acetabulum
Verpfropft to two different Rhizoide Acetabularia - species , so intermediate hats arise.
- Two rhizoids of the A. crenulata and one rhizoid A. acetabulum
This combination again creates intermediate hats, which, however, more closely resemble the A. crenulata .
- Exchange of plant parts
If you connect an old rhizoid to a young stem, the development process slows down. If the relationship between old and young is opposite, this process is accelerated. The primary core division process does not begin until the hat is fully formed. It shifts backwards when the hat is amputated. If the hat is cut off after this disintegration process has started, the peak can no longer form a new hat. If a new hat is grafted on, cysts form and the process of reproduction continues.
Systematics
- Acetabularia acetabulum (L.) PCSilva
- Acetabularia antillana (Solms) Egerod
- Acetabularia calyculus J.V. Lamour .
- Acetabularia crenulata J.V. Lamour.
- Acetabularia dentata Solms
- Acetabularia farlowii Solms
- Acetabularia kilneri J. Agardh
- Acetabularia major G. Martens
- Acetabularia myriospora A.B. Joly & Cord.-Mar.
- Acetabularia peniculus (R.Br. ex Turner) Solms
- Acetabularia ryukyuensis Okamura & Yamada
- Acetabulariaschenckii K.Möbius
- Acetabularia toxasii Troño, AESantiago & Ganz.-Fort.
Web links
Individual evidence
- ↑ AlgaeBase Taxonomy Browser: Genus: Acetabularia , accessed on May 11, 2018.
- ↑ Lexicon of Biology : Dasycladales . Spectrum, Heidelberg 1999.
- ↑ a b AlgaeBase: Acetabularia (click on the magnifying glass for Acetabularia), accessed on May 12, 2018.
- ^ Joachim W. Kadereit, Christian Körner, Benedikt Kost, Uwe Sonnewald: Strasburger Textbook of Plant Sciences . Springer Spectrum, Berlin / Heidelberg 2014, p. 597.