Acetabularia
Acetabularia sp.
The screen algae (Latin Acetabularia ) are a genus of unicellular algae, which can be large between 0.5 and 10 inches. The genus consists of about 15 different species. The different types can be distinguished by the shape of the screen. Because of the incorporation of lime in their cell wall, the genus of algae screen is heavily involved in the creation process of a reef.
- 4.2.1 rhizoid of Parvocaulis parvulus and stem of A. acetabulum
- 4.2.2 rhizoid of A. acetabulum and stem of A. crenulata
- 4.2.3 rhizoid of A. crenulata and rhizoid of A. acetabulum
- 4.2.4 Two rhizoids of A. crenulata and a rhizoid A. acetabulum
- 4.2.5 Exchange of parts of plants
- 6.1 Notes and references
- 6.2 Books
- 6.3 External links
Habitat and Distribution
Algae from the family of screen algae are found in tropical and subtropical seas. In the Mediterranean and Eastern Atlantic on one often affects the types Parvocaulis parvulus (synonyms: Acetabularia parvula and Acetabularia wettsteinii ) and Acetabularia acetabulum to. (In most older books latter type is still out as A. mediterranea. Recent research showed, however, that A. mediterranea and A. acetabulum belong to the same species ). The type Acetabularia crenulata is another representative of this genus, it can be up to five inches long and is found in the Caribbean. Screen algae can also be found around the West Indies.
Construction
The Acetabularia cell can be externally divided into three sections:
All of these sections have specific functions.
The cell walls often exhibit strong calcium deposits. Another special feature is that no pyrenoids are present in the many small chloroplasts. This is not strength, but it can be formed fructosans, which are broken down with the help of insulin.
Life cycle
The life cycle of these algae genus is 3 years. In the adjacent figure it is shown on the example of A. acetabulum. The cyst wall ruptures in the fourth spring after the last passage through the cycle and sets many isogametes free ( image part 1). A merger takes place exclusively between isogametes same algae and various cysts instead (Fig. Part 2). It develops in the first year a first unseparated, upright tube (Fig. Part 3), later a rhizoid with Basalblase. In it, the zygote nucleus is included, which grows to the size of 100 microns zoom. It is then referred to as a primary core ( part of the image 4). In the fall of hose dies and the A. acetabulum wintered in rhizoid and in the Basalblase. In the spring of the second year Schirmalge forms an additional hose. He owns at its peak several whorls of branched dichotomous branchlets (Fig. Part 5 ). When autumn has arrived again, it stalls also this hose and the A. acetabulum goes to hibernation. The third year is marked by the preparation of propagation. It is formed a third tube at the end of a whorl forms with straight, wide, lobe-shaped protuberances (sector chambers ). We call these structures then shield or shield radiation. If the screen is formed, the primary core is divided into up to 15,000 haploid secondary cores, which are transported to the plasma flow to the shield beam. They are deposited uniformly on the cell wall and form cysts. There, their volume increases greatly and they will primary cyst nuclei. They are sharply defined, thick-walled, provided with lime scale and lids covers. There, the primary nuclei divide mitotically very active (Fig. Part 6). The hose withered and there remain only the left cysts, which are cysts in peace. At the end of the winter dormant period, the primary cyst nuclei divide meiotically and form again the isogametes ( image part 7).
This results in a diplohaplontischer (ie partly diplontischer, partly haplontischer ) course of development, although only one form, namely there is the gametophyte. Due to the meiotic division of the nucleus (or nuclei ) reduces the ploidy of the otherwise diploid gametophytes and he is in the last cycle of vegetation therefore haploid. Arising from the Gametenverschmelzung new screen algae are diploid again. One and the same biological form diploid or haploid is so (depending on the vegetation cycle).
Importance
The genus Acetabularia is of great importance in various fields. On the one hand in geology, as many fossils have been created by the strong calcification already mentioned. Ten of the species still in existence today can already be detected in the Cretaceous period. In nature, she takes a position as a Riffbildner. In science Acetabularia has an outstanding position. 1932, the evidence of the importance of the cell nucleus could be provided to her. At that time, a molecular investigation was impossible. The demonstration was conducted at the microscopic level. It used to various graft and sharing experiments. Some of them are presented below. General can be a tremendous regenerative capacity of these algae species recorded. It is for 3 to 7 months viable to remain in a position after the loss of the cell nucleus to produce cellulose and protein and to undergo morphogenesis.
Partition experiments
Amputation of the rhizoids
If the rhizoid is removed, is formed from the stem of a new rhizoid, but that has no nucleus. The cell can survive for several months under favorable conditions, but is not ready for reproduction.
Amputation of the hat
After the amputation, morphogenic substances is given by the nucleus from the command for distribution, which initiate formation of the hat after a short time.
Amputation of rhizoid and hat
The stem regenerates depending on where the division differently. The larger the piece the easier the missing piece is newly formed. One differentiates three scenarios:
Can be seen therefrom, a polar distribution of at least two regeneration morphogenic substances which are located in the opposing fabric gradient. The development of the regenerated depends on the amount of these substances. In seedless section, these substances are not regenerated.
Double regeneration experiment
In this experiment, it was shown that the nucleated piece substances responsible for the regeneration to be produced. It is carried out in two steps. First, a piece of the stem tip is removed and later the rhizoid. The stem tip was modeled, because the formation of substances have already been produced and then transported to the top. It follows that the cell nucleus is responsible for training.
Grafting experiments
Rhizoid of Parvocaulis parvulus and stem of A. acetabulum
A nucleated Rhizoid the type Parvocaulis parvulus is separated from its stalk and his hat and stem of A. acetabulum is grafted onto this rhizoid. It develop first - whorl A. acetabulum, but the severity of the hat is clearly Parvocaulis parvulus.
Rhizoid of A. acetabulum and stem of A. crenulata
In this experiment, a stem of the A. crenulata is grafted onto the rhizoid A. acetabulum. But the result is different from that of the previous experiment. The result is an intermediate hat. If this separated, then only a hat the A. acetabulum developed.
Rhizoid of A. crenulata and rhizoid of A. acetabulum
Verpfropft you two rhizoids different Acetabularia species, arise intermediate hats.
Two rhizoids of A. crenulata and a rhizoid A. acetabulum
With this combination, in turn arise intermediate hats, which, however, more of A. crenulata similar.
Exchange of plant parts
If you connect an old rhizoid with a young stem, thus slowing down the development process. If the ratio is the opposite of old and young, so this process is accelerated. The primary nuclear division process begins when the hat is fully formed. It moves in the amputation of the hat to the back. If the hat separated after the beginning of the decay process, the Schirmalge is no longer able to form a new hat. If a new hat grafted, then form cysts and proliferation process progresses.
System
- Acetabularia acetabulum (L.) PCSilva ( syn. Acetabularia mediterranea )
- 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
- Acetabularia schenckii K.Möbius
- Acetabularia toxasii Trono, AESantiago & Ganz. -Fort.