Acetabularia

The name, Acetabularia, derives from the Latin word acetabulum, a broad, shallow cup used for dipping bread; the upturned cap of Acetabularia resembles such a cup. For this reason, it is also sometimes called mermaid's wineglass.[8]

In the 19th century, the same designation Acetabularia was proposed by George Edward Massee for a genus of fungi (now Cyphellopus), but this usage is obsolete and considered invalid as the algal name takes precedence.[9]

Acetabularia, as well as being unicellular, is also a uninucleate organism. It has three basic parts: its rhizoid, a short set of root-like appendages that contain the nucleus and anchor the cell to fissures in a substrate; its median stalk, which accounts for most of its length; and its apex, where its cap forms. There are usually several whorls of hair-like appendages close to the apex.

Acetabularia are among the largest single-celled organisms, having also a remarkably large nucleus. During sexual reproduction, the nucleus undergoes multiple rounds of mitosis, forming many daughter nuclei all within one nuclear membrane. These nuclei undergo meiosis and are transported to the tips of the branches, the sporangia, where they are released as gametes.[10]

Each Acetabularia cell is composed of three segments: the "foot" or basal segment which contains the nucleus, the "stalk", and the "cap". Hämmerling exchanged caps between individuals from two species, A. mediterranea and A. crenulata. A. mediterranea has a smooth, disc-shaped cap, while A. crenulata has a branched, flower-like cap.

After the exchange, each transplanted cap gradually changed from its original form to the form typical for the species of the base it was now attached to. This showed that the nucleus controlled the form of the cap.

In another experiment, Hämmerling inserted a nucleus from one species of Acetabularia into an intact Acetabularia of a different species. The Acetabularia then produced a hybrid cap with characteristics of both species. This showed that both nuclei influenced the form of the cap.[7] Hammerling's results showed that the nucleus of a cell contains the genetic information that directs cellular development.

Although a single cell, Acetabularia exhibits a remarkably complex shape and has therefore long been a model organism for studying gene expression and morphogenesis. It seems to transport messenger RNA molecules (in an inactive riboprotein form) from the nucleus to its apical tips, where they are translated into proteins. These molecules may be activated by proteolysis of their protein carrier molecules, but this has not been verified as yet.

In addition to its gradient in specific mRNA molecules, Acetabularia exhibits concentration gradients in several types of molecules, such as ascorbic acid.

Acetabularia has been used to study circadian rhythms.[11] Studies have shown Acetabularia has a diurnal circadian rhythm.[12] These rhythmic changes in respiratory and photosynthetic activity are maintained under constant conditions, even with the removal of the nucleus, showing the regulation of the rhythm is independent of the nucleus.[13] However, the nucleus isn't completely uninvolved, as it is responsible for the shifting of the cycles due to external changes. In one experiment a nucleus from a specimen trained on one circadian rhythm was transplanted into a de-nucleated plant on a rhythm that differed by 12 hours, over a period of days the donated nucleus changed the circadian rhythm of the receiving organism to that of the donor organism.[13]

Acetabularia species occasionally make their way into the aquarium trade. They are generally considered to be more difficult or unappealing macroalgae to care for in the reef aquarium, a fish-only, or a FOWLR (Fish Only With Live Rock) system, as they are delicate, readily eaten by herbivorous fish, grow slowly, and do not have the high nutrient uptake that reef aquarium refugium species (such as Chaetomorpha and Caulerpa) do. However, they are suitable for a macroalgae display tank, and thus macroalgae suppliers often carry species of Acetabularia.

• Largest organisms

• Serio, Donatella; Alongi, Giuseppina; Catra, Marcello; Cormaci, Mario; Furnari, Giovanni (1 January 2006). "Changes in the benthic algal flora of Linosa Island (Straits of Sicily, Mediterranean Sea)". Botanica Marina. 49 (2). doi:10.1515/BOT.2006.018. S2CID 84853252.
• Berger, Sigrid; Liddle, Larry B. (March 2003). "The life cycle of Acetabularia (Dasycladales, Chlorophyta): textbook accounts are wrong". Phycologia. 42 (2): 204–207. doi:10.2216/i0031-8884-42-2-204.1. S2CID 84575637. ProQuest 198599797.
• Berger, Sigrid; Fettweiss, Ulrike; Gleissberg, Stefan; Liddle, Larry B.; Richter, Ursula; Sawitzky, Heiko; Zuccarello, Giuseppe C. (September 2003). "18S rDNA phylogeny and evolution of cap development in Polyphysaceae (formerly Acetabulariaceae; Dasycladales, Chlorophyta)". Phycologia. 42 (5): 506–561. doi:10.2216/i0031-8884-42-5-506.1. S2CID 83544153. ProQuest 198633648.
• Bonotto, Silvano (February 1994). "Developmental biology of Acetabularia". Journal of the Marine Biological Association of the United Kingdom. 74 (1): 93–106. doi:10.1017/S0025315400035694. S2CID 84105975.
• Berger S, de Groot E, Heuhaus G, Schweiger M (1987). "Acetabularia: a giant single cell organism with valuable advantages for cell biology". European Journal of Cell Biology. 44: 349–370.
• Puiseux-Dao S (1970). Acetabularia and Cell Biology. New York: Springer Verlag. ISBN 0-236-17738-9.
• Schweiger, H. G. (1969). "Cell Biology of Acetabularia". Current Topics in Microbiology and Immunology. Vol. 50. pp. 1–36. doi:10.1007/978-3-642-46169-9_1. ISBN 978-3-642-46171-2. PMID 4907132.

Wikimedia Commons has media related to Acetabularia.

• www.accessexcellence.org
• Berger, Sigrid (2006).- Photo-Atlas of living Dasycladales.- ISBN 2-916733-01-9, Carnets de Géologie, Brest, Book / Livre 2006/02 (CG2006_BOOK_02), 348 p., 1 fig., 332 micrographs.
• UTEX culture collection of algae, at the University of Texas at Austin
• CCAP: Culture Collections of Algae and Protozoa