Botany Photo of the Day

Connor Fitzpatrick is the author of today's write-up. Connor writes:

Commonly known as mermaid's wineglasses, this algae comes courtesy of shyzaboy@Flickr during a beach exploration of the Grand Bahama Island. Given its location, it's very likely that this species is either Acetabularia crenulata or Acetabularia schenckii. The former has a large distribution: from coastal Florida, throughout the Gulf of Mexico and into Venezuela, the Caribbean Islands, India, the Philippines, and Australia. Acetabularia schenckii can be found off Florida, throughout the Gulf of Mexico and the northern coast of South America, although it has never been documented in the Bahamas.

The Acetabularia genus belongs to the Polyphysaceae family and contains twelve species. Like all other algae of the order Dasycladales, the Acetabularia are unicellular with a single nucleus (uninucleate). The thallus of the organism consists of a cap, a stalk, and a rhizoid, in which the nucleus can be found. Sexual reproduction is initiated with the formation of the cap at the stalk apex, at which point the nucleus undergoes a meiotic division followed by a series of mitotic divisions. The newly formed haploid nuclei travel up the stalk into the cap along with most of the cell contents. After this takes place the junction between the cap and stalk closes and gametangial walls begin to form enclosing the nuclei. The gametes are produced and released. Upon meeting, two gametes of opposite mating types will fuse and a new individual will form from the germinating zygote.

Another species of the genus, Acetabularia acetabulum, has proven instrumental in early studies of cell differentiation. In 1932, J.Hammerling conducted various experiments in which he grafted the enucleated (without a nucleus), cytoplasmic stalk portions of Acetabularia acetabulum onto a nucleate stalk of another species. The cap that grew from this individual was intially that of an Acetabularia acetabulum species, but if this cap was cut off the proceeding one would be that of the other species. Further experimentation led Hammerling to conclude that the regulation of cell differentiation took place in the cytosplasm, through the process called translation. Up until this point, it was believed that this regulation took place in the nucleus, through the process of transcription. Read more research on the ability of an enucleated fragment of Acetabularia mediterranea to initiate a cap (PDF).

The findings from early studies with Acetabularia helped clarify the central dogma of molecular biology, something which I had implicitly assumed to be indisputable. I guess being in school at a time when nothing but this dogma seems so absolute, it's hard for me to imagine a time when this wasn't the case. Thanks again to shyzaboy for a great shot! (original via BPotD Flickr Pool).