Field of Science

Sunday Protist resumed: Acetabularia

I've been thoroughly neglecting Archaeplastida... probably because I see its representatives everyday anyway. Archaeplastida is the superkingdom containing Glaucophytes, red algae, green algae and land plants*. Archaeplastids are characterised by primary plastid endosymbiosis, so most of them are photosynthetic. Hopefully I'll get around to discussing some exceptions later...

Since I like large complicated cells, today's menu features Acetabularia:

(UBC Botanical Garden)

Each of those umbrella-like things is a single uninucleate cell up to 6cm tall. At the base of the stalk is the rhizoid containing the nucleus. This little detail turned out to be extremely useful for establishing the cell organelle responsible for heredity back in the 30's by Hämmerling. A couple species of Acetabularia produce morphologically distinct caps, so Hämmerling cut off the caps and exchanged the stalks between the two species. The morphology of the regenerating cap was determined by the species of the nucleus-containing rhizoid, not the stalk: thereby strongly supporting the central role of the nucleus in heredity and the cell's 'information'.

I'd love to study cell morphogenesis in that thing! There seems to be a bit of work done on it here and there, but it is far from model organism status. Doesn't seem to have its genome sequenced yet, although I may be wrong on that. Being a unicellular organism relatively close to land plants, it could reveal some insights about plant cell development and evolution. The size would be wonderful for studying cytoskeletal dynamics. Acetabularia was at one point used as a model for circadian rhythm studies - it maintains its rhythm in the absence of the nucleus, implying a cytosolic component to biological clock regulations (briefly mentioned here).

However, for all I know, it may be hard to culture, do genetics with, etc.

(personally, I still prefer ciliates... ^_^ )

*Archaeplastida is also alternatively called Plantae, but I resent that naming. After being taught for so long that plants are the terrestrial multicellular green stuff, and being proud of recognising that 'seaweeds' aren't plants after all... they suddenly decide to name the whole freaking group Plants. Sorry, no. I find it rather unsettling when some protistologists refer to red algae or prasoniphytes as 'plants'. The conventional plants are refered to as 'land plants' (which I'm fine with to avoid confusion; although botanists give me funny looks when I do that...) Furthermore, the name Archaeplastida makes sense, since this group is defined by having plastids from primary endosymbiosis. Everything else got their plastids from them via secondary and tertiary endosymbiosis.
orry, but your Chlamydomonas is not a freaking plant, kthx.


  1. For some reason I find large single-celled organisms to be gross. Especially the one that makes its shell from its own waste product.
    This one, however, doesn't gross me out. But I do find it very strange that a single cell can grow so huge and maintain such a complex structure.

  2. That is a beautiful picture!
    I've only seen Acetabularia in preserved formalin disected sections before :)


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