Hammerling's Acetabularia

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Hämmerling's Acetabularia

Context: In the late 1930's J. Hämmerling was wondering where the genetic traits were stored inside the eukaryotic cell. Soon afterwards in 1944, Avery, MacCleod and McCarty showed that the traits were stored in a chemical called DNA - but that was in prokaryotic cells. How Hammerling went about doing this was one of the truly elegant and simple experiments in biology.

He started out with using some types of green algae of the Order of Dasycladales that were called Acetabularia. The morphologies of two species are shown to the left. Of particular interest to him were that these were single celled organisms, and they were asymmetical - meaning that he could discern different parts of a cell from each other.

He then figured that if the "traits" were bundled up in some manner and not distributed all throughout the cell, by merely cutting the cells in half and seeing which part could regenerate would be a pretty good hint as to where the "traits" resided in the cell. As you can see from the figure at the left, the heads of the algae withered when detached, and only the feet regenerated. Hence, he was pretty sure that the "traits" were somewhere stored in the feet of these algae.

He then got another bright idea that would conclusively show that the traits for each species resided in the feet. What he wanted to do was switch the top halves of each alga with the feet of the other. But first he had to make sure that his idea had a chance of working. He needed to do a control operation. He merely snipped off the top of a cell and then tried grafting it back onto its base. And he watched the grafted cell carefully to make sure that the top half didn't merely wither away, to be replaced by one regenerated by the base. His control, or "sham experiment" is shown to the right.

Now he was sure that his "surgical" techniques were working, so he went into the transplant business - switching top halves. Again he watched his "patients" carefully, and what he saw is shown below. After switching, no parts of the morphological hybrids withered, but over time the top halves slowly changed or "morphed" into the form that was dictated by the "traits'" instructions in the respective bases.

And, just to make sure, he went to higher power in his microscope to make sure that the feet contained that thing called a nucleus. They did! Hence, Hammerling concluded that the genes or traits resided in the nucleus - all of the cell's traits, and not just some of them. Why all? Because the cells could do all the steps of their life-cycles.


 


* Hämmerling, J. 1953. Nucleo-cytoplasmic relationships in the development of Acetabularia. J. Intern. Rev. Cytol. 2: 475-498. (Interestingly this was the same great year that Watson and Crick published their double helix paper, and when Jonas Salk started dispensing his anti-polio vaccine.)


How do we know that photosynthesis resides in chloroplasts? Endenmann's Expt

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