Tag Archives: research

We have DNA

DNA of Pseudopanax on agarose gel after electrophoresis

DNA of Pseudopanax on agarose gel after electrophoresis

The first step after collecting samples for genetic analyses is to extract the DNA. Lara and I do this for lancewood and five-finger plants (Pseudopanax) by:

  • freezing a small piece of leaf tissue in liquid nitrogen (-196 degrees C !) and grinding it as finely as possible.
  • adding a detergent to release the DNA from the cells of the leaf tissue.
  • adding chloroform.  The detergent and chloroform do not mix (like oil and water), but proteins and other things we do not want are drawn into the chloroform while the DNA is left in the detergent.
  • the detergent layer is removed, and alcohol is added to it.  This precipitates the DNA (i.e., makes it turn into a solid), and we can actually see it.  I don’t have any pictures of Pseudopanax DNA, but precipitated DNA all looks much the same – see this link.

It is possible to extract DNA using household items (see this link).

In order to analyse the DNA further we have to make it go back into solution. The alcohol is tipped off, and a small amount of salt solution is added; the DNA ‘dissolves’ in this.

To test the quality and quantity of the extracted DNA, we run a small amount of the DNA solution on an agarose gel in a process called electrophoresis (see link).

In the gel above, each lane corresponds to a separate sample, except the right-most lane which is a ‘ladder’ for sizing the DNA samples. A negative charge was applied at the top and a positive charge at the bottom. DNA is negatively charged, so its moves towards a positive charge.

The bright blobs indicated by the green arrow indicate that we got high quality (the DNA is in big pieces, as it hasn’t moved very far) and quantity (a brighter stain indicates more DNA) for most of these samples, which is great!

The sample labelled 5957 (my collection number) is a bit weak, while we didn’t get anything for sample 5964.

These DNA extractions are all from samples of fierce lancewood (Pseudopanax ferox), except 5966 which is P. macintyrei.

Adult tree of fierce lancewood, Pseudopanax ferox.

Adult tree of fierce lancewood, Pseudopanax ferox.

 

Pseudopanax macintyrei.

Pseudopanax macintyrei.

The next step in assessing the relationships of these plants is to genetically ‘fingerprint’ them.

Lancewood hunting

Field-work is one of the best aspects of working as a Natural Environment curator at Te Papa. I get to spend about three weeks a year in the field collecting plant specimens.

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Te Papa’s 4WD. If seen outside Wellington, there is a good chance this vehicle is being used to collect plants, whales, or fossils.

I’ve recently returned from ten days field-work in the South Island, collecting samples for our research on lancewood (horoeka, Pseudopanax crassifolius) and fierce lancewood (P. ferox). This is in collaboration with Lara Shepherd from Massey University. Lancewood is a common forest tree and we are using DNA analyses to determine where it survived in New Zealand during the last glacial period. This follows our previous research on the forest fern Hooker’s spleenwort (Asplenium hookerianum), which seems to have survived throughout New Zealand, and conflicts with evidence that Metrosideros trees (rata and pohutukawa) were confined to only a few refugia.

Fierce lancewood, named for its bigger ‘teeth’ on the leaf margins, is more sparsely distributed that lancewood. Given the discontinuous distribution of fierce lancewood, we expected each population to exhibit its own diagnostic set of genetic variation. Preliminary results suggest this might be true for Auckland and Wellington populations, but, at this stage, we can’t genetically distinguish populations from the southern South Island, indicating the geographic discontinuity there is a geologically-recent phenomenon. We collected specimens to augment our existing sampling (the northern South Island, in particular, was a bit of a gap for us for both lancewood and fierce lancewood).

pseudopanax_ferox_juvenile_leaf1
Apex of a leaf from a juvenile fierce lancewood, showing the curious ‘paint-splash’ coloration. I have heard it hypothesised that the prominent white splashes draw attention to the marginal ‘teeth’, themselves a putative defence against moa herbivory.

The trip was largely successful, with the weather good and the plants cooperative (in that we could find them where they were supposed to be). We now have to process the samples in the laboratory, which isn’t nearly as much fun but still necessary if we are to address the questions we’re interested in.

pseudopanax_ferox_juvenile2

A juvenile of fierce lancewood.

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