Wednesday 25 April 2012


In January, I attended the ASE Annual Conference in Liverpool. Among all the many amazing demonstrations, talks, workshops and exhibits, I got chatting to some of the representatives from SAPS, who were showing off a new protocol for plant totipotency experiments.

For those readers for whom organisms have to have been dead for a few million years before they're worth studying, totipotency refers to the ability of plant cells to differentiate into any other cell in the plant. Our cells lose that ability a few days after fertilisation, but the few that remain are referred to as stem cells. So basically all plant cells are stem cells if you like.

Last year, we did the standard Edexcel protocol of decapitating mustard explants and growing them in agar. Despite relatively good hygiene, this was mostly an exercise in just how filthy my AS students were - you should have seen what grew in the agar, and none of the growing things were mustard explants. Little grey worm things, anyone?

Being not overly optimistic about this year's students' personal hygiene, I was keen to try out an alternative route, and SAPS had a good protocol. It's so elegantly simple. Plain agar is used rather than nutrient agar, and it's made up using Milton tablets. A fresh cauliflower should be used, but the tiniest bits can be used, so with the leftovers the technicians can have cauliflower cheese for their lunch.

About three weeks before the Easter holidays, my AS groups did the plant totipotency practical. Just before the Easter holiday it was clear the experiment had worked, as bits were turning photosynthetic, but we decided to keep the experiment running for as long as possible.

All this came out of a couple of tiny little florets, no more than 3-4mm wide. There are some proper leaves, up at the top of the plant. But this one was really impressive:

Can you see a purple patch over on the right hand side? That is a cauliflower flower!

I am so delighted with this practical - I think of all the AS and A2 ones I've done this year, this has been my favourite. Some students' cauliflowers did not take to differentiating - for some students there was a pretty obvious explanation (they suspended it halfway down the agar column, completely suffocating it but preserving it beautifully), but others just went a little brown and sat there. I had about a dozen vials across both groups, and four of them worked superbly, which is a better success rate than the old root tip squash (another old faithful A-level practical).

I'm very grateful to SAPS for their advice - they were really helpful when we were having difficulties tracking down plain agar, and they even e-mailed me when they saw me chatting on Twitter to another teacher about the protocol.

Now I'm just going to see how long we can keep these little baby cauliflowers growing...

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