After spending a whole summer teaching on a different campus where it wasn’t feasible to keep up my garage-style experiments on Juglone, I am finally back at my home campus. One of the first things I did to avoid writing syllabi and setting up turnitin.com accounts was to try to repeat a previous experiment whose goal was to figure out if I could use a seed germination assay to quantitate juglone levels. In that experiment I took the stereotypically virologist approach by diluting my extract out and testing for inhibition of seed germination. Theoretically, there should be a dilution at which I should achieve 50% inhibition and if two samples (different trees, different parts of same tree or maybe the same tree at different times of the year) contain different amounts of juglone, I may be able to see that. There are all kinds of reasons why this might not work (sensitivity being a huge potential problem), but the beauty of all this is that I’m not under a grant deadline and real soon, I will be able to have my students asking real questions with this assay. Its also ridiculously cheap and easy to do.
Naturally, as I walk out in the forest to that same walnut tree I have been taking from, I decide that I am going to compare extract from the walnut hulls (which are now fat and green) to that from the leaves (according to some really old literature (a review-post is called for) there should be more in hulls). I also decided to forgo my previous habit of letting the extracts stir at room temperature overnight – I bet filtering and diluting immediately will give results (and allow students to do their own extractions and start germinations in the same lab period).
So it still dilutes out, although that first dilution has a pretty steep effect with the hull extract. I am not ready to believe that this means hulls have more until until it repeats. In doing this I saw something that I had forgotten about from last time: drying out is a problem and could be having a comparable effect to the extract. All of these plates looked ok, but I also did the exact same experiment with corn and had to throw that data out (some petri dishes dry out, some don’t). Parafilm will solve this, although that adds cost (maybe a grant wouldn’t be so bad (not)) and an extra step that students can mess up. Need to think on that. Also need to find a different, less expensive seed that is sensitive to walnut extract (peas, as you will recall, did not work out). Also need to bug our chemistry professors to help me get that colorimetric assay worked out.