Optiles that is, coleoptiles. They did well those colies. This week, as suggested last time (last paragraph of that post), I tried coleoptiles, the top part of the maize seedling shoot. This was a little bit nostalgic because coleoptiles featured in my Ph.D. experiments. Not only that, the seedlings were grown under dim red light then and now. So the whole thing is a bit of a throw-back. Still, the coleoptile has been a venerable object for studying growth in isolated segments. Seemed reasonable to try them.

I repeated the experiment I did last week. The protocol is working well. This time, I did not expose the seedlings to wisps of light from the computer screen, when I checked that the imaging routine was functional, and operations went smoothly. Back in my dissertation day, I was able to remove the coleoptile from the leaves it sheathes, quite literally removing the sword (leaves) from the sheath (coleoptile, a word that comes from a Greek or Latin word for sword sheath) by nicking it just above the node, and sliding it off. This time, I was able to do that for only about a quarter of them. I’ll have to practice.

Happily, the coleoptile segments in a given dish grew more uniformly than do mesocotyl segments. I got a clear optimum in response, where growth on 3 µM IAA was greater than either 1 µM or 10 µM. Couldn’t see that with mesocotyls, too much noise. That all might be coincidence, there were not that many segments in each treatment-dish (6 or 7), and only four treatment-dishes, but promising all the same.

However, the overall rate of growth was modest, a bit less than 5% per hour. I’d like to see faster growth. Now, I grew the seedlings far away from the light, in a tall sided box so that the seedlings were almost fully dark grown. This was evident from the long mesocotyls and relatively short coleoptiles. That is, the coleoptiles were growing slowly when I harvested them so they might respond in a lackluster way to the auxin. By growing them right under the red light LEDs, the mesocotyls will be short and the coleoptiles will grow faster. This might predispose them to faster growth in the dish. Perhaps.

Fast coleoptile growth however nice in principle causes a problem in practice. After a while they stop growing and allow the inner leaves to break through, but how long is that ‘while’? I need to define the duration of coleoptile growth. So, for next week I set up some seeds, put them under the red lights and I will simply observe every day to see how long the window is, and when it occurs. With that defined, unless it is ridiculously short, I can set up an actual experiment.