Made progress on imaging roots. With the batch of seeds started in a jelly roll the week before, I was able to tune up the focus and the lighting. Light comes from a roughly 2 inch by 2 inch square array of infrared light-emitting diodes. I have an old enlarger stand, minus the optics, to which I attach the array. I can rack it up and down but light is more or less straight overhead (well, over “root”). This is not ideal, there are bright and dark spots in the image. I could do better by bringing in an independent stand for the light and placing it to the font and side of the plate, although that can cause reflections of the front and back of the plate. For now, the overhead arrangement seems adequate.

Fig. 1. A timelapse movie of maize seedlings. The total time elapsed is 11 h, with frames captured every hour.

I set up a new jelly roll and was able to record root growth (Fig. 1). One problem with putting maize seedlings on an agar plate is that the kernels tend to fall down and the roots tend to stick up off the agar surface. That puts them in air, not a happy medium for a root. I solved both of these problems by placing a wet paper towel over the roots, just below the kernels. This shows up in the movie (Fig. 1) as the roughly textured region behind the roots. The agar-side of the plate faces the camera, agar being nicely transparent, and therefore the paper towel is on the back side of the root, not in anyone’s way. The paper towel by adhering strongly to the surface of the agar holds the roots on the surface, keeping them moist and this keeps kernels from moving at all. Happily the bond between paper towel and agar is not strong enough to stop root growth.

The program running the camera has a nice time-lapse feature that I set to capture an image every hour, for 12 hours. That way I could set it all up and come back the next day. To see how the roots grew, I measured the position of the tip in each frame and then used the Pythagorean formula (!) to calculate the distance between each point. That is plotted here (Fig. 2). The growth was reasonably uniform among the five roots (note the modest size of the error bars, which are standard error of the mean) but it did speed up over the first 6 or 7 hours. Not sure why. Maybe temperature fluctuations? I did not take care to exclude light from the computer during set up and maize roots are known to slow or stop growth in response to light. Or perhaps it was disturbing to them to be moved from jelly roll to agar plate plus paper towel?

Now I will repeat this a few times, without computer light, to see how stable the root growth pattern is, and also whether the protocol is reliable (does the paper towel fail? and so on). If that all goes well, then I can start the experiment which will begin with charting the kinetics of the root’s response to a microtubule inhibitor.