Changes in the microtubule network beneath the point of contact. Microtubules visualized in the cortical cytoplasm underlying the outer epidermal cell wall in a cotyledon of A. thaliana expressing TUA6-GFP . The surface of the epidermal cell was touched with a tungsten microneedle at time 0:00. The position of the needle is indicated by the shadow outlined by the V-shaped lines. The position of the tip of the needle is shown by a line of reflected light. Images A-L are projections of five optical sections taken at the times indicated in minutes and seconds. The first sign of a reaction in the array occurs at 3 minutes 16 seconds when a linear region of diffuse fluorescence appears to the left of the needle tip (small arrow in C). A more intense cloud of diffuse fluorescence subsequently forms at the needle tip (F-L). At the same time, a microtubule-depleted zone about 20 μm in diameter forms around the needle tip as indicated by the arrows in I. A movie showing the dynamics of microtubule rearrangement in this experiment is shown in Additional File 5. Bar = 10 μm.