Buckling and straightening are prominent actin filament behaviors. (A) A representative filament (asterisk) that undergoes continuous undulations and buckling is shown. The highlighted filament (red dots) almost completely changes shape between some consecutive frames. A measure of filament buckling, convolutedness, was applied to this example and the value is given on each frame at bottom left. The average convolutedness (±SEM) for this filament was 1.8 ± 0.4. Time points indicate elapsed time from start of video sequence. See also Video 6 (available). Bar, 2 µm. (B) A long, convoluted actin filament (asterisk) exhibits many aspects of dynamic behavior. Changes to convolutedness in the first three frames, precede a breakage event at 71 s (arrow). The newly created end (open arrowhead) immediately begins elongating at the rate of 1.2 µm/s. Between t = 91 s and t = 98 s, the filament straightens and the convolutedness value approaches one. Subsequently, numerous fragmentation events destroy the mother filament completely so that it is unrecognizable by t = 125 s. Values marked on the frame represent measure of convolutedness for the filament of interest and the average value (±SEM) was 1.2 ± 0.1. Time points indicate elapsed time from start of video sequence. See also Video 7 (available). Bar, 2 µm. (C) The average rate of change in convolutedness for different cell types and inhibitor treatments. Compared with the elongating epidermal cells from 3–5-d-old hypocotyls, both nongrowing cells and cells treated with latrunculin B or BDM showed a significant (P < 0.002) reduction in the rate of change of convolutedness. Data are presented as mean ± SD.