spr2-2 mutants show rapid minus-end depolymerization. (A and B) Confocal images (top) and kymographs (bottom) of MTs displaying minus end shrinking in etiolated hypocotyl cells of WT (A) and spr2-2 mutant (B). Arrowheads indicate minus ends. Dashed lines highlight the position of the minus end in the kymograph. (C) Boxplots for minus-end shrinking speed of MTs in WT (n = 142 MTs from seven cells) and spr2-2 (n = 154 MTs from six cells). Asterisks indicate a significant difference by Mann–Whitney U test (***, P < 0.001). (D) Rates of the transition from shrinkage to pause (r_sp) and pause to shrinkage (r_ps) of MT minus ends. The asterisks indicate a significant difference by rate ratio test (frequency of r_sp is n = 58 in WT and n = 25 in spr2-2; ***, P < 0.001, and r_ps is n = 76 in WT and n = 30 in spr2-2; ***, P < 0.001). (E) Fractions of time spent in dynamic polymer states of the minus end. Total time spent is 256 min from 107 minus ends in WT and 335 min from 154 minus ends in the spr2-2 mutant. (F and G) Boxplots for plus end shrinking and growth speeds, respectively, in WT (n = 230 MTs from seven cells) and spr2-2 mutant cells (n = 185 MTs from six cells). (H) Catastrophe and rescue rates of MT plus ends. The asterisks indicate a significant difference by rate ratio test (***, P < 0.001). Bars, 3 µm. Errors in bar graphs are SEM. In the boxplots, the box represents the range from the 25th to 75th percentile, the horizontal line marks the median value, and the whiskers span from the 2.5 to 97.5 percentile.