Figure 2.

Auxin-induced reorientation of cortical microtubules in isolated hypocotyl segments of A. thaliana. (A) An overview of the experimental setup used throughout this study. Hypocotyls were isolated from three-day-old etiolated seedlings of A. thaliana. The depletion of endogenous auxin and the resulting cessation of growth was allowed within following time of around one hour. Necessary chemical pre-treatments were applied in this period. Hypocotyls were then transferred to treatment media (e.g., containing auxin) and imaged by CLSM typically after one hour of treatments, or they were placed on a flatbed scanner for growth measurements. See Section 4 for details. (B) Isolated A. thaliana hypocotyls used in this study. Red rectangle marks the sub-apical region of active growth in three-day-old hypocotyls, where the orientations of microtubules were scored. (C) Auxin-induced growth of isolated A. thaliana hypocotyls. Auxin-depleted hypocotyls were placed on control or auxin-supplemented (IAA, 10 μM) media, and their growth was measured over a one hour period. The graph shows collated growth measurements from three experiments, each data point representing one hypocotyl. (D) Concomitant with growth, auxin (IAA, 10 μM) causes the reorientation of cortical microtubule arrays in the outer faces of hypocotyl epidermis, from predominantly longitudinal into predominantly oblique and transverse. Cells were scored into four categories based on the prevalent type of microtubule array observed. The GFP fluorescence is depicted in grayscale. The graph shows average percentage of cells in each category from three experiments. Error bars indicate standard deviation (only the lower bar is shown for clarity). Total cell numbers are given above the graph. The frequencies of cells with longitudinal arrays were compared with the mock treatment using t tests, p = 0.022 (*) for 30 min auxin treatment and p = 0.0003 (***) for 60 min auxin treatment.