GR24 affects primary root length in a concentration-dependent way. A, Primary root lengths of 8-d-old max1-1, max2-1, max4-1, and wild-type (wt) Arabidopsis plants grown on vertical MS plates containing 0.5% Suc and different levels of GR24. B, Primary root length of 12-d-old plants grown on vertical MS plates containing no Suc and 0 or 2.5 μm GR24. Data are means ± se (n = 16–20). C, Cortical meristem cell number, expressed as the number of cells in one cell file extending from the quiescent center to the first elongated cell, of 7-d-old Arabidopsis plants grown on vertical MS plates containing 0.5% Suc and 0 or 2.5 μm GR24. Data are means ± se (n = 5). Marks indicate a statistically significant difference compared with untreated (asterisk) or wild-type plants (x) as determined by Student’s t test (P < 0.05). D and E, Nomarski images of GUS-stained primary roots of max4 (D) and wild-type (E) plants containing the DR5-GUS reporter construct. Bars = 0.1 mm. [See online article for color version of this figure.]