Loss of ITPK1 results in compromised auxin responses. A, Relative root elongation of designated genotypes under increasing IAA concentrations. Six-day-old seedlings were transferred to solidified half-strength MS media, supplemented with 1% (w/v) sucrose and 0, 25, and 75-nM IAA as indicated and incubated for 5 days. Root lengths were evaluated by ImageJ. Error bars are sem (n=10–35). Different letters indicate significance in one-way ANOVA followed by Dunnett’s test (a and b, P < 0.05; a to c, P < 0.001; a to d, P < 0.001; b to c, P < 0.001; d and e, P < 0.001; b to d, P < 0.001; c to e, P < 0.001). The experiment was repeated twice with similar results. B, Relative root length of wild-type (Col-0), itpk1 mutant and selected complemented lines treated with 75-nM IAA. Six-day-old seedlings of designated genotypes were transferred to solidified half-strength MS media, supplemented with 1% (w/v) sucrose and 0.75-nM IAA. After 7-days of growth, images were taken and root lengths were evaluated by ImageJ. Error bars present sem (n = 10–35). Asterisks indicate statistical differences (treated wild-type versus all treated all other genotypes, Student’s t test; ***P < 0.0001). C–E, Root hair formation of designated genotypes under increasing IAA concentrations. Six-day-old seedlings were transferred to solidified [0.8% (w/v) phytagel], half-strength MS media supplemented with 1% (w/v) sucrose and with 0, 25, 50, or 75 nM IAA as indicated and incubated for 5 days. Representative root images (C) and quantifications of root hair density (D) and root hair length (E). Root hair lengths were evaluated by ImageJ. Boxplots show the first quartile, median and third quartile. The whiskers extend to the minimum and maximum values (D) with n = 10–12 independent roots, or to 5th and 95th percentile (E) with n = 457–951 independent root hairs from 10–12 roots. Different letters indicate significance in one-way ANOVA followed by Tukey’s test (P < 0.05). Scale bars, 500 µm. F, Lateral root density of designated genotypes under increasing IAA concentrations. Six-day-old seedlings were transferred to solidified half-strength MS media supplemented with 1% (w/v) sucrose and 0, 25, 50, or 75 nM IAA as indicated and incubated for 6 days. Boxplots show the first quartile, median and third quartile. The whiskers extend to the minimum and maximum values with n = 9–11 independent roots. Different letters indicate significance in one-way ANOVA followed by Tukey’s test (P < 0.05).