The itpk1-associated defects in root architecture and inositol polyphosphate profile are fully rescued by introducing a genomic ITPK1 construct. A, Primary root elongation of seedlings of wild-type (Col-0), itpk1 and two independent complemented itpk1 lines. The latter refer to the itpk1 T-DNA insertion line transformed with a genomic fragment containing a 1,839-bp region upstream of the ITPK1 start codon in translational fusion with a C-terminal G3GFP. Seeds were germinated on solidified half-strength MS agar media, supplemented with 1% (w/v) sucrose. After 7 days, seedlings were transferred to fresh media with the same composition and grown for additional 7 days until imaging. B, Complementation of short primary root elongation of itpk1 plants by an ITPK1 genomic fragment C-terminally fused to G3GFP. Six-day-old seedlings of designated genotypes were transferred to solidified half-strength MS media, supplemented with 1% (w/v) sucrose and allowed to grow for another 10 days. Error bars represent standard errors (se), n ≥ 23. Letters depict significance in a one-way analysis of variance (ANOVA) followed by Tukey’s test (a and b, P < 0.001). The experiment was repeated twice with similar results. C, CE–ESI–MS analysis of inositol polyphosphate levels of 2-week-old Arabidopsis wild-type (Col-0), itpk1 and complemented itpk1 seedlings as indicated. Plants were grown on solidified half-strength MS media, supplemented with 1% (w/v) sucrose, growth conditions are detailed in the methods section. InsP species are presented as percentage of total InsP₆. Data are means ± se (n = 6, biological replicates). Different letters indicate significance in one-way ANOVA followed by Tukey’s test (P < 0.05). D, Inositol polyphosphate enrichment from indicated plant extracts by TiO₂ pull down. Inositol polyphosphates were eluted from TiO₂ beads, separated by PAGE, and visualized by toluidine blue.