Figure 3: The stop1 and almt1 mutations largely uncouple the effects of −Pi on the EZ and RAM.

(a) Fe accumulation and distribution in primary root tips. Three-day-old seedlings of the indicated genotypes were transferred to +Pi or −Pi plates for 48 h prior to Perls/DAB staining. Note the accumulation of Fe in the EZ of the WT (white arrowhead) and in the SCN (black arrowhead). Bottom panel: magnification of the root tip of seedlings under −Pi. Images are representative of three independent experiments. Scale bar, 100 μm. (b) Four-day-old seedlings grown under +Pi were transferred 20 h in +Pi or −Pi before callose staining. The white arrowhead points to callose accumulation in the EZ; the red arrowheads point to callose accumulation in the SCN. Two independent experiments were performed with consistent results and one representative experiment is shown. Scale bar, 100 μm. (c) Time course of the Δ primary root length of WT and mutant seedlings transferred to −Pi. Two independent experiments were performed with consistent results and one representative experiment is shown (mean±s.d., n=8–14 seedlings per line). (d) Primary root meristem length of WT and mutant seedlings grown for 4 or 10 days in +Pi or −Pi medium (mean±s.d., n=14–25 meristems per condition; two-way ANOVA, multiple comparisons; ****P<0.0001). (e) Schematic diagram of the consequences of stop1, almt1 and lpr1;lpr2 mutations on accumulation of Fe and callose, and growth of the primary root under −Pi. The WT root (left) accumulates Fe and callose in the EZ and SCN (red strips and dots, respectively) and its growth is rapidly inhibited. In the lpr1;lpr2 mutant (right), there is no accumulation of Fe and callose and no inhibition of root growth. In the stop1 and almt1 mutants (middle), Fe and callose accumulates only in the SCN and the root growth inhibition is slow.