Figure 3
Spatial expression of MtNRLK1 and MtSUNN during nodulation. (A–F) Promoter:GUS activity of MtNRLK1 in nodule primordia (a,d, 4 days post-Rhizobium inoculation [dpi]), round-shaped nodules (B,E, 12 dpi) and nitrogen-fixing nodules (C,F, 24 dpi). (D–F) are bright-field pictures of longitudinal sections generated through nodules shown in (A–C), respectively. In nodule primordia, a weak GUS expression is observed at the base of the primordium (D). In round-shaped nodules, a blue staining is observed in the central infection zone (E). In elongated nodules, expression is restricted to the apical zone (C), with the highest expression in the proximal part of the meristem and in the infection zone (F). (G–l), Promoter:GUS activity of MtSUNN in the Rhizobium-inoculated root stele (J), round-shaped nodules (G,H,K, 12 dpi) and elongated nodules (I,L, 24 dpi). (J) is a bright-field picture of a section through a root vascular bundle; (K,L) are bright-field pictures of longitudinal sections through nodules shown in (h) and (i), respectively. A blue staining was observed in the phloem of the root vascular bundles (G,H, arrowheads; J, arrows) and at the base of the nodule vascular tissue (K, arrows). No expression was detected in the nodule apical meristem, infection and nitrogen fixation zones of round-shaped or elongated nodules (I,L). m, meristem; inf, infection zone; fix, nitrogen fixation zone, xy, xylem, co, cortex. Bars = 2 mm (A–C,G–I), 0.1 mm (J), 0.4 mm (D,E,K) and 1 mm (F,L).
