Fig. 1

The effect of the nrsym1 mutation on nodulation and plant growth. a Nodule phenotypes of WT, the nrsym1-1 mutant, and the nrsym1-2 mutant treated with 0 or 10 mM KNO₃ at 21 days after inoculation (dai). Arrowheads indicate small and premature nodules. Scale bars: 2 mm. b The number of nodules in WT, the nrsym1-1 mutants, and the nrsym1-2 mutants in the presence of different concentrations of KNO₃ (0–50 mM) at 21 dai (n = 9 plants). c The number of infection threads in WT and the nrsym1-1 mutants with 0 or 10 mM KNO₃ at 7 dai with rhizobia that constitutively express LacZ (n = 12 plants). d Relative nodule size (daily nodule size/nodule size on day 0) of WT and the nrsym1-1 mutants (n = 13–19 nodules). Individual nodule size was measured at 0, 5, 10, and 15 days after the transfer to agar plates with 0 or 10 mM KNO₃. *P < 0.05 (Student’s t-test compared 0 mM KNO₃-treated nodules with 10 mM KNO₃-treated nodules on the same day). ns, not significant. Scale bars: 0.5 mm. e Acetylene reduction activity (ARA; μmol h⁻¹  per g nodules) of nodules formed on WT and the nrsym1-1 mutants (n = 4 plants). Twenty-one dai plants without KNO₃ were supplied with 0 or 10 mM KNO₃, and after 3 days the ARA of nodules from each plant was measured. f Fresh shoot weight and (g) shoot to root fresh weight ratio of WT and the nrsym1-1 mutants grown in 0 or 10 mM KNO₃ on 21 dai (ino) or without rhizobia (unino; n = 10–12 plants). Error bars indicate SEM. *P < 0.05 by Student’s t-test. ns, not significant. Degrees of freedom are shown above the t-values (b–e). Columns with the same lower-case letter indicate no significant difference (Tukey’s test, P < 0.05; f, g)