Fig. 7.

Interactions between the effects of Pb²⁺ stress and the ratio of NO₃^– to NH₄⁺ supplied to Arabidopsis wild-type Col-0, and the nrt1.1-1 and chl1-5 mutants. Seedlings at 4 d old were transferred to medium with or without 300 μM Pb(CH₃COO)₂ and containing different ratios of NO₃^– to NH₄⁺, and measurements were taken after 7 d. (A) Root elongation, calculated as elongation with Pb relative to elongation of the same genotype without Pb under the same NO₃⁻/NH₄⁺ ratio. (B) pH of the growth medium, and Pb concentrations in (C) the roots and (D) the shoots. Data are means (±SE) of four biological replicates. Different letters indicate significant differences between means as determined using two-way ANOVA followed by Tukey’s multiple comparisons test (P<0.05). Significant interactions between NO₃⁻/NH₄⁺ ratio and genotype are indicated by an asterisk (*P<0.05). (This figure is available in colour at JXB online.)