Fig. 4

N source effect on main S-containing metabolites in roots and leaves of B. napus. Total sulfur (a) SO₄ ⁻² (b), glutathione (GSH and GSSG) (c) and glucosinolate (d) content. Plants were cultured with 0.5 and 1 mM nitrate (N0.5; N1) or ammonium (A0.5; A1). In panel A, different colours represent the proportion of sulfur in different compounds. Sulfur content from “other S-containing compounds” was calculated by subtracting the sum of S content in SO₄ ⁻², GSL, amino acids and glutathione from the total S concentration determined using an Elemental Analyser. Error bars at the top of the figure represent the SE of total S content. Values represent mean ± SE (n = 4). Different letters indicate statistical differences between treatments (ANOVA analysis with Duncan’s test, P < 0.05). Asterisk (*) indicates significant nitrogen source effect within each nitrogen concentration (t-test, P < 0.05)