GS (a) and NADH-GOGAT (b) specific activities. Seedlings were grown for 14 days in a Hoagland modified complete nutrient solution (0) and treated for the last 2 days with HS concentrations of 0, 1 and 5 mg C L−1. The specific activities were expressed as unit per milligramme protein. One unit corresponds to the production of 1 μmol of γ-glutamyl hydroxamate per minute in the case of GS and to the oxidation of 1 μmol of β-NADH per minute in the case of GOGAT at the assay conditions. Values are means of three independent determinations (±SE). Letters above bars indicate significant differences (P < 0.05).