Polyamines and proline are affected by cadmium stress in nodules and roots of soybean plants

The effect of moderate (50 μM) and high (200 μM) doses of Cd were studied in relation to polyamine (Pas) metabolism, proline level and the glutamine synthetase/glutamate synthase system (GS/GOGAT) activity in nodules and roots of soybean plants during 6 days of treatment. The lower Cd concentration increased putrescine (Put) in both nodules and roots, while 200 μM Cd increased Spm only in nodules and Put in roots. Spermidine (Spd) decreased in roots under both Cd concentrations. Arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) were both involved in Put biosynthesis in roots. In nodules, Put formation could mainly be attributed to ODC activity. Diamine oxidase (DAO) activity was severely reduced by 50 and 200 μM Cd either in nodules or roots. The GS/GOGAT system activity was depressed either with 50 or 200 μM Cd, but most significantly with the highest metal concentration. Under 200 μM Cd, GS activity decayed to 25% or 60% of the control in nodules and roots, respectively, while GOGAT decreased 85% in nodules and 79% in roots by day 4 of treatment. Ammonium increased greatly in nodules (200% over the controls) and roots (100%) under 200 μM Cd. Proline concentration increased significantly in nodules and roots under both Cd treatments, more markedly under 200 μM Cd. The relationship between Pas and proline accumulation and nitrogen assimilation is discussed.