RELATIONSHIP BETWEEN NITROGEN-FIXATION AND OXIDATIVE STRESS INDUCTIONIN NODULES OF SALT-TREATED SOYBEAN PLANTS

Two soybean (Glycine max L.) cultivars NaCl tolerant (377) and NaCl se nsitive (411), were grown on medium with 150 mM NaCl. Salt treatment p roduced a 50% decrease in leghemoglobin (Lb) in 411, while in 377 no s ignificant change was observed. Decreases of 50% in acetylene reductio n activity (ARA) occurred in 411, while in the tolerant 377 values rem ained similar to those of control plants. In lipid peroxidation, measu red as malondialdehyde (MDA) content, it was found that NaCl produced a 50% increase in sensitive 411 but failed to affect tolerant 377. Con comitantly, GSH content diminished 25% in 411 nodules and remained una ltered in 377 nodules. When antioxidant defense enzymes were measured, decreases with respect to controls of 50% in glutathione reductase (G R), 30% in ascorbate peroxidase (APOX), 20% in catalase (CAT) and 25% in superoxide dismutase (SOD) activities were found in 411. In contras t, increases of 15, 20, 30 and 80% were observed in 377 for GR, APOX, CAT and SOD, respectively. These results clearly indicate a correlatio n between N fixation and oxidative stress induced by salt treatment.