CHANGES IN THE ELECTROPHORETIC SPECTRA OF ANTIOXIDANT ENZYMES IN NITRATE-FED AND NITROGEN-FIXING SOYBEAN SUBJECTED TO GRADUAL WATER STRESS

The effect of two sources of nitrogen (nitrogen fixation or nitrate assimilation) and gradual water stress on theelectrophoretic spectra of peroxidase, catalase and superoxide dismutase was studied in soybean leaves. An increase in H2O2 production was observed, especially after the prolonged drought treatment. At 50% drought the activity of anionic peroxidase activity for isoenzymes Nos. 2 and 7+8 significantly increased (by 54 and 18%, respectively) in the leaves of nitrate-fed plants compared to the control plants; for nitrogen-fixing plants these values were 31 and 14%, respectively. In the case of cationic peroxidases, the application of 50% drought led to the inhibition of the moderately fast isoenzymes (Nos. 2 and 3, with Rm 0.5 and 0.65, respectively) and the activation of the fastest moving isoenzyme (No. 4, with Rm 0.8) in nitrate-fed soybean. The same tendency was observed in the leaves of nitrogen-fixing plants. The effect of restricted soil humidity on SOD activity was expressed as a change in...