NITRATE INDUCED NODULE SENESCENCE AND CHANGES IN ACTIVITIES OF ENZYMES SCAVENGING H2O2 IN CLUSTERBEAN (CYAMOPSIS-TETRAGONALOBA TAUB)

Well nodulated clusterbean (Cyamopsis tetragonaloba Taub.) plants raised in sand culture were treated for 3 and 6 days with 20 and 50 mol m-3 KNO3. Acetylene reduction activity as a measure of N2-ase activity showed a decrease of 32-68% 3 days after treatment and 54-82% after 6 days. The decrease in nodule leghemoglobin (Lb) was much slower. Lb content was 9-18% lower than the control 3 clays after treatment and 37-53% lower 6 days after treatment. Nitrate induced premature senescence of nodules also led to a decrease in ascorbic acid (ASC) and glutathione content of nodules as well as a decrease in their ascorbate (ASC) peroxidase, glutathione (GSSG) reductase and catalase activities. Peroxidase on the other hand showed an increase in its activity.