Effect of salinity on nodulation, glutamine synthetase and glutamate synthase activity in nodules of alfalfa (Medicago sativa L.)

Abstract

Bami cultivar of alfalfa (Medicago sativa) was inoculated with salttolerant Sinorhizobium meliloti in solution culture with different salt concentrations (0, 50, 75 and 100 mmoles l-1NaCl) added immediately at the time of inoculation. The results indicated that S. meliloti formed an infective and effective symbiosis with alfalfa under saline and nonsaline conditions. Salinity significantly decreased shoot and root dry weight, nodule weight and mean nodule weight. Roots were more sensitive than shoots, and N2 fixation was more sensitive to salinity than was plant growth. Analyses of ammonium assimilating enzymes in the nodule showed that glutamine synthetase appeared to be more tolerant to salinity than glutamate synthase, and that it limits ammonium assimilation under saline stress.