Pankaj Sharma and Attar Singh Yadav
Legume- Rhizobium nitrogen fixation is dramatically affected under drought and other environmental constraints. However, many efforts are going to unveil whether such regulation of nitrogen fixation is exerted, occur at nodule efficiency level. Proline has been reported to provide additional energy to support nitrogen fixation in legume root nodules. Proline dehydrogenase (ProDH) is a key enzyme, which catabolizes proline to yield energy. Therefore, in the present investigation symbiotic characterization of mutants of Rhizobium sp (Cajanus) defective in proline dehydrogenase under drought stress condition was undertaken. Ten wild type strains of Rhizobium sp (Cajanus) were screened for their ProDH activity and antibiotic resistance pattern. We selected one effective strain (Rspc-4) for Tn5 random mutagenesis. Out of 1500 transconjugants, twelve clones were adjudged as ProDH- mutants. Resistance to most of the antibiotics was similar in both parent and its ProDH- mutants. The proline dehydrogenase activity in cell and nodule extracts of mutant ProDH- was completely lacking. All the ProDH- mutants were nonnodulating (Nod-) on pigeonpea plants. The other symbiotic parameters of host plants inoculated with the mutants under normal and drought stress conditions were significantly lower than that of plants infected with the parent strain.
