Production of indole acetic acid in culture by a Rhizobium species from the root nodules of a monocotyledonous tree, Roystonea regia

The study of the rhizobial root nodules of the monocotyledonous tree Roysto nea regia revealed that the Rhizobium sp. isolated from the root nodules pr oduced high amounts (45.6 mug/ml) of indole acetic acid (IAA) from L-trypto phan supplemented basal medium. The IAA production reached its optimum usin g 3 mg/ml of L-tryptophan. The preferred carbon and nitrogen sources were g lucose and KNO3 and the optimum concentrations 1% and 0.02%, respectively. FeSO4 x 7 H2O was found to be the only metal ion that increased IAA product ion. An optimum IAA production was also achieved when the basal medium was supplemented with glucose (1%), FeSO4 x 7 H2O (10 mug/ml), KNO3 (0.02%) as well as EDTA (5 mug/ml) and L-tryptophan (3 mg/ml). The possible role of IAA production in the monocotyledonous tree-Rhizobium symbiosis is discussed. Hormone production is shown to be the beneficial as pect of this symbiosis as shown earlier in dicotyledonous plants.