 Root nodules containing Rhizobium bacteria have been found on R. regia trees in India. The presence of rhizobia-containing root nodules is usually associated with nitrogen fixation in legumes; this was the first record of root nodules in a monocotyledonous tree. Further evidence of nitrogen fixation was provided by the presence of nitrogenase (an enzyme used in nitrogen fixation) and leghaemoglobin, a compound which allows nitrogenase to function by reducing the oxygen concentration in the root nodule. In addition to evidence of nitrogen fixation, the nodules were also found to be producing indole acetic acid, an important plant hormone.
