Nitrogen fixation of Azorhizobium in artificially induced root para-nodules in wheat

Nodule-like structures (para-nodules) can be induced in wheat roots by low concentrations of 2,4-dichlorophenoxyacetic acid (2,4-D), a synthetic analogue of the plant growth hormone indole-acetic acid. Growth of nodulated wheat plants was not affected by 2,4-D treatment. Infection of these para-nodules by adding oxygen-tolerant Azorhizobium caulinodans isolated from stem nodules of the tropical legume Sesbania rostrata resulted in massive proliferation of bacterial cells in the intercellular spaces as well as inside the para-nodular cells. Para-nodules colonized by Azorhizobium caulinodans not only reduced acetylene, but also transferred fixed nitrogen to the plant, contributing up to 16-23% of the nitrogen budget of infected wheat.