Electron microscopic study of associative n2-fixing bacteria in roots of rice seedlings

The association between rice roots and N2-fixing bacteria was investigated. Root tips of rice seedlings inoculated with Nt-fixing bacteria strains isolated from the rhizosphere of rice were examined by transmission electron microscopy. Many bacteria were found to adhere to the fibrillar materials covering the root cap cells and epidermal cells. The largest number of bacteria was observed in the intercellular spaces between epidermal cells and root cap cells that were sloughing off, or between the remaining root cap cells and root cap cells which were sloughing off. The discrepancy between previous studies reporting the absence of microorganisms at the root apex and our findings can be explained by proposing the following hypothesis. Firstly, microorganisms in the intercellular spaces may not always be detected by scanning electron microscopy. Secondly, the distribution of N2-fixing associative bacteria in the rhizosphere, appears to be different from that of other microorganisms.