INSITU LOCALIZATION OF RHIZOBIUM MESSENGER-RNAS IN PEA ROOT-NODULES - NIFA AND NIFH LOCALIZATION

Here we demonstrate that Rhizobium mRNAs can efficiently be detected in developing root nodules with the in situ hybridization technique. We have been able to localize the Rhizobium nifH mRNA as well as the transcript of the regulatory nifA gene. Therefore, we expect that the in situ hybridization technique can generally be applied to locate Rhizobium mRNAs in root nodules. In pea nodules, the nifA and nifH mRNAs are first detectable in the third to fourth cell layer of the late symbiotic zone. In these cell layers, these mRNAs are detectable immediately at maximal levels. In older parts of the late symbiotic zone, the level of nifH mRNA remains constant, whereas the level of nifA mRNA decreases. Finally, the pattern of nif mRNA accumulation was compared with that of nodulin mRNAs.