ULTRASTRUCTURE OF THE ENDOPHYTE AND LOCALIZATION OF NIFH TRANSCRIPTS IN ROOT-NODULES OF CORIARIA-NEPALENSIS WALL BY IN-SITU HYBRIDIZATION

Studies on the root nodules of Coriaria nepalensis Wall. using light a nd electron microscopy revealed that infected cortical cells are enlar ged and form a compact kidney-shaped region with an acentric stele. Wi thin a single cell, the actinomycetous endophyte has branched hyphae a nd elongate vesicles. Hyphae penetrate the host cell wall in different directions. Inside the host cell, the hyphae are located in the perip heral region of the cytoplasm near the host cell whilst the vesicles a re positioned towards the centre of the cell around the central vacuol e. No septa formation was observed in the microsymbiont vesicles. Host cell mitochondria were aggregated near the hyphal/vesicular junction of the endophyte. In situ hybridization studies demonstrated that the nifH transcripts are unequally distributed over the infected cortical cells. In infected cells, nifH mRNA was located in the region occupied by the elongate vesicles of the endophyte near the host cell central vacuole. The results indicate that the elongate vesicles of the nodule endophyte of C. nepalensis are functionally identical to the spherica l vesicles of the nodule endophyte of Alnus.