Ultrastructural Study on the Rhizobia in Alhagi sparsifolia

The rhizobia in the root nodules of Alhagi sparsifolia were studied by transmission electron microscopy.The results indicated that the size,shape,distribution and fine structures of the rhizobia were related with the stage host cell development.The rhizobia in young infected cells were small,few in number,spherical or spheroidal and generally located near the cell walls or nucleus of the host cell.In comparison,the rhizobia in mature infected cells were larger,greater in number,varied in shape,and distributed throughout the nodule cells.The rhizobia in the mature cells also had poly-hydroxy butanoic acid (PHB) and curapos.We hypothesize that spherical rhizobia carry out the function of reproduction in root nodules of Alhagi sparsifolia.This hypothesis is based on the fact that the spherical rhizobia were observed at all stages of the infected host cells development.Furthermore,among the different shapes that were observed for the rhizobia cells,only the spherical rhizobia were seen to reproduce.