Abstract: Rhzobia enteres the nodule cells of leucaena roots with the aid of infection thread which contains rhizobia in embedding matrix when the infection thread penetrated the nodule cells. This matrix surrounded by the infection thread wall of host plant is probably a product secreted by bacteria. While the infection thread wall is surrounded by plasmalemma whichn connected with infection cells. During the process of nodule development, bacteria released from the top or side of infection thread enteres the cytoplasm of infection cells again. Morphological and structural changes hapen in both infected cells and non-infected cells. The characteristics of the change in cell structure related to nitrogen-fixing function are pointed out.

Key words: Nodule cell of Leucaena leucocephala, Releasing bacteria from infection thread, Rhizobia bacteroid, Ultrastruture