Formation and abortion of root nodule primordia in Lupinus luteus L.

Lupinus luteus L., infection occurred via the curled root hair. Bradyrhizob ia penetrated its cell wall, probably by localized digestion, and then mult iplied into the interior of the root hair. Some rhizobia escaped the penetr ation site before the host cell built a new wall around it. Escaped bacteri a passed the distance to the root hair cell base, probably in the space bet ween the cell wall and plasma membrane. At the root hair cell base, cell wa ll penetration and matrix escape occurred again. After escaping the matrix, rhizobia were endocytotically directed to the interior of the dedifferenti ated cortex cell, and during subsequent mitosis were segregated to the prox imal derivative. Thus the cell became the bacteroid tissue initial. The bac teria that remained within the penetration site were immobilized here due t o the production of cell wall around them. Internalized bacteria were initi ally associated with large numbers of vesicles bearing cell-wall-like matri x. In abortive primordia the bacteria penetrated the cell walls of competen t cells, and associations of bacteria and cell-wall-like matrix surrounded with a membrane were produced. At this stage, symbiosis was arrested and th e symbiosomes were degraded. Necrosis or lysis of some primordium cells was observed.