The legume-Rhizobium symbiosis: a cell surface interaction.

This review will examine the early stages of infection of legume roots by strains of Rhizobium that induce nitrogen-fixing nodules. The object is to show that, at least in terms of ultrastructure, the interactions between the plant and the rhizobia occur at the cell surface interface between these organisms. This situation exists at all stages, from the time the bacteria attach to the surface of the root hairs to the time they occur as the nitrogen-fixing form in the cytoplasm of the nodule cells, enclosed by peribacteroid membranes.