ABSTRACT
Nodules on legumes and also the nonlegume Parasponia exhibit different morphologies. Nodule cells can be considered to be bathed in a medium containing C sources provided by plant photosynthesis. Sucrose is considered to be the main energy source transported into the nodules for bacterial nitrogen fixation. Legumes entering into N2-fixing symbioses can be broken down into two groups; those whose nodules export amides or ureides. Bacteroids are defined as the specialized stage of the life cycle of symbiotic bacteria, occurring when they inhabit host cells. The peribacteroid space (PBS) is defined as the space between the symbiotic partners. The peribacterioid membrane (PBM) forms a continuous envelope around the prokaryote, and various numbers of bacteroids are contained within each membrane, between 1 and 20, depending on species and the age of the nodule. Mitochondria in infected cells are cristae-rich through intensive folding of the inner mitochondrial membrane and move to the cell periphery.
