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Roots Root nodules Root nodules are formed on roots in some species as a result of a symbiotic relationship with bacteria. The plant benefits from having the bacteria, which fixes atmospheric nitrogen into a form (nitrate) that the plant can use for growth. Root nodules in black medic (Medicago). Back to root microbe menu Next Back to root main menu Back to vegetative parts main menu Main menu Roots Root nodules Legumes (Fabaceae) represent the largest plant family associated with nitrogen-fixing bacteria. The major bacteria involved include Rhizobium and Bradyrhizobium. Root nodules in peanut (Arachis). Back to root microbe menu Back Next Back to root main menu Back to vegetative parts main menu Main menu Roots Root nodules A cross-section of a soybean root nodule shows that the central portion of the nodule contains a proliferation of cells infested with many bacteroids. Bacteroid containing cells Sclerenchyma sheath Root cortex Vascular bundles Back to root microbe menu Back Next Back to root main menu Back to vegetative parts main menu Main menu Roots Root nodules A closer look at the central core of the nodule shows that almost all cells are infected with bacteroids and that the infected cells contain an overly large nucleus. Nuclei Back to root microbe menu Back Next Back to root main menu Back to vegetative parts main menu Main menu Roots Root nodules Cycads also a form mutualistic, symbioses with a nitrogen fixing cyanobacteria in a structure called coralloid roots. Back to root microbe menu Back Back to root main menu Back to vegetative parts main menu Main menu
