Editing Root nodule (section)

{{Short description|Plant part}}
[[File:Nitrogen fixation Fabaceae en.svg|thumb|upright=1.25|A simplified diagram of the relation between the plant and the symbiotic bacteria (cyan) in the root nodules]]
'''Root nodules''' are found on the [[root]]s of [[plant]]s, primarily [[legume]]s, that form a [[symbiosis]] with [[nitrogen-fixing bacteria]].<ref name="Wagner">{{cite journal |last1=Wagner |first1=Stephen C. |date=2011 |title=Biological Nitrogen Fixation |url=https://www.nature.com/scitable/knowledge/library/biological-nitrogen-fixation-23570419 |journal=Nature Education Knowledge |volume=3 |issue=10 |page=15}}</ref> Under [[nitrogen]]-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as [[rhizobia]].<ref>{{cite journal |last1=Wang |first1=Qi |last2=Yang |first2=Shengming |date=2017 |title=Host-secreted antimicrobial peptide enforces symbiotic selectivity in ''Medicago truncatula'' |journal=PNAS |volume=114 |issue=26 |pages=6854–6859 |bibcode=2017PNAS..114.6854W |doi=10.1073/pnas.1700715114 |pmc=5495241 |pmid=28607058 |doi-access=free}}</ref> This process has evolved multiple times within the legumes, as well as in other species found within the [[Rosid]] clade.<ref>{{Cite journal |last1=Doyle |first1=Jeff J. |last2=Luckow |first2=Melissa A. |date=2003 |title=The Rest of the Iceberg. Legume Diversity and Evolution in a Phylogenetic Context |journal=Plant Physiology |language=en |volume=131 |issue=3 |pages=900–910 |doi=10.1104/pp.102.018150 |issn=1532-2548 |pmc=1540290 |pmid=12644643}}</ref> [[Legume]] crops include [[bean]]s, [[pea]]s, and [[soybean]]s.

Within legume root nodules, nitrogen gas (N<sub>2</sub>) from the atmosphere is converted into [[ammonia]] (NH<sub>3</sub>), which is then assimilated into [[amino acids]] (the building blocks of proteins), [[nucleotides]] (the building blocks of [[DNA]] and [[RNA]] as well as the important energy molecule [[Adenosine triphosphate|ATP]]), and other cellular constituents such as [[vitamin]]s, [[flavone]]s, and [[plant hormones|hormones]].{{citation needed|date=October 2022}} Their ability to [[Nitrogen fixation|fix gaseous nitrogen]] makes legumes an ideal agricultural organism as their requirement for nitrogen fertilizer is reduced. Indeed, high nitrogen content blocks nodule development as there is no benefit for the plant of forming the symbiosis. The energy for splitting the nitrogen gas in the nodule comes from sugar that is translocated from the leaf (a product of [[photosynthesis]]). [[Malate]] as a breakdown product of [[sucrose]] is the direct carbon source for the bacteroid. Nitrogen fixation in the nodule is very oxygen sensitive. Legume nodules harbor an iron containing protein called [[leghaemoglobin]], closely related to animal [[myoglobin]], to facilitate the diffusion of oxygen gas used in respiration.