~ 624 ~ International Journal of Chemical Studies 2018; 6(4): 624-630 P-ISSN: 2349–8528 E-ISSN: 2321–4902 IJCS 2018; 6(4): 624-630 © 2018 IJCS Received: 28-05-2018 Accepted: 29-06-2018 Richa Sharma Department of Biological Sciences Sam Higginbottom University of Agriculture, Technology and Sciences Allahabad, Uttar Pradesh, India Devendra Kumar Kurrey Department of Biological Sciences Sam Higginbottom University of Agriculture, Technology and Sciences Allahabad, Uttar Pradesh, India Nisha Maurya Department of Biological Sciences Sam Higginbottom University of Agriculture, Technology and Sciences Allahabad, Uttar Pradesh, India Correspondence Richa Sharma Department of Biological Sciences Sam Higginbottom University of Agriculture, Technology and Sciences Allahabad, Uttar Pradesh, India Root nodulation process and its soil ameliorating benefits: A review Richa Sharma, Devendra Kumar Kurrey and Nisha Maurya Abstract Legume plants have an extraordinary ability to combine with microorganisms which range from non- specific to very specific interaction. Legume rhizobial symbiosis results in large growth and metabolic changes for both microorganisms and hosts, while providing plants with fixed nitrogen. In a complex signal exchange rhizobia leads to selective colonization of plant cells within nodules, development of new organ known as nodule on the roots of host plants. Although the nodulation mechanism is highly specific, it contains same subset of phytohormones of plants, i.e. auxin, cytokinin, and ethylene, which are essential for root development. In addition, the formation of nodule triggered by rhizobia affect the development of host root system and indicating that microorganisms may change the developmental pathways of host. A prime example of nodulation by rhizobia is how microorganisms and plants have coevolved and illustrate how microbial colonization may affect plant developmental pathways. Keywords: Root nodule, nod factor, rhizobia, nitrogenase and nitrogen assimilation Introduction Besides anchoring plants in the soil, roots are essential for mineral nutrition and water uptake. When exposed to fluctuations in the soil environment such as drought or nitrate or phosphate availability, roots activate compensating mechanisms ranging from changes in nutrient uptake ability to changes in root architecture (Desnos 2008). Nitrogen is essentially the most important nutrient required by plant cells for the synthesis of enzymes, proteins, chlorophylls, DNA and RNA, which is essential for the growth of the plant and the production of food (Matiru et al. 2004) [41] . However, the availability of nitrogen in many soils is limited, and although 78.1% of the Earth's atmosphere contains nitrogen gas (N2), plants are unable to use this kind of nitrogen (Ferguson et al. 2010) [25] . However certain plants are blessed with the capacity of fixing atmospheric nitrogen due to their ability of establishing symbiotic relation with some bacteria. Root nodules are among such globular structure formed on the roots of certain plants, notably legumes and alder, by symbiotic association between the plant and a nitrogen-fixing microorganism. Rhizobium in the case of legumes and Frankie in the case of alder and a variety of other plants (Lackie 2013) [36] . Root nodules are fully differentiated plant organs that harbor procaryotic nitrogen-fixing endosymbionts. The capacity to establish a root nodule symbiosis is confined to a single group of higher plants, the Rosid clade I. Within this clade, six tribes have evolved the capacity to nodulate with Frankie (a Gram-positive endosymbiont) while, within the Leguminosae (Fabaceae), symbiosis is established exclusively with members of the Rhizobium superfamily (which are all Gram-negative endosymbionts). The study of nodules has mainly involved crop legumes such as soybean, peas, beans, and alfalfa (Brewin 2001) [7] . N utilizes from soil and seed is required for plant productivity. About 25-30% of the total plant N (80-110 kg N per hectare per season) is supplied through the N2 fixation process (Harper 1971) [29] . Through symbiotic association with soil microbes, the legumes act as soil- improvement components of the agricultural system and increase the agricultural ecosystem. They are able to meet the great demand of N through the assimilation and absorption of inorganic N from the soil for crop plants (International Atomic Energy Agency, 2008) [34] . Rhizosphere a narrow region of the soil surrounding the roots that is directly influenced by root secretions and associated soil Microorganisms. The leguminous plants with Rhizobium in nodules are responsible for converting NH 3 from atmospheric N in the N-accumulation process where nitrogenase enzymes are involved. Many bacteria having hydrogenase to oxidize hydrogen in a reaction performed nitrogen fixation.