**8. Summary and prospects for research on urease from legumes**

In summary there are several indications that urease is important for efficient nitrogen assimilation. The urease substrate urea is derived from ureides and arginine. Arginine, is the richest nitrogen repository among the amino acids of legumes and plant seeds storage proteins. Urease are significant during the fixation of nitrogen in "tropical" legumes for example soybean and other plants. Urease-negative plants accumulate substantial, non-utilizable urea in both maternal and embryonic tissue. During germination of urease-negative seeds, further urea accumulates as a dead end in nitrogen metabolism. Although this accumulation may not be a lethal defect for large protein-rich legume seeds like soybean, small or protein-poor seeds, such as *Arubidopsis*, may be severely retarded or blocked in germination by the lack of an active urease. The better known, abundant legume seed ureases, for example, canatoxin urease, may perform a chemical defense function, similar to those postulated for some ureases of pathogenic bacteria. The ureases characterized to date, both from plants and bacteria, resemble each other in primary structure

#### *Function of Urease in Plants with Reference to Legumes: A Review DOI: http://dx.doi.org/10.5772/intechopen.102646*

and in their requirement for accessory genes. Although the functions of the accessory genes have not yet been fully characterized they are undoubtedly involved in insertion of a nickel cofactor at the urease active site. A study of urease has revealed what may be a universal phenomenon in plant biochemistry: that enzyme profiles may be a composite of both plant and microbial activities. Indeed, the microbial contributions may be physiologically significant to the plant; in legume such as soybean it has been observed that bacteria are responsible for generating urea from ureides and mitigating urea accumulation in some urease negative mutants. In the future, there is a real need to quantify nitrogen fluxes through urea and to assess in the field and greenhouse the effects of urease inactivation on germination, seedling vigor, protein deposition, etc. Such studies are best performed in isogenic plant lines differing in the presence or absence of urease. Leguminous plants such as Soybean is so far the best experimental subject in light of its battery of urease mutants, its importance as a protein crop, and knowledge of its physiology. The ability to eliminate the abundant embryo specific urease, exclusively, will allow us to focus on its possible defense roles, especially when the seed urease-negative trait is combined with those eliminating lectins [82], protease inhibitors [129], and other putative defense factors. Obviously, improved understanding of the extent of plant-bacterium interdependence requires that we successfully cure plants of the bacterium. It is not clear whether this has been achieved, even in plants regenerated from cell culture. Finally, we need the knowledge and understanding of the nature of ureases' control and also to find out if urease is participate in the ensemble of N assimilatory enzymes whose expression is coordinately controlled.
