Natural hyperaccumulators of Ni provide examples of how this metal may move in soybean. A series of urease-negative mutants in soybean has been exploited to determine the origins of urea and the conditions influencing its accumulation. In soybean, most fixed N is 'presented' to green tissues as ureides, breakdown products of purines formed in the nodule. While it had long been assumed that ureides are degraded to urea, the urease-negative mutants indicate that ureides are degraded to ammonia, bypassing urea. Part of this separation involves controlling the movement of arginine into the mitochondrion, the site of arginase mitochondrial .
Current studies are on the isolation and characterization of arginine transporters.
In addition to varying P availability other variables are genotypic differences in P use efficiencies and transgenic plants altered in P-sensing and in putative signal transduction pathways. Finally, Polacco's group examines the role of Ni and various accessory proteins in activating apo-urease. Interestingly, one of the soybean accessory proteins resembles a protein required for Ni activation of hydrogenase, a bacterial enzyme not yet identified in plants. Soybean Genes Involved in Nickel Insertion into Urease. E-mail the Webmaster.