EXECUTIVE SUMMARY The myriad of human activities including strategic and energy development at various DOE installations have resulted in the contamination of soils and waterways that can seriously threaten human and ecosystem health. Development of efficacious and economical remediation technologies is needed to ameliorate these immensely costly problems. Bioremediation (both plant and microbe-based) has promising potential to meet this demand but still requires advances in fundamental

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... e. For bioremediation of heavy metals, the three-way interaction of plant root, microbial community, and soil organic matter (SOM) in the rhizosphere is critically important for long-term sustainability but often underconsidered. Particularly urgent is the need to understand processes that lead to metal ion stabilization in soils, which is crucial to all of the goals of bioremediation: removal, stabilization, and transformation. We have developed the tools for probing the chemistry of plant rhizosphere and generated information regarding the role of root exudation and metabolism for metal mobilization and sequestration. Relevance, Impact, and Technology Transfer In the long run, this research should lead to fundamental advances in the understanding of plant-microbe interactions and how these interactions govern the long-term fate of heavy metals in belowground ecosystems. There should be direct applicability of these tools and knowledge to facilitate and enhance field implementation and monitoring of metal bioremediation. METHODS AND RESULTS Our work has focused on examining the influence of important rhizosphere factors (i.e. root exudation chemistry and SOM) on metal ion accumulation and metabolism in crop plants such as barley, wheat, and rice. In order to understand the chemistry involved in metal ion mobilization by plants, we developed advanced NMR methodology in combination with GC-MS for a comprehensive profiling of root exudates (Fan et al., 1997a; Fan and Lane, in press), which has been a difficult challenge by conventional approach. Using a similar approach, the intracellular profiles of metal reactive compounds (MRC) in plants were also acquired, which is important to the understanding of how metal ions are sequestered within plants. Moreover, we have completed the development of a rapid and parallel sample analysis (gel electrophoretic) method for characterizing tissue thiol-rich peptides (important to sequestration of Cd and other heavy metals) .