This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Cadmium (Cd) is a highly toxic pollutant of soils, which inhibits plant growth and yield production, and is frequently accumulated by agriculturally important crops with a significant potential to impair animal and human health. However, in China, up to 20 million hectare has been polluted by this metal. Plants hyperaccumulating Cd are of considerable interest for potential phytoremediation of the contaminated soils. Sedum alfredii has been identified as a Cd hyperaccumulator native to China, and the better understanding of its physiological and molecular mechanisms in hyperaccumulating Cd may contribute to its potential use in phytoremediation. Here, the speciation of metal ions was one of the important aspects in metal hypertolerance of hyperaccumulators. Some ligands (sulfur, oxygen/nitrogen coordinated) was suggested to be involved in the detoxification of metals in the hyperaccumulating plants which exhibited as transport, chelation, compartmentation and cellular restoration. This work is a frontier research on cellular localization and speciation of Cd in the hyperaccumulator S. alfredii by using micro-SXRF and XAS. XAS is an element specific method and, therefore, particularly suited for analyzing the in vivo ligand environment of Cd in plants. Much work has been done by our research group on physiological characterization of uptake, translocation and accumulation of Zn and Cd in S. alfredii, and several experimental evidence has been obtained for the explanation of Zn localization and speciation in the S. alfredii by micro-SXRF and XAS experiments in BSRF, China, and KEK-PF, Japan. Still, it is necessary to further understand the speciation of Cd at cellular levels by using micro-SXRF and XAS, which is not detectable in BSRF or KEK. Thus, we apply for this experiment at SSRL station aiming at explaining the speciation of Cd in S. alfredii and its homeostatic mechanisms of Zn and Cd hyperaccumulation in S. alfredii.
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