HEAVY METALS IN HYPERACUMULATOR PLANTS

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Heavy metal uptake in plants is not only an important basic research area, but also has an impact on human nutrition and its application for the phytoremediation of contaminated soils as well as for the commercial extraction of metals from naturally metal-rich soils otherwise unsuitable for conventional mining operations. These plants are able to accumulate several percent of metals in the dry mass of their above-ground parts. The unusual physiology of these plants is a topic of intensive worldwide research efforts, being the speciation of the metals inside the plant one of the presently most interesting research topics. In a recent study (K¿pper et al., 2004) in tissues where the epidermis comprises the largest tissue volume (e.g. leaves), mainly weak oxygen ligands were found. In other tissues, a significant proportion of the ligands were strong ligands (sulphur ligands for cadmium and histidine for zinc). The planned project shall elucidate, by directly measuring EXAFS of individual selected cells of various functions, in frozen-hydrated samples, whether these differences between tissues really originate from a different speciation of the metal in specific cell types. This knowledge would reveal if different tissues, or cells with different function in the same tissue, may need a different strategy of protection from heavy metal toxicity. Such differences have been assumed but so far were never investigated. Preliminary studies in July 2004 pointed out problems and solutions regarding the resolution needed for a future successful completion of these experiments.