Speziesanalytik von Cadmium und Thallium in nativen Rapspflanzen (Brassica napus)
Speciation of cadmium and thallium in native rape (Brassica napus)
The speciation of cadmium and thallium was studied in leaves from unpolluted rape of two different growth stages. In average the cytoplasmic fraction contained 37% of the whole cadmium or 84% of the whole thallium, respectively. Gel filtration of the cytoplasmic samples revealed a high (M>80,000 g/mol) and two low molecular weight cadmium species (M=4400 g/mol), but only one thallium species (M=3800 g/mol). No free ionic species have been detected. The determinations of metals were performed by ET-AAS, with a recovery between 60% and 90%. The low molecular weight species containing most of the cadmium was further purified by means of ion-exchange chromatography and gel filtration. The resulting strong anionic peptide showed a low absorption at 280 nm. The molar cadmium/peptide ratio was about 1/140. An amino acid analysis indicated no cysteine or methionine. Conclusively, the main cytoplasmic cadmium species in native rape neither belongs to the well known classes of sulphureous phytochelatins nor to the metallothioneins.
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