title: Characterization of Cd translocation and identification of the Cd form in xylem sap of the Cd-hyperaccumulator Arabidopsis halleri.
abstract: Arabidopsis halleri is a Cd hyperaccumulator; however, the mechanisms involved in the root to shoot translocation of Cd are not well understood. In this study, we characterized Cd transfer from the root medium to xylem in this species. Arabidopsis halleri accumulated 1,500 mg kg(-1) Cd in the shoot without growth inhibition. A time-course experiment showed that the release of Cd into the xylem was very rapid; by 2 h exposure to Cd, Cd concentration in the xylem sap was 5-fold higher than that in the external solution. The concentration of Cd in the xylem sap increased linearly with increasing Cd concentration in the external solution. Cd transfer to the xylem was completely inhibited by the metabolic inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP). Cd concentration in the xylem sap was decreased by increasing the concentration of external Zn, but enhanced by Fe deficiency treatment. Analysis with 113Cd-nuclear magnetic resonance (NMR) showed that the chemical shift of 113Cd in the xylem sap was the same as that of Cd(NO3)2. Metal speciation with Geochem-PC also showed that Cd occurred mainly in the free ionic form in the xylem sap. These results suggest that Cd transfer from the root medium to the xylem in A. halleri is an energy-dependent process that is partly shared with Zn and/or Fe transport. Furthermore, Cd is translocated from roots to shoots in inorganic forms.
authors.affiliation: Research Institute for Bioresources, Okayama University, Kurashiki 710-0046, Japan.
authors.forename: Daisei
authors.initials: D
authors.lastname: Ueno
authors.forename: Takashi
authors.initials: T
authors.lastname: Iwashita
authors.forename: Fang-Jie
authors.initials: FJ
authors.lastname: Zhao
authors.forename: Jian Feng
authors.initials: JF
authors.lastname: Ma
mesh_terms: D000222:Adaptation, Physiological / Q000187:drug effects; D017360:Arabidopsis / Q000145:classification / Q000187:drug effects / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002104:Cadmium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D007501:Iron / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000378:metabolism; D012996:Solutions; D013997:Time Factors; D052584:Xylem / Q000187:drug effects / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology
chemical_list: D012996:Solutions; D002104:Cadmium; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D007501:Iron; D015032:Zinc