title: Characteristics of cadmium uptake in two contrasting ecotypes of the hyperaccumulator Thlaspi caerulescens.
abstract: Uptake of Cd and Zn by intact seedlings of two contrasting ecotypes of the hyperaccumulator Thlaspi caerulescens was characterized using radioactive tracers. Uptake of Cd and Zn at 2 degrees C was assumed to represent mainly apoplastic binding in the roots, whereas the difference in uptake between 22 degrees C and 2 degrees C represented metabolically dependent influx. There was no significant difference between the two ecotypes in the apoplastic binding of Cd or Zn. Metabolically dependent uptake of Cd was 4.5-fold higher in the high Cd-accumulating ecotype, Ganges, than in the low Cd-accumulating ecotype, Prayon. By contrast, there was only a 1.5-fold difference in the Zn uptake between the two ecotypes. For the Ganges ecotype, Cd uptake could be described by Michaelis-Menten kinetics with a V(max) of 143 nmol g(-1) root FW h(-1) and a K(m) of 0.45 microM. Uptake of Cd by the Ganges ecotype was not inhibited by La, Zn, Cu, Co, Mn, Ni or Fe(II), and neither by increasing the Ca concentration. By contrast, addition of La, Zn or Mn, or increasing the Ca concentration in the uptake solution decreased Cd uptake by Prayon. Uptake of Ca was larger in Prayon than in Ganges. The results suggest that Cd uptake by the low Cd-accumulating ecotype (Prayon) may be mediated partly via Ca channels or transporters for Zn and Mn. By contrast, there may exist a highly selective Cd transport system in the root cell membranes of the high Cd-accumulating ecotype (Ganges) of T. caerulescens.
authors.affiliation: IACR-Rothamsted, Agriculture and the Environment Division, Harpenden, Hertfordshire AL5 2JQ, UK. Fangjie.Zhao@bbsrc.ac.uk
authors.forename: Fang-Jie
authors.initials: FJ
authors.lastname: Zhao
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Hamon
authors.forename: Enzo
authors.initials: E
authors.lastname: Lombi
authors.forename: Mike J
authors.initials: MJ
authors.lastname: McLaughlin
authors.forename: Steve P
authors.initials: SP
authors.lastname: McGrath
mesh_terms: D001665:Binding Sites; D019607:Brassicaceae / Q000187:drug effects / Q000502:physiology*; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology; D002106:Cadmium Radioisotopes; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002413:Cations, Divalent / Q000494:pharmacology; D002473:Cell Wall / Q000502:physiology; D007700:Kinetics; D018517:Plant Roots / Q000187:drug effects / Q000502:physiology*; D013045:Species Specificity; D014700:Verapamil / Q000494:pharmacology; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology; D015037:Zinc Radioisotopes
chemical_list: D002106:Cadmium Radioisotopes; D002121:Calcium Channel Blockers; D002413:Cations, Divalent; D015037:Zinc Radioisotopes; D002104:Cadmium; D014700:Verapamil; D015032:Zinc; D002118:Calcium