Enhanced Cd2+-selective root-tonoplast-transport in tobaccos expressing Arabidopsis cation exchangers

V. Koren'kov, S. Park, N. H. Cheng, C. Sreevidya, J. Lachmansingh, J. Morris, K. Hirschi, G. J. Wagner

Research output: Contribution to journalArticlepeer-review

87 Scopus citations


Several Arabidopsis CAtion eXchangers (CAXs) encode tonoplast-localized transporters that appear to be major contributors to vacuolar accumulation/sequestration of cadmium (Cd2+), an undesirable pollutant ion that occurs in man largely as a result of dietary consumption of aerial tissues of food plants. But, ion-selectivity of individual CAX transporter types remains largely unknown. Here, we transformed Nicotiana tabacum with several CAX genes driven by the Cauliflower Mosaic Virus (CaMV) 35S promoter and monitored divalent cation transport in root-tonoplast vesicles from these plants in order to select particular CAX genes directing high Cd 2+ antiporter activity in root tonoplast. Comparison of seven different CAX genes indicated that all transported Cd2+, Ca 2+, Zn2+, and Mn2+ to varying degrees, but that CAX4 and CAX2 had high Cd2+ transport and selectivity in tonoplast vesicles. CAX4 driven by the CaMV 35S and FS3 [figwort mosaic virus (FMV)] promoters increased the magnitude and initial rate of Cd2+/H + exchange in root-tonoplast vesicles. Ion selectivity of transport in root-tonoplast vesicles isolated from FS3::CAX4-expressing plant lines having a range of gene expression was Cd2+>Zn2+»Ca 2+»Mn2+ and the ratios of maximal Cd2+ (and Zn2+) versus maximal Ca2+ and Mn2+ transport were correlated with the levels of CAX4 expression. Root Cd accumulation in high CAX4 and CAX2 expressing lines was increased in seedlings grown with 0.02 μM Cd. These observations are consistent with a model in which expression of an Arabidopsis-gene-encoded, Cd2+-efficient antiporter in host plant roots results in greater root vacuole Cd2+ transport activity, increased root Cd accumulation, and a shift in overall root tonoplast ion transport selectivity towards higher Cd2+ selectivity. Results support a model in which certain CAX antiporters are somewhat more selective for particular divalent cations.

Original languageEnglish (US)
Pages (from-to)403-411
Number of pages9
Issue number2
StatePublished - Jan 2007
Externally publishedYes


  • Arabidopsis cation exchanger
  • Cadmium
  • Metal-selectivity
  • Tobacco
  • Tonoplast

ASJC Scopus subject areas

  • Genetics
  • Plant Science


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