Cadmium impairs ion homeostasis by altering K+ and Ca2+ channel activities in rice root hair cells

Authors

  • SUN LI,

    1. NJU–NJFU Joint Institute for Plant Molecular Biology, School of Life Sciences, Nanjing University, Nanjing 210093, China
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  • JINGLING YU,

    1. NJU–NJFU Joint Institute for Plant Molecular Biology, School of Life Sciences, Nanjing University, Nanjing 210093, China
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  • MINJIE ZHU,

    1. NJU–NJFU Joint Institute for Plant Molecular Biology, School of Life Sciences, Nanjing University, Nanjing 210093, China
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  • FUGENG ZHAO,

    Corresponding author
    1. NJU–NJFU Joint Institute for Plant Molecular Biology, School of Life Sciences, Nanjing University, Nanjing 210093, China
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  • SHENG LUAN

    Corresponding author
    1. NJU–NJFU Joint Institute for Plant Molecular Biology, School of Life Sciences, Nanjing University, Nanjing 210093, China
    2. Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA
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F. Zhao. Fax: +86 25 8359 2684; e-mail: fgzhao@nju.edu.cn; S. Luan. Fax: +510 642 4995; e-mail: sluan@nature.berkeley.edu

ABSTRACT

Cadmium (Cd2+) interferes with the uptake, transport and utilization of several macro- and micronutrients, which accounts, at least in part, for Cd2+ toxicity in plants. However, the mechanisms underlying Cd2+ interference of ionic homeostasis is not understood. Using biophysical techniques including membrane potential measurements, scanning ion-selective electrode technique for non-invasive ion flux assays and patch clamp, we monitored the effect of Cd2+ on calcium (Ca2+) and potassium (K+) transport in root hair cells of rice. Our results showed that K+ and Ca2+ contents in both roots and shoots were significantly reduced when treated with exogenous Cd2+. Further studies revealed that three cellular processes may be affected by Cd2+, leading to changes in ionic homeostasis. First, Cd2+-induced depolarization of the membrane potential was observed in root hair cells, attenuating the driving force for cation uptake. Second, the inward conductance of Ca2+ and K+ was partially blocked by Cd2+, decreasing uptake of K+ and Ca2+. Third, the outward K+ conductance was Cd2+-inducible, decreasing the net content of K+ in roots. These results provide direct evidence that Cd2+ impairs uptake of Ca2+ and K+, thereby disturbing ion homeostasis in plants.

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