Plant Physiology Preview
Published on October 15, 2004; 10.1104/pp.104.046672
Received May 19, 2004
Returned for revision May 30, 2004
Accepted May 30, 2004
Cesium Toxicity in Arabidopsis
Corrina R. Hampton , Helen C. Bowen , Martin R. Broadley , John P. Hammond , Andrew Mead , Katharine A. Payne , Jeremy Pritchard , and Philip J. White *
Warwick HRI, Warwick CV35 9EF, United Kingdom; School of Biological Sciences, The University of Birmingham, Birmingham B15 2TT, United Kingdom
Warwick HRI, Warwick CV35 9EF, United Kingdom
Plant Sciences Division, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, United Kingdom
Warwick HRI, Warwick CV35 9EF, United Kingdom; Plant Sciences Division, University of Nottingham, Sutton Bonington Campus, Loughborough LE12 5RD, United Kingdom
School of Biological Sciences, The University of Birmingham, Birmingham B15 2TT, United Kingdom
* Corresponding author; email: philip-j.white{at}warwick.ac.uk.
Cesium (Cs) is chemically similar to potassium (K). However, although K is an essential element, Cs is toxic to plants. Two contrasting hypotheses to explain Cs toxicity have been proposed: (1) extracellular Cs+ prevents K+ uptake and, thereby, induces K starvation; and (2) intracellular Cs+ interacts with vital K+-binding sites in proteins, either competitively or noncompetitively, impairing their activities. We tested these hypotheses with Arabidopsis (Arabidopsis thaliana). Increasing the Cs concentration in the agar ([Cs]agar) on which Arabidopsis were grown reduced shoot growth. Increasing the K concentration in the agar ([K]agar) increased the [Cs]agar at which Cs toxicity was observed. However, although increasing [Cs]agar reduced shoot K concentration ([K]shoot), the decrease in shoot growth appeared unrelated to [K]shoot per se. Furthermore, the changes in gene expression in Cs-intoxicated plants differed from those of K-starved plants, suggesting that Cs intoxication was not perceived genetically solely as K starvation. In addition to reducing [K]shoot, increasing [Cs]agar also increased shoot Cs concentration ([Cs]shoot), but shoot growth appeared unrelated to [Cs]shoot per se. The relationship between shoot growth and [Cs]shoot/[K]shoot suggested that, at a nontoxic [Cs]shoot, growth was determined by [K]shoot but that the growth of Cs-intoxicated plants was related to the [Cs]shoot/[K]shoot quotient. This is consistent with Cs intoxication resulting from competition between K+ and Cs+ for K+-binding sites on essential proteins.
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