Cesium-insensitive mutants of Arabidopsis thaliana

The molecular analysis of solute transport across the plasma membrane in animals and microorganisms has been aided by the analysis of well-defined transport mutants. To obtain mutant plants with genetic defects in cation transport, the inhibitory effect of monovalent cations (Li⁺, Na⁺, Rb⁺, and Cs⁺) on Arabidopsis thaliana seed germination was tested. Cesium was unique in that at low concentration it strongly inhibited seedling development. In this report it is demonstrated that cesium is a competitive inhibitor for potassium transport in A. thaliana and its toxicity is closely tied to the level of potassium supplied. Conditions were obtained to maximize the cesium-sensitivity for seed germination in a large population, and selection for resistance using M₂ seeds derived from ethyl methane sulfonate (EMS)-treated plants yielded several dozen resistant plants. Seeds derived from these plants yielded cesium-insensitive mutant lines with heritable changes in energy-dependent potassium uptake. In progeny from a backcross to wild-type plants, at least one of the lines showed the segregation ratio expected for a single-gene recessive mutation and an RFLP analysis mapped the mutant locus to the top of chromosome 4.