Cesium‐insensitive mutants of Arabidopsis thaliana

Summary 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 concentrations 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 M 2 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.