Department of Plant Sciences

Understandings of molecular mechanisms of boron action in plants remain limited to those known in cell walls. Toxicity mechanisms are largely unknown. In order to obtain the insights into mechanisms of boron toxicity, screening of Arabidopsis thaliana mutants sensitive to excess boron was conducted. The screening strategy was to select plants that grow reasonably well under normal boron condition (0.03 mM boric acid), but not under high boron condition (3 mM boric acid). We used root growth as a selection parameter. About 20,000 ethyl methanesulfonate (EMS) mutagenized M2 seeds of Arabidopsis thaliana (ecotype Col-0) were grown on plates containing high levels of boric acid (3 mM). After 2 weeks, plants showed short-root were transferred to media containing normal levels of boric acid (0.03 mM) and those plants that recovered growth were selected. The phenotypes were reevaluated at M3 generation and reselected plants were crossed with Col-0 for genetic analysis. Finally, we isolated 7 recessive mutants. Most of the mutants showed extremely shorter roots than wild type under boron toxicity, but not under the normal condition, indicating its sensitivity to excess boron.