bor1-1, an Arabidopsis thaliana mutant that requires a high level of boron

bor1-1 (high boron requiring), an Arabidopsis thaliana mutant that requires a high level of B, was isolated. When the B concentration in the medium was reduced to 3 mu M, the expansion of rosette leaves was severely affected in bor1-1 but not in wild-type plants. In a medium containing 30 mu M B the mutant grew normally but showed female sterility, whereas the wild type was able to set seeds. These defects of the bor1-1 mutant were not detected with supplementation of 100 mu M B. In vivo concentrations of B in bor1-1 mutants were lower than those of the wild type, especially in the inflorescence stems. Tracer experiments using B-10 suggested that the mutant has defects in uptake and/or translocation of B. The mutation was mapped on the lower arm of chromosome 2.