Arrested Embryos from the bio1 Auxotroph of Arabidopsis thaliana Contain Reduced Levels of Biotin

The bio1 auxotroph of Arabidopsis thaliana is a recessive embryonic lethal that forms normal plants in the presence of biotin. The purpose of this study was to determine whether aborted seeds produced by heterozygous plants grown without vitamin supplements contained reduced levels of biotin. Two methods were used to determine the biotin content of mutant and wild-type tissues: streptavidin binding in microtiter plates and growth of the biotin-requiring bacterium Lactobacillus plantarum. Total biotin was measured in extracts prepared from immature seeds prior to desiccation. Aborted seeds produced by heterozygous (bio1/BIO1) plants contained some biotin in the maternal seed coat but virtually no detectable biotin in the arrested embryo. This lack of biotin was not observed in arrested embryos from other mutants with similar patterns of abnormal development. These results are consistent with the model that bio1 tissues are defective in biotin synthesis. The alternative model of increased degradation is inconsistent with the recessive nature of the mutation and the ability of rescued plants to continue growing for several weeks following removal of supplemental biotin.