Growth in vitro of arrested embryos from lethal mutants ofArabidopsis thaliana.

Seventeen embryo-lethal mutants ofArabidopsis thaliana with lethal phases ranging from the globular to mature cotyledon stages of development were analyzed by culturing arrested embryos on nutrient media designed to promote either callus formation or the completion of embryo development and the recovery of homozygous mutant plants. Enriched media supplemented with vitamins, amino acids, and nucleosides were used to identify potential auxotrophic mutants. Wild-type embryos produced extensive callus on basal and enriched media supplemented with 2,4-D and kinetin. Numerous roots developed when wildtype callus was grown in the presence of NAA and kinetin. Mutant embryos arrested prior to the heart stage of development formed only a slight amount of callus on basal and enriched media. Arrested embryos from mutants 122G-E and 112A-2A reached a later stage of development and gave the most interesting responses in culture. 122G-E mutant embryos failed to grow on basal media but produced extensive callus and homozygous mutant plants on enriched media. The specific nutrient required for growth of this mutant remains to be determined. Arrested embryos from mutant 112A-2A developed into abnormal plants without roots when placed in culture. Mutant callus also failed to form roots on a variety of root-inducing media. Expression of this mutant gene therefore disrupts development of the root apical meristem during both embryogenesis in vivo and organogenesis in vitro.