An examination of mature kernels of 17 defective kernel mutants believed to be good candidates for designation as developmental type mutants revealed that 14 of the mutants were of this type, since they were unable to form leaf primordia during kernel development. Nine of the 14 mutants are located to chromosome arm and five arms are represented (1S, 1L, 3L, 4L, and 5L). These developmental mutants are blocked at several different points in the embryonic sequence ranging from the proembryo through the transition to the coleoptilar stage (Abbe and Stein, 1954). Among the 14 mutants 12 appear to be stage specific and two mutants range in expression from the transition to the coleoptilar stage. Since all of these mutants have a defective endosperm, as well as a defective embryo, an examination of embryo-endosperm interaction is warranted to determine whether the defective endosperm is responsible for the defective condition of the embryo or whether it is the genetic constitution of the embryo itself that determines its developmental fate. Among the nine developmental type mutants located to chromosome arm, five are allelic and located on 1S. An examination of one of these mutants on 1S and the four other located mutants was performed using kernels (from the arm locating ear) that contained a genetically normal endosperm and a genetically mutant embryo and kernels that contained a genetically mutant endosperm and a genetically normal embryo. In all five cases examined, the genetically mutant embryos were defective and were not aided in their development by the presence of a normal endosperm. Data are incomplete for the reciprocal arrangement but for two mutants it is evident that a genetically mutant endosperm results in death of a genetically normal embryo after germination at the seedling stage. It appears therefore, to the extent that data are available, that it is the genotype of the embryo that determines its developmental fate, that it cannot be helped by a normal endosperm, but that, in some cases, a defective endosperm can produce seedling death. The results to date indicate that the developmental-type mutants should be valuable in studying the genetic regulation of embryonic development as well as embryo-endosperm interaction.
William F. Sheridan and M. G. Neuffer
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