Among the defective kernel mutants there are two types of developmental mutants: (1) those that are blocked prior to the formation of leaf primordia and (2) those that form leaf primordia but fail to germinate when tested in culture or at kernel maturity (Sheridan and Neuffer, J. Hered. 73:319-329, 1982). We have examined four mutants (cp*-E1113A. rgh*-E1210, fl*-E1253B, and dcr*-E1428) of the first type and one (cp*-E1399A) of the second type. Mutant E1113A is located on 1L; the remaining four have not been located to chromosome arm.
All five developmental mutants were examined at intervals to determine when a mutant phenotype was first apparent, to document the course of development, and to assess the stage specificity of their blocks. Homozygous mutant kernels from segregating self-pollinated ears of Missouri-grown materials were examined by paraffin sectioning at early (13-17 days post-pollination), middle (17-35 days) and late (36-60 days) stages of development. These materials were kindly provided by M. G. Neuffer. North Dakota-grown materials were examined by paraffin sectioning and in fresh dissections at kernel maturity (60 days or later).
Embryos of the five mutants were markedly retarded in their size and developmental stage (Figure 1). This was evident from the time mutant kernels were first distinguishable. The mutants differed, however, in the course of their development (Table 1). Four of the mutants, E1113A, E1210, E1399A and E1428, were stage specific in their blocks. The fifth, E1253B, was blocked variably just before to just after formation of the first leaf primordium (Figure 1). The stage-specificity and the variety of developmental profiles and arrest phenotypes of these five mutants suggest that they represent specific genes controlling diverse processes in embryo development.
Table 1. Morphological Characterization of Developmental Mutants
Janice K. Clark and William F. Sheridan
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