CHARACTERIZATION OF THE DOMINANT STATURE MUTANT OF MAIZE

Abstract

D8 originally designated as the dominant stature mutant of maize, was characterized and shown to be incompletely dominant. The study included morphological measurements, cytology, hormone studies, and enzyme and protein analysis. The effect of the D8 mutation can be detected after 40 hours of germination of the coleoptile. Dwarf (D8/d8) seedling length is 1/2 of the normal sib length for coleoptile, first leaf, and mesocotyl. The cell measurements indicate that cell elongation and cell division are involved in the size discrepancy. Mature dwarf plants have shorter internodes and the shorter, wider leaves are a darker green than the normal plant. The homozygous D8/D8 displays normal meiotic division and pollen formation is normal upto the 2 nucleate stage. Pollen viability of the homozygote is low and no seed was obtained in crosses involving this genotype. Several biological stains were used to test pollen viability with the results indicating greater than 85% viability for the heterozygote and less than 15.6% viability for the homozygote. The examination of the pachytene chromosomes of heterozygotes indicates a loop on a large chromosome. This loop is only found in the D8 heterozygote and implies a duplication or deficiency may be involved with the D8 phenotype. Avena straight growth bioassay for auxin displayed no significant difference in auxin production between dwarf and normal coleoptile tips. The D8 dwarf seedlings responded to the exogenous application of auxin, kinetin, and casamino acids in the same pattern as the normal seedlings, but never attained normal stature. Gibberellic acid (GA) and cyclic adenosine monophosphate (cAMP) exogenous applications displayed a difference in dwarf and normal response patterns and implies that the utilization or destruction of these substances may be involved. The investigation of Laemmli gel patterns for the three genotypes failed to show a difference. The soluble proteins formed 27 bands from the coleoptiles of each phenotype. Adh-1 gel patterns and pollen staining was utilized to examine the possibility of a deletion overlapping this locus. The Adh-1 locus has been mapped proximal to the D8 locus. The results indicate the Adh locus is not included in the putative D8 deletion.