Date of Award

January 2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

William F. Sheridan

Abstract

The maize zygote normally develops over approximately 45-days into a mature embryo comprised of five or six leaf primordia and several root primordia. The developing embryo passes through the proembryo, transition, coleoptilar and stage 1 (first leaf primordium) morphogenetic stages followed by the iterative formation of additional leaf primordia during stages 2 through 6 according to Abbe and Stein (1954). Using ethyl methanesulfonate (EMS) treatment of maize pollen from W22 inbreed we have produced lethal embryo specific (emb) mutants that have no obvious effects on endosperm development except for some reduction in kernel size in some cases. Thirteen emb mutants were selected for further study. Ten mature kernels that exhibited the emb phenotype were dissected for morphological analysis. Eight of the embryo specific mutants had their development blocked at the transition to coleoptilar stage. One embryo specific mutant had its development blocked from the proembryo stage to the coleoptilar stage. Two embryo specific mutants were blocked from the coleoptilar stage to stage 1 or later. Two embryo specific mutants were blocked from the coleoptilar stage to beyond stage 1. Germination tests of 25 kernels samples containing mutant embryos revealed that almost all had zero germination although some did germinate albino seedlings from both normal and mutant kernels. The use of EMS resulted in 30 self-pollinated ears out of 238 producing emb phenotype which is a frequency of 12.6%. The abundance of EMS-induced mutations blocked early in embryo development suggest an abundance of genes acting during this period to regulate the changing patterns of signaling molecules that underlie the cellular changes occurring during the proembryo and coleoptile stages. In order to further understand embryo development, 10 fluorescent protein constructs were evaluated in normal developing embryos from the proembryo stage to stage 1. Additionally, 11 fluorescent protein constructs were crossed with the emb mutant lines to later evaluate how the mutations affect expression patterns as compared to the normal embryos. Two of the constructs involved with auxin transport, PIN1, and auxin inducible tissue expression, DR5, were more thoroughly evaluated. The work performed here is foundational to understanding the genes involved in embryogenesis and will aid in developing a systems biology for embryogenesis.

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