Degree Type

Dissertation

Date of Award

1993

Degree Name

Doctor of Philosophy

Department

Botany

First Advisor

Harry T. Horner

Second Advisor

Reid G. Palmer

Abstract

Various aspects of early embryo, endosperm, and ovule development are described in soybean utilizing techniques in autoradiography, cytophotometry, image analysis, and light and electron microscopy. Pollen tube passage to the egg is facilitated by the break down of nucellar cells subtending the abfunicular synergid and degeneration of the latter prior to fertilization. Autoradiographic evidence indicates that the accumulation of [superscript]14C label assimilates within the ovular tissues is spatially and temporally regulated. At the zygote through proembryo stages, labeled assimilates enter the embryo sac micropylarly via the wandlabrinthe and chalazally via the hypostase. Nutrient movement into the lateral regions of the embryo sac seems to be blocked by a cuticle between the inner integument and embryo sac. At the globular embryo stage, the differentiation of the endothelium, fragmentation of the embryo sac cuticle, vascularization of the integuments, and the wall ingrowths of the cellular endosperm aid in the movement of label into the lateral regions of the embryo sac. Other features important in nutrient flux to the embryo are the: persistent acellular condition of the chalazal process; endospermic sheath surrounding the globular embryo; cuticle on the surface of the globular embryo but not on the suspensor; and transfer cell-like nature of the suspensor cells. Cellularization of the endosperm involves the formation of anticlinal sheet-like walls from the central cell wall. These walls fuse at their edges to form cylinders. Periclinal walls are laid down within the cylinders to form layers of endosperm cells centripetally. Degeneration of the endosperm appears to be an autolytic process and not due to physical breakage by the encroaching embryo. The mean size and ploidy condition (2C-4C) of the embryo nuclei is fairly stable at all stages studied. Only a few nuclei (3%) of the late heart-shaped embryo have ploidy levels above 4C. Free-nuclear endosperm nuclei are larger than those of the cellular endosperm. Most endosperm nuclei are in the expected 3C-6C ploidy range, but elevated ploidy levels are noted during endosperm cellularization. Endosperm senescence is correlated with nuclear DNA loss over time.

DOI

https://doi.org/10.31274/rtd-180813-11909

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Mark Alan Chamberlin

Language

en

Proquest ID

AAI9334967

File Format

application/pdf

File Size

185 pages

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