Degree Type

Dissertation

Date of Award

1998

Degree Name

Doctor of Philosophy

Department

Agronomy

First Advisor

Ricardo J. Salvador

Abstract

An understanding of cellular events contributing to normal endosperm formation in the maize kernel may provide better models of the construction of grain yield. A commercial hybrid maize, Dekalb 580, was grown in a controlled environment to study dynamics of cellular events in three regions during endosperm development, and to ascertain if this genotype has an indeterminate pattern of endosperm cell division. Longitudinal sections in two planes of endosperm show uniform sizes for both nuclei and cells during the early stages of endosperm development. As endosperm develops, nuclei and cells become increasingly variable in size. In addition, cells acquire irregular shapes. Starch granules are more densely packed in the central and peripheral cells than in basal cells. Histochemistry reveals that mean starch granule diameter and volume sharply increase between 20 and 30 days after pollination (dap). Granules in peripheral endosperm cells follow similar trends, but then remain significantly unchanged (P < 0.05), whereas central endosperm cells show another sharp increase 40 to 50 dap, when maximum volume is achieved. A decrease in mean nuclear diameter and volume was observed after 30 dap. During this time, nuclear size in the central kernel continues to increase until a peak level is reached at 40 dap. Regardless of differences in cell sizes within various regions, a pattern of incremental development until a peak level at 30 dap is common, excepting peripheral cells that maintain almost the same size after 30 dap. Aleurone cells follow a similar trend, though their nuclei show a consistent increase in size throughout the developmental period. The developmental pattern of whole endosperm cells differs from that of nuclei, and this difference is manifested by cells and nuclei of the central kernel, which reach maximum volume at 30 and 40 dap, respectively. Photocytometry indicates that number of endosperm nuclei reaches maximum at 20 dap and plummets thereafter. Thus, the number of cells formed in an endosperm is determined quite early during development of grain. Starch granules reach peak levels 30 to 40 dap and remain essentially constant throughout grain development. Flow cytometry reveals patterns of DNA endoreduplication that paralleled those of nuclear size.

DOI

https://doi.org/10.31274/rtd-180813-5010

Publisher

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

Copyright Owner

Anthony Onwuli Iheanyi Anaele

Language

en

Proquest ID

AAI9826509

File Format

application/pdf

File Size

108 pages

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