THE PLANT CELL, Vol 6, Issue 6 845-861, Copyright © 1994 by American Society of Plant Biologists
Female Gametophyte Development in Maize: Microtubular Organization and Embryo Sac Polarity
B. Q. Huang and W. F. Sheridan
Department of Biology, University of North Dakota, Grand Forks, North Dakota 58202-9019
The developmental stages of the maize embryo sac were correlated with the
corresponding silk lengths of ear florets in the female inflorescence. The
development of embryo sacs in the ovules of spikes occurs in a gradient
pattern with the initiation of the embryo sac beginning at the base of the
ear and progressing to the top. At the beginning of meiosis, the presence
of conspicuous cortical microtubules coincides with the extensive
elongation of the megasporocyte. The spindles at metaphase I and II align
along the long axis of the megasporocyte leading to the linear alignment of
the dyad and tetrad of megaspores. During megagametogenesis, micropylar and
chalazal nuclei of the embryo sac undergo synchronized divisions and
migration at the second and third mitosis. Radiate perinuclear microtubules
are present during the interphase of the second and third mitosis, and
inter-sister nuclear microtubules occur at the late four-nucleate embryo
sac. The configuration and orientation of the spindles, phragmoplasts, and
pairs of nuclei result in precise positioning of the nuclei. The fusion of
the polar nuclei and the formation of a microtubule organizing center-like
structure in the filiform apparatus occur right after the first division of
the antipodal cells. The different patterns of organization of microtubules
in the cells of the mature embryo sac reflect their structural adaptations
for their future function.
