FEMALE GAMETOPHYTE DEVELOPMENT IN MAIZE - MICROTUBULAR ORGANIZATION AND EMBRYO SAC POLARITY

The developmental stages of the maize embryo sec were correlated with the corresponding silk lengths of ear florets in the female infloresce nce. The development of embryo sacs in the ovules of spikes occurs in a gradient pattern with the initiation of the embryo sec beginning at the base of the ear and progressing to the top. At the beginning of me iosis, the presence of conspicuous cortical microtubules coincides wit h the extensive elongation of the megasporocyte. The spindles at metap hase I and II align along the long axis of the megasporocyte leading t o the linear alignment of the dyad and tetrad of megaspores. During me gagametogenesis, micropylar and chalazal nuclei of the embryo sac unde rgo synchronized divisions and migration at the second and third mitos is. Radiate perinuclear microtubules am 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 ori entation 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 th e filiform apparatus occur right after the first division of the antip odal cells. The different patterns of organization of microtubules in the cells of the mature embryo sec reflect their structural adaptation s for their future function.