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Morphological changes in the nuclear degeneration of the synergid (mainly the synergid that receives the pollen tube) and antipodal cells inTriticum aestivumwere studied. Although located in the same embryo sac, and derived from the same megaspore, nuclear degeneration of the synergid and antipodal cells differs greatly. Nuclear degeneration in the synergid is characterized by pycnosis, i.e., total chromatin condensation, nuclear deformation and distinct shrinkage in volume, followed by the formation of an irregular and densely stained mass-the degenerated nucleus-while the nucleolus disappears prior to the degradation of chromatin. In contrast, in the nuclear degeneration of antipodal cells, chromatin is only partly condensed and the nuclear volume changes only slightly after the distinct chromatin condensation. Chromatolysis then occurs, i.e., stainable contents disappear while the nuclear envelope is retained. The nucleoli persist after the disappearance of the chromatin. The possible functions of nuclear degeneration of synergid and antipodal cells are discussed, especially with respect to the guidance of pollen tube growth and the proliferation of free-nuclear endosperm. The degeneration of synergids and antipodal cells inT. aestivumare distinct forms of programmed cell death, regarded as cytoplasmic cell death and nuclear degradation in advance of cell death, respectively. [ABSTRACT FROM AUTHOR]

The antipodal cells have been the stepchildren in most investigations of the female gametophyte. In Hordeum vulgare cv. Bomi, three antipodal cells are originally developed chalazally but because of differential growth of the embryo sac they soon become laterally situated and their number increases to 35-50 cells and the shape, size and structure of the cells change in the time before as well as after fertilization. The cells persist until about 60-70 h after pollination. At that time, the embryo consists of about 12-15 cells and a cellularization of the nuclear endosperm has started peripherally. The size of nuclei, and especially nucleoli, in the antipodal cells increases tremendously in the investigated period and the amounts of organelles also change. The walls of antipodals are diversified depending on which cells they are separating, and wall invaginations are developed especially between antipodal cells and surrounding nucellar cells in the placental region. The mitochondria appear in various shapes in section view, very often as cups or dumbbells with a rim in the ends containing cristae and a thin cristae-free base. These bases are sometimes stretched out as thin parts and at last a simple parting occurs. Binary fissions of the plastids happen especially in the hours before and just after egg fertilization. ER is extraordinarily well developed in the whole period of investigation and many ribosomes are attached to the membranes. Dictyosomes form numerous vesicles, especially in the antipodals near the nucellar cells in the placental region. These ultrastructural details support the opinion that antipodal cells may play an important role in the embryo sac and are able to be responsible for the supply of nutrition for the whole gametophyte and take part in the supply of nutrition during embryo formation. [ABSTRACT FROM AUTHOR]