Fine Structure of Nucellar Cells During Development of the Embryo Sac in Oenothera biennis L.

Abstract

Developing nucellar cells in Oenothera biennis L. present distinct patterns of differentiation at the chalaza and around the embryo sac. The cytoplasm of nucellar cells surrounding the tetrad of megaspores displays cytolysomes, lipid bodies and membranes of smooth ER enveloping different cytoplasmic components. Concomitant to the differentiation of the embryo sac the nucellar cells constituting these ‘parietal layers’ undergo cytoplasmic degeneration with shrinkage and flattening. In addition to the regular nucellar cells the chalaza at this stage presents three other types: One with pycnotic nuclei, paramural bodies and cytoplasm filled with polymorphic vacuoles containing membranes, granular or flocculent material and multivesicular bodies. A second cell type shows swollen perinuclear cisternae around their pycnotic nuclei and large cytoplasmic vacuoles accumulating tannins. The third type of cells is characterized by large numbers of starch grains and advanced disorganization of cytoplasmic organelles; these cells probably become reservoirs after death.