Female Germ Unit: Organization, Isolation, and Function

This chapter focuses on megagametophytes and examines the female germ unit from four new perspectives: (1) the ultrastructure and cytochemistry of megagametophyte development and cellularization, (2) the organization and function of the female germ unit in reproduction, (3) the isolation and characterization of embryo sacs and their component cells, and (4) the involvement of the cytoskeleton in megagametophyte development and function. The development of the megagametophyte is divided into two connected developmental phases: (1) megasporogenesis, which entails the formation and maturation of the initial products of meiosis, followed by (2) megagametogenesis, which begins with the mitotic division of the meiotic products and continues through the cellularization and maturation of the megagametophyte. The female germ unit is comprised of the egg, two synergids, and the central cell. As such, it constitutes the minimum number of cells required to (1) receive the pollen tube, (2) cause the discharge of the sperm into the receptive portion of the female gametophyte, and (3) undergo double fertilization.