The Ultrastructure of the Embryo Sac before Fertilization in Arundo Formosana Hack.

Abstract

The mature embryo sac of Arundo formosana Hack. contains an egg apparatus composed of an egg cell and two synergid cells at the micropylar end, a central cell with two large polar nuclei in the middle, and a mass of 8 to 18 antipodal cells at the chalazal end. The egg apparatus shares a cell wall with the central cell at the micropylar end and there is only a plasma membrane surrounding at the chalazal end. The cytoplasm of the egg is rich in mitochondria, starch-containing plastids and oil drops. Two synergid cells are very similar and strong polarized; mitochondria are distributed at the micropylar end and surrounding the filiform apparatus; plastids are only distributed at the chalazal end; and dictyosomes and dilated ER vescicles are numerous. The central cell has a complex organized cytoplasm that is rich in organelles; the two polar nuclei are partially fused; and many ingrowth walls occur adjacent to the nucellus. The antipodal cells contain a large amount of ER and ribosome. Plasmodesmata are present in the cell wall between the embryo sac cells, but not adjacent to the nucellus. After pollination, the egg shows a considerable increase in polarity. The persistent synergid cell retains its original constitution and the degenerated synergid cell is filled with the electron dense materials. The number of dictyosomes and the quantities of oil drops and starch increase in the central cell. In the antipodal cells, most of the rough ER becomes parallel with the cell walls; some dense-staining particles may be present between the plasma membranes and the cell walls; and the ingrowth walls occur adjacent to the nucellus.