The Initiation, Development and Removal of Embryo Sac Wall Ingrowths in the Developing Seeds of Solanum nigrum L. An Ultrastructural Study

In developing seeds of Solanum nigrum L., wall ingrowths developed at the extreme micropylar and chalazal ends of the embryo sac. In the micropylar region, the wall ingrowths were initiated at the three-celled endosperm stage starting at the base of the zygote then progressing for a short distance chalazalwards. They developed quickly with the most elaborate around the base of the suspensor. The chalazal wall ingrowths developed along the surfaces of the chalazal cup, the antipodal cup and the hypostase. Those along the hypostase were initiated at the four-celled, those in the chalazal and antipodal cups at the 20-celled endosperm stages. The most elaborate developed along the base of the antipodal cup; the most simple were along the base of the chalazal cup. Small electron-lucent invaginations of the plasmalemma which later became filled with fibrillar material, were the earliest indication of wall ingrowth formation. Removal of the wall ingrowths commenced at the mid-globular stage of embryo development and was completed by the mid-heart-shaped stage. In the micropylar region, wall ingrowth removal was rapid, starting with the loss of the fibrillar component followed by the thinning of the cell wall. However, along the hypostase and antipodal cup, a heterogeneous layer of varying electron densities and a thinner, more electron dense layer was laid down over the ingrowths. This was followed by the removal of the fibrillar component. The initiation, removal and location of the embryo sac wall ingrowths is discussed in connection with understanding the nutritional relationships between maternal tissue, endosperm and embryo.