EMBRYO SAC DEVELOPMENT IN SOYBEAN: THE CENTRAL CELL AND ASPECTS OF FERTILIZATION

Abstract

Development of the soybean central cell and events associated with fertilization are described. Central cell development involves the simultaneous formation of numerous multigrain amyloplasts, development of wall ingrowths, reduction of the cell's major vacuole, and nuclear migration. As these processes reach completion, a phase of lytic activity begins. This activity ultimately results in both the breakdown of most multigrain amyloplasts in the central cell and the reestablishment of the cell's large vacuole. While these processes occur, the egg and synergid cells continue development. Examination of the egg apparatus after plasmogamy but prior to karyogamy reveals several changes. Whereas the synergid containing the pollen tube is degenerate and the distribution of organelles in the persistent synergid has changed, the egg cell with a free sperm nucleus exhibits higher levels of metabolite storage and changes in its wall structure. The walls of the newly formed sporophyte are similar to those of egg apparatus cells (Folsom and Cass, Canadian Journal of Botany 68: 2135–2147 [1990]) in that they seem to lack a middle lamella. This layer becomes apparent only in the two‐celled proembryo. While these changes occur in the egg, zygote, and proembryo, synergids undergo different degradative pathways.