Sedum acre embryogenesis: polyploidization in the suspensor

Cytological processes of differentiation in the embryo suspensor of Sedum acre L. were compared with the development of the embryo proper. The zygote undergoes an asymmetric division to produce an apical cell and a basal cell, which becomes the basal cell of the suspensor. The mature differentiated suspensor consists of a large haustorial basal cell and 3-4 chalazal cells. The basal cell nucleus gradually grows to a considerable size, and the amount of nuclear DNA also increases. The highest degree of ploidy (1024C) was observed in basal cells in large >100-celled embryos. Chromocenters at low (8C-16C) and middle (32C-64C) levels of ploidy, and endochromocenters at higher (128C-256C) and the highest (512C-1024C) levels of ploidy were observed. Changes in DNA content, nucleus size and chromatin structure point to endoreduplication as the mechanism of polyploidization of the suspensor in Sedum acre.