Polyploidization of suspensor basal cell in Triglochin maritimum L. (Juncaginaceae)

Differentiation of the suspensor in Triglochin maritimum L. (2n = 48) was s tudied in comparison with the development of the embryo proper. The zygote divides into the apical cell and the basal cell, which becomes the basal ce ll of the suspensor. The fully differentiated suspensor consists of 2-3 ste m cells and a large basal cell. A single, huge nucleus is situated in the c entral part of the cell. Measurements of the nuclear DNA content and nuclea r volume of the suspensor basal cell indicated its degree of ploidy, which could reach a maximum 256C. Lower ploidy levels - 4C, 8C and 16C - characte rize the basal cell of small, 3-10-celled embryos. Nuclei with the highest ploidy levels of 128C and 256C were found only in fully differentiated basa l cells of more than 100-celled embryos. During polyploidization there were some changes in the chromatin structure of polyploid nuclei. Chromocenters at low levels of ploidy, endochromocenters at the middle levels, and bundl e-like aggregations of chromatin at the highest levels of ploidy were obser ved. The lack of mitoses, rhythmic enlargement of DNA content and nuclear v olume of the basal cell, as well as the characteristic structure of its chr omatin point to endoreduplication as a mechanism of polyploidization in the suspensor.