Differentiation of the suspensor in Triglochin maritimum L. (2n = 48) was studied in comparison with the development of the embryo proper. The zygote divides into the apical cell and the basal cell, which becomes the basal cell of the suspensor. The fully differentiated suspensor consists of 2-3 stem cells and a large basal cell. A single, huge nucleus is situated in the central part of the cell. Measurements of the nuclear DNA content and nuclear volume of the suspensor basal cell indicated its degree of ploidy, which could reach a maximum 256C. Lower ploidy levels - 4C, 8C and 16C - characterize 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 basal 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 bundle-like aggregations of chromatin at the highest levels of ploidy were observed. The lack of mitoses, rhythmic enlargement of DNA content and nuclear volume of the basal cell, as well as the characteristic structure of its chromatin point to endoreduplication as a mechanism of polyploidization in the suspensor.
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