Abstract:

We used transmission electron microscopy to study the ultrastructural changes in egg cell, zygote and two-celled proembryo of Beta vulgaris to provide information on the reproductive biology of angiosperms and related research into sugar beet. The mature egg cell was an inactive cell with only a few polysomes. At the early zygote stage, a large number of ribosomal precursors were produced by the nucleolus, and many polysomes appeared in the cytoplasm, which suggests a high level of metabolism. Zygote at the dormancy stage had a small nucleolus and marked decrease in ribosomes, as shown by a few polysomes, which suggests decreased metabolism. Zygotes in the prophase of mitosis and two-celled proembryo became active again in metabolism, for a prominent nucleolus, high density of ribosomes and increased number of polysomes in the cytoplasm. Polysomes change in number as “few-many-few-many” during the development of the egg, early zygote stage, zygote at dormancy, zygote in prophase of mitosis and two-celled proembryo in sugar beet, which indicates that such changes in metabolism as “low-high-low-high” activity may relate to the transformation from gametophyte to sporophyte generation.