Seeds Alapaja (Cupressaceae) from the Cretaceous of Western Siberia and their paleo-DNA

The article presents the results of cytoembryological research of the structure of fossil seeds in coniferous plants Alapaja cf. uralensis (Cupressaceae) from the Cenomanian–Turonian deposits of Western Siberia (age about 91.5 ± 8.5 Mya), and the results of the Feulgen test for the preservation of their structures' paleo-DNA in the nuclei. The study revealed the presence of fragments of embryo, megagametophyte and nucellus in the seed. The presence of megaspore membrane was also identified in the seed. The seed coat is 2–3-layered, the upper layer is very thin and presents just partially, and the middle layer of testa is represented by sclerotesta, the lower layer cells are fused into a single mass. It was established that nuclei are present in the cells of the embryo, megagametophyte and nucellus, however, in most cases, the DNA-deoxyribose skeleton, serving as a target for the Schiff reagent during the Feulgen reaction, is not cytologically detected in the nuclear chromatin. Only in two cases: in fragments of presumably embryonic tissue and megagametophyte, nuclei with a positive reaction according to Felgen were found, which indicates the preservation of aldehyde groups of deoxyribose in the nuclei of its individual parts.