5/5/2023 0 Comments Metasequoia occidentalis![]() ![]() ![]() Such structures are observed in the cell nuclei of various fossil plants (Ozerov et al., 2006, Bomfleur et al., 2014, Glauser et al., 2014). Within each of the nucleolus-like structures there is an unstained area, similar to the so-called ‘nucleolus vacuole’ or ‘cavity’ (Plate I, B–D). The preparations contain Feulgen-stained nuclei of leaf are ordinary epidermal cells that carry a weakly colored sphere, whose size, position and volumetric relationships are compatible with the nucleolus. Apparently, the host Results and discussion The fossil plant locality is situated on the banks of the Tavda River between the villages of Antropovo and Nizhnyaya Pristan (ca. Later it was suggested that the Siberian specimens described as M. Gorbunov from the Tertiary deposits, West Siberia in 1954 (Gorbunov, 1957). The studied samples, originally assigned to Metasequoia disticha, were collected by Dr. occidentalis karyotype morphology closely resembles the karyotype of the modern species M. occidentalis) had about 22 chromosomes in the somatic cells diploid karyotype. Our observations on anaphase figures in the leaves of early Oligocene Metasequoia confirm the suggestion of Miki and Hikita (1951) that fossil M. occidentalis (Newb.) Chaney (Liu et al., 1999). disticha (Heer) Miki (Gorbunov, 1957) but later were ascribed to M. In this report, we show the preservation of Feulgen-positive nuclei and anaphase chromosomes within 29–33 Myr ago compressed leaves of Metasequoia from West Siberia that have previously been identified as M. Well-preserved cell nuclei and chloroplasts have been documented for many additional plant fossils of 15–180 Myr age (Zhilin and Yakovleva, 1994, Vikulin, 1999, Schoenhut et al., 2004, Wang et al., 2014). These reports of amplifiable chloroplast DNA preservation in Clarkia deposits corresponded well with the cytological observations of Niklas (1983) reported on the preservation of chloroplasts and their internal structure in ancient tissues of the Clarkia leaf fossils. It was shown that the fraction of endogenous DNA in the fossils is non-linearly decreasing with the increase in sediment age (Kirkpatrick et al., 2016) therefore presuming that in some cases a residual endogenous DNA becomes more recalcitrant with increasing fossil age (Soltis and Soltis, 1993, Kirkpatrick et al., 2016). (2016) recently sequenced rDNA of chloroplast genome of the fossil diatom Chaetoceros and Thalassiosira, ranging in age to 1.4 Myr. The authentity of the fossil DNA sequenced by Golenberg, Soltis and their colleagues gets an indirect support from the fact, that Kirkpatrick et al. Indeed, among 11 single nucleotide substitutions that varied between the rbcL of the fossil Taxodium and the present-day living Taxodium, 10 were C to T and G to A substitutions (Soltis et al., 1992), which are generally the most typical and frequent nucleotide substitutions in paleo-DNA samples (Hofreiter et al., 2001, Pääbo et al., 2004, Kistler et al., 2020). However, note that for the DNA amplification of the Clarcia ckay-deposited fossils non species-specific primers were used and it is scarcely probable that in each case the contaminant DNA would exactly correspond to sequence related to the studied fossil Magnolia, Persea and Taxodium plants, respectively. ![]() For each of case an exogenous DNA contamination was assumed to be present (probably PCR related), as the experiments were conducted in the laboratories working with contemporary plants DNA (Hebsgaard et al., 2005). Certain skepticism still prevails about these results (Pääbo et al., 2004, Hebsgaard et al., 2005, Kistler et al., 2020). fossils from the Miocene Clarkia beds (Golenberg et al., 1990, Soltis et al., 1992, Kim et al., 2004. This property of plants has enabled at least two independent research teams to sequence the chloroplast genes of 17–20 Myr old Magnolia L., Persea Mill. ![]() Perhaps plant cell walls and the antioxidant and antibacterial activities of intracellular condensed tannins, tocopherols, and flavonoids provide defense against biopolymer degradation during fossilization (Niklas, 1983, Logan et al., 1993, Schoenhut et al., 2004, Yang et al., 2005, Ozerov et al., 2006, Ozerov et al., 2020, Gupta et al., 2009, Mustoe, 2018). There is a peculiarity either in the structure or biochemistry of plant cells or in the processes of plant fossilization that contributes to long-term morphological preservation of nuclei and chloroplasts (Niklas, 1983, Schoenhut et al., 2004, Ozerov et al., 2006, Ozerov et al., 2020, Bomfleur et al., 2014, Wang et al., 2014) as well as molecular preservation of some biopolymers in plant fossils (Logan et al., 1993, Schoenhut et al., 2004, Yang et al., 2005, Ozerov et al., 2006, Ozerov et al., 2020, Gupta et al., 2009). ![]()
0 Comments
Leave a Reply. |