Endosymbiotic Organization of Eukaryotic Cells
Section 2.10. It would be much easier for the investigators, if the existence
and evolutionary development of the cells had not been so long and
mutually dependent owing to contacts and interactions. These two
unavoidable circumstances have exerted their influence upon their
structural organization.
During last several decades the concept of endosymbiotic nature of
eukaryotic cells is gaining more and more adherents. The idea that some of
cell organelles are symbiotic inclusions is expressed by Schimper (1883)
more than a century ago. Mereschkovsky (1905), Famintzin (1907), Kozo
Polyanskii (1924) develop it further on the basis of their morphological
similarity with independently existed prokaryotic cells. As early as in 1868
Famintzin have arrived at the conviction, that chlorophyll grains resemble
Chlorella and Xanthella and tried to obtain pure cultures of chloroplasts.
Correns (1909) and Baur (1909) have described the first cases of
cytoplasmic heredity in Mirabilis jalapa and Pelargonium zonale. Ruth
Sager (1975) and Lynn Margulis (1983) are ardent adherents of this idea
with important contributions to its further development. The process of the
origin of eukaryotic cells by symbiosis is shown in Fig. 2–84.
Accumulating more data on cytoplasmic heredity made the
investigators try to find the reasons for this phenomenon. The Mendel’s rule
about a symmetrical segregation of hereditary features in gametes in
proportion 2:2 has been seriously violated in cases when the heredity is
transferred only in the female line asymmetrically, and the proportion of
gametes is 4:0. Besides, it has been established the presence of
autonomously replicated cytoplasmic structures (plasmids, bacteriophages,
etc.) moving from one cell to another being in close interrelations with the
chromosomes in nuclei, without any synchron with the phases of mitotic
processes realized in them. It had been impossible to explain these cases
from the viewpoint of chromosome theory, which in its classic aspect
defines the chromosomes in nucleus to be the only carriers of hereditary
features. There have been accepted two types of inheriting: Mendelian and
non-Mendelian.
It is necessary to emphasize that in the period 1910—1960 the data on
the existence of cytoplasmic genes have accumulated very slowly and very
often they have not been acknowledged. The literature on cytoplasmic
heredity has been considered a “spot” discrediting the science. Only in the
forties of our century, under the influence of a number of remarkable
discoveries in this field, it became possible to suppose a genetic autonomy
of organelles in the cytoplasm.