A mechanism of mitosis is described based on the data, collated as a result of studies of
mitoses in vivo in
Tradescantia stamen hair cells. In the analysis of the mitotic processes attention was paid not only to the microscopic but also to the submicroscopic organization of the mitotic elements, and upon their continuous physico-chemical changes all the mitotic processes were discussed.
(1) To explain the fundamental problem of the mitotic mechanism the writer has discussed and compared the different views, proposed as a consequence of the investigations of the achromatic figure
in vivo and in fixed preparations, and demonstrated that the disappearance of the nuclear membrane in the metaphase is an artifact caused by fixatives. In the living state of the mitotic cell the nuclear membrane is maintained continuously from the prophase up to the beginning of the telophase, changing its shape and also its structure.
(2) As a result of these studies and taken together with a consideration of the submicroscopic structure of the polar cap stage, the intranuclear origin of the spindle substances, the developmental processes of the spindle fibers, and the chromosome movement in the prometaphase are ascribed to the bipolar force of the mitotic cell and the conversion of the molecular configuration of the nucleoproteins.
(3) The fibrillar structure of the spindle body is divided into two kinds. One kind constitutes the ground fibrillar structure and takes no immediate part in the chromosome movement in the anaphase. The other kind is the chromosomal fiber or the traction fiber which grows along the ground fibrills from the kinetochore to the spindle poles. This fiber may be a bundle made up of the ground fibrills enclosed by the kinetochore substances. The traction fibers may become short by the dissolution of their kinetochore substances and by the disintegration of their molecular fibrills: these changes occur successively in the poles of the anaphase spindle.
(4) The chromosome movement in the anaphase is described as a result of the shortening of the traction fibers, which act as pulling forces upon the kinetochore of the daughter chromosomes.
(5) The substantial continuity between spindle body and the phragmoplast, the process for reconstructio i of the metabolic nuclei from the daughter chromosomes, the development of the cell-plate, of the cell-wall, and of the neclear membrane of the daughter nuclei are demonstrated experimentally and interpreted submicroscopically.
(6) In the theoretical interpretation of the mitotic mechanism the following factors should be considered: (a) the reversible denaturation of the nucleoproteins:-mainly the conversion of the molecular configuration from corpuscular to fibrillar by the unfolding of the polypeptide chains, and vice versa, (b) the bipolar force in the mitotic cells, (c) the existence of the spindle body delimited by a surface film, (d) the action of the kinetochore substances, (e) the shortening of the traction fibers and (f) the swelling of the atractoplasm.
View full abstract