Karyokinesis is a continuous morphological change of one metabolic nucleus which becomes two independent daughter nuclei via karyokinetic stages.
In fixation cytology including present electron microscope studies, this principle on concerning the morphological continuation of the dividing nucleus is ignored, especially in higher plants and animals, because of the common concept about the breakdown of the nuclear membrane before spindle formation. The nuclear membrane in metaphase and also in succeeding stages fulfills an important role as an intracellular biological membrane morphologically and physiologically.
1. Chromonemata in a metabolic nucleus develop into chromosomes by addition of a chromosome matrix, and by coiling. Simultaneously the nucleus increases its volume. On the contrary, the daughter chromosomes at both spindle poles in telophase, change into chromonemata by releasing their matrix and unravelling coiling. Thus the daughter nuclei are dehydrated in plant cells but very little dehydrated in animal cells.
2. The nuclear sap in a metabolic nucleus changes into the atractoplasm, spindle ground substance, by transforming nuclear sap globular proteins into fibrous ones which become arranged in parallel with each other under the influence of cell polarity and form a tactoid as a whole. Thus the spherical metabolic nucleus becomes a spindle-form karyokinetic nucleus, generally described as a metaphase spindle, which possesses the essential contour for setting up an energy source (ATP) at both spindle poles. This interpretation of the metaphase spindle formation is backed up by the appearance of spindle-shape birefringence in living cells under polarization microscope.
3. By the fibrillation of proteins which starts from both spindle poles toward the equator of nucleus, the scattered chromosomes in the periphery of late prophase nuclear cavity are brought into the equator and form a metaphase plate.
4. Different from protista, including fungi and algae, the nucleus in higher plants and animals increases its volume to accomodate enough space for metaphase plate formation in prometaphase, for poleward migration of chromosomes in anaphase and for accomplishment of independent daughter chromosome groups at both spindle poles in telophase. Simultaneously, the spindle membrane, by increasing its surface area becomes a strained state and fragile toward fixation (coagulation) shock and dehydration, when fixed by routine fixatives including electron microscopic techniques. Thus it happens that the misinterpretation of the breakdown of the nuclear membrane before spindle formation has been described as an orthodox explanation in cytology books.
6. The parallel arranged spindle back-ground fibrils lay a track to conduct the flow of kinetochore substance exuded from each kinetochore site of the chromosomes toward the spindle poles. This flow forms the spindle back-ground fibrils on the track into a bundle and also forms a kinetochore fiber between each kinetochore and its corresponding spindle pole.
7. By aid of chemical energy (ATP), each kinetochore fiber, when it arrived at each corresponding spindle pole, disintegrates from its terminal and becomes continuously short. Finally, each kinetochore accompanying chromosome arm(s) arrives at and occupies the spindle pole at the end of anaphase.
8. During the shortening of kinetochore fibers in anaphase, the disintegrated kinetochore fiber proteins become daughter nuclear sap proteins. On the other hand, the daughter nuclear membrane is reformed from the spindle membrane at each spindle pole by replicating its membranous structure at the molecular level and enveloping in it the daughter chromonemata, nuclear sap and the reappearing nucleoli at the end of telophase.
9. Further changes such as those of daughter chromosomes, their chromonematization by releasing of the chromosome matrix, unravelling of coils and by changes in hydration