Experimental Studies of Abnormal Nuclear and Cell Divisions

I. Observation with living cells of the effects of neutral salts and heavy metal salts

Abstract

1) In the solutions of alkali metal salts in high concentrations, cells are plasmolyzed, and chromosomes and nuclei become a homogeneous mass. After the replacement of the medium with water, the cells are deplasmolyzed and the chromosomes undergo the process of nuclear reconstruction to produce bi-nucleate cells or di-diploid nuclei.
In medium concentrations the plasmolysis does not occur, but the vacuoles in the cytoplasm become enlarged, the cytoplasmic streaming ceases to take place, and the cytoplasmic strands increase in refractivity, decr asing in number. The chromosomes become refractive, and are clumped together into a mass which gradually decreases in size. The spindle also decreases in size. The resting nucleus is made also smaller and smaller, and shows a thicker and refractive chromonema structure. The clumped chromosomes can undergo the nuclear reconstruction process, if the medium is replaced with water at a suitable time, and a di-diploid nucleus or a bi-nucleate cell is produced. When the affection is weaker, an incomplete cell plate is formed between the two daughter nuclei. The abnormalities caused by these solutions of medium concentrations are essentially similar to those observed in the cases of the high concentrations and of a hypertonic sugar solution except the cytoplasmic vacuolization, instead of which phenomenon plasmolysis occurs in the latter two. In this case of medium concentrations too, the formations of the di-diploid nuclei and bi-nucleate cells are attributable chiefly to the dehydration of the spindle and chromosomes, which is on the part of chromosomes followed by an untimely nuclear reconstruction process and on the part of the spindle by denaturalization occurring as a result of the removal of the reagents by replacing them with water, as we have already seen in the cases of alkaloids and narcotics (SIGENAGA, 1937).
The degree of easiness in obtaining the di-diploid nucleus and binucleate cell differs in different salts, and they are obtained most easily under the influence of KSCN, and less easily by KNO₃, K₂SO₄, NaNO₃, NaCI, etc. NH₄Cl affects cells most weakly of all the alkali metal salts examined, in the medium concentrations even no abnormal cells and nuclei being obtainable in this case.
2) Alkali earth metal salts cause plasmolysis when the solutions are of high concentrations, and in this case the di-diploid nuclei or binucleate cells are obtained after the solutions are replaced with water. In medium concentrations no such abnormal cells or nuclei are obtainable, and the only abnormality which is noticeable is the prolongation in the process of telophasic nuclear reconstruction.
3) The combined effects of alkali metal salts and alkali earth metal salts are studied. The results obtained show that the KNO₃ solution of a medium concentration can no longer exhibit its effects on mitosis when a little quantity of CaCl₂ is added. In this case the mitosis can proceed normally.
4) In most heavy metal salts with which we studied, plasmolysis occurs when the concentration is high. Deplasmolysis occurs when the solutions are replaced with water, but the cells finally become coagulated to death. Only in the case of Pb (NO₃)₂, both di-diploid nuclei and binucleate cells are obtainable. In the cases of medium and low concentrations too, most salts cause cell coagulation. So far as the present experiments are concerned, no attempt of replacing the solution with water at a first stage toward coagulation can give rise to the formation of the abnormal cells and nuclei; the result is either coagulation of the cell to death or progress of mitosis in the normal manner. The case of the AgNO₃ solution used in a low concentration, in which both di-diploid nuclei and bi-nucleate cells are formed after the solution is replaced with water, is an only exception which we observed