Mechanism Of Cell Division Research Articles

The mechanism of cell division. Hydrostatic pressure effects upon dividing egg cells

The mechanism of cell division. Hydrostatic pressure effects upon dividing egg cells

I - The life history of some marine plankton diatoms

The diatoms are divided into two big groups, the Pennatae and the Centricae. The first group consists mainly of bottom forms which are either attached or show free movement, whereas the non-motile, suspended Centricae form the main bulk of the planktonic diatoms. The present work is concerned with the second group only. A knowledge of the essential structure of the cell, which is very similar in both groups, is of great importance for understanding the life history of the diatoms. The cell walls consist of two parts which overlap each other like the two halves of a pill box; the valves forming the top and bottom, the connecting bands or girdle the sides of the box. In the course of cell division the two halves of the cell wall become separated and each daughter cell forms a new valve and new connecting bands to fit into the old girdle. Owing to the silicification of the cell membranes, growth is possible only along the pervalvar axis, the longitudinal axis of the “box”. Consequently the diameter of one cell is slightly smaller than that of its sister cell, i.e. by twice the width of the cell wall. In a population this peculiar mechanism of cell division leads to a continuous decrease of the average cell size.

STIMULATIVE EFFECTS OF X-RAYS ON PLANT GROWTH

used for clinical diagnosis and therapy. The practical applications of x-rays in medicine and surgery make it necessary to know the effect which x-rays produce upon the living organism. Many investigators have suggested on the basis of general observations that small doses of x-rays may stimulate cellular activity and growth, but convincing proof of such action has been wanting. In more recent years such claims have been discounted in favor of the belief that x-rays are always more or less destructive in action, and tend to retard growth. It is not the purpose of this preliminary report to survey the literature dealing with the effects of x-ray treatments upon plants. It has been found that every part of the plant body can be profoundly modified by appropriate treatments. Cytological and histological examination of treated cells and tissues reveals striking changes in the organization of the protoplasm and of organs derived from the treated meristems. Most frequently the results described are of a destructive nature. The protoplasm is partially disorganized; chromosomes are vacuolated or fragmented; the cell division mechanism functions imperfectly, showing unequal distribution of chromosomes, non-disjunctions, translocation of pieces of chromosomes from one to some other non-homologous chromosome, etc. Gene changes may be produced, often injurious in character, with resulting lethal effects and tendency to sterility. The results obtained by McKay and Goodspeed (5) on cotton are typical. Many mutations have been induced in maize and barley (7, 8), and tobacco (1), but it has been questioned whether there are any progressive evolutionary changes induced by x-ray treatments. All vegetative parts are subject to injury by x-rays. Root tips may become bulbous and swollen, with tumor-like enlargements in which giant cells may occur. Stems become fasciated under strong treatments. Leaves are injured readily ; they become asymmetric and crumpled in appearance, develop deep sinuosities, and often show irregular development of chlorophyll. The sunflower shows these injuries in typical fashion, the leaves becoming pocked and marked as though they were suffering from a mosaic 1 This investigation was aided in part by a grant to the University of Chicago from the Eockefeller Foundation.

Colloids as Regulators of the Division Energy of Cells

While the mechanism of cell division is through morphological study, now well established, little is known of the forces which either initiate or control the process. Neoplasia is but the clinical manifestation of uncontrolled cell division, hence any investigations which indicate the forces initiating or controlling cell division have a distinct bearing on the question of cancer. The results of the experiments recorded in this paper indicate that the purely physical in contrast to the chemical conditions of the fluids which surround a cell, have a profound influence upon the rate of cell division. We believe that the importance, as well as the existence of, this factor has previously been unrecognized. It was elsewhere (1) suggested that the truth or fallacy of an hypothesis, which had been advanced seeking to explain the genesis of cancer, might be proved by work with unicellular organisms. Subsequently Packard, (2) adopting this suggestion, showed that the division rate of paramoecia could be influenced in the directions suggested by the hypothesis, by altering the calcium sodium ratio of the hay infusion along the lines indicated. At a later date further investigations were placed on record (3) showing that malignant tissue, when placed in a balanced salt solution having a calcium sodium ratio analagous to that which inhibited the division rate of paramoccia quite uniformly lost weight. Under the same conditions, using the same solution, benign tissue gained weight. It was found that if a colloid were added to the salt solution, benign tissue gained less weight than in the absence of the colloid, while malignant tissue lost more weight.1

The Mechanism of Cell-Division

ABSTRACT The nucleolus in the nucleus of an Echinus oocyte always orientates itself gravitationally on the floor of the nucleus. When the oocyte is disturbed the nucleolus falls through the fluid contents of the nucleus with an average velocity of 0·4 μ per sec. Gravity has no direct action on the direction of the cleavage planes in Echinus eggs, but it orientates the whole egg within the fertilisation membrane. During the first cleavage the mitotic axis can lie in any position in respect to gravity, but if its position deviates appreciably from the horizontal then (as soon as the cell elongates by cleavage) the whole egg moves so as to bring its centre of gravity into equilibrium with gravity and with the frictional forces acting between the egg and the fertilisation membrane. During the second cleavage the mitotic axis must lie in a plane parallel to the first cleavage furrow in conformity with Hertwig’s Law. If its position deviates from the horizontal, then the egg orientates itself to gravity. In this way the second division gives rise to four blastomeres resting as a flat plate on the floor of the fertilisation membrane, independently of whatever position was occupied by the mitotic axis. The third cleavage is also in accord with Hertwig’s Law and no gravitational disturbances occur. The direction of each cleavage plane is determined by the resultant of three factors: (a) the forces underlying Hertwig’s law, (b) gravity, (c) friction between the egg and its fertilisation membrane.

The Mechanism of Cell-Division

ABSTRACTThe fact that dividing cells are usually only found in actively growing tissues does not necessarily prove that growth and cell-division are two closely correlated phenomena. Growth may be defined as an increase in the amount of organised material which is present in the cell and which is essentially part of the living machine. Cell-division, on the other hand, only implies the cleavage of the cell into two or more parts. The purpose of this work is to enquire into the relationship between the two phenomena when they are taking place together. The material used was the segmenting eggs of Echinus miliaris.

The mechanism of cell division

The mechanism of cell division

Further explanatory remarks concerning the chemical mechanics of cell-division

When oil-droplets are submerged by the addition of chloroform to the oil and sufficiently alkaline threads be brought in contact with a sufficient proportion of an equatorial circumference, division of the droplets into two occurs. In cell-division the cleavage furrow is a region of low superficial tension, the poles of the egg are regions of high superficial tension.Butschli andMcClendon's view to the contrary is shown to involve a contradiction of the laws of molecular attraction in liquids.McClendon's evidence in support of his hypothesis has been shown to be fallacious.

Further remarks on the chemical mechanics of cell-division

1) In a previous communication I have advanced the view that cell-division is attributable to an equatorial diminution in surface tension, due possibly to cholin or a soap of cholin formed as a byeproduct in nuclear synthesis. I illustrated this view by experiments in which alkaline threads were laid across droplets of rancid olive oil floated upon water; division of the droplets resulted from the equatorial diminution in surface-tension, due to the equatorial formation of soap. 2) In a recent articleMcClendon has questioned the correctness of this interpretation, basing his objections, in the main, upon the fact that when the oil-drops are made to sink by the addition of alcohol to the water, they can no longer be made to divide by the equatorial application of soap. 3) In this communication various sources of error inMcClendon's experiments are pointed out and it is shown that oil-droplets do not divide in alcohol water mixtures containing more than 50% alcohol because of the presence of the alcohol and not because they are submerged. If, on the contrary, we cause the oil-drops to sink in water by adding chloroform to the oil, division of the drops is readily secured by laying alkaline threads across them. 4) The results of these experiments confirm the view that cell-division is attributable to an equatorial diminution of surface tension, and it is further pointed out that the contrary view, namely that cell-division is due to an equatorial increase in surface tension, is hydromechanically untenable.

Note on the chemical mechanics of cell-division

1) If a thread moistened with a base, or a sufficiently concentrated solution of the base, be laid across a diameter of a drop of oil containing a trace of fatty acid, the drop undergoes division along that diameter. 2) If the thread be merely smeared with a soap of the base, even in the presence of considerable excess of fatty acid, the same result is achieved; the effect is therefore due to soap formation and not to hydroxylions. 3) The mechanical division of the droplets is brought about by violent streaming movements from the equator of the drop towards the poles, due to the lowering of the surface-tension in the equatorial region brought about by the soap. It is pointed out that these facts confirmLoeb's hypothesis that cell-division is brought about through the mechanical agency of streaming phenomena. 4) It is suggested that the equatorial lowering of surface-tension and consequent streaming phenomena which lead to cell-division are brought about by cholin or soaps of cholin liberated in the cell through the splitting of Lecithin in Nuclein synthesis.

Mechanics of Cell Division

Previous articleNext article FreeCurrent LiteratureMechanics of Cell DivisionCharles J. ChamberlainCharles J. Chamberlain Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 44, Number 1Jul., 1907 Article DOIhttps://doi.org/10.1086/329257 Views: 46 Journal History This article was published in the Botanical Gazette (1876-1991), which is continued by International Journal of Plant Sciences (1992-present). PDF download Crossref reports no articles citing this article.