Polyploid Mitoses Research Articles

Early histogenesis of transplanted mouse mammary glands

Mammary duct-segments, each 0.6 mm long, from virgin female mice were isografted into the mammary gland-free fat pads of young female mice by Hoshino's quantitative transplantation technique. The hosts were sacrificed at intervals from 24 hous to 21 days. No recognizable mammary structures were recovered earlier than 72 hours after transplantation. In hosts treated with estrogen and progesterone before and after transplantation, regenerating mammary gland tissues were recovered from just over 50% of the grafts, whether or not the donor was pretreated with 3-methylcholanthrene. Mitoses were more often observed in regenerating mammary glandular tissues, which had been transplanted from donors pretreated intraperitoneally with 20 mg of 3-methylcholanthrene nine hours before donation to hormone-treated hosts, and some of the mitoses exhibited chromosomal bridges and polyploid mitoses. Estrogen-progesterone enriched environment apparently enhanced regeneration of mammary transplants. The present experiments suggest that the transplanted mammary tissue seemed to dissociate to individual cells before 72 hours following transplantation and regenerate from them into single mammary glands, and that one dose of 3-methylcholanthrene may cause histologically-visible changes in epithelial cells of rerenerating mammary grafts.

Inhibition of Polytene Chromosome Formation in <i>Phaseolus</i> by Polyploid Mitoses

The course of the cell cycles during the early development of the suspensor in Phaseolus coccineus and Ph. vulgaris is a factor influencing the occurrence of polytene chromosomes within the mature, highly endopolyploid nuclei. If there is a continuous sequence of endomitotic cycles, giant chromosomes arise. If the early endopolyploidization is interrupted by a polyploid (4x, 8x, or 16x) mitosis, the nuclear structure remains diffuse, also during the subsequent endomitotic growth of the nuclei.A scheme is given to demonstrate that a specific short-cut of the cell cycle is necessary for the origin of polytene chromosomes in general.

Factors Limiting the Stimulation of Polyploid Mitoses in Intact Pea Roots and Excised Root Segments

Although polyploid mitoses can be elicited in pea root segments 1 mm in length cultured on a defined medium, the same medium failed to elicit any polyploid mitoses when applied to the roots of intact pea plants. Auxin treatments, which are effective in eliciting polyploid mitoses in the roots of other plants, were also ineffective when applied to pea roots. Polyploid mitoses were not obtained when excised whole pea roots were cultured on a medium which effectively induced such mitoses in 1-mm segments, nor were polyploid mitoses found when the roots were fed basally with this medium. Polyploid mitoses were observed in 1-mm root segments split in half along the axis of the vascular cylinder and cultured with the cut surface against the surface of the medium so that the vascular cylinder was oriented parallel to the surface of the medium. If these segments were turned so that the vascular cylinder was still oriented parallel to the surface of the medium, but so that the cut surface was up and the intact epidermis in contact with the culture medium, no polyploid mitoses were observed. Thus wounding alone does not initiate polyploid mitoses. The appearance of polyploid mitoses requires the presence of a cut surface in contact with the culture medium. Root segments 3 mm in length were cultured with one cut surface against the surface of the culture medium and the vascular cylinder oriented perpendicular to the culture medium. After 74 hr in culture the segments were cut into three 1-mm pieces-top, middle, and bottom. A significant number of diploid mitoses was observed in all three pieces, although there were fewer mitoses in the top piece than in the bottom. A significant number of polyploid mitoses was observed only in the bottom piece. The orientation of the 3-mm segments (basal or apical end down) had little effect on the results. Thus not only does the appearance of polyploid mitoses require that a cut surface of the root be in contact with the medium but polyploid mitoses are also elicited only within 1 mm of this cut surface. These facts make the failures to elicit polyploid mitoses in excised roots and roots of whole plants easily understandable; that is, the necessary stimulatory substances presumably never reached the root tissues. Wounding of the intact root by passing a needle through it stimulates mitoses of both diploid and polyploid cells. We suggest that interference of the normal flow of hormonal materials, probably of a cytokinin, from the root tip toward the root base (shoot) is responsible for the local accumulation of stimuli leading to polyploid mitoses.

Cytological Studies on Rhizobial Nodule Initiation inPisum

SUMMARYA cytological analysis has been made of the first cell divisions in the cortical cells of the seedling root of the garden pea, Pisum sativum L., variety Little Marvel, resulting from the penetration of the infection thread of the bacterial symbiont Rhizobium leguminosarum during rhizobial root nodule formation. In the study of a carefully timed sequence during nodule initiation it has been found that first mitoses occur six days after inoculation of the seedling root with the bacterium, that each such mitosis is typically polyploid, usually tetraploid but sometimes octaploid or higher and that in this first mitotic event typically one can observe diplochromosomes, indicating that the cortical cell responsive to the bacterial thread penetration had undergone endo-mitotic reduplication prior to the infection. Using Feulgen-stained squash preparations together with phase contrast microscopy it has been possible to establish clearly the association between these first polyploid mitoses and the presence...

DNA synthesis in relation to polyploid mitoses in excised pea root segments cultured in vitro

Diploid and polyploid mitoses were observed in pea root segments cultured on a medium containing auxins and kinetin for 72 to 74 hr. Initial diploid mitoses were observed as early as 24 hr after the beginning of culture; initial polyploid mitoses were observed only after about 60 hr. The presence of kinetin was not required for the first 24 hr in culture for the appearance of polyploid mitoses at 74 hr. However, kinetin must be present in the culture medium after 24 hr. Auxin was required during the first 24 hr of the culture and its continuous presence may be required for polyploid mitoses. The question whether DNA synthesis must occur preceding the initial diploid and polyploid mitoses in cultured segments was studied using 5-fluoro-deoxyruridine and tritiated thymidine. The results, while not definitive, support the hypothesis that DNA synthesis is required for most of the mitoses, both diploid and polyploid. The same methods were used to study the time of DNA synthesis. In those cells in which DNA synthesis took place it seemed to occur between about 24 and 10 hr before mitosis for both polyploid and diploid mitoses. The results on the timing of the hormone requirements and the time of DNA synthesis make it unlikely that auxin or kinetin acts in this system primarily by directly triggering DNA synthesis.

Nutritional Requirements for Polyploid Mitoses in Cultured Pea Root Segments

AbstractDiploid and polyploid mitoses could be stimulated in excised segments of the mature region of pea roots grown on a sterile culture medium. Diploid mitoses were observed in segments cultured on water alone for 72 hours. Their frequency was increased by the presence of salts, sucrose, vitamins, and any two or all three of the following: an amino mixture, auxins, and kinetin.Polyploid mitoses were observed 72 hours after the beginning of the culture period in segments cultured on salts, sucrose, vitamins, auxins, and kinetin. Polyploid mitoses required the presence of auxins and kinetin in the culture medium. Their frequency was not affected by the presence of a reduced nitrogen source. Light treatments had no effect on the frequency of diploid or polyploid mitoses.Diploid mitoses were first observed about 24 hours after the beginning of the culture and their frequency increased thereafter. Experiments with colchicine showed that diploid cells were entering mitosis for the first time as late as 60 hours after the beginning of the culture.Polyploid mitoses showed a long lag time when compared with diploid mitoses. They began at about 60 hours and their frequency increased thereafter. Experiments with colchicine showed that polyploid cells were entering mitosis for the first time as late as 84 hours after the beginning of the culture.The presence of kinetin in the medium was not required during the first 24 hours in culture for the appearance of polyploid mitoses at 74 hours. However, the presence of kinetin was required after 24 hours. Auxin was required at some time during the first 24 hours of the culture and its continuous presence may be required for the stimulation of polyploid mitoses.

Adaptation of mammalian cells to cold: II. Cold-induced endoreduplication and polyploidy

By repeated exposures to 4°C for several weeks, the number of polyploid cells in a line of mouse L fibroblasts was increased to 46 per cent in comparison with 12 per cent in the original population. 26 per cent of these polyploid cells contained diplochromosomes indicating preceding DNA endoreduplication. The cold-adapted cells contained also an increased number of small metacentric and submetacentric chromosomes, both in the “normoploid” and polyploid mitoses.

Alterazioni Cromosomiche dei Leucociti Indotte nel Bambino da Irradiazioni Diagnostiche — (Nota preliminare)

SUMMARYThe Authors have observed a high rate of chromosomal morphologic alterations in leukocyte cultures in 10 children who had previously undergone Roentgen irradiation for diagnostic purposes. Temporary alterations have been observed, such as interruptions of chromatine on the proteic thread, defined as achromatic lesions of one or more chromatids; fragmentations of chromatids; fragments without centromere; deletions; ring-chromosomes; dicentric and tricentric chromosomes and, in certain cases, increase of polyploid mitoses, both on account of endo-reduplications or of a lacking cytoplasm division.

Endoreduplication in Human Fibroblast Cultures

Chromosome preparations using hypotonic pretreatment and air drying have been examined from 5 different human euploid fibroblast cultures. Between 0.1 and 4.1% of mitoses are found to be tetraploid with the chromosomes arranged as diplochromosomes. 0.5–5.8% of the mitoses are tetraploid with randomly positioned chromosomes. Differences in the frequency of polyploid mitoses between two cultures set up from one biopsy may be greater than between cultures from different individuals. The structure of the chromosomes forming diplochromosomes is identical to that of the chromosomes in diploid mitosis. In prophase the two chromosomes of a diplochromosome lie close together but are not linked at the centromere. In late prophase and metaphase the two chromosomes of a diplochromosome usually remain together but sometimes lie apart. In late anaphase and telophase no pairing of daughter chromosomes can be found. In prophases of cells from females, one of the chromosome pairs, presumably an X-diplochromosome, may show heteropyknosis. It is assumed that diplochromosomes originate mainly through endoreduplication. The mitosis following a mitosis with diplochromosomes will presumably show the chromosomes in random position. Autoradiographic studies using <sup>3</sup>H-thymidine show that diplochromosomes originate from two successive chromosome duplications. The cycle leading to diplochromosomes has approximately the same duration as two cycles of a diploid cell. The late labelling pattern, especially the late labelling X-chromosome in cells of females, is found in diplochromosomes in the same order as in chromosomes of diploid cells. The grain pattern of diplochromosomes labelled during first chromosome duplication indicates a semi-conservative mode of segregation.

The relation of DNA synthesis and mitosis in tobacco pith tissue cultured in vitro.

DNA synthesis and mitosis were initiated in cultured tobacco pith tissue by means of IAA and kinetin. DNA classes were determined by microspectrophotometric measurements (Feulgen); autoradiographs (tritiated thymidine) served to ascertain whether or not nuclei had undergone DNA synthesis during culture. All mitoses in “new” cells (resulting from divisions in culture) were diploid and had been preceded by DNA synthesis in culture. Whereas many of the “old” cells (which had not previously divided in culture) found in diploid or polyploid mitosis had undergone DNA synthesis during culture, others had not. Such non-radioactive mitoses still occurred after 16 days. In view of this, a 4 C nucleus in differentiated tissue should be considered as potentially both diploid and tetraploid, for it appears impossible to predict whether it would, upon restoration of conditions conducive to DNA synthesis and mitosis, enter a diploid mitosis or, after undergoing DNA synthesis, a tetraploid one. A high nuclear DNA content seems to have a much more inhibiting effect on the onset of DNA doubling than on that of mitosis. Somatic polyploidization is understood as the result of two DNA doublings between which mitosis was omitted, or aborted, or in effect undone by a failure of cytokinesis leading to fusion during a later mitosis.

NUCLEAR DIFFERENCES IN ALLIUM CEPA ROOT TISSUES AS REVEALED THROUGH INDUCTION OF MITOSIS WITH INDOLEACETIC ACID

Treatment with the growth substance indoleacetic acid was used to stimulate mitosis in differentiated tissues of Allium cepa roots in order to establish whether nuclear differences, specifically in chromosome number, exist normally and are merely revealed by treatments, or whether these nuclear differences are produced by the treatment. With the concentrations of indoleacetic acid and durations of treatment used, evidence was obtained that: chromosome number differences exist in the differentiated tissues of onion root prior to any treatment and that the appearance of these differences after treatment is a matter of revelation and not of causation. The evidence obtained in these investigations comes indirectly from observations of nuclear size and structure and directly from rare spontaneous mitoses in untreated roots, and in the treated roots (i) from the absence of nuclear abnormalities which might explain otherwise the origin of polyploid cells, (ii) from the uniform occurrence of certain chromosome numbers in specific root tissues, (iii) from proportions of diploid and polyploid divisions during mitotic induction, and (iv) from the lack of relationship between total mitotic activity and number of polyploid mitoses. A gradient of endomitotic polyploidization exits in certain tissues along the longitudinal axis of the onion root.

Polyploid Mitoses, Extranuclear Bodies, and Mitotic Aberrations in Seedlings of <i>Lilium Maximowiczii</i> Regel

In seedlings of Lilium Maximowiczii Regel., polyploid mitoses, Feulgenpositive bodies present in the cytoplasm, and mitotic disturbances were found. The relation between cytoplasmic bodies and mitotic disturbanes was discussed. Both mitotic aberrations and extranuclear bodies were most frequently observed at the start of germination, less frequently at later stage, and have never observed in seedlings about 1.2 cm. in length. One interpretation was given for the origin of extranuclear bodies in somatic cells. The numerical aberration of the chromosomes was found in seedlings of this lily.

New Evidence on Endopolyploidy in Differentiated Plant Tissues

SUMMARY1) Experimental mitosis stimulation in the differentiated root tissues in some species of Monocotyledons was obtained by treatment with some concentrations (generally, from 10 to 50 p. p. m.) of sodium 2,4-dichlorophenoxyacetate.2) In Tables I and II the percentages of polyploid mitoses in the cortex tissue in some of the species investigated herein are reported. In addition, a survey of the distribution of polyploidy in the various tissue layers in the roots of the species examined is given in the text.3) Polyploid cells showed 4n and 8n mitoses with « pairs » and « groups of four » chromosomes respectively. Only in one root in Bellevalia romana polyploid mitoses with single chromosomes, indicative of a second mitotic cycle in differentiated cells, were observed.A detailed description of the course of both 4n and 8n mitoses in differentiated root cells in the species studied is reported. The greatest variability in the behaviour of both centromere and relational coiling in 4n mitoses was observed ...

NUCLEAR CONDITIONS IN NORMAL STEM TISSUE OF VICIA FABA

Previous cytological studies of plant tumors have been carried out on unsuitable material, and on the assumption that the normal tissues in which tumors are induced are exclusively diploid. The present study investigates the condition in normal stem cortex and pith of Vicia faba, in which tumors can be regularly induced through inoculation with pure cultures of Agrobacterium rubi. Mitoses were induced by treatment with indole-3-acetic acid, and it was found that a very considerable degree of polyploidy exists in both tissues. In the pith the percentage of polyploid mitoses increases with some regularity from the nodal to the mid-internodal region, where it may be as high as 50% of the total. In the cortex, the difference in this regard is less striking, but still exists. Both tetraploid and octoploid cells were found, the latter being less than 10% of the total. In both cases, there was usually close association of homologues in both pro- and metaphase, but in the cortex a considerable number of nuclei did not show this association. The pairing is at times accompanied by chiasma formation. These findings must be taken into account in studying the relation of polyploidy to tumor development.

Polyploid Mitosis in the Normal Development of Mimosa pudica

Polyploid Mitosis in the Normal Development of Mimosa pudica

Polyploid Mitosis as a Normally Occurring Factor in the Development of Allium cepa L.

Polyploid Mitosis as a Normally Occurring Factor in the Development of Allium cepa L.