Levels Of Polyploidy Research Articles

Chromosome numbers of eight taxa of Aconitum L. in Korea and their systematic significance (Ranunculaceae)

Various aneuploidy and polyploidy have been reported in the genus Aconitum L. (ca. 300 species worldwide, Ranunculaceae), and there is a demonstrated association between major lineage diversification and polyploidy. This study reports chromosome counts of eight Aconitum from Korea, including the first counts for A. japonicum Thunb. subsp. napiforme (H. Lv. & Vaniot) Kadota (2n = 32) and A. longecassidatum Nakai (2n = 16). The study also includes chromosome numbers for two taxa on the Critically Endangered species list in Korea. Among Korean native species, chromosome numbers in Aconitum subgenus Aconitum range from 2n = 16 to 2n = 64 with diverse levels of polyploidy (2x, 4x, and 8x), whereas Aconitum subg. Lycoctonum exhibits only diploids (2n = 16). Greater chromosome number diversity in subg. Aconitum than subg. Lycoctonum might explain higher species diversity within the former subgenus (more than 250 species worldwide). Investigating chromosome number diversity of Aconitum in a phylogenetic framework will be a critical step to understand species richness of the genus.

In vitro tetraploid induction from leaf explants of Populus pseudo-simonii Kitag.

Tetraploid plants were produced from leaf explants of diploid Populus pseudo-simonii by treating the leaves with colchicine. Leaf explants were cultured on MS basal medium containing 1.78μM BA and 1.08μM NAA for 0, 6 and 12days, and then transferred to the same MS liquid medium with colchicine at concentrations of 25, 50 and 75μM for 1, 2 and 3days. The highest efficiency of tetraploid induction was 14.6% by treating leaf explants that were pre-cultured for 6days and then cultured in liquid MS with 50μM colchicine for 3days. Flow cytometric analysis was used to screen the tetraploids out from the regenerated plants and chromosome number counting was employed to confirm the polyploidy level. Size and frequency of leaf stomata between diploid and tetraploid plants were demonstrated to have significant differences.

Flavonoid chemistry of Fallopia sect. Reynoutria (Polygonaceae) in Korea

Fifteen populations comprising three taxa and a putative hybrid of Fallopia sect. Reynoutria in Korea were examined for their leaf flavonoid constituents. Nineteen flavonoid compounds were isolated and identified; they were glycosylated derivatives of the flavonols quercetin and kaempferol, and of the flavones apigenin and luteolin. Among them, quercetin 3-O-galactoside and quercetin 3-O-glucoside were major flavonoid constituents, and present in all taxa. The flavonoid data appear to be very useful for taxon delimitation, and all taxa examined are readily distinguished by their flavonoid profiles. In addition, the flavonoid data suggest that the Nonsan population may be of hybrid origin involving F. japonica var. japonica, F. forbesii, and F. sachalinensis. In F. japonica var. japonica, there is no apparent correlation between their levels of polyploidy and flavonoid chemistry, but geographical variation of the flavonoid profiles among some populations was detected.

Extensive chromosome number variation in Aster ageratoides var. pendulus (Asteraceae)

Aster ageratoides var. pendulus, a recently described taxon, is endemic to Mt Hupingshan of north-western Hunan, China. Field observations and collections were made from the only known population. Root-tip squashes were used to determine the chromosome numbers of 96 plants and 61 seedlings from the achenes of eight sample plants. The results show that var. pedulus is a swarm of 30 cytotypes with nearly continuous chromosome numbers from 2n = 60 to 2n = 92. Chromosome numbers of 61 seedlings vary from 2n = 61 to 2n = 91, belonging to 18 cytotypes. The chromosome number variation of var. pendulus is highly unusual not only in the A. ageratoides polyploid complex but also in angiosperms. Such an enormous continuous variation of chromosome numbers could have arisen by the combined effect of hybridization, recent origin and high levels of polyploidy.

Arabidopsis homologues of the histone chaperone ASF1 are crucial for chromatin replication and cell proliferation in plant development

Anti-silencing function1 (ASF1) is an evolutionarily conserved histone chaperone. Studies in yeast and animals indicate that ASF1 proteins play important roles in various chromatin-based processes, including gene transcription, DNA replication and repair. While two genes encoding ASF1 homologues, AtASF1A and AtASF1B, are found in the Arabidopsis genome, their function has not been studied. Here we report that both AtASF1A and AtASF1B proteins bind histone H3, and are localized in the cytoplasm and the nucleus. Loss-of-function of either AtASF1A or AtASF1B did not show obvious defects, whereas simultaneous knockdown of both genes in the double mutant Atasf1ab drastically inhibited plant growth and caused abnormal vegetative and reproductive organ development. The Atasf1ab mutant plants exhibit cell number reduction, S-phase delay/arrest, and reduced polyploidy levels. Selective up-regulation of expression of a subset of genes, including those involved in S-phase checkpoints and the CYCB1;1 gene at the G₂-to-M transition, was observed in Atasf1ab. Furthermore, the Atasf1ab-triggered replication fork stalling constitutively activates the DNA damage checkpoint and repair genes, including ATM, ATR, PARP1 and PARP2 as well as several genes of the homologous recombination (HR) pathway but not genes of the non-homologous end joining (NHEJ) pathway. In spite of the activation of repair genes, an increased level of DNA damage was detected in Atasf1ab, suggesting that defects in the mutant largely exceed the available capacity of the repair machinery. Taken together, our study establishes crucial roles for the AtASF1A and AtASF1B genes in chromatin replication, maintenance of genome integrity and cell proliferation during plant development.

Population Diversity and Polyploidy Incidence in 3 <i>Silene</i> Species. A Cytological Approach

Cytological studies were performed in 20 populations of 3 Silene species of the section Auriculatae L., Silene gynodiocia Ghazanfar, S. crispans Litw., S. indeprensa Schischk. The populations studied had 2n=2x=24, 2n=4x=48 and 2n=8x=96 chromosome number, showing 2 polyploidy levels for S. indeprensa and S. gynodiocia. The chromosomes were mostly metacentric and submetacentric but 1 pair of teloentric chromosome was observed in the octaploid Dargaz population of S. indeprensa. The ANOVA test showed no significant difference among populations of S. indeprensa and populations of S. gynodiocia for size of the chromosomes, mean chromosome length, A1 and A2 indices as well as TF value. This indicates that no significant chromatin loss or gain has occurred in the process of karyotype differentiation in these populations, and in the case of octaploid and tetraploid populations, still the mean value of chromosomes are maintained. However, the species differed significantly for CV value, indicating that during species diversification a change has occurred in the size of chromosomes within a karyotype due to structural changes of the chromosomes. Meiosis analysis showed that the chromosomes mainly form bivalents and univalents in the metaphase of meiosis I, although some amounts of quadrivalents were observed in all populations including diploids due to heterozygote translocations. T-test analysis showed significant difference in the relative values of total and terminal chiasmata as well as a number of ring bivalents between the populations having 2n=24 and 2n=48 chromosome number indicating that with an increase in polyploidy level, significant change has occurred in the number of genes controlling chiasma frequency. The occurrence of unreduced pollen grains indicates the role of this phenomenon in polyploidy incidence in the species studied.

Comparative cytogenetic analysis of diploid and hexaploid Chenopodium album Agg

Two cytotypes of <em>Chenopodium album</em>, diploid (2n=2x=18) and hexaploid (2n=6x=54), were analysed using flow cytometry and a FISH experiment. The genome size was indicated as 1.795 pg for the diploid and 3.845 pg for the hexaploid plants which suggested genome downsizing in the evolution of hexaploid cytotype. Double FISH with 25S rDNA and 5S rDNA allowed three to five homologue chromosome pairs to be distinguished depending on the cytotype. The Variation in size and number of rDNA sites between the polyploid <em>C. album</em> and its putative diploid ancestor indicated that rDNA loci underwent rearrangements after polyploidization. Flow cytometry measurements of the relative nuclear DNA content in the somatic tissue of <em>C. album</em> revealed extensive endopolyploidization resulting in tissues comprising a mixture of cells with a different DNA content (from 2C to 32C) in varying proportions. The pattern of endopolyploidy was characteristic for the developmental stage of the plant and for the individual organ. Polysomaty was not observed in the embryo tissues however endopolyploidization had taken place in most tested organs of seedlings. The endopolyploidy in diploid and hexaploid <em>C. album</em> was compared to find any relationship between the pattern of polysomaty and polyploidy level in this species. This revealed that polyploid plants showed a decline in the number of endocycles as well as in the frequency of endopolyploidy cells compared to diploid plants.

Cytohistological Studies During Cotton Somatic Embryogenesis With Brassinosteroid Application

The histology and chromosome alterations of somatic embryo initiation and development in cotton ( Gossypium hirsutum L. cv. Coker) was examined during in vitro exogenous brassinosteroid (BR) application. Calli developed from hypocotyl explants were subjected to 0.5 μM BR. After 10 weeks of calli cultures with somatic embryos at different developmental stages were fixed for histological examinations. The histological examination showed that two types of embryogenic cells induced; epidermal or subepidermal. The embryogenic mass and somatic embryos were mostly derived from several morphologically competent cells from subepidermal cases; however single progenitor cells for epidermal situations. Chromosome behaviour of the cells surrounding embryogenic cells showed abnormal divisions and higher level of polyploidy on BR treated calli when compared to control group.

Stathmin-Mediated Dysregulation of Microtubules Impairs Megakaryocyte Maturation and Platelet Production

AbstractAbstract 548Maturation of megakaryocytes (MK) consists of unique processes like polyploidization and proplatelet formation that are critical for efficient platelet production. Both processes are highly dependent on dynamic changes in the microtubule (MT) cytoskeleton. MT form a complex, spherical mitotic spindle that mediates polyploidization, represent the structural scaffold for proplatelet extension and enable the transport of cytoplasmic organelles into nascent platelets. While the structural organization of the MT cytoskeleton in MK is very well described at the morphological level, the mechanisms responsible for the regulation of MT dynamics during these processes are largely unknown. Stathmin is a highly conserved MT-regulatory protein that modulates MT dynamics by promoting MT depolymerization. Previous studies suggested a potential role for stathmin in MK polyploidization. However, these studies that were performed in chemically-induced transformed cell lines reached contradictory conclusions about the role of stathmin in megakaryopoiesis. We addressed this controversy by utilizing a more physiologically relevant experimental model of megakaryopoiesis in which primary human MK are grown in tissue culture. First, we optimized a MK liquid culture system that allows for efficient generation of mature MK capable of producing platelets in culture. Using this system, we demonstrated that the high levels of stathmin mRNA in proliferating MK progenitors markedly decline with maturation. We used an FIV-based lentiviral expression system to prevent this physiological downregulation of stathmin expression and investigated the effects of sustained expression on MK maturation. The sustained expression of a constitutively active form of stathmin in MK resulted in approximately 2-fold reduction in glycoprotein GPIb expression, 3.5-fold reduction in platelet factor 4 expression and loss of up-regulation of GATA-1 expression which is normally seen during maturation. This demonstrates that the sustained activity of stathmin prevents the up-regulation of three different markers of MK maturation, supporting the hypothesis that physiological downregulation of stathmin is required for proper MK differentiation. We also investigated the effects of sustained stathmin expression on polyploidization by fluorescence in situ hybridization. These studies show that stathmin inhibited the ability of MK to achieve high levels of polyploidy. Finally, we evaluated the effects of sustained stathmin expression on the ability of MK to produce platelets in vitro. We found that the number of platelets derived by MK expressing sustained levels of stathmin was reduced by approximately 50% compared to those produced by control MK. This demonstrates that sustained stathmin expression has a negative effect on platelet production, supporting the importance of MT polymerization in this process. This is the first demonstration that alterations of expression of a MT-regulatory protein can interfere with platelet production by primary MK. In summary, these studies support the importance of MT regulation during MK maturation and suggest that the physiologic downregulation of stathmin expression is biologically important in the processes of MK maturation and platelet production. Very high levels of stathmin expression are frequent in hematological malignancies such as leukemias and myelodysplastic syndrome. Inefficient platelet production is one of the most important features of these malignancies where bleeding from low platelet counts is one of the most common causes of death. Our studies open new avenues of investigation into the mechanisms responsible for MK maturation that may prove relevant for pathological conditions characterized by aberrant stathmin expression and/or function. Disclosures:No relevant conflicts of interest to declare.

Sensitivity of BRCA2 mutated human cell lines to Aurora kinase inhibition

Aurora kinases play a vital part in successful mitosis and cell division. Aberrant Aurora-A and -B expression is commonly seen in various types of tumors. Small molecule Aurora inhibitors have already entered clinical trials. Aurora-A amplification has been shown to be associated with breast tumors from BRCA2-mutation carriers and such patients might therefore be candidates for treatment with Aurora kinase inhibitors. There is a need to identify markers that can predict sensitivity to Aurora inhibition. In this study sensitivity to the inhibitor ZM447439 was tested on a panel of 15 non-malignant and malignant epithelial cell lines that differed with respect to BRCA2 and p53 status and related to level of Aurora kinase expression. The IC(50) value for cell survival ranged from 1.9-8.1 μM and was not related to presence or absence of BRCA2 mutation. The levels of Aurora-A and -B expression correlated with each other but sensitivity towards ZM447439 did not correlate with levels of Aurora-A and -B mRNA expression, alone. Cells treated with the Aurora kinase inhibitor completed mitosis but cytokinesis was inhibited resulting in polyploidy and multinucleation. Different levels of polyploidy could not be fully explained by defects in p53. Only cell lines with a combination of high Aurora-A and -B expression, BRCA2 mutation and p53 defects showed more sensitivity towards Aurora inhibition than other cell lines. In conclusion, BRCA2-mutated cells showed variable sensitivity towards Aurora kinase inhibition. The level of sensitivity could not be predicted by Aurora expression levels alone but BRCA2 mutated tumors with high Aurora expression and non-functional p53 are likely candidates for treatment with Aurora inhibitors.

Characterization of the Karyotype in Patients with Multiple Myeloma by the Combination of Karyotype Analysis, FISH and CGH

Cytogenetic and molecular cytogenetic investigations from bone marrow samples were performed in 83 patients with multiple myeloma. Karyotype analyses were made after cultivation with and without growth factors. The polyploidy level ranged from 3n to 6n. For each patient the composite karyotype was delineated. The number of abnormalities per aberrant cell was in a range from 1 to 17 (x =3,7). The comparison of CGH and FISH results showed an accordance of 92%. In total, 57% of cells showed chromosomal aberrations.

Estimating polyploidy levels in fossil <em>Salix</em>: A critical review of cell size proxy methods

Studies have used cell size as a proxy to estimate polyploidy levels, the number of chromosome sets in somatic cells, in modern and fossil plant species. This paper critically evaluates these methods by reviewing cell size- and polyploidy-related literature, and provides new cell size data from herbarium material and fossil remains of willow genus Salix. The 40 extant taxa used in the study include most of the polyploidy levels encountered in Salix (2n = 38, 76, 114, 152, 190). Diploid and tetraploid species were morphologically similar to the fossil specimens. Specimens from alpine and arctic regions, forms rarely found in the fossil record, were included to extend the range of polyploidy levels. Measurements taken for this study were on the petiole epidermal cells of fossil and herbarium specimens and the stomatal guard cell complexes of herbarium material. A literature review reveals cell size may not relate only to DNA content, but to a plant’s age, nutritional state and the seasonal timing of organ development. Cell size measurements show that cultivated plants grown at elevations more than 800 m below their original place of growth have a significant increase in cell size. Leaf length-to-width ratio, infrageneric classification, and adaptation to dry or humid environments also correlate with cell size. Cell size proxies for estimating polyploidy levels in fossil willows provide only accurate results if morphologically similar modern plant material from natural habitats is used as a reference for comparison. Leaves should be similar in overall shape, base and apex shape, blade length and width, length-to-width ratio, petiole length, petiole-to-blade length ratio, venation pattern, and margin dentition.

Contribution to Cytotaxonomy of Iranian Cirsium (Asteraceae)

A meiotic study was performed on 21 populations of 17 Cirsium species growing in Iran. The species of C. spectabile, C. congestum, C. strigosum, C. ciliatum, C. osseticum, C. aduncum, C. haussknechtii, C. turkestanicum, C. echinus, C. obvallatum, C. libanoticum, C. alatum, C. echinus, C. obvallatum, C. libanoticum, C. hygrophilum and C. arvense had 2n=2x=34 chromosome number, while the species of C. lappaceum, C. vulgare and C. elodes showed 2n=4x=68. The chromosome numbers of C. spectabile, C. strigosum, C. haussknechtii, C. lappaceum, C. turkestanicum and C. libanoticum are new to science and a new polyploidy level (4x) has been reported for C. elodes. The ANOVA test revealed significant differences for chiasma frequency and chromosome pairing among the species studied and the Pearson coefficient of correlation determined showed significant positive correlation between intercalary chiasmata and the mean number of quadrivalents. Although diploid species and populations are expected to form only bivalents in metaphase I, quadrivalents were formed in C. arvense, C. ciliatum, C. congestum, C. echinus, C. strigosum and C. libanoticum possibly due to the occurrence of heterozygote translocations. Interestingly enough, tetraploid species of C. lappaceum did not form any quadrivalents showing diplontic behavior. The occurrence of large pollen grains (possibly 2n pollen grains) was observed along with smaller (normal) pollen grains in species and populations showing tripolar cells. Cytological characteristics may be used in species delimitation in Cirsium but may not be used in sectional delimitation of the genus.

Cytogenetical analysis of 12 taxa of <i>Genista</i> L. (Fabaceae) from Turkey

In this study, cytogenetical analyses of 12 taxa belonging to the genus Genista L. and grown naturally in Turkey were conducted. These taxa include G. acanthoclada, G. albida, G. anatolica, G. aucheri, G. burdurensis, G. carinalis, G. involucrata, G. januensis subsp. lydia, G. sandrasica, G. sessilifolia, G. tinctoria and G. vuralii. Chromosome numbers of all the taxa, except G. tinctoria, are introduced to the scientific community for the first time. Somatic metaphase chromosomes of the genus were determined as 2n = 18, 36, 46, 48, 52, 72 and 144. Polyploidy was observed in the cells of G. albida (2n = 18, 2n = 4x = 36), G. tinctoria (2n = 36, 48, 2n = 4x = 96), G. januensis subsp. lydia (2n = 46, 2n = 4x = 92), G. burdurensis and G. sessilifolia (2n = 48, 2n = 4x = 96). Somatic chromosomes of the G. sandrasica are very small, thus exact ploidy level of polyploidy was not determined. Karyotype analysis of G. albida and G. involucrata were performed via an Image Analysis System. Keywords: Genista; Leguminosae; chromosome number; karyotype; Turkey. DOI: 10.3329/bjpt.v16i2.3927 Bangladesh J. Plant Taxon. 16(2): 151-156, 2009 (December)

Cellular senescence induced by aberrant MAD2 levels impacts on paclitaxel responsiveness in vitro

Background:The mitotic arrest deficiency protein 2 (MAD2) is a key component of the mitotic spindle assembly checkpoint, monitoring accurate chromosomal alignment at the metaphase plate before mitosis. MAD2 also has a function in cellular senescence and in a cell's response to microtubule inhibitory (MI) chemotherapy exemplified by paclitaxel.Methods:Using an siRNA approach, the impact of MAD2 down-regulation on cellular senescence and paclitaxel responsiveness was investigated. The endpoints of senescence, cell viability, migration, cytokine expression, cell cycle analysis and anaphase bridge scoring were carried out using standard approaches.Results:We show that MAD2 down-regulation induces premature senescence in the MCF7 breast epithelial cancer cell line. These MAD2-depleted (MAD2↓) cells are also significantly replicative incompetent but retain viability. Moreover, they show significantly higher levels of anaphase bridges and polyploidy compared to controls. In addition, these cells secrete higher levels of IL-6 and IL-8 representing key components of the senescence-associated secretory phenotype (SASP) with the ability to impact on neighbouring cells. In support of this, MAD2↓ cells show enhanced migratory ability. At 72 h after paclitaxel, MAD2↓ cells show a significant further induction of senescence compared with paclitaxel naive controls. In addition, there are significantly more viable cells in the MAD2↓ MCF7 cell line after paclitaxel reflecting the observed increase in senescence.Conclusion:Considering that paclitaxel targets actively dividing cells, these senescent cells will evade cytotoxic kill. In conclusion, compromised MAD2 levels induce a population of senescent cells resistant to paclitaxel.

MORPHOLOGICAL AND POLYPLOIDY VARIATION OF STRAWBERRY PLANTS OBTAINED BY CROSS POLLINATION OF FRAGARIA VESCA AND F. × ANANASSA

For future production in Japan using genetically modified (GM) octoploid strawberry plants, the possibility exists of genetic pollution of wild diploid strawberry plants through spontaneous hybridization with GM plants. The objective of this study was to clarify the possibility of hybridization between an octoploid cultivar and F. vesca, which is the most closely related species to octoploid species. As male and female parents, F. × ananassa cv. 'Sachinoka' (2n=56) and F. vesca cv. 'Baron Solemacher' (2n=14) were used, respectively. In all, 66 seedlings were obtained from 100 seeds. The petiole length, the leaf blade length and width, and the numbers of runners, vegetative buds and inflorescences were recorded. In addition, polyploidy levels of the hybrid plants were analyzed using flow cytometry and chromosome counting. The hybrids were divided into A type (23 plants) and B type (43 plants) according to their morphological characteristics. Results of flow-cytometry analysis and chromosome counting showed that A type was a diploid of F. vesca and that B type was a hybrid of pentaploid. Consequently, we inferred that hybrids that had the genes of octoploid strawberry cultivars appeared at high frequency.

Recent progress in plant genome size evolution

It has been known that eukaryotic genomes span a wide range of sizes regardless of organism complexity. The observed differences in genome size are primarily due to polyploidy level and abundance of non-coding DNA, especially the contribution of transposable elements (TEs). Here we reviewed the current progress in genome size variation of plant species and the underlying evolutionary forces that contribute to genome expansion or contraction. Polyploidization and the accumulation of transposable element are the primary contributors to genome expansion. As to the mechanisms of DNA loss, unequal homologous recombination and illegitimate recombination are thought to be the counterbalances to the unlimited expansion of a genome. The evolutionary direction of plant genome size is also discussed, which tends to favor larger genomes with deletion mechanisms acting to only attenuate genome expansion but not reverse.

Isolation and characterization of a cotton cdh-like gene

Cotton fiber cells elongate without dividing to form economically valuable spinnable fiber. Reports of the ploidy level of fiber cells are variable. Early reports indicated an increase in nuclear DNA content in young fibers; however, subsequent reports failed to observe such a significant increase in ploidy level. Evaluation and analysis of genes involved in regulation of DNA synthesis and other aspects of cell cycle regulation identified relevant genes that were present in fiber cells though usually at low levels. We report the isolation and characterization of another gene likely to be involved in cell cycle/DNA synthesis control. This gene was similar to a gene from Medicago species that controls entry into anaphase by regulating the activity of the anaphase promoting complex ability to ubiquinate selected proteins. The cotton gene was composed of nine exons and the deduced translational sequences have motifs similar to a Medicago gene expressed in highly polyploid cells. Based on this similarity the cotton gene was designated Ghcdh. Ghcdh is highly expressed in meristems and leaves but is present at much lower levels in fiber cells. These data are consistent with the lower levels of polyploidy reported for cotton fiber. A simple sequence repeat was identified in the gene that may be exploited as a marker to map this gene and associate it with important traits in cotton.

DNA content, chromatin supraorganization, nuclear glycoproteins and RNA amounts in hepatocytes of mice expressing insulin-dependent diabetes

Chromatin supraorganization and extensibility and nuclear glycoprotein content have been reported to change in hepatocytes from mice during development and aging, as well as under starvation and refeeding conditions. In non-obese diabetic (NOD) mice, the expression of insulin-dependent diabetes may be accompanied by metabolic changes in the liver. These changes are likely to be similar to those involved in the aging processes of non-diabetic animals. Therefore, we hypothesized that the chromatin organization, as well as the physical properties and compositions of hepatocyte nuclei would also be affected in NOD mice in the same way as those in aged non-diabetic mice. Nuclear image parameters were evaluated by image analysis of Feulgen-stained preparations. Chromatin extensibility in response to gravity was observed with polarized light after lysis and toluidine blue staining. The Con-A response of nuclear glycoproteins was evaluated with scanning microspectrophotometry. These charateristics were assessed using hepatocyte imprints from female NOD mice after a 28-day period of diabetes expression. Observations and measurements were made in comparison to healthy BALB/c mice. Total RNA amounts were determined for livers of NOD and BALB/c mice. Enhanced polyploidy levels, a decrease in chromatin higher-order packing states, an increased frequency of extended chromatin fiber formation, and deeper Con-A-responsive chromatin areas were observed in the hepatocytes of the NOD mice expressing insulin-dependent diabetes. Reduced amounts of total RNA were also found in the livers of these mice. Our findings for NOD mice expressing insulin-dependent diabetes are consistent with previously reported data for old-aged mice of the inbred strain A/Uni and may reflect changes in transcriptional activities associated with the stressful physiological demands on the liver during the expression of diabetes.

New chromosome number reports in tragacanthicAstragalusspecies

Cytological studies were performed in 12 populations of 10 tragacanthic Astragalus species from 3 sections of the genus Astragalus L., growing in Iran. The species of A. verus, A. caspicus, A. meyerei showed 2n = 2x = 16, A. gossypinus showed 2n = 2x = 14, A. microcephalus, A. denudatus, A. dschuparensis and A. hirticalyx showed 2n = 4x = 32, A. brachycalyx and A. compactus showed 2n = 6x = 48 chromosome number. The chromo- some number of A. verus, A. caspicus, A. meyerei, A. gossypinus, A. hirticalyx, A. brachycalyx and A. compactus are new to science while, the chromosome numbers obtained for A. microcephalus and A. denudatus support the earlier studies. Only diploid and tetraploid levels have been reported in the old world thorny Astragalus species, but the occurrence of 2n = 6x = 48 in A. brachycalyx and A. compactus increases the polyploidy level occurring in this group. The species studied showed metacentric and sub-metacentric chromosomes in their karyotype. The size of chromosomes varied from 2.20 µm in A. compactus to 5.51 µm in A. hirticalyx. The species studied differed significantly in the size of their chromosomes and also in karyotype formulae indicating the role of quantitative and qualitative change in the chromatin (DNA) material along with polyploidy in the species diversification.