DNA Content Of Populations Research Articles

DNA CONTENT AND CYTOGENETIC CHARACTERISTICS OF Gymnocalycium quehlianum (CACTACEAE) ALONG AN ALTITUDINAL GRADIENT

Important changes in vegetation types occur along elevational gradients. The genus Gymnocalycium is endemic to southern South America, and its species are distributed along elevational gradients. In particular, Gymnocalycium quehlianum is a globular cactus endemic to the Sierras de Córdoba. Studying cytogenetic aspects and DNA content in populations throughout their distribution is key to understanding the species. DNA content and cytogenetic characteristics were analyzed in four populations of G. quehlianum (615, 744, 948 and 1257 masl). The genome size in the four populations varied between 3.55 and 4.30 pg. The populations were diploid (2n = 22). All populations showed the karyotype formula of 10 metacentrics (m) + 1 submetacentric (sm). The species presented symmetrical karyotypes and constitutive heterochromatin CMA+/DAPI- associated with nucleolar organizing regions, always found in the first pair of m chromosomes. The 18-5.8-26S rDNA locus is found in the terminal regions of the first pair of chromosomes m, and the 5S locus is adjacent to the 18-5.8-26S locus. A tendency for DNA content to decrease with increasing altitude was observed. Key words: Gymnocalycium quehlianum, chromosome number, cytogenetic, DNA content, altitudinal gradient

Estimation of nuclear DNA content in populations of Atriplex halimus L. (Chenopodiaceae) by flow cytometry

Abstract Atriplex halimus L. is a perennial native shrub of the Mediterranean Basin with an excellent tolerance to drought and salinity. The aim of this work was to estimate nuclear DNA content in populations of A. halimus L. by flow cytometry, an efficient method to estimate ploidy levels and to determine nuclear DNA content in plants. Flow cytometry is a technique which permits rapid estimation of nuclear DNA content. Because of its speed, precision and convenience, this method of analysis of nuclear DNA content finds an enormous number of applications which cover basic research, breeding and production. The results obtained indicate that the technique might greatly simplify the analysis of plant genomes at the molecular level.

Determination of Ploidy Level and Nuclear DNA Content in Tunisian Populations of Atriplex halimus L.

Atriplex halimus L. (Chenopodiaceae) (Saltbush) is a perennial species used as a fodder shrub for livestock in arid and semi-arid areas, particularly in North Africa. The aim of this work was to determine whether differences in ploidy level and/or nuclear DNA content exist among populations from widely-separated sites in Tunisia. We determined nuclear DNA content and chromosome numbers for populations of A. halimus from seven different locations (Gabes, Medenine, Tataouine, Monastir, Tunis, Sidi Bouzid, Kairouan). The chromosome counts showed that all the Tunisian populations, plus a population from Eraclea (Italy), were tetraploid (2n = 4x = 36) whereas a population from Cala Tarida (Spain) was diploid (2n = 2x = 18). With respect to nuclear DNA, the 2C DNA content of population Cala Tarida was estimated to be 2.41 pg. There was no significant difference among the tetraploid populations (or among plants within populations), whose 2C DNA content ranged from 4.92 to 4.97 pg.

ASSOCIATION OF PLOIDY AND SEXUAL SYSTEM IN LYCIUM CALIFORNICUM (SOLANACEAE)

In North American Lycium (Solanaceae), the evolution of gender dimorphism has been proposed as a means of restoring outcrossing after polyploidization causes the loss of self-incompatibility. Previous studies of this process in Lycium focused on comparisons between species that differ in ploidy. We examined intraspecific variation in floral morphology and DNA content in populations of L. californicum to determine correlations between sexual system and cytotype. We also used nuclear ITS and GBSSI sequence data to determine whether diploid and polyploid forms represent the same phylogenetic species, and the phylogeographic relationships among populations and ploidy levels. Within populations, no variation in ploidy was found, although among populations there was a perfect correspondence between sexual system and cytotype. Diploid populations were all hermaphroditic, whereas tetraploid populations were all gender dimorphic. There was no clear geographic pattern to the occurrence of diploid and tetraploid forms. Phylogenetic analysis confirms that L. californicum, regardless of ploidy, forms a monophyletic group within the genus Lycium. Sequences from diploid and polyploid individuals did not form reciprocally monophyletic clades, indicating either multiple gains of polyploidy, ongoing gene flow between cytotypes, or lack of lineage sorting since the evolution of polyploidy. The correspondence between ploidy and sex expression is consistent with the hypothesis that polyploidization triggers the evolution of gender dimorphism in this and other Lycium species.

Determination of ploidy and nuclear DNA content in populations of Atriplex halimus (Chenopodiaceae)

Nuclear DNA contents were determined by flow cytometry for 20 populations of the perennial C4 shrub Atriplex halimus L. (Chenopodiaceae) originating from the Mediterranean basin and Fuerteventura (Canary Islands). Two populations were also analysed for chromosome number: one (from Ibiza, Spain), with a 2C nuclear DNA content of 2.40 pg, was shown to be diploid (2n = 2x = 18), whilst the other (from Sicily, Italy), with 5.11 pg, was tetraploid (2n = 2x = 36). With respect to nuclear DNA content, two groups of populations were detected, diploids with 2.40–2.44 pg and tetraploids with 4.77–5.13 pg. The diploid populations were mainly from the western Mediterranean (Spain and France) and Fuerteventura, whereas tetraploids were generally, but not exclusively, from more arid areas in North Africa and the eastern Mediterranean. In general, the diploid and tetraploid populations corresponded to the subspecies halimus and schweinfurthii, respectively. For certain populations having morphologies intermediate between those considered typical of these two subspecies, nuclear DNA contents showed them to be tetraploid. There was significant variation in nuclear DNA content among the tetraploid populations, with greater values in the more easterly populations.

ASSOCIATION OF PLOIDY AND SEXUAL SYSTEM IN LYCIUM CALIFORNICUM (SOLANACEAE)

In North American Lycium (Solanaceae), the evolution of gender dimorphism has been proposed as a means of restoring outcrossing after polyploidization causes the loss of self-incompatibility. Previous studies of this process in Lycium focused on comparisons between species that differ in ploidy. We examined intraspecific variation in floral morphology and DNA content in populations of L. californicum to determine correlations between sexual system and cytotype. We also used nuclear ITS and GBSSI sequence data to determine whether diploid and polyploid forms represent the same phylogenetic species, and the phylogeographic relationships among populations and ploidy levels. Within populations, no variation in ploidy was found, although among populations there was a perfect correspondence between sexual system and cytotype. Diploid populations were all hermaphroditic, whereas tetraploid populations were all gender dimorphic. There was no clear geographic pattern to the occurrence of diploid and tetraploid forms. Phylogenetic analysis confirms that L. californicum, regardless of ploidy, forms a monophyletic group within the genus Lycium. Sequences from diploid and polyploid individuals did not form reciprocally monophyletic clades, indicating either multiple gains of polyploidy, ongoing gene flow between cytotypes, or lack of lineage sorting since the evolution of polyploidy. The correspondence between ploidy and sex expression is consistent with the hypothesis that polyploidization triggers the evolution of gender dimorphism in this and other Lycium species.

Hypoxia induces DNA overreplication and enhances metastatic potential of murine tumor cells.

Cultured cells subjected to oxygen deprivation have been shown to undergo anomalous DNA synthesis, which can result in DNA overreplication and the generation of cellular variants [Rice, G. C., Hoy, C. & Schimke, R. T. (1986) Proc. Natl. Acad. Sci. USA 83, 5978-5982]. In the present study, murine tumor cells were exposed to severe hypoxia and then tested for their ability to form experimental metastases. Upon reoxygenation, cells transiently, yet dramatically, increased their metastatic potential. Flow cytometric analysis confirmed that hypoxia and reoxygenation induced cell cycle perturbations and DNA overreplication in these tumor cell lines. Fibrosarcoma cells with overreplicated DNA isolated by fluorescence-activated cell sorting proved to be highly metastatic, although cells with 2-4 times the haploid DNA content in populations treated with hypoxia were also markedly more metastatic than oxic populations. These results support the hypothesis that hypoxic conditions existing in regions of solid tumors promote cellular heterogeneity and tumor progression.

A simple method for counting adherent cells: Application to cultured human monocytes, Macrophages and multinucleated giant cells

A simple method was devised for counting small numbers (10 4−10 6) of adherent mononuclear phagocytes, including populations containing multinucleated giant cells, which often arise during cultivation of human blood monocytes. Coverslips with adherent cells were transferred into small volumes (50–200 μl) of 0.1 M citric acid, pH 2.2, containing 0.05% naphthol blue black and 1.0% of either Triton X-100 or Cetavlon. Triton X-100 was adequate for use with monocytes and macrophages from early cultures. However, Cetavlon was preferable for use with older cultures of adherent human mononuclear cells in order to prevent aggregation of the nuclei from giant cells. When multinucleated cells were present, separately stained coverslips were inspected to determine the mean number of nuclei per cell. This value, together with the number of nuclei per coverslip, permitted calculation of the number of cells per coverslip. The latter value is not readily derived from measurements of protein or DNA content in populations containing multinucleated giant cells. This counting method was simpler and more sensitive than several previously reported methods for enumerating adherent macrophages.