Nuclear DNA content variation among Central European Koeleria taxa

BACKGROUND AND AIMS: Polyploidization plays an important role in the evolution of many plant genera, including Koeleria. The knowledge of ploidy, chromosome number and genome size may enable correct taxonomic treatment when other features are insufficient as in Koeleria. Therefore, these characteristics and their variability were determined for populations of six central European Koeleria taxa. METHODS: Chromosome number analysis was performed by squashing root meristems, and ploidy and 2C nuclear DNA content were estimated by flow cytometry. KEY RESULTS: Three diploids (K. glauca, K. macrantha var. macrantha and var. pseudoglauca), one tetraploid (K. macrantha var. majoriflora), one decaploid (K. pyramidata) and one dodecaploid (K. tristis) were found. The 2C nuclear DNA content of the diploids ranged from 4.85 to 5.20 pg. The 2C DNA contents of tetraploid, decaploid and dodecaploid taxa were 9.31 pg, 22.89 pg and 29.23 pg, respectively. The DNA content of polyploids within the K. macrantha aggregate (i.e. within K. macrantha and K. pyramidata) was smaller than the expected multiple of the diploid genome (K. macrantha var. macrantha). Geography-correlated variation of DNA content was found for some taxa. Czech populations of K. macrantha var. majoriflora had a 5.06% smaller genome than the Slovak ones. An isolated eastern Slovakian population of K. tristis revealed 8.04% less DNA than populations from central Slovakia. In central and north-west Bohemia, diploid and tetraploid cytotypes of K. macrantha were sympatric; east from this region diploid populations, and towards the west tetraploid populations were dominant. CONCLUSIONS: Remarkable intra-specific inter-population differences in nuclear DNA content were found between Bohemian and Pannonian populations of Koeleria macrantha var. majoriflora and between geographically isolated central and eastern Slovakian populations of K. tristis. These differences occur over a relatively small geographical scale.     

2C DNA variation and relationships among New World species of the genus Lupinus (Fabaceae)

The 2C DNA values in 38 species and accessions of the genus Lupinus (Fabaceae) from the New World have been analysed using flow cytometry. They are representatives of North and South American species (the Atlantic and the Andean regions). Estimated 2C DNA values ranged from 1.08 pg in L. pusillus to 2.68 pg in L. albicaulis (both from North America), that is a variation of more than 2.5-fold. The variation for North American lupins was much higher than that for South American ones. Statistical analysis of the data resulted in a grouping that showed for North American lupins some correlation with the length of life cycle. Discussion concerns some aspects of the evolution of the genus.     

Nuclear DNA content inCelosia (Amaranthaceae)

Nuclear DNA amount of five species ofCelosia ranging from 2x to 12x varies from 3.26 (2x) to 9.70pg (12x). The diploidC. trigyna has twice as much DNA/basic genome as other taxa, which is commensurate with its taxonomic position and genetic isolation. There is insignificant variation in DNA/basic genome among 4x, 8x, and 12x taxa. Therefore, DNA/nucleus shows a strong positive correlation with ploidy level. The different accessions of 4x taxa show constancy of DNA amounts. There is no correlation of seed weight with DNA amount.     

Nuclear DNA content of some important plant species

Nuclear DNA contents of more than 100 important plant species were measured by flow cytometry of isolated nuclei stained with propidium iodide.Arabidopsis exhibits developmentally regulated multiploidy and has a 2C nuclear DNA content of 0.30 pg (145 Mbp/1C), twice the value usually cited. The 2C value for rice is only about three times that ofArabidopsis. Tomato has a 2C value of about 2.0 pg, larger than commonly cited. This survey identified several horticultural crops in a variety of families with genomes only two or three times as large asArabidopsis; these include several fruit trees (a pricot, cherry, mango, orange, papaya, and peach). The small genome sizes of rice and the horticultural plants should facilitate molecular studies of these crops.     

Nuclear DNA amounts in Macaronesian angiosperms

Nuclear DNA contents for 104 Macaronesian angiosperms, with particular attention on Canary Islands endemics, were analysed using propidium iodide flow cytometry. Prime estimates for more than one-sixth of the whole Canarian endemic flora (including representatives of 11 endemic genera) were obtained. The resulting 1C DNA values ranged from 0.19 to 7.21 pg for Descurainia bourgeauana and Argyranthemum frutescens, respectively (about 38-fold difference). The majority of species, however, possessed (very) small genomes, with C-values <1.6 pg. The tendency towards small nuclear DNA contents and genome sizes was confirmed by comparing average values for Macaronesian and non-Macaronesian representatives of individual families, genera and major phylogenetic lineages. Our data support the hypothesis that the insular selection pressures in Macaronesia favour small C-values and genome sizes. Both positive and negative correlations between infrageneric nuclear DNA amount variation and environmental conditions on Tenerife were also found in several genera.     

Flow cytometric measurement of nuclear DNA content inCapsicum (Solanaceae)

Nuclei were isolated from leaf tissue of differentCapsicum species and the relative fluorescence intensity was measured by flow cytometry after propidium iodide staining.Pisum sativum nuclei with known nuclear genome size (9.07 pg) were used as internal standard to determine nuclear DNA content of the samples in absolute units. The 2C DNA contents ranged between 7.65 pg inC. annuum and 9.72 pg inC. pubescens, and the general mean of the genus was 8.42 pg. These values correspond, respectively, to 1C genome size of 3.691 (C. annuum), 4.690 (C. pubescens) and 4.063 (general mean) Mbp. In general, white-flowered species proved to have less DNA, with the exception ofC. praetermissum, which displayed a 2C DNA content of 9.23 pg. It was possible to divide the studied species into three main groups according to their DNA content, and demonstrate differences in DNA content within two of the three species complexes established on the basis of morphological traits.     

Nuclear DNA content of Solanum species grown in vitro, as determined by flow cytometry

The DNA relative content in nuclei from several Solanum species, which were used as partners for somatic hybridization, were determined using a flow cytometry method. The nuclei were isolated mechanically or via protoplasts from leaves of in vitro grown plants. In the case of S. nigrum as well as S. tuberosum cv. Bzura and dihaploid clone H8105, the nuclei were also obtained from suspension cultured cells by lysis of protoplasts. The source and the method of nuclei isolation affected the pattern of nuclear DNA in the genotypes studied. The mesophyll nuclei showed two distinct peaks on the DNA histograms, whereas the DNA peaks produced by cell suspension nuclei were broad and less distinct. The DNA content in the nuclei, calculated from the DNA histograms of the samples and a DNA standard historgam (Trout Red Blood Cells, having DNA content of 5.05 pg per nucleus), were much lower in mesophyll nuclei than in those obtained from the cell suspension for the same genotypes. The results are discussed in respect of the genetic instability of Solanum genotypes. The usefulness of a flow cytometry approach in somatic hybridization research is also discussed.     

Nuclear DNA content in the genus Hepatica (Ranunculaceae)

Using flow cytometry, we measured the nuclear DNA contents of all known taxa in Hepatica. Nuclear DNA content of Hepatica falconeri (diploid, crenate leaf lobes) was significantly lower than that of diploid entire species. Among the tetraploid species, crenate species had lower DNA contents than the entire taxon H. nobilis var. pubescens. The DNA content of the tetraploid species was more than double that of the diploid species among the same leaf-type groups.     

Hybridization and genome size evolution: timing and magnitude of nuclear DNA content increases in Helianthus homoploid hybrid species

Hybridization and polyploidy can induce rapid genomic changes, including the gain or loss of DNA, but the magnitude and timing of such changes are not well understood. The homoploid hybrid system in Helianthus (three hybrid-derived species and their two parents) provides an opportunity to examine the link between hybridization and genome size changes in a replicated fashion. Flow cytometry was used to estimate the nuclear DNA content in multiple populations of three homoploid hybrid Helianthus species (Helianthus anomalus, Helianthus deserticola, and Helianthus paradoxus), the parental species (Helianthus annuus and Helianthus petiolaris), synthetic hybrids, and natural hybrid-zone populations. Results confirm that hybrid-derived species have 50% more nuclear DNA than the parental species. Despite multiple origins, hybrid species were largely consistent in their DNA content across populations, although H. deserticola showed significant interpopulation differences. First- and sixth-generation synthetic hybrids and hybrid-zone plants did not show an increase from parental DNA content. First-generation hybrids differed in DNA content according to the maternal parent. In summary, hybridization by itself does not lead to increased nuclear DNA content in Helianthus, and the evolutionary forces responsible for the repeated increases in DNA content seen in the hybrid-derived species remain mysterious.     

Nuclear DNA content in Salmo fibvenl in Lake Posta Fibreno, Italy

The nuclear DNA content of Salmo fibreni , endemic to Lake Posta Fibreno, and of the sympatric Salmo trutta macrostigma , was evaluated using flow cytometric (FCM) analysis. The DNA content was 6-29 pg/nucleus for male and significantly greater at 6-41 pg/nucleus for female S, fibreni; and 6-37 pg/nucleus for male S, trutta macrostigma .     

中国吊钟花属植物核DNA含量(2C-值)与倍性水平研究

植物核DNA含量(2C-值)与倍性水平是重要的植物学基本特征,是进行种群进化、物种分类和生态学等研究的有力证据.为确定中国吊钟花属(Enkianthus Lour.)各物种的核DNA含量与倍性水平并探究该属植物在种间、种内核DNA含量差异,该研究以6种中国吊钟花属植物共23个居群60个样品为试验材料,以水稻品种'日本晴...     

Taxonomic implications of genome size for all species of the genus Gasteria Duval (Aloaceae)

Nuclear DNA content (2C) is used as a new criterion to investigate all species of the genus Gasteria Duval including the three recently described species Gasteria polita van Jaarsv., G. pendulifolia van Jaarsv. and G. glauca van Jaarsv.. The 122 accessions investigated have the same chromosome number (2n=2x=14), with exception of three tetraploid plants found. The nuclear DNA content of the diploids, as measured by flow cytometry with Propidium Iodide, is demonstrated to range from 32.8–43.2 pg. This implies that the largest genome contains roughly 10¹⁰ more base pairs than the smallest. Based on DNA content the species could be divided in five groups: G. rawlinsonii Oberm. with 32.8 pg, 13 mostly inland species with 34.3–36.0 pg, five coastal species with 36.5–39.0 pg and Gasteria batesiana Rowley with 43.2 pg. The thirteen species with 34.3–36.0 pg could be divided further, in a group of eight species occupying mainly very restricted areas with 34.3–35.1 pg and a second group of five species with 35.2–36.0 pg mainly occupying large areas. These five groups did not coincide very well with the two sections and four series of Gasteria based on a cladistic analysis by van Jaarsveld et al. (1994). Based on its long leafy branches, location in the centre of Gasteria species distribution and its by far lowest DNA content, G. rawlinsonii might be the most primitive member of the genus. Nuclear DNA content as measured by flow cytometry is shown to be relevant to provide additional information on the relationships between Gasteria species.     

Estimation of the nuclear DNA content of gossypium species

BACKGROUND AND AIMS: Gossypium is an economically important, globally distributed taxon comprising more than 50 species. DNA content estimates from about half of the species indicate over a 3-fold variation exists. However, the nine DNA content estimates for G. hirsutum reveal over a 2-fold difference for this species alone. Recent reports have shown that several plant compounds can bias DNA content estimates obtained by commonly used methods. The purpose of this research was to examine the standardization procedures used for DNA content determinations with flow cytometry as applied to Gossypium, and generate revised DNA content estimates for all available Gossypium species using best-standard practices. METHODS: Flow cytometry was used to measure fluorescence of isolated Gossypium nuclei stained with propidium iodide. Fluorescence values were converted to DNA content estimates based on the nuclear fluorescence of standard genotypes of barley, corn and rice. Various combinations of nuclei preparations relative to the standards were evaluated for their influence on the estimates. KEY RESULTS: Both external standardization and internal standardization with Oryza sativa 'IR36' yielded statistically similar DNA content estimates for Gossypium. Internal standardization with Hordeum vulgare 'Sultan' resulted in a high estimate of DNA content. Nuclear DNA content estimates were generated for 37 Gossypium species using external standardization. Estimates of ancestral genome sizes reveal that both increases and decreases in nuclear DNA content have occurred. Variation in intraspecific and intragenomic DNA content was low, and the allopolyploid AD-genome size was nearly the additive of its progenitor genomes. CONCLUSIONS: Due to unknown factors, internal standardization with H. vulgare 'Sultan' may not be appropriate for DNA content determinations of Gossypium. The current DNA content estimates support accepted cytogenetic divisions of the genus. Gossypium is a genus that exhibits genome constancy both through speciation within genomic groups and allopolyploidization.     

Variability of microsatellites BM224 and Bcal7 in populations of green toads (Bufo viridis complex) differing by nuclear DNA content and ploidy

The variability of microsatellites BM224 and Bcal7 was studied for the first time in three species of the diploid-polyploid complex of Bufo viridis (B. viridis, B. oblongus, and B. pewzowi). The locus Bcal7 was established to be monomorphic in all samples studied. In microsatellite BM224, three allele variants were found. Among tetraploid toads, the western Asiatic species B. oblongus was characterized by one allele only, the eastern B. pewzowi, by the two other alleles. A similar distribution was also revealed in triploid individuals on the borders of range between tetraploid and diploid species. Among the diploid species B. viridis samples, all three allele variants of microsatellite BM224 were observed. Their distribution in the area proved to be geographically determined. In diploid toads, a similarity was revealed between the distribution of microsatellite BM224 alleles and variability of the nuclear DNA content.     

The systematic value of nuclear DNA content in Galanthus

Genome size (Cx-value) was applied as a new criterion to investigate the relationships within the genus Galanthus L. (Amaryllidaceae). More than 150 samples representing all species, from wild and cultivated material, were investigated. Most species of Galanthus have the same basic chromosome number (2n=2x=24). However, the somatic nuclear DNA contents (2C), as measured by flow cytometry with propidium iodide was shown to range from 48.6 to 90.4 pg for the diploids. This implies that the largest genome contains roughly 4 × 10¹⁰ more base pairs than the smallest and has chromosomes that are nearly twice as large. On this basis we assumed that nuclear DNA content as measured using flow cytometry may be used to produce easily obtainable systematic data. Triploidy in G. rizehensis and G. alpinus var. bortkewitschianus, tetraploidy in G. elwesii and hexaploidy in G. lagodechianus were confirmed by flow cytometry. In addition, as well as a number of polyploid cultivars, triploids were also found in G. nivalis and tetraploids and hexaploids in G. transcaucasicus and G. elwesii, respectively. DNA content confirmed the close relationships in some species pairs, including: G. nivalis and G. reginae-olgae, G. krasnovii and G. platyphyllus, G. gracilis and G. elwesii. Further investigation of the taxonomic status of these pairs is suggested. As a rapid diagnostic tool, applicable even in the case of dormant bulbs or sterile plants, flow cytometry has applications for conservation and in particular the monitoring of the trade in bulbous plants.     

Nuclear DNA content in species ofEleusine (Gramineae): A critical re-evaluation using laser flow cytometry

Interest in dinitroaniline herbicide resistant biotypes ofEleusine indica, and an as yet undetermined taxon ofEleusine, necessitated a revaluation of reported nuclear genome size estimates for available species in the genus. Laser flow cytometry showed that the nuclear DNA content of six of the seven species examined had 15 to 50% less DNA than reported previously. It was also determined that roots, as contrasted to leaves, possessed a large fraction of nuclei at the 4C or 8C DNA content level, in diploid or tetraploid species, respectively (i.e. the G2/M peak). Two major reasons for the previously reported overestimation may include sampling only of root tissues where endopolyploid and normal diploid nuclei both occur and the inappropriate choice of onion nuclei as an internal standard.     

Nuclear DNA content of Vitis species,cultivars, and other genera of the Vitaceae

The nuclear DNA content was analyzed in Vitis species, hybrid cultivars, and genera of the Vitaceae using flow cytometry. Significant variation was found among Vitis species, hybrids, and other genera of the Vitaceae (Ampelopsis and Parthenocissus). DNA content was estimated to range from 0.98 to 1.05 pg/2C within V. labrusca (ns) and 0.86 to 1.00 pg/2C within V. vinifera (ns). Genotypes from Vitis and Parthenocissus were similar in nuclear DNA content (approximately 1.00 pg/2C) whereas they differed significantly from Ampelopsis (1.39 pg/2C). No correlation between DNA content and the center of origin of genotypes of the Vitaceae was noted. Based on the present study, the Vitis genome size is 475 Mbp, 96% of which is non-coding. Knowledge of DNA content is useful in order to understand the complexity of the Vitis genome and to establish a relationship between the genetic and physical map for map-based cloning.     

Intra- and interspecific variation in DNA content in Cistus (Cistaceae)

Flow cytometry, using propidium iodide and 4',6-diamidano-2-phenylindole staining, was used to estimate the nuclear DNA content (2C) and the proportion of A-T base pairs in 16 species of the Mediterranean genus Cistus. Genome sizes were shown to be constant within species, since no significant intraspecific variation in 2C DNA content was detected. At the genus level, up to about 1.5-fold differences in absolute DNA amounts were observed, ranging from 3.92 pg in C. crispus to 5.88 pg in C. monspeliensis. The (AT) : (GC) ratio was close to 1, and was similar for all species examined, ranging from 47.87% A-T content in C clusii, to 50.67% in C. populifolius. Pink-flowered species (subgenus Cistus) had lower DNA amounts than white-flowered species (subgenera Leucocistus and Halimioides). However, the distribution of DNA amounts in Cistus appeared to be continuous and did not permit a clear separation of infra-generic ranks in the genus.     

Genome size variation in the genus Carthamus (Asteraceae, Cardueae): systematic implications and additive changes during allopolyploidization

BACKGROUND AND AIMS: Plant genome size is an important biological characteristic, with relationships to systematics, ecology and distribution. Currently, there is no information regarding nuclear DNA content for any Carthamus species. In addition to improving the knowledge base, this research focuses on interspecific variation and its implications for the infrageneric classification of this genus. Genome size variation in the process of allopolyploid formation is also addressed. METHODS: Nuclear DNA samples from 34 populations of 16 species of the genus Carthamus were assessed by flow cytometry using propidium iodide. KEY RESULTS: The 2C values ranged from 2.26 pg for C. leucocaulos to 7.46 pg for C. turkestanicus, and monoploid genome size (1Cx-value) ranged from 1.13 pg in C. leucocaulos to 1.53 pg in C. alexandrinus. Mean genome sizes differed significantly, based on sectional classification. Both allopolyploid species (C. creticus and C. turkestanicus) exhibited nuclear DNA contents in accordance with the sum of the putative parental C-values (in one case with a slight reduction, frequent in polyploids), supporting their hybrid origin. CONCLUSIONS: Genome size represents a useful tool in elucidating systematic relationships between closely related species. A considerable reduction in monoploid genome size, possibly due to the hybrid formation, is also reported within these taxa.     

Genome size and base composition variation in natural and experimental Narcissus (Amaryllidaceae) hybrids

Background and Aims

Although there is evidence that both allopolyploid and homoploid hybridization lead to rapid genomic changes, much less is known about hybrids from parents with different basic numbers without further chromosome doubling. Two natural hybrids, Narcissus × alentejanus (2n = 19) and N. × perezlarae (2n = 29), originated by one progenitor (N. cavanillesii, 2n = 28) and two others (N. serotinus, 2n = 10 and N. miniatus, 2n = 30, respectively) allow us to study how DNA content and composition varies in such hybrids.

Methods

Flow cytometry measurements with two staining techniques, PI and DAPI, were used to estimate 2C values and base composition (AT/GC ratio) in 390 samples from 54 wild populations of the two natural hybrids and their parental species. In addition, 20 synthetic F₁ hybrid individuals were also studied for comparison.

Key Results

Natural hybrids presented 2C values intermediate between those found in their parental species, although intra-population variance was very high in both hybrids, particularly for PI. Genome size estimated from DAPI was higher in synthetic hybrids than in hybrids from natural populations. In addition, differences for PI 2C values were detected between synthetic reciprocal crosses, attributable to maternal effects, as well as between natural hybrids and those synthetic F₁ hybrids in which N. cavanillesii acted as a mother.

Conclusions

Our results suggest that natural hybrid populations are composed of a mixture of markedly different hybrid genotypes produced either by structural chromosome changes, consistent with classic cytogenetic studies in Narcissus, or by transposon-mediated events.