Intrachromosomal Asymmetry Index Research Articles

Chromosome numbers and karyotype of five species from Seriphidium (Asteraceae)

Chromosome data are important for elucidating intergeneric relationships and delimiting infrafamilial tribes in plants. This paper reports karyological data for 12 Seriphidium (Bess.) Poljak. species from China, of these, five count as new reports and the others have been reported elsewhere. We also report the tetraploid level in S. schrenkianum for the first time. The karyotype formulae and types for the five new reports are: S. schrenkianum (Ledeb.) Poljak. 2n = 4x = 36 = 22m + 12sm + 2st, S. sublessingianum (Kell.) Poljak. 2n = 2x = 18 = 14m + 4sm and S. transiliense (Poljak.) Poljak. 2n = 2x = 18 = 4M + 6m + 2m(SAT) + 4sm + 2sm(SAT), belong to 2A type; S. cinum (Berg. ex Poljak.) Poljak. 2n = 2x = 18 = 8m + 10sm and S. sawanense Y. R. Ling et C. J. Humphries 2n = 2x = 18 = 10m + 2m(SAT) + 6sm, belong to 2B type. Furthermore, we estimated karyotype asymmetry in the 12 species by using an intrachromosomal asymmetry index and an interchromosomal asymmetry index. The data increase information about the karyosystematics of Seriphidium.

Cytotaxonomy of species of Vernonia, section Lepidaploa, group Axilliflorae (Asteraceae, Vernonieae)

Mitotic chromosomes of eight populations of six species of Vernonia sensu Baker (Asteraceae, Vernonieae, section Lepidaploa, group Axilliflorae) were studied to assess the validity of maintaining the genus as proposed currently (sensu Baker) or of splitting it into several smaller genera (sensu Robinson). The species were collected in areas of ‘cerrado’ and ‘campo rupestre’ in southern and central-western Brazil. The chromosome numbers were 2n = 20–40 and karyotypic analysis showed a predominance of metacentric chromosomes, with some submetacentrics. B chromosomes were seen in one population of V. geminata. The chromosomes varied in length from 0.9 to 4.6 µm, with a total chromatin length of 29.7–45.0 µm and a symmetry index of 41.2–46.9%. The intrachromosomal asymmetry index varied from 0.13 to 0.29, and the interchromosomal asymmetry index varied from 0.15 to 0.21. The dispersion diagram showed that population 1 of V. geminata had the most asymmetrical karyotype. These results do not provide sufficient evidence for a conclusive cytotaxonomic discussion of Vernonia, mainly because of the impossibility of associating any infrageneric group with specific karyotypic characters, and also because of the small number of species analysed so far. © 2007 The Linnean Society of London. Botanical Journal of the Linnean Society, 2007, 154, 99–108.

Cytotaxonomic studies in six species ofVernonia(Asteraceae: Vernonieae)

Abstract In this report, we describe a mitotic analysis (Giemsa technique) of six species of the genus Vernonia sensu Baker (Asteraceae, Vernonieae, section Lepidaploa) in order to assess the validity of maintaining this genus (sensu Baker) or dividing it into several lesser genera (sensu Robinson). Specimens of the seven species were collected in “cerrado” and “campo rupestre” areas in the states of São Paulo, Minas Gerais and Goiás. The chromosomal numbers (2n=32 and 2n=34) and karyotypes revealed a predominance of metacentric chromosomes, with some sub-metacentrics. The chromosome sizes varied from 1.2 to 4.9 μm, the total chromatin length (TCL) ranged from 31.3 to 50.7, and the asymmetry index TF% ranged from 42.3 to 44.4. The intrachromosomal asymmetry index (A1) varied from 0.15 to 0.19, while the interchromosomal asymmetry index (A2) ranged from 0.14 to 0.21. A dispersion diagram showed that population 1 of V. polyanthes had the most asymmetrical karyotype. These results still do not allow a comprehensive and conclusive cytotaxonomic discussion of this group, mainly because of the lack of a characteristic or standard karyotype for most infrageneric groupings (sections and subsections) and also because most species have not yet been analyzed cytogenetically. Nevertheless, the available data indicate only a tenuous relationship between the chromosome numbers observed here and reported in the literature compared to the taxonomic reorganization of the genera Lessingianthus, Vernonanthura and Chrysolaena proposed by Robinson.

Karyotype Variation in South American Elymus (Triticeae)

Karyotypes of eight tetraploid (2n = 28) South American species of Elymus, were symmetrical (arm ratios: 0 70-0.78) and uniform (intrachromosomal asymmetry index: 0.105-0 133). Significant differences in arm ratio and asymmetry index were found among tetraploid species and also among geographically isolated populations within one species. Variation was nearly continuous, and significant differences were found only between the extreme values. The opposite situation was found among three hexaploid species (2n = 42) that can be readily differentiated by significant differences in karyotype parameters Significantly higher intrachromosomal asymmetry indexes in E. erianthus (6x, 2n = 42) and E mendocinus (8x, 2n = 56) indicated relatively larger differences in chromosome size between the genomes of the progenitors of these polyploid species Low variation in the tetraploid species and high variation in the hexaploid and octoploid species were also found in the number and morphology of chromosomes with secondary constrictions (CSCs). Tetraploid species with the genome formula SSHH (S from Pseudoroegneria and H from Hordeum) showed only four CSCs from the S genome of Pseudoroegneria. The presence of CSCs from both S and H genomes in synthetic SSHH tetraploids and in natural SSHHHH hexaploids indicated absence of suppression of nucleolar organizing region (NOR) activity (amphiplasty) between the NORs from the S and H genomes. On the basis of karyotype and molecular data, it was hypothesized that the nucleolar organizing regions from the H genome were eliminated or highly reduced during the evolution of the tetraploid species.

Karyotype of Cuphea lanceolata Ait. and Cuphea viscosissima Jacq.

Cuphea lanceolata Alton and C. viscosissima Jacq. are potential germplasm sources of medium‐chain fatty acids. The fertile hybrid between these two species is being used to develop unproved cultivars as a domestic source of these important oils. A total of 1401 Giemsa C‐banded chromosomes from 145 root‐tip cells of these two species are karyotyped with the assistance of computer imaging techniques. Karyotype was defined by measuring individual chromosomes, computing the relative chromosome length and arm ratios, and identifying specific heterochromatic and euchromatic regions of individual chromosomes. The karyotype of these two species (2n = 12) consists of one pair of satellited chromosomes, two pairs of metacentric chromosomes, and two pairs of submetacentric chromosomes. Chromosome 2 is submetacentric in C. viscosissima but metacentric in C. lanceolata. The differences in relative chromosome length between homologous chromosomes of C. viscosissima and C. lanceolata were not significant. Karyotype asymmetry indices are the numerical expression for the general morphology of plant karyotypes. The intrachromosomal asymmetry index is 0.43 and 0.47 and the interchromosomal asymmetry index is 0.25 and 0.26 for C. lanceolata and C. viscosissima, respectively. The similarity of homologous chromosomes and C‐banding patterns indicate a close phylogenetic relationship between C. viscosissima and C. lanceolata.