The association of cytogenetic and molecular techniques has contributed to the analysis of chromosome organization and phylogeny in plants. The fluorochrome GC-specific CMA3, fluorescent in situ hybridization (FISH) and RAPD (Random Amplified Polymorphic DNA) markers were used to investigate chromosome structure and genetic relationships in Hypochaeris (Asteraceae). Seven species native to South America, and two species introduced from Europe (H. glabra and Hypochaeris sp) were studied. FISH with rDNA probes identified one or two loci of 18S-5.8S-25S rDNA in the South American Hypochaeris species and one locus in the European species. Only one 5S rDNA locus was seen in all species studied. Blocks of GC-rich heterochromatin (CMA-positive bands) associated to 18S-5.8S-25SrDNA loci were detected in all species investigated. Co-location of 5S rDNA and CMA bands was also observed, except for three South American species and Hypochaeris sp. In two South American species, additional CMA bands not related to rDNA were observed on the long arm of chromosome 2, near to the centromere. Hypochaeris glabra exhibited additional CMA-positive signals distributed at pericentromeric regions, on the short arms of all chromosomes. A total of 122 RAPD markers were used to determine the genetic relationships among species. The level of polymorphism was very high, revealing two genetic groups comprising the South American and the European species, thus supporting a previous hypothesis of monophyly of the South American Hypochaeris species. The coefficients of genetic similarity between European and South American species were 0.35, on average. Polymorphism was also high within the two groups. The genetic associations observed with RAPD markers were consistent with chromosome characteristics. Species carrying similar distribution of 45S rDNA loci and CMA-positive signals were included in the same group revealed by RAPDs. Cytogenetic and molecular data support the view that not only chromosome rearrangements, but also changes in DNA sequence took place during the diversification of the South American Hypochaeris species.

The Asteraceae, one of the largest families of flowering plants, contains about 1,100 genera and 20,000 species, and is well known for its extensive karyotypic variation. In this study, conventional Feulgen staining, C-CMA3 banding, and fluorescence in situ hybridization with a 45S rDNA probe were used to determine the chromosome number and the number and physical position of GC-rich heterochromatin and 45S rDNA sites in three Asteraceae weed species (Crepis japonica, Galinsoga parviflora and Chaptalia nutans). The three species exhibited karyotype differences in the chromosome number and shape, as a commom feature of Asteraceae. However, the 45S rDNA sites always occurred on the short chromosomal arms, associated with GC-heterochromatin. Althought of these differences, it suggests that commom features of plant karyotype are maintained.

Rhynchospora tenuis Link (Cyperaceae) is a weed widely distributed in Brazil that presents a small number of holocentric chromosomes (2n = 4) with some autopolyploid populations (2n = 8). The haploid number n = 2 is considered as a derivative of the base number x = 5. 45S rDNA probes and telomeric DNA were hybridized in both chromosome races of R. tenuis, looking for indications of chromosome fusions. The results showed that hybridization sites of the telomeric probe were restricted to end chromosome regions whereas rDNA sites were terminally located. The chromosome race with n = 4 exhibited a doubled number of sites, with similar size and location to the hybridized sequences, confirming its autopolyploid origin. Furthermore, the terminal location of the single 45S rDNA site in the 2n = 4 race suggested that disploid reduction in Rhynchospora, from n = 5 to n = 2, was followed by elimination or reorganization events, keeping the terminal distribution of these sites, as in an others species of the genus.

Cariótipos de 14 populações, incluindo oito espécies do gênero Lobelia foram estudados usando metáfases mitóticas de raízes. Todas as populações mostraram-se tetraplóides com 2n = 28 cromossomos. O número cromossômico básico x = 7 foi confirmado para o gênero. A análise dos cariótipos mostrou que os tamanhos cromosômicos variaram de 1,05 µm a 2,02 µm com predominâcia de tipos cromossômicos M e SM. Os cariótipos foram similares entre si com pequenas variações intra e interespecíficas no tamanho do complemento haplóide, índice de simetria e posição do centrômero em alguns pares cromossômicos. Esses resultados mostraram que os cariótipos das lobélias brasileiras do subgênero Tupa podem ter sido originados por poliploidia associada a rearranjos cromossômicos, possivelmente em pequenos segmentos de cromatina.

Karyotypes of 14 populations including eight species of the genus Lobelia were studied using root tip mitotic metaphases. All populations were tetraploid with 2n = 28 chromosomes. The chromosome base number x = 7 was confirmed for the genus. Karyotype analysis showed that chromosome size varied from 1.05 µm to 2.02 µm with predominance of M and SM chromosome types. The karyotypes were similar among themselves with small intra- and interspecific variations on the size of haploid sets, symmetry indexes and centromere position of some chromosome pairs. These results showed that karyotypes of Brazilian lobelias of the subgenus Tupa were probably due to polyploidy associated with chromosomal rearrangements probably in small chromatin segments.

Cromossomos holocêntricos de seis espécies de Rhynchospora (R. ciliata, R. pubera, R. riparia e R. barbata (2n = 10), R. nervosa (2n = 30) and R. globosa (2n = 36)) foram corados com os fluorocromos CMA3/DAPI ou tratados para bandeamento C e seqüencialmente corados com Giemsa ou CMA3/DAPI. Variabilidade no padrão de bandas foi encontrada entre as espécies estudadas. A heterocromatina foi observada em regiões terminais e intersticiais dos cromossomos, indicando que os cromossomos holocêntricos de Rhynchospora mostram um padrão de distribuição de heterocromatina similar àqueles dos cromossomos monocêntricos de plantas.

Holocentric chromosomes of six species of Rhynchospora, R. ciliata, R. pubera, R. riparia and R. barbata (2n = 10), R. nervosa (2n = 30) and R. globosa (2n = 36), were stained with CMA3/DAPI fluorochromes or treated with C-banding and sequentially stained with Giemsa or CMA3/DAPI. Variability in banding pattern was found among the species studied. Heterochromatin was observed on terminal and interstitial chromosome regions, indicating that the holocentric chromosomes of Rhynchospora show a heterochromatin distribution pattern similar to those plant monocentric chromosomes.