ABSTRACT
Abstract Sisyrinchium is the largest genus of Iridaceae in the Americas and has the greatest amount of cytological data available. This study aimed at investigating how genomes evolved in this genus. Chromosome number, genome size and altitude from species of sect. Viperella were analyzed in a phylogenetic context. Meiotic and pollen analyses were performed to assess reproductive success of natural populations, especially from those polyploid taxa. Character optimizations revealed that the common ancestor of sect. Viperella was probably diploid (2n = 2x =18) with two subsequent polyplodization events. Total DNA content (2C) varied considerably across the phylogeny with larger genomes detected mainly in polyploid species. Altitude also varied across the phylogeny, however no significant relationship was found between DNA content changes and altitude in our data set. All taxa presented regular meiosis and pollen viability (> 87%), except for S. sp. nov. aff. alatum (22.70%), suggesting a recent hybrid origin. Chromosome number is mostly constant within this section and polyploidy is the only source of modification. Although 2C varied considerably among the 20 taxa investigated, the diversity observed cannot be attributed only to polyploidy events because large variations of DNA content were also observed among diploids.
ABSTRACT
Cytogenetic characterization was carried out on 12 accessions from Aster squamatus (Spreng.) Hieron., Pterocaulon polystachyum DC, and Solidago microglossa DC by studying their meiotic behavior and pollen viability. These species are from the Asteraceae family, native to Rio Grande do Sul State, Brazil, and are important for medicinal use. Young inflorescences with four accessions of each species were collected, fixed in ethanol-acetic acid (3:1), and conserved in ethanol 70 percent until use. The method used was that of squashing the anthers and coloring with acetic orcein 2 percent. Meiosis was regular in all accessions, presenting chromosomal associations preferentially bivalent, where n=10 was found for Aster squamatus and n=9 for Pterocaulon polystachyum, and Solidago microglossa. The studied accessions presented a Meiotic Index (MI) that varied from 65 percent to 87 percent in Aster squamatus, 85 percent to 92 percent in Pterocaulon polystachyum, and 64 percent to 92 percent in Solidago microglossa, indicating meiotic stability, although irregularities appeared during the cellular division. The pollen viability estimative was high in all studied accessions. These results indicate that the studied species can be included in future studies of genetic breeding.
Foi realizada a caracterização citogenética de doze acessos de Aster squamatus, Pterocaulon polystachyum e Solidago microglossa, espécies da família Asteraceae, nativas do Rio Grande do Sul, Brasil, por meio do estudo do comportamento meiótico e da viabilidade polínica, que possuem grande importância para uso medicinal. Inflorescências jovens de quatro acessos de cada espécie foram fixadas em álcool-ácido acético (3:1) e conservadas em álcool 70 por cento até o uso. O método utilizado foi o de esmagamento de anteras e a coloração com orceína acética 2 por cento. A meiose foi regular em todos os acessos, apresentando associações cromossômicas preferencialmente em bivalentes, encontrando-se n=10 para Aster squamatus e n=9 para Pterocaulon polystachyum e Solidago microglossa. Os acessos apresentaram índice meiótico que variou de 65 por cento a 87 por cento em Aster squamatus, de 85 por cento a 92 por cento em Pterocaulon polystachyum e de 64 por cento a 92 por cento para Solidago microglossa, indicando estabilidade meiótica, apesar de o aparecimento de irregularidades durante a divisão celular. A estimativa da viabilidade polínica foi alta para todos os acessos estudados. Esses resultados indicam que as espécies estudadas podem ser incluídas em futuros trabalhos de melhoramento genético.
ABSTRACT
The Passifloraceae is represented by species of tropical and subtropical origin. The Passiflora is the richest genus with approximately 450 species, 200 of them being native to Brazil. Recent karyological studies have reported the basic chromosome number for the Passiflora genus as x = 6, whereas x = 9, x = 10 and x = 12 were established as secondary basic numbers. High rates of fertility occur in most Passiflora species, since both meiotic index and pollen viability are above 90 percent. Unusual meiotic behavior has been described in some taxa. Unviable pollen were observed in some diploids species. The genome size varies from 1.83 to 5.36 pg, and significant interspecific variance has been observed. Studies using the FISH methodology have shown that there are two to three rDNA 45S sites and one 5S site in the species analyzed. In this review, information about the above-mentioned studies is presented and discussed in detail.
A família Passifloraceae é representada por espécies de origem tropical e subtropical. Passiflora é o gênero mais rico, com aproximadamente 450 espécies, cerca de 200 delas nativas do Brasil. Recentes estudos cariológicos têm relatado o número básico de cromossomos para o gênero Passiflora como sendo x = 6, enquanto x = 9, x = 10 e x = 12 foram considerados números básicos secundários. Altas taxas de fertilidade são observadas na maioria das espécies de Passiflora, uma vez que o índice meiótico e a viabilidade polínica apresentam-se acima de 90 por cento.Comportamento meiótico irregular tem sido descrito para alguns taxas. Grãos de pólen inviáveis foram observados em espécies diplóides. O tamanho do genoma varia de 1,83 a 5,36 pg, e variação interespecífica significativa tem sido observada. Estudos usando a metodologia de hibridização in situ (FISH) tem demonstrado haver de dois a três sites de DNAr 45S e um site de DNAr 5S nas espécies analisadas. Nesta revisão, informações sobre os estudos acima mencionados são apresentados e discutidos em detalhes.