We studied the karyotypes of four Brazilian Cestrum species (C. amictum, C. intermedium, C. sendtnerianum and C. strigilatum) using conventional Feulgen staining, C-Giemsa and C-CMA3/DAPI banding, induction of cold-sensitive regions (CSRs) and fluorescent in situ hybridization (FISH) with rDNA probes. We found that the karyotypes of all four species was 2n = 2x = 16, with, except for the eighth acrocentric pair, a predominance of meta- and submetacentric chromosomes and various heterochromatin classes. Heterochromatic types previously unreported in Cestrum as neutral C-CMA3(0)/DAPI0 bands, CMA3+ bands not associated with NORs, and C-Giemsa/CSR/DAPI- bands were found. The heterochromatic blocks varied in size, number, position and composition. The 45S rDNA probe preferentially located in the terminal and subterminal regions of some chromosomes, while 5S rDNA appeared close to the centromere of the long arm of pair 8. These results suggest that karyotype differentiation can occur mainly due to changes in repetitive DNA, with little modification in the general composition of the conventionally stained karyotype.

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.