Structure, behaviour and repetitive DNA of B-chromosomes in <i>Cestrum nocturnum</i> (Solanaceae)

The <i>Cestrum</i> genus is karyotypically exceptional in Solanaceae. It is characterised by a basic number <i>x</i> = 8, a large chromosomal and genomic size, complex heterochromatin patterns, B-chromosomes (Bs) with particular heterochromatin and distribution of 18–5.8–26S and 5S rDNA. <i>Cestrum nocturnum</i> L. has a diploid number of 2<i>n</i> = 16 plus a variable number of B-chromosomes. The aims of work was to analyse their numerical variation, structure and behaviour of <i>C. nocturnum</i> B-chromosomes by classical and molecular cytogenetics. The individuals analysed had 2<i>n</i> = 16 + 0−13 B-chromosomes. All B-chromosomes were metacentric and smaller than A-chromosomes. The number of B-chromosomes showed a great variability between and within individuals, thereby denoting the occurrence of events that promote mitotic and meiotic instability. Cytogenetic techniques made it possible to observe that B-chromosomes are rich in heterochromatin, probably with AT- and GC-rich regions. In addition, molecular techniques allowed to detect homologous sequences of transposable element conserved domains of Ty1-<i>Copia</i> and Ty3-<i>Gypsy</i> superfamilies. These sequences were located by FISH in all B-chromosomes and some A-chromosomes. Our results showed that repetitive DNA could play an important role in chromosomal evolution as well as in the stability of B-chromosomes in <i>C. nocturnum.</i>