No abstract

Sites of 5S and 45S rDNA are more commonly located on different chromosomes of most angiosperms. Previous investigations have shown that in the subfamily Aurantioideae these sites may appear closely linked (adjacent sites), as in Poncirustrifoliata, or completely isolated, as in some species of Citrus. In the present work, the distribution of rDNA sites was investigated in representatives of 9 genera of Aurantioideae by FISH and CMA banding, aiming to understand the evolution of adjacent sites in the subfamily. A total of 57 rDNA sites were observed, 40 of them being adjacent to each other. All adjacent sites displayed the 45S rDNA array more terminally located. Assuming that the linked 5S-45S rDNA arrangement was the ancestral condition in Aurantioideae, the isolated rDNA sites observed in Clausena excavata,Bergera koenigii, and Fortunella obovata, as well as the complete linkage loss in Citrus maxima and C. medica indicates that unlinked sites arose independently several times in the evolution of the group. The linkage loss may be due to independent dispersion of one or both rDNA sequence families followed by deletion of the corresponding array in the adjacent site. The possible mechanisms behind these events and their occurrence in other groups are discussed.

ABSTRACT. We investigated the karyotypes of 13 species of six sections of the genus Inga (Leguminosae-Mimosoideae) from Brazil. We used conventional Giemsa staining to identify numerical chromosomal variations and looked for karyotypic evolutionary patterns. The karyotypes generally had small chromosomes, varying from metacentric to submetacentric, with a basic number x = 13. Nine of the species showed 2n = 2x = 26 (I. thibaudiana, I. cayennensis, I. ingoides, I. edulis, I. vera, I. subnuda, I. striata, I. bollandii, and Inga sp), while 2n = 4x = 52 was seen in a population of Inga cylindrical and of I. capitata, and in five populations of I. laurina. Additionally, 2n = 8x = 104 was observed in a population of I. cayennensis. Eight of these counts were new, while the counts of 2n = 52 for I. laurina and 2n = 26 for I. marginata, I. vera, I. subnuda, and I. edulis confirmed previous studies. We did not find cytological stability among the sections studied, with occurrence of significant intra-and inter-specific numerical variations. We conclude that polyploidy has played a significant role in karyotypic evolution in this group and that it occurred independently in several sections of the genus.