Ribosomal RNA genes in species of theCynareae tribe (Compositae). II

Summary The structure of the ribosomal DNA has been analyzed in three species of theCynareae tribe using Southern blot hybridization.Silybum marianum possesses two types of ribosomal genes 12.3 and 13.4 kb long;Cirsium vulgare has at least four types of rDNA repeats 10.6, 10.5, 11.7 and 11.9 kb long;Carlina acaulis only one type of ribosomal genes 9.7 kb long. The rRNA genes of the three species studied showed an identical restriction mapping in the 18 S and 25 S regions. However species differentiation in length and/or nucleotide sequences are present in the external spacer and very probably in the internal transcribed spacer.By cytophotometric studies and byin vitro rRNA/DNA filter hybridization, the DNA amount/4 C nucleus and the rDNA percentage were calculated in nine species of theCynareae tribe:Cynara cardunculus subsp.scolymus (artichoke),Cynara cardunculus subsp.cardunculus (wild artichoke),Onopordon acanthium, O. illyricum, Galactites tomentosa, Carduus nutans, Silybum marianum, Cirsium vulgare andCarlina acaulis. The DNA amount/4 C nucleus in eight species are similar, ranging from 4.24 pg inGalactites tomentosa to 5.96 pg inCirsium vulgare, whileCarlina acaulis has a DNA amount/ 4C nucleus of 11.8 pg. The rDNA percentages range from 0.192% inOnopordon acanthium to 1.022% inSilybum marianum, whileCarlina acaulis has 0.038% of rDNA. This latter species is clearly distinct within theCynareae tribe.