Heterogeneity of the internal transcribed spacer 1 (ITS1) in Tulipa (Liliaceae)

Heterogeneity of the internal transcribed spacer ITS1 of the rDNA within in dividuals of Tulipa gesneriana L., T. kaufmanniana Regel, and their intersp ecific hybrids was analyzed by PCR-RFLP, using the polymorphic restriction enzymes RsaI and HinfI, and by nucleotide sequence analysis. In most cases, the sum of the sizes of the restriction fragments was higher than the enti re length of the undigested ITS fragment, indicating heterogeneity at the r estriction sites within an individual. Differences in band intensities with in the restriction patterns indicate the occurrence of variation in copy nu mber of these different ITS1 variants within individuals. Automated sequenc ing without a visual inspection often failed to detect existing heterogenei ty within sequences, resulting in a discrepancy between the sequencing and restriction analysis results. By visual interpretation of the sequences, th e restriction patterns could mostly be predicted well. Fluorescence in situ hybridization (FISH) experiments in four Tulipa species revealed the occur rence of several rDNA spots. The number of rDNA loci varied from seven in T , gesneriana 'Christmas Marvel' to ten in T. australis Link. This might exp lain the occurrence of heterogeneity in ITS sequences in Tulipa, as homogen ization of variants has to take place over different loci.