No abstract

Subrepeating sequences of 325 bp found in the ribosomal intergenic spacer (IGS) of Vicia faba and responsible for variations in the length of the polycistronic units for rRNA were isolated and used as probes for in situ hybridization. Hybridization occurs at many regions of the metaphase chromosomes besides those bearing rRNA genes, namely chromosome ends and all the heterochromatic regions revealed by enhanced fluorescence after quinacrine staining. The DNA homologous to the 325 bp repeats that does not reside in the IGS was isolated, cloned and sequenced. It is composed of tandemly arranged 336 bp elements, each comprising two highly related 168 bp sequences. This structure is very similar to that of the IGS repeats and ca. 75% nucleotide sequence identity can be observed between these and the 168 bp doublets. The most obvious difference lies in the deletion, in the former, of a 14 bp segment from one of the two related sequences. It is hypothesized that the IGS repeats are derived from the 336 bp elements and have been transposed to ribosomal cistrons from other genome fractions. The possible relations between these sequences and others with similar structural features found in other species are discussed.

-The genus Scorzonera L. s.l. encompasses enormous morphological variation and has created problems for taxonomists. Podospermum has been treated as either a section of a broadly defined Scorzonera or as an independent genus. In Italy, there are twelve Scorzonera species and three Podospermum species. The relationship between these species is not at all clear. To clarify these relationships, a survey, including thirteen of the fifteen taxa found in Italy, was carried out using: i) sequence analysis of ribosomal internal transcribed spacer (ITS) and external transcribed spacer (ETS) regions; ii) analysis of Amplified Fragment Length Polymorphisms (AFLPs); iii) chromosome counts. In addition, to broaden the scope of the work and allow taxonomically significant interpretation of the data to be made, sequences from a range of related species were obtained from the EMBL nucleotide sequence database. Our analyses clearly indicate that Scorzonera s.l. is a polyphyletic grouping. The three approaches used were consistent with each other although showing different levels of resolution. There was broad division, on the basis of chromosome number, either 2n = 12 or 14. This was supported by PCO analysis of AFLP fragments which indicate three groups. Finally, phylogenetic analysis of sequence data produced four to six highly supported clades that might appropriately be given independent taxonomic status.

rDNA fragments, including the whole intergenic spacer (IGS) region of P. coccineus, were cloned into dephosphorylated pUC 13 plasmid. Four clones of different insert size were analysed. Restriction patterns and physical maps of these length variants (pPH1, pPH2, pPH5, pPH6) were performed through complete Eco RI cleavage and partial digestion with Hpa II, Hae III, Sau 3AI, Sma I. Evidence was obtained that the length heterogeneity of the four genes was mainly due to a differing number of about 170 bp sub-repeating elements in the IGS. Indeed, there are 16 of these in pPH1, about 34 in pPH2, 10 in pPH5 and about 60 in pPH6. The sequence analysis of pPH6 sub-repeats revealed that there are two types of sub-repeats: short ones (S) of 162 bp and long ones (L) of 176 bp. The homology between S and L is high (93.8%). S and L elements are present in at least three of the four genes investigated, as shown by a restriction pattern obtained with Hae III digestion to completion. The relative frequency of S and L types, however, differs among the four genes. The possible functional meaning of the sub-repeat structure is discussed on the basis of the homology between the S and L sequences on the one hand and on the other the ribosomal sequences of: i) Xenopus promoter(s); ii) wheat block A sub-repeats; iii) presumptive promoter(s) of wheat.

The two taxa, Narcissus poëticus and N. radiiflorus, although apparently quite morphologically distinct, grow together and there has been some debate as to whether they should be considered as a single or two separate species. In order to throw some light on this debate, a survey of amplified fragment length polymorphism (AFLP) was conducted to examine genetic diversity/similarity among 120 individuals of N. poëticus and N. radiiflorus obtained from two populations coming from sites separated by more than 100 km. In addition, a karyological study of the two taxa was carried out to determine chromosome number and morphology, the number of nucleoli and banding pattern with the fluorochromes chromomycin A 3 and DAPI. Using two AFLP primer pairs, a total of 103 clearly scorable fragments were amplified; of which 91 (88%) were polymorphic (78% if polymorphism is described as the most common band not present in more than 95% of individuals sampled). Cluster analysis and principal coordinates analysis of the calculated similarity matrix revealed there to be only a low level of genetic diversity between the entities constituting the populations and species. The genetic distance between the individual belonging to the different populations of the same species was slightly greater than that between species. Comparative chromosome analysis showed no differences in the two taxa at the cytological level.