Two repeated DNA sequences isolated from a partial genomic DNA library of Helianthus annuus, p HaS13 and p HaS211, were shown to represent portions of the int gene of a Ty3 /gypsy retroelement and of the RNase-Hgene of a Ty1 /copia retroelement, respectively. Southern blotting patterns obtained by hybridizing the two probes to BglII- or DraI-digested genomic DNA from different Helianthus species showed p HaS13 and p HaS211 were parts of dispersed repeats at least 8 and 7 kb in length, respectively, that were conserved in all species studied. Comparable hybridization patterns were obtained in all species with p HaS13. By contrast, the patterns obtained by hybridizing p HaS211 clearly differentiated annual species from perennials. The frequencies of p HaS13- and p HaS211-related sequences in different species were 4.3x10(4)-1.3x10(5) copies and 9.9x10(2)-8.1x10(3) copies per picogram of DNA, respectively. The frequency of p HaS13-related sequences varied widely within annual species, while no significant difference was observed among perennial species. Conversely, the frequency variation of p HaS211-related sequences was as large within annual species as within perennials. Sequences of both families were found to be dispersed along the length of all chromosomes in all species studied. However, Ty3 /gypsy-like sequences were localized preferentially at the centromeric regions, whereas Ty1/ copia-like sequences were less represented or absent around the centromeres and plentiful at the chromosome ends. These findings suggest that the two sequence families played a role in Helianthusgenome evolution and species divergence, evolved independently in the same genomic backgrounds and in annual or perennial species, and acquired different possible functions in the host genomes.

Tandem repeats belonging to three DNA sequence families ( OeTaq80, OeTaq178, and OeGEM86) were isolated from the nuclear DNA of Olea europaea cv. Carolea and dot-hybridized to the genomic DNA of 14 hypothetically different Olea species, 78 olive cultivars, and 14 wild olives. The copy number per unreplicated haploid genome of OeTaq80- and OeTaq178-related sequences was in the 10(7)-10(6) range and that of OeGEM86-related sequences was in the 10(5) range in cultivars, wild olives and some Olea species. A large variation in the frequency of repeats belonging to each sequence family was observed within each group of plants. Positive correlations existed in each genome between the frequencies of repeats belonging to each family, and their overall frequency was positively correlated to the genome size. Duncan grouping showed that the frequency variation of tandem repeats within each group of plants was not continuous. Two main groups and several subgroups of genotypes could be separated within both the olive cultivars and the wild olives. Discrete areas in the Mediterranean Basin could be delimited by the geographic distribution of cultivated olives with different genotypes and the wild plants were associated with the cultivars in these areas according to genotypic similarity. The Olea species could be divided into four genotypic groups. Three of these, comprising accessions from Asia and North Africa, showed similarity with the genotypes of cultivars and wild olives. These results suggest a polyphyletic origin of cultivated olives from different wild Olea forms distributed throughout the Mediterranean Basin.

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.

Summary. Automated karyotype analyses, nuclear DNA contents, and sequences of rDNA internal transcribed spacers of the nine species in Vicia sect. faba are reported.As karyomorphological parameters are used to evaluate the karyotype evolution, so the determination of the heterochromatin by Feulgen absorption at different thresholds of optical density provided further evidence on the chromatin organization within Vicia sect. faba. The comparison of sequences of rDNA spacers has enabled the definition of the phylogenetic relationships between the analyzed species.

Findings obtained using different approaches indicated the occurrence of genomic size variations within V. faba. Significant differences in the basic amount of nuclear DNA (up to 34.6 per cent) between 39 local populations collected from the Mediterranean Basin were observed by means of Feulgen/DNA cytophotometry. By contrast, no difference in genome size was found when five commercial varieties were compared. Dot blot hybridization of FokI V. faba repeats to genomic DNAs showed up to fourfold differences in the redundancy of these sequences in the nuclear DNA of different accessions. In agreement with the cytophotometric findings, a significant, positive correlation was determined between the DNA contents of populations and the copy numbers of DNA sequences related to FokI repeats. Significant differences between accessions were found in the length of the chromosome complement at metaphase, and these differences were particularly apparent in certain chromosome pairs. A positive correlation was found between the length of the complement and the genome size of the populations. These results are discussed in relation to other data in the literature on intraspecific nuclear DNA changes.Keywords: DNA cytophotometry, FokI DNA sequences, intraspecific DNA changes, karyometry, repetitive DNA, V/cia faba. tntroduction Today, there is a growing consensus of opinion that proliferation or deletion of nuclear DNA sequences does not occur only in the case of divergence and evolution of species. Indeed, many results obtained in different materials have shown that fluid domains, which are capable of rapid quantitative changes, may exist in the genome. These DNA domains, which are generally made up of repeated sequences, possibly occur more commonly, and express their ability to vary more frequently, in plant genomes than in animal genomes (reviewed for plants by Walbot & Cullis, 1985;Cionini, 1989; Bassi, 1990; Cullis, 1990; NagI, 1990).Redundancy variation of DNA sequences may accompany certain developmental processes. It has been suggested that they play a regulatory role in development (Frediani et a!., 1994 and references Because they may be of great biological importance and since many of their aspects are poorly understood, the above-mentioned genomic changes deserve thorough investigation. These changes have been shown to occur in many plant species (see Cavallini & Natali, 1991 show redundancy variations in Helianthus annuus (Natali et al., 1993), while quantitative differences in the nuclear DNA between populations of hexaploid Festuca arundinacea are mainly the result of changes in a fraction of highly repeated sequences (Ceccarelli et a!., 1992). The chromosomal organization of varying DNA sequences, as well as the mechanism by which intraspecific alterations in genome size and organization are produced and controlled, are almost entirely unknown.We investigated the nuclear DNA changes in Vicia faba by studying a number of local populationscollected from the Mediterranean Basin. Results are reported of DNA cytophot...