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.

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.

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The nucleotide sequence of the first internal transcribed spacer (ITS1) belonging to different ribosomal RNA genes from Pinus pinea are reported. The analyzed ITS1 can be distinguished on the basis of their length, being one 2631 bp and the other 271 bp long. Nucleotide comparison of these regions did not show appreciable sequence homology. The larger ITS1 contains five tandem arranged subrepeats with size ranging between 219 bp and 237 bp. The nucleotide sequence of the 5.8S and the ITS2 regions belonging to the larger ribosomal RNA gene are also reported.

Tandemly repeated DNA sequences about 60 bp in length, which may be isolated by digestion with FokI restriction endonuclease, were studied by means of molecular and cytological hybridization in Vicia faba and other Vicia species. The results obtained can be summarized as follows: (i) FokI repeats are almost species specific to V. faba, since they hybridize to a minimum extent to genomic DNA of only two out of five related species; (ii) these tandemly repeated elements display variability in structure even within one and the same array, where different repeats may share not more than 71% homology; (iii) their redundancy in the genome of V. faba is remarkably high and varies largely between land races (copy numbers per haploid, 1C, genome range from 21.51 x 10(6) to 5.39 x 10(6)); (iv) FokI repeats are clustered in differing amounts in each subtelocentric pair of the chromosome complement and are missing or present in a nondetectable amount in the submetacentric pair; (vi) chromosome regions that bear these repeats associate closely to varying degrees in interphase nuclei. These results are discussed in relation to possible functional roles that tandemly repeated DNA sequences such as the FokI elements might play.

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 amount and spatial organization of the heterochromatin in nuclei of the shoot meristem and the frequency in the nuclear DNA of sequences belonging to a family of tandem repeats were investigated in cultivars of Olea europaea and related species. Significant differences between Olea species and between cultivars of O. europaea were observed: (i) in the spatial organization of the heterochromatin in interphase nuclei as determined by the number and surface area of the chromocentres; (ii) in genome size; and (iii) in the amount of condensed chromatin as measured by cytophotometry carried out at different thresholds of optical density. DNA elements belonging to a family of tandem repeats about 80 bp in length (OeTaq80 repeats) were isolated from the genomic DNA of an olive cultivar. It was shown: (i) by nucleotide sequence comparisons, that these repeats display variability in structure even within the same array, where different elements may share no more than 74% homology; (ii) by in situ hybridization, that OeTaq80-related DNA sequences are mainly localized in the heterochromatin at the chromosome ends; (iii) by dot-blot hybridization experiments, that these sequences are highly represented in the genome of all the olive cultivars and the majority of Olea species studied, and that their frequency may differ significantly even between olive cultivars; and (iv) by calculating the copy number of OeTaq80-related sequences per haploid (1C) genome, that the redundancy of these DNA elements may differ significantly between the genomes tested. It is suggested that the inter- and intraspecific changes in the nuclear and genomic traits observed can contribute to the understanding of the phylogenetic relationships between Olea species and in defining parameters to be exploited in varietal identification within cultivated olives.

The intergenic spacer (IGS) region of rDNA in Olea europaea is 5,629 bp long and it can be subdivided, on the basis of the different features, into six regions; two of them, located upstream and downstream of the putative transcription initiation site (TIS), respectively, contain prominent and unrelated subrepeats (s.r.). The upstream s.r. are 75-86 bp in length and the downstream ones are about 160 bp in length. The first type is represented by a high number (36) of iterations, which share a mutual similarity of 82.5%. A single sequence (TATTATAGGGGGGAGG) is found, which fits the reported TIS of plants and the position +1 would correspond to the adenine at position 3,622 after the 3′ end of 25 S ribosomal RNA (rDNA) genes. Moreover, in Olea IGS region some unusual features are observed and discussed in relation to analogous data present in the literature.