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.

The development of plants belonging to natural populations of hexaploid Festuca arundinacea with different basic amounts of nuclear DNA was studied. A previous investigation showed that the genome sizes of the populations correlate positively with the mean temperature during the year and with that of the coldest month at the stations. Mitotic cycle time is affected by nuclear DNA content; in a population with a C-value of 6.05 pg, it is 3 h shorter than in a population with a Cvalue of 8.28 pg. In contrast, the genome size affects neither the proportion of cells entering mitosis in the meristems, nor the enlargement of cells in differentiated leaf tissues. By studying plant development in 30 populations, it was found that their genome size correlates negatively with the seed germination power (P= 0.036) and the early growth of both the seminal root (P= 0.009) and the first foliage leaf (P= 0.099). By contrast, the genome size correlates positively with the height of the highest culm (P 0.014) and other quantitative characters of the plants at anthesis, as well as with their flowering time (P 0.037). It is suggested that the variations in the basic amount of nuclear DNA within F. arundinacea have a role in improving the fitness of plants in environments differing in climatic factors such as temperature.

Following the results of a previous investigation which showed significant differences (up to 34.6 per cent) in the basic amount of nuclear DNA between local populations of Vicia faba, the development of plants obtained from seeds collected from different populations was studied. Both cell proliferation in the meristems and cell enlargement in differentiated tissues are affected by the genome size. DNA content and the mitotic index in the root meristem are negatively correlated. The higher proportion of cells entering mitosis in the meristems of plants with a lower amount of DNA is not the result of alterations of the duration of the mitotic cycle, which was found to be quite comparable in two populations with largely differing genome sizes. Cell growth was studied in the epicotyl cortex and the leaf epidermis. In both differentiated tissues, cells were longer or had larger surface areas in populations with higher amounts of DNA than in populations with lower amounts of DNA. By studying plant development, positive correlations were found between the genome size and both the germination power of the seeds and the growth rate of the epicotyl. In contrast, negative correlations were found between the basic amount of nuclear DNA and both the height of the main stem and the fresh weight of plants at anthesis. The possible role that intraspecific alterations of the nucleotype may play in environmental adaptation and species evolution is briefly discussed.

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.

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.