F. Maggini

Amplification of ribosomal cistrons during the maturation of metaxylem in the root ofAllium cepa

SummaryA mixture of 18 S and 25 S3H-rRNA fractions was used for cytological hybridization with DNA of immature metaxylem cells ofAllium cepa in different stages of development. Labelling by3H-rRNA was detected over nucleolus associated DNA of almost all investigated stages and in correspondence of DNA bodies of one stage. Utilizingin vitro DNA-rRNA hybridization technique it was shown that DNA, extracted from root portions where extra synthesis of DNA occurs in metaxylem cells, contains approximately 6-fold rDNA than DNA extracted from meristems. Since the frequency of metaxylem cells among root cells is very low, the detected difference demonstrates a conspicuos amplification process. To our knowledge this is the first report on the quantitative estimation of amplification of ribosomal cistrons in plants.

Nuclear DNA contents, rDNAs, chromatin organization, and karyotype evolution in Vicia sect. Faba.

SummaryAutomated karyotype analyses, nuclear DNA contents, and sequences of rDNA internal transcribed spacers of the nine species inVicia 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 withinVicia sect.faba. The comparison of sequences of rDNA spacers has enabled the definition of the phylogenetic relationships between the analyzed species.

The chromosome complement of Olea europaea L.: characterization by differential staining of the chromatin and in-situ hybridization of highly repeated DNA sequences

The chromosome complement of olive (Olea europaea L.) has been characterized by differential staining of the chromatin and chromosomal localization of highly repeated DNA sequences and ribosomal cistrons. DAPI staining produces different-sized positive bands in various locations on all the chromosomes. By combining this band pattern with the results obtained from cytological hybridization of OeTaq80, OeTaq178, and OeGEM86 DNA tandem repeats, most of the pairs can be distinguished from each other, in spite of the large number of chromosomes (2n=46), their small size and similar morphology. Different tandem-repeated DNA sequences may be contained into single heterochromatic chromosome regions, even though there are regions where repeats of only one family are present. OeTaq80- and OeGEM86-related DNA sequences are rather specific to the heterochromatin at the chromosome ends, while most sequences related to the longer OeTaq178 probe are confined to interstitial heterochromatin. Some exceptions suggest that major chromosomal rearrangements occurred during genome evolution. Polymorphism, which may differentiate olive cultivars, was observed within chromosome pairs I, V, and VII.

Ribosomal RNA genes of Phaseolus coccineus. I

AbstractrDNA 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 subrepeat 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.

Repetitive DNA sequences as probes for phylogenetic analysis in Vicia genus

Abstract In the process of further characterizing phylogenetic relationships among Vicia species of the subgenus Vicia, four different molecular DNA markers were used: a tandemly repeated DNA sequences about 60 bp in length (FokI), a 336 bp element (pVf7) homologous to the IGS repeats (but that does not reside in the policistronic rDNA units); a family of repeated DNA sequences (VfB) of about 1200 bp in length (that might be derived from a mobile DNA element) and a family of repeated DNA sequences (VfM) of about 60 bp that can be considered a minisatellite-like sequence (EMBL accession nr. AJ242773). The comparison of the obtained results has enabled the definition of the phylogenetic relationships among the analysed species confirming that V. faba, V. bithynica and the species of Narbonensis section, represent three distinct taxonomic groups according to the Maxted’s classification (1993). VfB and VfM marker discriminate inside the sect. Narbonensis, too, evidencing a greater affinity between some species.

Ribosomal RNA genes of Phaseolus coccineus V. Relationship between rDNA phenotype and somatic differentiation.

SummarySize variations in the intergenic spacer of ribosomal DNA were detected between individual plants of openly pollinatedPhaseolus coccineus. Eleven days after sowing, two plant samples were examined: slowly developing plants with a length less than 40 cm; and fast developing plants with a length greater than 70 cm. The two samples were characterized by different plant weight and, at maturity, by highly distinctive seed yield. They also exhibited distinct patterns of protein expression as analyzed by 2-D electrophoresis. In particular a 38 kDa protein, related to malate dehydrogenase on the basis of its N-terminal sequence, was present at higher concentration and higher activity levels in fast developing plants. Intergenic spacer length variants were detected in both samples at approximately 180 bp intervals. More than one spacer length variant was present in each individual plant. At least 13 different intergenic spacer hybridization patterns were in fact detected: some patterns occurred equally in both slowly and fast developing samples while the majority of patterns was significantly different between the two samples.