Fabio Maggini

Individual variation of the nucleolus organizer regions in Allium cepa and A. sativum

Intraspecific variability of rDNA content in two cultivars of Allium cepa and in a strain of Allium sativum (U type) was studied by filter hybridization of 3H-rRNA with DNA extracted from roots of individual bulbs. The range of variation in% hybrid values was 2-fold (0.052% to 0.106%) and 2.5-fold (0.049% to 0.124%) in the two Allium cepa cultivars, but it was much smaller (0.048% to 0.061%) in the Allium sativum strain. — In both Allium cepa cultivars studied plants were observed carrying two, three or four nucleolus organizers per cell; cytological polymorphism of the nucleolus organizer regions was demonstrated by Giemsa C-banding. The number of ribosomal cistrons per genome of the bulb does not seem to be strictly dependent upon the number of nucleolus organizers per cell, and no relationship was detected between Giemsa banding pattern of nucleolar chromosomes and rDNA content of the bulb.

Lengths and nucleotide sequences of the internal spacers of nuclear ribosomal DNA in gymnosperms and pteridophytes

The nucleotide sequences of the internal transcribed spacers (ITS1 and ITS2) of the nuclear ribosomal DNA were analyzed in species belonging to gymnosperms and pteridophytes. The lengths of the ITSs of sixteen species of gymnosperms and seven species of pteridophytes were estimated. The gymnosperms have ITS1 regions larger than those observed in the pteridophytes and angiosperms (ca. 610–3100 bp versus 159–360 bp). On the other hand, the ITS2 regions appear to be of a conserved length (182–370 bp). We have determined the complete nucleotide sequences of ITS regions from four gymnosperm species and five pteridophyte species by cloning the PCR products. Sequence analysis showed the presence of three short tandem arranged subrepeats of about 70 bp in the 1112 bp ITS1 ofEphedra fragilis. Pyrimidine rich (about 90%) DNA segments of 40–50 bp were observed in the ITS1 ofGinkgo biloba. A highly conserved 16 bp long sequence known to be present in the ITS1 of the angiosperm species has been also found in the ITS1 ofCycas revoluta, Taxus baccata andEphedra fragilis.

The use of Osmium for Staining the Nucleolus in Squash Technique

SUMMARYWith reference to the squash technique, the authors propose some schedules for staining the nucleolus utilizing osmium tetroxide combined with thermic treatment.

Nucleotide sequence of the internal transcribed spacers and 5.8s region of ribosomal DNA in Phus pinea L

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.

Ribosomal RNA genes in biotypes ofScilla peruviana (Liliaceae)

Scilla peruviana biotypes have different chromosome numbers due to changes in the nucleolar chromosomes and polyploidy. We have examined two diploid (2n = 15 and 2n = 16) and two tetraploid biotypes (2n = 28 and 2n = 32). From the results of rRNA/DNA filter hybridizations it appears that rDNA percentages of the diploid biotypes are, approximately, 2.2-fold higher than those of the tetraploid biotypes. To examine the rRNA gene structure we have utilizedSouthern blot hybridization after DNA digestions with three restriction enzymes: Eco RI, Hind III and Bam HI. From the band analysis of both single and double digestions it has been possible to reveal the presence, in the diploid biotypes, of three gene types, heterogeneous both for length and for nucleotide sequences in the external spacer. The three rRNA genes are 12 600, 12 700, and 12 800 base pairs long and they have a different position of the Hind III sites in the external spacer. On the other hand, a single gene type of 12 600 base pairs, identical to the first type of the diploid biotypes, surprisingly exists in the tetraploid biotypes. Considerations on the rRNA gene regulation and evolution are made.

New insights in Salicornia L. and allied genera (Chenopodiaceae) inferred from nrDNA sequence data

A phylogenetic analysis was performed based on ITS DNA sequences of fourteen samples from different sources of six species of Salicornia, the three allied genera Arthrocnemum, Sarcocornia and Halocnemum of the same tribe Salicornieae, and other genera of the subfamily Salicornioideae used in previous studies. Bassia hirsuta, Camphorosma monspeliaca (subfamily Chenopodioideae) and four species of Suaeda (subf. Suaedoideae) were chosen as outgroups. Results show that the annual genus Salicornia is a sister group to the perennial genera Sarcocornia, Arthrocnemum and Halocnemum. Moreover, the phylogenetic analysis based on ITS results distinguished two groups of Salicornia species which fitted with ploidy level: one group consisted of diploid species, and the second of tetraploid ones. Sarcocornia and Arthrocnemum are shown to be closely related, even though the species investigated here exhibited an evident distance between their ITS sequences. On the basis of our results, these two genera should be united. Bienertia (already separated as Bienertieae) was confirmed as probable outgroup to the subf. Salicornioideae, while Kalidium (subf. Salicornioideae, tribe Halopeplideae) was an outgroup to the rest of the Salicornioideae (tribe Salicornieae). The group Allenrolfea plus Halocnemum was the most basal of the tribe Salicornieae amongst those investigated in this study. The two samples of Halocnemum strobilaceum used in this work displayed numerous changes (transitions and transversions) in their respective sequences, probably related to their morphological and chorological differentiation. On the basis of our analysis, the most probable basal chromosome number for Salicornieae appears to be 2n = 18. The same number would also be the base number for the annual genus Salicornia and the perennial Arthrocnemum ( + Sarcocornia), with polyploidy arising independently in the two groups.

Homologies of ribosomal RNA nucleotide sequences in monocots

SummaryCompetitive hybridization among ribosomal RNA was used to estimate homologies of nucleotide sequences in monocots. Homologies have been measured with respect toAllium cepa (Liliaceae) andZea mays (Graminaceae). It was found that nucleotide sequences are highly conserved withinLiliaceae, while some divergences were found withinGraminaceae.

RIBOSOMAL RNA GENES IN THE GENUS PINUS. I

SUMMARYRibosomal gene structure in Pinus pinea, P. halepensis and P. nigra has been analyzed by means of Southern blot hybridization after DNA digestions with Eco RI, Bam HI and Sac I restriction enzymes. Phage cloning, plasmid subcloning and partial nucleotide sequencing of the Pinus pinea rDNA demonstrated that the intergenic spacer (IGS) and the first internal transcribed spacer (ITS1) are very much longer than in angiosperm species, while the second internal transcribed spacer (ITS2) is closely related to angiosperms: our estimates are of 23 kb approximately for IGS and 2.64 kb and 0.25 kb for the ITS1 and ITS2 respectively in the more highly represented ribosomal genes.

The Ribosomal RNA Gene Number and the Length of the Nucleolar Secondary Constrictions in Bellevalia Romana and B. Dubia (Liliaceae): A Possible Correlation

SUMMARYKaryological analyses and rRNA/DNA hybridization experiments were carried out in Bellevalia romana and B. dubia (Liliaceae). B. romana (2 n=8) has four short NORs and 3,200 genes for ribosomal RNA; B. dubia (2 n=8) has six NORs clearly longer than those of B. romana and 9,800 rRNA genes. The gene numbers are calculated on the basis that both species possess 24 × 10−12 g/2C nucleus. A correlation between cytological and molecular hybridization results is made.

Nucleotide Sequence of the Internal Transcribed Spacers of Ribosomal DNA in Picea Abies Karst

The nucleotide sequences of the internal transcribed spacers (ITS1 and ITS2) of ribosomal DNA from Picea abies are reported. Two types of ITSl of 2784 bp and 3271 bp long exist, whereas only one ITS2 type 238 bp long is present in this species. The shorter ITSl is characterized by three shorter subrepeats: ssrl, ssr2 and ssr3, 221 bp, 227 bp and 226 bp long respectively. Between the ssrl and ssr2 sub-repeats are inserted three longer sub-repeats: LSR1, LSR2 and LSR3, 480 bp, 480 bp and 581 bp long respectively. The similarity between the three ssr range from 66% to 79% and between the three LSR range from 65% to 96%. At the end of the LSR3 a microsatellite of 14 CT elements is present. The longer ITSl type is due to a duplication of the LSR1, most probably obtained by unequal crossing-over and it has an identity of 97.3% with the shorter ITSl type.