Migration of repetitive DNAs during evolution of the permanent translocation heterozygosity in the oyster plant (Tradescantia section Rhoeo).

Due to translocation heterozygosity for all chromosomes in the cell complement, the oyster plant (Tradescantia spathacea) forms a complete meiotic ring. It also shows Rabl-arrangement at interphase, featured by polar centromere clustering. We demonstrate that the pericentromeric regions of the oyster plant are homogenized in concert by three subtelomeric sequences: 45S rDNA, (TTTAGGG)n motif, and TSrepI repeat. The Rabl-based clustering of pericentromeric regions may have been an excellent device to combine the subtelomere-pericentromere sequence migration (via inversions) with the pericentromere-pericentromere DNA movement (via whole arm translocations) that altogether led to the concerted homogenization of all the pericentromeric domains by the subtelomeric sequences. We also show that the repetitive sequence landscape of interstitial chromosome regions contains many loci consisting of Arabidopsis-type telomeric sequence or of TSrepI repeat, and it is extensively heterozygous. However, the sequence arrangement on some chromosomal arms suggest segmental inversions that are fully or partially homozygous, a fact that could be explained if the inversions started to create linkages already in a bivalent-forming ancestor. Remarkably, the subterminal TSrepI loci reside exclusively on the longer arms that could be due to sharing sequences between similarly-sized chromosomal arms in the interphase nucleus. Altogether, our study spotlights the supergene system of the oyster plant as an excellent model to link complex chromosome rearrangements, evolution of repetitive sequences, and nuclear architecture.

The Role of Probiotics and Their Metabolites in the Treatment of Depression.

Depression is a common and complex mental and emotional disorder that causes disability, morbidity, and quite often mortality around the world. Depression is closely related to several physical and metabolic conditions causing metabolic depression. Studies have indicated that there is a relationship between the intestinal microbiota and the brain, known as the gut-brain axis. While this microbiota-gut-brain connection is disturbed, dysfunctions of the brain, immune system, endocrine system, and gastrointestinal tract occur. Numerous studies show that intestinal dysbiosis characterized by abnormal microbiota and dysfunction of the microbiota-gut-brain axis could be a direct cause of mental and emotional disorders. Traditional treatment of depression includes psychotherapy and pharmacotherapy, and it mainly targets the brain. However, restoration of the intestinal microbiota and functions of the gut-brain axis via using probiotics, their metabolites, prebiotics, and healthy diet may alleviate depressive symptoms. Administration of probiotics labeled as psychobiotics and their metabolites as metabiotics, especially as an adjuvant to antidepressants, improves mental disorders. It is a new approach to the prevention, management, and treatment of mental and emotional illnesses, particularly major depressive disorder and metabolic depression. For the effectiveness of antidepressant therapy, psychobiotics should be administered at a dose higher than 1 billion CFU/day for at least 8 weeks.

Chloroplast competition is controlled by lipid biosynthesis in evening primroses.

In most eukaryotes, organellar genomes are transmitted preferentially by the mother, but molecular mechanisms and evolutionary forces underlying this fundamental biological principle are far from understood. It is believed that biparental inheritance promotes competition between the cytoplasmic organelles and allows the spread of so-called selfish cytoplasmic elements. Those can be, for example, fast-replicating or aggressive chloroplasts (plastids) that are incompatible with the hybrid nuclear genome and therefore maladaptive. Here we show that the ability of plastids to compete against each other is a metabolic phenotype determined by extremely rapidly evolving genes in the plastid genome of the evening primrose Oenothera Repeats in the regulatory region of accD (the plastid-encoded subunit of the acetyl-CoA carboxylase, which catalyzes the first and rate-limiting step of lipid biosynthesis), as well as in ycf2 (a giant reading frame of still unknown function), are responsible for the differences in competitive behavior of plastid genotypes. Polymorphisms in these genes influence lipid synthesis and most likely profiles of the plastid envelope membrane. These in turn determine plastid division and/or turnover rates and hence competitiveness. This work uncovers cytoplasmic drive loci controlling the outcome of biparental chloroplast transmission. Here, they define the mode of chloroplast inheritance, as plastid competitiveness can result in uniparental inheritance (through elimination of the "weak" plastid) or biparental inheritance (when two similarly "strong" plastids are transmitted).

Chloroplast nucleoids are highly dynamic in ploidy, number, and structure during angiosperm leaf development.

Chloroplast nucleoids are large, compact nucleoprotein structures containing multiple copies of the plastid genome. Studies on structural and quantitative changes of plastid DNA (ptDNA) during leaf development are scarce and have produced controversial data. We have systematically investigated nucleoid dynamics and ptDNA quantities in the mesophyll of Arabidopsis, tobacco, sugar beet, and maize from the early post-meristematic stage until necrosis. DNA of individual nucleoids was quantified by DAPI-based supersensitive epifluorescence microscopy. Nucleoids occurred in scattered, stacked, or ring-shaped arrangements and in recurring patterns during leaf development that was remarkably similar between the species studied. Nucleoids per organelle varied from a few in meristematic plastids to >30 in mature chloroplasts (corresponding to about 20-750 nucleoids per cell). Nucleoid ploidies ranged from haploid to >20-fold even within individual organelles, with average values between 2.6-fold and 6.7-fold and little changes during leaf development. DNA quantities per organelle increased gradually from about a dozen plastome copies in tiny plastids of apex cells to 70-130 copies in chloroplasts of about 7 µm diameter in mature mesophyll tissue, and from about 80 plastome copies in meristematic cells to 2600-3300 copies in mature diploid mesophyll cells without conspicuous decline during leaf development. Pulsed-field electrophoresis, restriction of high-molecular-weight DNA from chloroplasts and gerontoplasts, and CsCl equilibrium centrifugation of single-stranded and double-stranded ptDNA revealed no noticeable fragmentation of the organelle DNA during leaf development, implying that plastid genomes in mesophyll tissues are remarkably stable until senescence.

Pericentromere clustering in Tradescantia section Rhoeo involves self-associations of AT- and GC-rich heterochromatin fractions, is developmentally regulated, and increases during differentiation.

A spectacular but poorly recognized nuclear repatterning is the association of heterochromatic domains during interphase. Using base-specific fluorescence and extended-depth-of-focus imaging, we show that the association of heterochromatic pericentromeres composed of AT- and GC-rich chromatin occurs on a large scale in cycling meiotic and somatic cells and during development in ring- and bivalent-forming Tradescantia spathacea (section Rhoeo) varieties. The mean number of pericentromere AT-rich domains per root meristem nucleus was ca. half the expected diploid number in both varieties, suggesting chromosome pairing via (peri)centromeric regions. Indeed, regular pairing of AT-rich domains was observed. The AT- and GC-rich associations in differentiated cells contributed to a significant reduction of the mean number of the corresponding foci per nucleus in relation to root meristem. Within the first 10 mm of the root, the pericentromere attraction was in progress, as if it was an active process and involved both AT- and GC-rich associations. Complying with Rabl arrangement, the pericentromeres preferentially located on one nuclear pole, clustered into diverse configurations. Among them, a strikingly regular one with 5-7 ring-arranged pericentromeric AT-rich domains may be potentially engaged in chromosome positioning during mitosis. The fluorescent pattern of pachytene meiocytes and somatic nuclei suggests the existence of a highly prescribed ring/chain type of chromocenter architecture with side-by-side arranged pericentromeric regions. The dynamics of pericentromere associations together with their non-random location within nuclei was compared with nuclear architecture in other organisms, including the widely explored Arabidopsis model.

Horizontal genome transfer as an asexual path to the formation of new species.

Allopolyploidization, the combination of the genomes from two different species, has been a major source of evolutionary innovation and a driver of speciation and environmental adaptation. In plants, it has also contributed greatly to crop domestication, as the superior properties of many modern crop plants were conferred by ancient allopolyploidization events. It is generally thought that allopolyploidization occurred through hybridization events between species, accompanied or followed by genome duplication. Although many allopolyploids arose from closely related species (congeners), there are also allopolyploid species that were formed from more distantly related progenitor species belonging to different genera or even different tribes. Here we have examined the possibility that allopolyploidization can also occur by asexual mechanisms. We show that upon grafting--a mechanism of plant-plant interaction that is widespread in nature--entire nuclear genomes can be transferred between plant cells. We provide direct evidence for this process resulting in speciation by creating a new allopolyploid plant species from a herbaceous species and a woody species in the nightshade family. The new species is fertile and produces fertile progeny. Our data highlight natural grafting as a potential asexual mechanism of speciation and also provide a method for the generation of novel allopolyploid crop species.

A representative of arylcyanomethylenequinone oximes effectively inhibits growth and formation of hyphae in Candida albicans and influences the activity of protein kinases in vitro.

In this study, we applied various assays to reveal new activities of phenylcyanomethylenequinone oxime-4-(hydroxyimino) cyclohexa-2,5-dien-1-ylidene](phenyl)ethanenitrile (4-AN) for potential anti-microbial applications. These assays demonstrated (a) the antimicrobial effect on bacterial and fungal cultures, (b) the effect on the in vitro activity of the kinase CK2, (c) toxicity towards human erythrocytes, the Caco-2 cancer cell line, and embryonic development of Zebrafish. We demonstrated the activity of 4-AN against selected bacteria and Candida spp. The MIC ranging from 4 µg/ml to 125 µg/ml proved effective in inhibition of formation of hyphae and cell aggregation in Candida, which was demonstrated at the cytological level. Noteworthy, 4-AN was found to inhibit the CK2 kinase with moderate potency. Moreover, at low concentrations, it did not exert any evident toxic effects on human erythrocytes, Caco-2 cells, or Zebrafish embryos. 4-AN can be a potential candidate as a novel drug against Candida infections.

Emodin, a natural inhibitor of protein kinase CK2, suppresses growth, hyphal development, and biofilm formation of Candida albicans.

Emodin (1,3,8-trihydroxy-6-methyl-anthraquinone) is a natural secondary plant product, originally isolated from the rhizomes of Rheum palmatum. Many reports show its diuretic, vasorelaxant, antibacterial, antiviral, anti-ulcerogenic, immunosuppressive, hepatoprotective, anti-inflammatory and anticancer potential. Emodin is a pleiotropic molecule capable of interacting with several major molecular targets, e.g. NF-κB, AKT/mTOR and STAT3. The compound can also act as an inhibitor of some protein kinases, with special affinity to protein kinase CK2. The aim of the presented report was to evaluate antifungal properties of emodin and its activity towards CK2 isolated from Candida cells. Our studies revealed that the compound suppressed growth of the cells of reference strains as well as clinical Candida strains, with minimal inhibitory concentration and minimal fungicidal concentration values between 12.5 and 200 µg/mL. Moreover, at a low concentration, the compound was able to effectively stop hyphal formation, thus showing a distinct antivirulent potential. Interestingly, we showed that emodin added to Candida culture inhibited the phosphorylation of many cellular proteins, presumably owing to the inhibition of protein kinase CK2. Notably, the enzyme isolated from the Candida cells was susceptible to emodin with IC50 of 2.8 µg/mL. Indeed, our computational modelling revealed that emodin was able to occupy the ATP-binding pocket of CK2. Copyright © 2017 John Wiley & Sons, Ltd.

Translocations of chromosome end-segments and facultative heterochromatin promote meiotic ring formation in evening primroses.

Due to reciprocal chromosomal translocations, many species of Oenothera (evening primrose) form permanent multichromosomal meiotic rings. However, regular bivalent pairing is also observed. Chiasmata are restricted to chromosomal ends, which makes homologous recombination virtually undetectable. Genetic diversity is achieved by changing linkage relations of chromosomes in rings and bivalents via hybridization and reciprocal translocations. Although the structural prerequisite for this system is enigmatic, whole-arm translocations are widely assumed to be the mechanistic driving force. We demonstrate that this prerequisite is genome compartmentation into two epigenetically defined chromatin fractions. The first one facultatively condenses in cycling cells into chromocenters negative both for histone H3 dimethylated at lysine 4 and for C-banding, and forms huge condensed middle chromosome regions on prophase chromosomes. Remarkably, it decondenses in differentiating cells. The second fraction is euchromatin confined to distal chromosome segments, positive for histone H3 lysine 4 dimethylation and for histone H3 lysine 27 trimethylation. The end-segments are deprived of canonical telomeres but capped with constitutive heterochromatin. This genomic organization promotes translocation breakpoints between the two chromatin fractions, thus facilitating exchanges of end-segments. We challenge the whole-arm translocation hypothesis by demonstrating why reciprocal translocations of chromosomal end-segments should strongly promote meiotic rings and evolution toward permanent translocation heterozygosity. Reshuffled end-segments, each possessing a major crossover hot spot, can furthermore explain meiotic compatibility between genomes with different translocation histories.

Chloroplast DNA in mature and senescing leaves: a reappraisal.

The fate of plastid DNA (ptDNA) during leaf development has become a matter of contention. Reports on little change in ptDNA copy number per cell contrast with claims of complete or nearly complete DNA loss already in mature leaves. We employed high-resolution fluorescence microscopy, transmission electron microscopy, semithin sectioning of leaf tissue, and real-time quantitative PCR to study structural and quantitative aspects of ptDNA during leaf development in four higher plant species (Arabidopsis thaliana, sugar beet [Beta vulgaris], tobacco [Nicotiana tabacum], and maize [Zea mays]) for which controversial findings have been reported. Our data demonstrate the retention of substantial amounts of ptDNA in mesophyll cells until leaf necrosis. In ageing and senescent leaves of Arabidopsis, tobacco, and maize, ptDNA amounts remain largely unchanged and nucleoids visible, in spite of marked structural changes during chloroplast-to-gerontoplast transition. This excludes the possibility that ptDNA degradation triggers senescence. In senescent sugar beet leaves, reduction of ptDNA per cell to ∼30% was observed reflecting primarily a decrease in plastid number per cell rather than a decline in DNA per organelle, as reported previously. Our findings are at variance with reports claiming loss of ptDNA at or after leaf maturation.

Variable amounts of DNA related to the size of chloroplasts III. Biochemical determinations of DNA amounts per organelle.

Plastid genomes (plastomes) are part of the integrated compartmentalised genetic system of photoautotrophic eukaryotes. They are highly redundant and generally dispersed in several regions (nucleoids) within organelles. DNA quantities and number of DNA-containing regions per plastid vary and are developmentally regulated in a way not yet understood. Reliable quantitative data describing these patterns are scarce. We present a protocol to isolate fractions of pure plastids with varying average sizes from leaflets (8 microm average diameter, corresponding from approximately a dozen to 330 genome equivalents per organelle and on average four to seven copies per nucleoid. The ratio of plastid/nuclear DNA changed continuously during leaf development from as little as 0.4% to about 20% in fully developed leaves. On the other hand, mesophyll cells of mature leaves differing in ploidy (di-, tri- and tetraploid) appeared to maintain a relatively constant nuclear genome/plastome ratio, equivalent to about 1,700 copies per C-value.

A novel, simple and rapid nondenaturing FISH (ND-FISH) technique for the detection of plant telomeres. Potential used and possible target structures detected.

We report a new technique-nondenaturing FISH (ND-FISH)-for the rapid detection of plant telomeres without the need for prior denaturation of the chromosomes. In its development, two modified, synthetic oligonucleotides, 21 nt in length, fluorescently labelled at their 5' and 3' ends and complementary to either the cytidine-rich (C(3)TA(3)) or guanosine-rich (T(3)AG(3)) telomeric DNA strands, were used as probes. The high binding affinity of these probes and the short hybridization time required allows the visualization of plant telomeres in less than an hour. In tests, both probes gave strong signals visualized as double spots at both chromosome ends; this was true of both the mitotic and meiotic chromosomes of barley, wheat, rye, maize, Brachypodium distachyon and Rhoeo spathacea. They were also able to detect telomere motifs at certain intercalary sites in the chromosomes of R. spathacea. To investigate the nature of the target structures detected, the chromosomes were treated with RNase A and single strand-specific nuclease S1 before ND-FISH experiments. Signal formation was resistant to standard enzymatic treatment, but sensitive when much higher enzyme concentrations were used. The results are discussed in relation to current knowledge of telomere structure.

Ribosomal DNA, tri- and bi-partite pericentromeres in the permanent translocation heterozygote Rhoeo spathacea.

High- and low-stringency FISH and base-specific fluorescence were performed on the permanent translocation heterozygote Rhoeo spathacea (2n = 12). Our results indicate that 45S rDNA arrays, rDNA-related sequences and other GC-rich DNA fraction(s) are located within the pericentromeric regions of all twelve chromosomes, usually colocalizing with the chromomycin A(3)-positive bands. Homogenization of the pericentromeric regions appears to result from the concerted spread of GC-rich sequences, with differential amplification likely. We found new 5S rDNA patterns, which suggest a variability in the breakpoints and in the consequent chromosome reorganizations. It was found that the large 5S rDNA locus residing on each of the 8E and 9E arms consisted of two smaller loci. On each of the two chromosome arms 3b and 4b, in addition to the major subtelomeric 5S rDNA locus, a new minor locus was found interstitially about 40% along the arm length. The arrangement of cytotogenetic landmarks and chromosome arm measurements are discussed with regard to genome repatterning in Rhoeo.

Molecular marker systems for Oenothera genetics.

The genus Oenothera has an outstanding scientific tradition. It has been a model for studying aspects of chromosome evolution and speciation, including the impact of plastid nuclear co-evolution. A large collection of strains analyzed during a century of experimental work and unique genetic possibilities allow the exchange of genetically definable plastids, individual or multiple chromosomes, and/or entire haploid genomes (Renner complexes) between species. However, molecular genetic approaches for the genus are largely lacking. In this study, we describe the development of efficient PCR-based marker systems for both the nuclear genome and the plastome. They allow distinguishing individual chromosomes, Renner complexes, plastomes, and subplastomes. We demonstrate their application by monitoring interspecific exchanges of genomes, chromosome pairs, and/or plastids during crossing programs, e.g., to produce plastome-genome incompatible hybrids. Using an appropriate partial permanent translocation heterozygous hybrid, linkage group 7 of the molecular map could be assigned to chromosome 9.8 of the classical Oenothera map. Finally, we provide the first direct molecular evidence that homologous recombination and free segregation of chromosomes in permanent translocation heterozygous strains is suppressed.

A simple non-toxic ethylene carbonate fluorescence in situ hybridization (EC-FISH) for simultaneous detection of repetitive DNA sequences and fluorescent bands in plants.

The major drawbacks of standard plant fluorescence in situ hybridization (FISH) designed for double-stranded DNA probes include requirement for experimentally determined heat denaturation of chromosomes at high temperatures and at least overnight hybridization. Consequently, processing with chromosomal preparations may easily result in heat-induced deterioration of chromosomal structural details, is time-consuming, and involves the use of toxic formamide and formaldehyde. Here, I have described a simple and appealing non-toxic procedure with ethylene carbonate (EC)-a formamide-substituting solvent and double-stranded repetitive DNA probes. Applying EC as a component of the hybridization solution at 46 °C not only allowed successful overnight hybridization but also gave a possibility to reduce the hybridization time to 3 h, hence converting the technique into a 1-day procedure. Importantly, the EC-FISH tended to preserve well chromosome structural details, e.g., DAPI-positive bands, thus facilitating simultaneous FISH mapping and chromosome banding on the same slide. The procedure requires no formaldehyde and RNA-se treatment of chromosomes, and no heat denaturation of chromosomal DNA. The key condition is to obtain high-quality cytoplasm-free preparations. The method was reproducible in all the plants studied (Allium, Nigella, Tradescantia, Vicia), giving a species-specific signal pattern together with clear DAPI bands on chromosomes. The procedure described here is expected to give a positive stimulus for improving gene-mapping approaches in plants.

1,4-Naphthoquinone derivatives potently suppress Candida albicans growth, inhibit formation of hyphae and show no toxicity toward zebrafish embryos.

PURPOSE: In this study, we applied various assays to find new activities of 1,4-naphthoquinone derivatives for potential anti-Candida albicans applications. METHODOLOGY: These assays determined (a) the antimicrobial effect on growth/cell multiplication in fungal cultures, (b) the effect on formation of hyphae and biofilm, (c) the influence on cell membrane integrity, (d) the effect on cell morphology using atomic force microscopy, and (e) toxicity against zebrafish embryos. We have demonstrated the activity of these compounds against different Candida species and clinical isolates of C. albicans. KEY FINDINGS: 1,4-Naphthoquinones significantly affected fungal strains at 8-250 mg l-1 of MIC. Interestingly, at concentrations below MICs, the chemicals showed effectiveness in inhibition of hyphal formation and cell aggregation in Candida. Of note, atomic force microscopy (AFM) analysis revealed an influence of the compounds on cell morphological properties. However, at low concentrations (0.8-31.2 mg l-1), it did not exert any evident toxic effects on zebrafish embryos. CONCLUSIONS: Our research has evidenced the effectiveness of 1,4-naphthoquinones as potential anti-Candida agents.

Karyotype and nuclear DNA content of hexa-, octo-, and duodecaploid lines of Bromus subgen. Ceratochloa.

The subgenus Ceratochloa of the genus Bromus includes a number of closely related allopolyploid forms or species that present a difficult taxonomic problem. The present work combines data concerning chromosome length, heterochromatin distribution and nuclear genome size of different 6x, 8x and 12x accessions in this subgenus. Special attention is paid to the karyotype structure and genomic constitution of duodecaploid plants recently found in South America. Hexaploid lineages possess six almost indistinguishable genomes and a nuclear DNA content between 12.72 pg and 15.10 pg (mean 1Cx value = 2.32 pg), whereas octoploid lineages contain the same six genomes (AABBCC) plus two that are characterized by longer chromosomes and a greater DNA content (1Cx = 4.47 pg). Two duodecaploid accessions found in South America resemble each other and apparently differ from the North American duodecaploid B. arizonicus as regards chromosome size and nuclear DNA content (40.00 and 40.50 pg vs. 27.59 pg). These observations suggest that the South American duodecaploids represent a separate evolutionary lineage of the B. subgenus Ceratochloa, unrecognized heretofore.

Meiotic events in Oenothera - a non-standard pattern of chromosome behaviour.

The genus Oenothera shows an intriguing extent of permanent translocation heterozygosity. Reciprocal translocations of chromosome arms in species or populations result in various kinds of chromosome multivalents in diakinesis. Early meiotic events conditioning such chromosome behaviour are poorly understood. We found a surprising uniformity of the leptotene-diplotene period, regardless of the chromosome configuration at diakinesis (ring of 14, 7 bivalents, mixture of bivalents and multivalents). It appears that the earliest chromosome interactions at Oenothera meiosis are untypical, since they involve pericentromeric regions. During early leptotene, proximal chromosome parts cluster and form a highly polarized Rabl configuration. Telomeres associated in pairs were seen at zygotene. The high degree of polarization of meiotic nuclei continues for an exceptionally long period, i.e., during zygotene-pachytene into the diplotene contraction stage. The Rabl-polarized meiotic architecture and clustering of pericentromeres suggest a high complexity of karyotypes, not only in structural heterozygotes but also in bivalent-forming homozygous species.

Tissue culture triggers chromosome alterations, amplification, and transposition of repeat sequences in Allium fistulosum.

Structural alterations in nuclei and chromosomes of cells derived from callus culture of Allium fistulosum have been studied with fluorescent in situ hybridization (FISH) using 5S ribosomal DNA (rDNA), 45S rDNA, and 375-bp repeat probes. A high frequency of chromosome abnormalities was found to be caused by the loss of telomere-located 375-bp repeats, chromosome fusion, and subsequent breakage-fusion-bridge cycles. Products of chromosome fusions and monocentric and regularly shaped chromosomes showed additional 375-bp repeat and 45S rDNA clusters at unusual sites, suggesting dynamic copy-number changes and transposition of these repeats. Southern hybridization revealed no differences in the 375-bp repeat and 45S rDNA repeat array order or the degree of methylation between DNA isolated from leaves or tissue-culture cells. In addition, protruding, spike-like structures positive for 375-bp repeats were identified on the surface of different-sized nuclei. Transmission electron microscopy analysis revealed the accumulation of densely packed chromatin within spike-like structures. Because root calyptra cells showed similar structures, it is likely that heterochromatic spike-like structures are a feature of nondividing cells at the onset of programmed cell death.

FISH-aimed karyotyping and characterization of Renner complexes in permanent heterozygote Rhoeo spathacea.

Fluorescence in situ hybridization (FISH) using 25S rDNA, 5S rDNA, and telomere sequences as probes was carried out in the complex permanent heterozygote Rhoeo spathacea. Telomere sites were exclusively terminal. All 10 25S rDNA loci were located distally and appeared transcriptionally active after silver staining. Six distal and 2 interstitial 5S rDNA sites were detected; 2 of the distal sites strictly colocalized with 25S rDNA loci. The 2 intercalary 5S rDNA loci occurred in short arms of 2 chromosomes that conjoined at meiosis. Chromosomes differed as to the amount of AT-rich centric heterochromatin, suggesting involvement of pericentromeric regions in translocations. The possibility of Robertsonian-like rearrangements was discussed. Double target FISH with ribosomal probes along with DAPI fluorescence gave the basis for full chromosome identification in mitosis. The 2 Renner complexes are structurally balanced, both having 5 25S and 4 5S rDNA sites. Centromere clustering, telomere association, a high number of NOR sites, and a strong tendency for formation of joint nucleoli contribute to the preservation of highly polarized Rabl arrangement at interphase. These findings were discussed in relation to meiotic catenation in Rhoeo.