Chromosomal organization of ribosomal genes and NOR-associated heterochromatin, and NOR activity in some populations of Allium commutatum Guss. (Alliaceae)

The position and the number of 18S-5.8S-26S and 5S rDNA loci, characterization of nucleolar organizing region (NOR)-associated heterochromatin and NOR activity assessment are given for six south-eastern Adriatic populations of Allium commutatum Guss. The karyotype characteristics were identical for all the populations studied, even those of distant islands. Diploid karyotypes (2 n = 16) always possessed two NOR-bearing chromosome pairs with pericentric and median secondary constrictions (SCs) on the short arm of the chromosomes VII and VIII. Fluorescent in situ hybridization (FISH) confirmed that these were the only sites of 18S-5.8S-26S rRNA genes. NOR-associated heterochromatin was of the constitutive character as shown after C-banding. Differential fluorochrome banding with Chromomycin A3 (CMA) and 4,6-diamidino-2-phenylindole (DAPI) revealed that this heterochromatin comprises both GC- and AT-rich DNA segments. Heteromorphism of C- and CMA-bands was noticed between homologous NOR-bearing chromosomes. The maximum number of four active NORs was correlated with the maximum number of four nucleoli in interphase. Variability of NOR-activity, expressed as number and size of silver stained NORs, existed between cells and between individuals of the same population. The different size of homologous and nonhomologous silver stained NORs was correlated with the extension of SCs. The only 5S rDNA locus was in an intercalary position on short arm of the chromosome VI, at the region of AT-rich constitutive heterochromatin. Dimorphism of C-bands and DAPI/Hoechst(H)-fluorescent bands was noticed between homologous chromosomes VI. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 99–108.     

Variation in chromosome numbers, CMA bands and 45S rDNA sites in species of Selaginella (Pteridophyta)

BACKGROUND AND AIMS: Selaginella is the largest genus of heterosporous pteridophytes, but karyologically the genus is known only by the occurrence of a dysploid series of n=7-12, and a low frequency of polyploids. Aiming to contribute to a better understanding of the structural chromosomal variability of this genus, different staining methods were applied in species with different chromosome numbers. METHODS: The chromosome complements of seven species of Selaginella were analysed and, in four of them, the distribution of 45S rDNA sites was determined by fluorescent in situ hybridization. Additionally, CMA/DA/DAPI and silver nitrate staining were performed to investigate the correlation between the 45S rDNA sites, the heterochromatic bands and the number of active rDNA sites. KEY RESULTS: The chromosome numbers observed were 2n=18, 20 and 24. The species with 2n=20 exhibited chromosome complement sizes smaller and less variable than those with 2n=18. The only species with 2n=24, S. convoluta, had relatively large and asymmetrical chromosomes. The interphase nuclei in all species were of the chromocentric type. CMA/DA/DAPI staining showed only a weak chromosomal differentiation of heterochromatic bands. In S. willdenowii and S. convoluta eight and six CMA+ bands were observed, respectively, but no DAPI+ bands. The CMA+ bands corresponded in number, size and location to the rDNA sites. In general, the number of rDNA sites correlated with the maximum number of nucleoli per nucleus. Ten rDNA sites were found in S. plana (2n=20), eight in S. willdenowii (2n=18), six in S. convoluta (2n=24) and two in S. producta (2n=20). CONCLUSIONS: The remarkable variation in chromosome size and number and rDNA sites shows that dramatic karyological changes have occurred during the evolution of the genus at the diploid level. These data further suggest that the two putative basic numbers of the genus, x=9 and x=10, may have arisen two or more times independently.     

玉米rRNA基因的组织和表达模式

玉米(Zea mays)只有1对45S rDNA位点并在分裂期染色体形成次缢痕, 是研究植物细胞rRNA基因组织和表达模式的简单模型。采用荧光原位杂交(fluorescence in situ hybridization, FISH)、CPD(PI与DAPI组合)染色和银染技术, 分析了玉米根尖分生细胞rRNA基因的组织和表达模式。45S rDNA探针在所有间期细胞核中显示2种杂交信号: 荧光强烈地位于核仁周边的纽, 而相对较弱地分布于核仁内的点。在部分细胞中可观察到点与纽相连或从纽发出; 点的数目越多, 纽变得越小; 点的数目多少与细胞的活性呈正相关。研究结果表明, 纽代表了处于凝缩状态的非活性的rDNA染色质, 纽解凝缩形成的点是rRNA基因活跃转录的细胞学表现; 不同阶段间期核的点的数目变化反映了被活化的rRNA基因数目不同。间期和前期细胞的CPD染色和相继的银染结果显示, 大部分rDNA染色质没有参与核仁的形成。rDNA FISH显示, 同一间期细胞的2个同源rDNA位点的表达水平存在差异, 同源染色体次缢痕的长度差异以及Ag-NOR和银染核仁的异态性进一步证实了这种差异的存在。FISH结果显示, 早中期细胞的rDNA染色质相对解凝缩, 银染在所有早中期细胞和部分中期细胞显示了明显的核仁, 表明玉米的rRNA基因在有丝分裂早中期有较活跃的转录, 其转录在晚中期才停止。     

玉米rRNA基因的组织和表达模式

玉米（Zea mays）只有1对45S rDNA位点并在分裂期染色体形成次缢痕,是研究植物细胞rRNA基因组织和表达模式的简单模型。采用荧光原位杂交（fluorescence in situ hybridization,FISH）、CPD（PI与DAPI组合）染色和银染技术,分析了玉米根尖分生细胞rRNA基因的组织和表达模式。45S rDNA探针在所有间期细胞核中显示2种杂交信号：荧光强烈地位于核仁周边的纽,而相对较弱地分布于核仁内的点。在部分细胞中可观察到点与纽相连或从纽发出;点的数目越多,纽变得越小;点的数目多少与细胞的活性呈正相关。研究结果表明,纽代表了处于凝缩状态的非活性的rDNA染色质,纽解凝缩形成的点是rRNA基因活跃转录的细胞学表现;不同阶段间期核的点的数目变化反映了被活化的rRNA基因数目不同。间期和前期细胞的CPD染色和相继的银染结果显示,大部分rDNA染色质没有参与核仁的形成。rDNA FISH显示,同一间期细胞的2个同源rDNA位点的表达水平存在差异,同源染色体次缢痕的长度差异以及Ag-NOR和银染核仁的异态性进一步证实了这种差异的存在。FISH结果显示,早中期细胞的rDNA染色质相对解凝缩,银染在所有早中期细胞和部分中期细胞显示了明显的核仁,表明玉米的rRNA基因在有丝分裂早中期有较活跃的转录,其转录在晚中期才停止。     

Intra- and interspecific chromosome polymorphisms in cultivated Cichorium L. species (Asteraceae)

Endive (Cichorium endivia L.) and chicory (C. intybus L.) both have 2n = 18, but until now, there has been no detailed karyomorphological characterization. The present work evaluated five accessions of each species using FISH with rDNA probes and fluorochrome staining with CMA and DAPI. Both species presented distinct banding patterns after fluorochrome staining: while endive had proximal CMA⁺⁺/DAPI⁻ bands in the short arms of pairs 1, 2 and 3, chicory had proximal CMA-positive bands in chromosomes 1 and 3 and interstitial in the short arm of chromosome 8. Among endive accessions, FISH procedures revealed conserved position and number of 5S and 45S rDNA sites (two and three pairs, respectively), associated with the CMA-positive bands. Notwithstanding, polymorphisms were detected within chicory accessions regarding the number and the distribution of rDNA sites in relation to the most frequent karyotype (two pairs with 45S and one with 5S rDNA). The karyological markers developed allowed karyotypic differentiation between both species, uncovering peculiarities in the number and position of rDNA sites, which suggest chromosome rearrangements, such as translocations in chicory cultivars. The interspecific and intraspecific polymorphisms observed emphasize the potential of karyomorphological evaluations, helping our understanding of the relationships and evolution of the group.     

The karyotype of Nothoscordum arenarium Herter (Gilliesioideae, Alliaceae): A populational and cytomolecular analysis

The genus Nothoscordum Kunth comprises approximately 20 species native to South America. Karyologically, the genus is remarkable for its large chromosomes and Robertsonian translocations. Variation in chromosome number has been recorded in a few polyploid species and it is unknown among diploids. This study presents the chromosome number and morphology of 53 individuals of seven populations of N. arenarium Herter (2n = 10). In addition, karyotype analyses after C-banding, staining with CMA and DAPI, and in situ hybridization with 5S and 45S rDNA probes were performed in six individuals from one population. All individuals exhibited 2n = 10 (6M + 4A), except for one tetraploid (2n = 20, 12M + 8A) and one triploid (2n = 15, 9M + 6A) plant. C-banding revealed the presence of CMA(+) /DAPI (-) heterochromatin in the short arm and in the proximal region of the long arm of all acrocentric chromosomes. The 45S rDNA sites co-localized with the CMA (+) regions of the acrocentrics short arms, while the 5S rDNA probe only hybridized with the subterminal region of a pair of metacentric chromosomes. A change in the pattern of CMA bands and rDNA sites was observed in only one individual bearing a reciprocal translocation involving the long arm of a metacentric and the long arm of an acrocentric chromosome. These data suggest that, despite isolated cases of polyploidy and translocation, the karyotype of N. arenarium is very stable and the karyotypic instability described for other species may be associated with their polyploid condition.     

Cytological heterozygosity and the hybrid origin of sweet orange [Citrus sinensis (L.) Osbeck]

Citrus sinensis chromosomes, although small in size, present a remarkable differentiation of bands with the fluorochromes CMA and DAPI. These bands suggest that some heteromorphisms are fixed in this species. To investigate the extension of these heteromorphisms, ten cultivars of C. sinenesis were analysed with CMA/DAPI staining and, in some of them, the 18S–5.8S–25S rRNA and 5S rRNA genes were located by in situ hybridization. CMA/DAPI staining showed exactly the same CMA⁺/DAPI⁻ banding pattern for all cultivars. In situ hybridization revealed three 18S–5.8S–25S rRNA gene sites, two proximally located on two similar chromosomes and one terminally located on a third non-related chromosome. Two 5S rRNA gene sites were observed in this species, with one located proximal to the telomeric 18S–5.8S–25S rDNA site. Both cytological approaches revealed an invariable, heterozygotic karyotype among sweet orange cultivars. Based on these data, the putative hybrid origin of the species is discussed. Received: 9 April 1999 / Accepted: 22 June 1999     

Karyotype analysis of Lilium longiflorum and Lilium rubellum by chromosome banding and fluorescence in situ hybridisation.

Detailed karyotypes of Lilium longiflorum and L. rubellum were constructed on the basis of chromosome arm lengths, C-banding, AgNO3 staining, and PI-DAPI banding, together with fluorescence in situ hybridisation (FISH) with the 5S and 45S rDNA sequences as probes. The C-banding patterns that were obtained with the standard BSG technique revealed only few minor bands on heterologous positions of the L. longiflorum and L. rubellum chromosomes. FISH of the 5S and 45S rDNA probes on L. longiflorum metaphase complements showed overlapping signals at proximal positions of the short arms of chromosomes 4 and 7, a single 5S rDNA signal on the secondary constriction of chromosome 3, and one 45S rDNA signal adjacent to the 5S rDNA signal on the subdistal part of the long arm of chromosome 3. In L. rubellum, we observed co-localisation of the 5S and 45S rDNA sequences on the short arm of chromosomes 2 and 4 and on the long arms of chromosomes 2 and 3, and two adjacent bands on chromosome 12. Silver staining (Ag-NOR) of the nucleoli and NORs in L. longiflorum and L. rubellum yielded a highly variable number of signals in interphase nuclei and only a few faint silver deposits on the NORs of mitotic metaphase chromosomes. In preparations stained with PI and DAPI, we observed both red- and blue-fluorescing bands at different positions on the L. longiflorum and L. rubellum chromosomes. The red-fluorescing or so-called reverse PI-DAPI bands always coincided with rDNA sites, whereas the blue-fluorescing DAPI bands corresponded to C-bands. Based on these techniques, we could identify most of chromosomes of the L. longiflorum and L. rubellum karyotypes.     

Comparative karyotype analysis ofCeratozamia mexicana andMicrocycas calocoma (Zamiaceae) using fluorochrome banding (CMA/DAPI) and fluorescence in situ hybridization of ribosomal DNA

Orcein staining, differential staining with CMA and DAPI, and FISH with an rDNA probe were used to compare somatic chromosomes ofCeratozamia mexicana andMicrocycas calocoma. CMA-positive dots and hybridization signals appeared on chromosomes at early interphase and mitotic prophase, but in significantly different number in the two species. InCeratozamia mexicana, the CMA-positive and DAPI-negative bands and the hybridization signal were located at the terminal region of the long arm of three median-centromeric chromosomes, the terminal region of the short arm of two median-centromeric chromosomes and the terminal region of the long arm of two subterminal-centromeric chromosomes. InMicrocycas calocoma, they were located at the pericentric region of two median-centromeric chromosomes. These chromosome data suggested thatMicrocycas has no simple Robertsonian relationship toCeratozamia.     

A simple chromosomal marker can reliably distinguishes <Emphasis Type="Italic">Poncirus</Emphasis> from <Emphasis Type="Italic">Citrus</Emphasis> species

Several chromosome types have been recognized in Citrus and related genera by chromomycin A₃ (CMA) banding patterns and fluorescent in situ hybridization (FISH). They can be used to characterize cultivars and species or as markers in hybridization and backcrossing experiments. In the present work, characterization of six cultivars of P. trifoliata (“Barnes”, “Fawcett”, “Flying Dragon”, “Pomeroy”, “Rubidoux”, “USDA”) and one P. trifoliata × C. limonia hybrid was performed by sequential analyses of CMA banding and FISH using 5S and 45S rDNA as probes. All six cultivars showed a similar CMA⁺ banding pattern with the karyotype formula 4B + 8D + 6F. The capital letters indicate chromosomal types: B, a chromosome with one telomeric and one proximal band; D, with only one telomeric band; F, without bands. In situ hybridization labeling was also similar among cultivars. Three chromosome pairs displayed a closely linked set of 5S and 45S rDNA sites, two of them co-located with the proximal band of the B type chromosomes (B/5S-45S) and the third one co-located with the terminal band of a D pair (D/5S-45S). The B/5S-45S chromosome has never been found in any citrus accessions investigated so far. Therefore, this B chromosome can be used as a marker to recognize the intergeneric Poncirus × Citrus hybrids. The intergeneric hybrid analyzed here displayed the karyotype formula 4B + 8D + 6F, with two chromosome types B/5S-45S and two D/5S-45S. The karyotype formula and the presence of two B/5S-45S chromosomes clearly indicate that the plant investigated is a symmetric hybrid. It also demonstrates the suitability of karyotype analyses to differentiate zygotic embryos or somatic cell fusions involving trifoliate orange germplasm. During the submission of this paper, we analyzed 25 other citrus cultivars with the same methodology and we found that the chromosome marker reported here can indeed distinguish Poncirus trifoliata from grapefruits, pummelos, and one variegated access of Citrus, besides the previously reported access of limes, limons, citrons, and sweet-oranges. However, among 14 mandarin cultivars, two of them displayed a single B/5S-45S chromosome, whereas in Citrus hystrix D.C., a far related species belonging to the Papeda subgenus, this chromosome type was found in homozygosis. Since these two mandarin cultivars are probably of hybrid origin, we assume that for almost all commercial cultivars and species of the subgenus Citrus this B type chromosome is a useful genetic marker.     

Nucleoli and ribosomal RNA cistron numbers in Hordeum species and interspecific hybrids exhibiting suppression of secondary constriction

The interspecific hybrids of Hordeum exhibit selective suppression of secondary constriction formation in the chromosome(s) contributed by one of the two parents. A comparison of the number of SAT (secondary constriction) chromosomes in the metaphase cells and the maximum number of nucleoli in interphase cells revealed that the chromosomes capable of organising nucleoli were not always reflected through secondary constriction formation. — The rDNA (DNA complementary to rRNA) amounts were estimated by DNA-rRNA filter hybridisation in diploid and polyploid species of Hordeum and their hybrids. While similar rDNA proportions were present in diploid and autotetraploid lines of H. bulbosum, there were up to threefold differences between H. vulgare and allohexaploids. Furthermore, differences were also apparent between species of same ploidy level. Ribosomal RNA (18S+5.8S+26S) cistron numbers in each of the five experimental hybrids exhibiting the selective suppression of secondary constriction formation revealed no selective loss of rDNA. — The presence of a higher number of nucleoli than the number of SAT chromosomes seen and the presence of expected number of rRNA cistrons suggest that the suppression of secondary constriction formation is not due to selective loss of rDNA.     

Chromosomal markers distinguish hybrids and non-hybrid accessions of mandarin

Mandarin is the common name of a heterogeneous group of Citrus species with a large range of variation in morphological and molecular characters as well as in number of species. Aiming to identify chromosome markers and to clarify the relationship within this group, the karyotype of 13 mandarin accessions were analyzed using CMA/DAPI staining and in situ hybridization with 5S and 45S rDNA probes. The CMA band pattern together with the position of rDNA sites revealed that mandarins can be separated karyologically into three groups: a) C. sunki and C. reshni; b) the Mediterranean mandarin, C. deliciosa, and the closely related C. tangerina cv. Dancy and C. reticulata cv. Cravo; c) the remaining cultivars, which are cytologically heterozygous and most probably interspecific hybrids. The former two groups are assumed to be pure species together with C. medica and C. grandis. A chromosome marker for mandarin species was identified and the relationship among the pure species and some hybrids is discussed.     

Physical mapping of the 18S-25S and 5S ribosomal RNA genes in diploid bananas

Fluorescent in situ hybridisation (FISH) was used to determine the number and distribution of the 18S-25S and 5S rDNA sites on mitotic chromosomes of 6 wild and 2 edible diploid (2n=22) accessions belonging to the two banana species, Musa acuminata and M. balbisiana. FISH with the 18S-25S probe resulted in signals on one pair of chromosomes, the position of signals corresponded to the secondary constriction at the end of a short arm. The intensity of labelling was different between the homologues and the larger site corresponded to a larger secondary constriction. This labelling pattern was observed consistently in all genotypes. On the other hand, differences in the number of 5S sites were observed between the accessions. While in some of the wild seeded species, the 5S rDNA was localised on two pairs of chromosomes, hybridisation signals appeared on three pairs of chromosomes in other wild accessions. Quite unexpectedly, only five sites of 5S rDNA were reproducibly observed in the two vegetatively propagated diploid edible cultivars, Pisang Mas and Niyarma Yik, evidence for structural heterozygosity. A dual colour FISH showed that in all accessions, the satellite chromosomes carrying the 18S-25S loci did not carry the 5S loci. The results demonstrate that molecular cytogenetics can be applied to Musa and that physical cytogenetic maps can be generated. This revised version was published online in July 2006 with corrections to the Cover Date.     

Karyotype analysis of Nicotiana kawakamii Y. Ohashi using DAPI banding and rDNA FISH

Prometaphase cells were used to analyze the karyotype of Nicotiana kawakamii Y. Ohashi by means of sequential Giemsa/CMA/DAPI staining and multicolor fluorescence in situ hybridization with 5S and 18S rDNA. Observation of the DAPI-stained prometaphase spreads indicated that N. kawakamii had six pairs of large chromosomes, one pair of medium-sized chromosomes and five pairs of small chromosomes. The six pairs of large chromosomes possessed remarkable DAPI bands, and each could be identified from both the DAPI banding pattern and the length of the short arm. The DAPI banding pattern was approximately identical to the CMA and Giemsa banding patterns. Hybridization signals of the 18S rDNA probe were detected on two pairs of large chromosomes. In addition, two pairs of small chromosomes were identified based on the position of the 5S rDNA signals. An idiogram of N. kawakamii chromosomes was produced based on DAPI bands and rDNA loci. Received: 17 July 2000 / Accepted: 4 September 2000     

Nuclear DNA content,base composition,heterochromatin and rDNA in Picea omorika and Picea abies

Two closely related spruces, Picea abies and Picea omorika, a Balkan paleoendemic species, often share habitats, yet never hybridize in nature. The present study adresses their characteristics such as nuclear DNA content, base composition, heterochromatin and rDNA pattern. The genome size of P. abies was 10% larger than that of P. omorika when assessed by flow cytometry, respectively 2C=37.2 pg and 33.8 pg; although when estimated as total chromosome length it was virtually the same. The heterochromatin Chromomycin-A (CMA)/ DAPI fluorochrome banding patterns of both P. abies and P. omorika are given here for the first time. Simultaneous FISH (fluorescent in situ hybridization) using 18S-26S and 5S rDNA probes revealed 16 18S rDNA sites in P. omorika, 12 18S rDNA sites in P. abies, and a single 5S rDNA locus in both species. The genomes have about 41% GC. The number and position of CMA/DAPI bands and rDNA loci provide good chromosome markers to clarify the karyotypes of the two species. Received: 18 October 2000 / 14 June 2001     

The relationships among lemons, limes and citron: a chromosomal comparison

Lemons, limes and citron constitute a group of closely related Citrus species, whose species delimitations and taxonomic relationships are unclear. In order to identify karyotypic similarities and species relationships within this group, the CMA+/DAPI- banding pattern and the distribution of the 5S and 45S rDNA sites of 10 accessions of lime, lemon, and citron were investigated. The four cultivars of C. limon analyzed showed the same pattern of CMA+ bands and rDNA sites, suggesting that they originated from a single germplasm, later differentiated by distinct somatic mutations. The lemons C. jambhiri, C. limonia and C. volkameriana displayed karyotypes very similar to each other, but they differed from C. limon by the absence of a single chromosome with one band in each telomere. The limes, C. aurantifolia and C. limettioides, seemed less related to each other and exhibited different heteromorphic chromosome pairs. In C. aurantifolia, the presence of a chromosome type unknown in all other Citrus species cytologically known so far supports the assumption that this accession may be derived from a hybrid with a species from the subgenus Papeda or from another genus. Citrus medica was the only homozygous accession of this group and all of its chromosome types were clearly represented in limes and lemons, some of them forming heteromorphic pairs. The analysis of the distribution of rDNA sites allowed a further refinement of the comparison among accessions. The lemons and limes were heterozygous for all rDNA sites, whereas C. medica was entirely homozygous. These data support the hypothesis that C. medica is a true species while the other nine accessions are hybrids.     

Physical mapping of rRNA genes by fluorescent in-situ hybridization and structural analysis of 5S rRNA genes and intergenic spacer sequences in sugar beet (Beta vulgaris)

A digoxigenin-labelled 5S rDNA probe (pTa-794) and a rhodamine-labelled 18S-5.8S-25S rDNA probe (pTa71) were used for double-target in-situ hybridization to root-tip metaphase, prophase and interphase chromosomes of cultivated beet,Beta vulgaris L. After in-situ hybridization with the 18S-5.8S-25S rDNA probe, one major pair of sites was detected which corresponded to the secondary constriction at the end of the short arm of chromosome 1. The two rDNA chromosomes were often associated and the loci only contracted in late metaphase. In the majority of the metaphase plates analyzed, we found a single additional minor hybridization site with pTa71. One pair of 5S rRNA gene clusters was localized near the centromere on the short arm of one of the three largest chromosomes which does not carry the 18S-5.8S-25S genes. Because of the difficulties in distinguishing the very similarly-sizedB. vulgaris chromosomes in metaphase preparations, the 5S and the 18S-5.8S-25S rRNA genes can be used as markers for chromosome identification. TwoXbaI fragments (pXV1 and pXV2), comprising the 5S ribosomal RNA gene and the adjacent intergenic spacer, were isolated. The two 5S rDNA repeats were 349 bp and 351 bp long, showing considerable sequence variation in the intergenic spacer. The use of fluorescent in-situ hybridization, complemented by molecular data, for gene mapping and for integrating genetic and physical maps of beet species is discussed.     

Cytogenetic studies in South American species of Serjania (Sapindaceae: Paullinieae)

Abstract

Serjania Mill. (Paullinieae) is considered the most important neotropical genus of Sapindaceae due to species number and its widespread distribution. In this study, 14 species belonging to three sections were analyzed using conventional staining, C/CMA/DAPI banding, and fluorescence in situ hybridization (FISH) with a 18S-5.8S-26S rDNA probe. New chromosome counts are reported for Serjania crassifolia, Serjania platycarpa, and Serjania regnellii, all with 2n = 24, which is remarkably constant for Serjania. The karyotypes are moderately asymmetric, and variations observed in A1 and A2 indices show resemblances between S. platycarpa, Serjania hebecarpa, and S. crassifolia, and between Serjania communis, Serjania gracilis, and S. regnellii. The banding pattern was homogeneous in Serjania. C/DAPI bands (AT-rich sites) were not clearly evidenced, but changes in the number and position of GC-rich sites (CMA bands) were observed. These segments were associated with 18S-5.8S-26S rDNA sites. The significance of the results is discussed in relation to chromosomal data available for the genus and in regard to the infrageneric treatment of Serjania.