B chromosomes are additional dispensable chromosomes that may be present in some individuals, populations, or species, which have probably arisen from the A chromosomes but follow their own evolutionary pathway. Supposedly, B chromosomes do not contain major genes except for ribosomal DNA (rDNA) sequences that have been mapped on the supernumerary chromosomes of many plants and animals. This paper is a new report of B chromosome occurrence in plants. B chromosomes with nucleolar organizing regions (NORs) were found in a diploid sample of Nierembergiaaristata D. Don (sub nom. N. stricta Miers) (2n = 2x = 16). This is an extreme case in which B chromosomes possess not only strong nucleolar activity, as revealed by conventional staining methods, AgNOR and fluorescence banding, and fluorescent in situ hybridization (FISH), but also show nucleolar competition with the A chromosomes. The observed phenomenon could be analogous to the nucleolar dominance or ‘differential amphiplasty’ phenomenon that occurs in interspecific hybrids.

Keywords:
Nucleolar dominance, Solanaceae, B chromosomes, Nierembergia, Nucleolar activity
1.
Acosta MC: Estudio cromosómico en Nierembergia y géneros afines (Nicotianeae-Solanaceae). PhD thesis, (Universidad Nacional de Córdoba Argentina, 2006).
2.
Acosta MC, Ordóñez A del V, Cocucci AA, Moscone EA: Chromosome reports in South American Nicotianeae (Solanaceae) with particular reference to Nierembergia. Ann Mo Bot Gard 93:634–646 (2006).
3.
Bakkali M, Cabrero J, López-León MD, Perfectti F, Camacho JPM: Population differences in the expression of nucleolus organizer regions in the grasshopper Eyprepocnemisplorans. Protoplasma 217:185–190 (2001).
4.
Battaglia E: Cytogenetics of B-chromosomes. Caryologia 17:245–299 (1964).
5.
Beukeboom LW: Bewildering Bs: an impression of the 1st B-Chromosome Conference. Heredity 73:328–336 (1994).
6.
Bloom SE, Goodpasture C: An improved technique for selective silver staining of nucleolar organizer regions in human chromosomes. Hum Genet 34:199–206 (1976).
7.
Bowen CC: Freezing by liquid carbon dioxide in making slides permanent. Stain Technol 31:87–90 (1956).
8.
Camacho JPM, Sharbel TF, Beukeboom LW: B-chromosome evolution. Philos Trans R Soc Lond B Biol Sci 355:163–178 (2000).
9.
Carr GD, Carr RL: Micro- and nucleolar-organizing B-chromosomes in Calycadenia (Asteraceae). Cytologia 47:79–87 (1982).
10.
Cocucci AA, Hunziker AT: Nierembergia, in Hunziker AT (ed): Flora Fanerogámica Argentina. 256 Solanaceae, parte 1. Subtr. VIIb. Nierembergiinae, pp 3–14 (Proflora, Córdoba 1995).
11.
Delgado M, Caperta A, Ribeiro T, Viegas W, Jones RN, Morais-Cecílio L: Different numbers of rye B chromosomes induce identical compaction changes in distinct A chromosome domains. Cytogenet Genome Res 106:320–324 (2004).
12.
Dhar MK, Friebe B, Koul AK, Gill BS: Origin of an apparent B chromosome by mutation, chromosome fragmentation and specific DNA sequence amplification. Chromosoma 111:332–340 (2002).
13.
Di Fulvio TE: Recuentos cromosómicos en Nierembergia (Solanaceae). Kurtziana 9:141–142 (1976).
14.
Di Fulvio TE: Poliploidía en Nierembergia ( Solanaceae). Kurtziana 17:25–30 (1984).
15.
Dnyansagar VR, Pingle AR: Effects of fragments and probable origin of B-chromosomes in Solanumviarum Dunal. Cytologia 44:561–569 (1979).
16.
Field BL, Houben A, Timmis JN, Leach CR: Internal transcribed spacer sequence analyses indicate cytoevolutionary patterns within Brachycome Cass. (Asteraceae). Plant Syst Evol 259:39–51 (2006).
17.
Green DM: Muller’s ratchet and the evolution of supernumerary chromosomes. Genome 33:818–824 (1990).
18.
Jones RN: B chromosome systems in flowering plants and animal species. Int Rev Cytol 40:1–100 (1975).
19.
Jones RN: Tansley Review No. 85: B chromosomes in plants. New Phytol 131:411–434 (1995).
20.
Jones RN, Rees H: B-chromosomes (Academic Press, London 1982).
21.
Jones RN, Houben A: B chromosomes in plants: escapees from the A chromosome genome? Trends Plant Sci 8:417–423 (2003).
22.
Jong K: Laboratory manual of plant cytological techniques (Royal Botanic Garden, Edinburgh 1997).
23.
Kodama Y, Yoshida MC, Sasaki M: An improved silver staining technique for nucleolus organizer regions by using nylon cloth. Jpn J Human Genet 25:229–233 (1980).
24.
Leach CR, Houben A, Field B, Pistrick K, Demidov D, Timmis JN: Molecular evidence for transcription of genes on a B chromosome in Crepiscapillaris. Genetics 171:269–278 (2005).
25.
Levin DA, Palestis BG, Jones RN, Trivers R: Phyletic hot spots for B chromosomes in angiosperms. Evolution 59:962–969 (2005).
26.
Maluszynska J, Schweizer D: Ribosomal RNA genes in B chromosomes of Crepiscapillaris detected by non-radioactive in situ hibridization. Heredity 62:59–65 (1989).
27.
Moens PB: The transmission of a heterochromatic isochromosome in Lycopersiconesculentum. Can J Genet Cytol 7:296–303 (1965).
28.
Morais-Cecílio L, Delgado M, Jones RN, Viegas W: Modification of wheat rDNA loci by rye B chromosomes: a chromatin organization model. Chromosome Res 8:341–351 (2000).
29.
Moscone EA, Matzke MA, Matzke AJM: The use of combined FISH/GISH in conjunction with DAPI counterstaining to identify chromosomes containing transgene inserts in amphidiploid tobacco. Chromosoma 105:231–236 (1996).
30.
Murata M, Shibata F, Yokota E: The origin, meiotic behavior, and transmission of a novel minichromosome in Arabidopsisthaliana. Chromosoma 115:311–319 (2006).
31.
Page BT, Wanous MK, Birchler JA: Characterization of a maize chromosome 4 centromeric sequence: evidence for an evolutionary relationship with the B chromosome centromere. Genetics 159:291–302 (2001).
32.
Pikaard CS: Nucleolar dominance: uniparental gene silencing on a multi-megabase scale in genetic hybrids. Plant Mol Biol 43:163–177 (2000a).
33.
Pikaard CS: The epigenetics of nucleolar dominance. Trends Genet 16:495–500 (2000b).
34.
Plowman AB, Bougourd SM: Selectively advantageous effects of B chromosomes on germination behaviour in Alliumschoenoprasum L. Heredity 72:587–593 (1994).
35.
Pontes O, Lawrence RJ, Neves N, Silva M, Lee J-H, et al: Natural variation in nucleolar dominance reveals the relationship between nucleolus organizer chromatin topology and rRNA gene transcription in Arabidopsis. Proc Natl Acad Sci USA 100:11418–11423 (2003).
36.
Schmidt T, Schwarzacher T, Heslop-Harrison JS: Physical mapping of rRNA genes by fluorescent in-situ hybridization and structural analysis of 5S rRNA genes and intergenic spacer sequences in sugar beet (Betavulgaris). Theor Appl Genet 88:629–636 (1994).
37.
Schwarzacher T, Ambros P, Schweizer D: Application of Giemsa banding to orchid karyotype analysis. Plant Syst Evol 134:293–297 (1980).
38.
Schweizer D: Simultaneous fluorescent staining of R bands and specific heterochromatic regions (DA-DAPI bands) in human chromosomes. Cytogenet Cell Genet 27:190–193 (1980).
39.
Sen S: Nature and behaviour of B chromosomes in Alliumstracheyii Baker and Urgineaindica Kunth. Cytologia 39:245–251 (1974).
40.
Silva MJJ, Yoyenaga-Yassuda Y: B chromosomes in Brazilian rodents. Cytogenet Genome Res 106:257–263 (2004).
41.
Sýkorová E, Yoong Lim K, Fajkus J, Leitch AR: The signature of the Cestrum genome suggests an evolutionary response to the loss of (TTTAGGG)n telomeres. Chromosoma 112:164–172 (2003).
42.
Tate JA, Acosta MC, McDill J, Moscone EA, Simpson BB, Cocucci AA: Phylogeny and character evolution in Nierembergia (Solanaceae): molecular, morphological, and cytogenetic evidence. Syst Bot 34:198–206 (2009).
43.
Tsuchiya T: Cytogenetics of a new type of barley with 16 chromosomes. Chromosoma 26:130–139 (1969).
44.
Wanzenböck E-M, Schöfer C, Schweizer D, Bachmair A: Ribosomal transcription units integrated via T-DNA transformation associate with the nucleolus and do not require upstream repeat sequences for activity in Arabidopsisthaliana. Plant J 11:1007–1016 (1997).
45.
Zutshi U, Kaul BL: Meiotic studies in some exotic non-tuberous species of Solanum. Cytologia 39:225–232 (1974).
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