The so‐called primitive genera of Genisteae (Fabaceae): systematic and phyletic considerations based on karyological data

A karyological analysis of the so‐called primitive genera of Genisteae has shown that they have a relatively homogeneous chromosome complement: all species tend to have a somatic chromosome number 2n = 48, which can increase to 2n = 52, presumably as a result of hyperaneuploidy. Karyological data suggest that Argyrocytisus, Cytisophyllum and Petteria may be considered as distinct genera rather than being assigned to Cytisus, with 2n = 52 for the first of these and 2n = 50 for the other two genera. They may be interpreted as relict monotypic genera as a result of the presence of a stabilized aneuploidy. Karyological characters exclude a recent origin of Genisteae from Thermopsideae. On the contrary, they are consistent with the hypothesis that Genisteae and Thermopsideae are independently derived from a basic papilionoid stock, of which present day Sophoreae are the remainder. At least two lines would lead from Sophoreae to the taxa of the ‘genistoid alliance’, one to Thermopsideae and the other ‘podalyrioid alliances’ (Podalyrieae and Mirbelieae), with the prevailing basic number of x = 9, and the other to Genisteae, with a basic number of x = 12 persisting in some present day genera, including Cytisus s.l. From this lineage, a wide range of secondary basic numbers has been formed, mostly by descending aneuploidy. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 232–248.     

Towards resolving the systematics of Cerastium subsection Cerastium (Caryophyllaceae): a cytogenetic approach

Analyses of mitotic chromosome numbers and nuclear DNA content were performed for 39 populations of 17 perennial Cerastium taxa from south‐eastern Europe. The DNA content ranged from 2C = 2.43 to 8.78 pg, revealing four ploidy levels corresponding to 4x (2n = 36), 8x, 12x and 16x. High‐polyploid cytotypes with a greater range of ploidy (up to 2n = 144) occur mostly in the central mountainous parts of the Balkan Peninsula. The chromosome number was determined for the first time for C. dinaricum (2n = 36 + 1B), C. decalvans subsp. orbelicum (2n = 36), C. decalvans subsp. glutinosum (2n = 36), C. neoscardicum (2n = 144), C. malyi subsp. serpentini (2n = 144) and C. moesiacum s.s. (2n = 144). New chromosome counts were recorded for C. arvense subsp. strictum (2n = 108), C. banaticum subsp. kosaninii (2n = 36) and C. grandiflorum (2n = 36). For the first time, flow cytometry was used to estimate C values for six species (15 taxonomic entities). The intraspecific variation quotient of C values is high, ranging from 1.003 in C. malyi to 1.306 in C. decalvans subsp. decalvans. The variation in chromosome size among both tetra‐ and octoploid members of Cerastium is much more prominent than in most other angiosperm polyploid series. Significant genome downsizing after polyploidization was observed in some investigated taxa. Differences in ploidy levels and monoploid genome size values confirm the taxonomic status of C. decalvans subsp. glutinosum and C. decalvans subsp. leontopodium. The results obtained indicate a possible close relationship between C. banaticum and C. grandiflorum, but not C. arvense. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 182 , 205–224.     

半蒴苣苔属植物染色体制片优化及染色体数目和倍性研究

染色体数目和倍性是系统与进化生物学和遗传学研究中十分重要的基础信息。为探索半蒴苣苔属染色体制片的适宜条件以及染色体数目的进化模式及其与物种的进化关系，该研究基于半蒴苣苔属染色体数目的进化历史，并根据该属植物具有叶片扦插繁殖的特性，采用叶片水培生根法获取半蒴苣苔(Hemiboea subcapitata)、弄岗半蒴苣苔(H.longgangensis)、龙州半蒴苣苔(H.longzhouensis)、江西半蒴苣苔(H.subacaulis var.jiangxiensis)、华南半蒴苣苔(H.follicularis)和永福半蒴苣苔(H.yongfuensis)6种植物的根尖材料，分析不同实验条件对染色体制片效果的影响，对染色体制片实验的条件进行优化及染色体计数，结果表明：(1)9:30—10:00取材，解离10 min以及染色15 min为半蒴苣苔属染色体制片的适宜条件。(2)上述6种半蒴苣苔属植物均为二倍体，染色体数目均为32(2n=2x=32)。(3)除个别物种染色体数目有变化以外，该属大部分物种染色体数目可能为2n=2x=32且染色体数目变化可能是非整倍化的作用，与物种进化没有明...     

Cytogeography of European perennial species of Cyanus (Asteraceae)

To reveal the general cytogeographical pattern of Cyanus section Protocyanus in Europe, DNA ploidy and/or chromosome numbers were newly examined for 160 populations by flow cytometry (450 plants) and/or chromosome counting (30 plants). Furthermore, previously published karyological data were revised (236 records). Our analyses confirmed chromosome counts of 2n = 22 for all newly investigated samples of the C. triumfetti group (the records for C. semidecurrens and C. ternopoliensis are new), C. diospolitanus and C. achtarovii; 2n = 44 for C. montanus and C. mollis; and 2n = 20 for C. lingulatus, C. napulifer, C. nissanus, C. orbelicus, C. thirkei, C. tuberosus and C. velenovskyi. The chromosome count of 2n = 20 is the first report for C. epirotus. The cytotype 2n = 40 was newly recorded for the Crimean endemic C. fuscomarginatus and Calabrian and Greek populations of C. graminifolius. The cytotypes 2n = 20 and 2n = 40 were confirmed for C. pindicola. For the first time triploidy (2n～3x～30) was found in C. nissanus, C. thirkei and in a newly discovered hybrid, C. epirotus × C. graminifolius. Two contrasting ecogeographical patterns emerged: cytotypes derived from the base chromosome number x = 11 (2n = 22, 44) are widespread in northern latitudes and ecologically diverse, whereas cytotypes with x = 10 (2n = 20, 30, 40) are confined to mountains in southern Europe. In general, tetraploids have smaller ranges than diploids. The new combinations Cyanus section Protocyanus (Dobrocz.) Ol?avská comb. nov. and Cyanus ternopoliensis (Dobrocz.) Ol?avská comb. nov. are provided. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 230–257.     

Flow cytometric,chromosomal and morphometric analyses challenge current taxonomic concepts in the Portulaca oleracea complex (Portulacaeae,Caryophyllales)

Portulaca oleracea is a noxious annual weed of worldwide distribution in temperate to tropical climates. Its taxonomy has been treated in contradictory ways in the past. Various microspecies have been described, lumped into a single species by other authors. We re‐examined the importance of seed size and ploidy variation, previously applied as the most important taxonomic characters, for systematic classification based on accessions from Europe, Asia, Africa and South America using flow cytometry, chromosome counting and morphometry. Sixteen microspecies and six transitional forms, covering the ploidy and seed character variation, proposed for the complex, were studied from 178 populations. Portulaca grandiflora was included as a reference species from outside the complex. DNA hyper‐pentaploidy or hexaploidy were inferred for the majority of accessions which exhibited the full range of seed size. It is recommended that the only species of lower ploidy (either diploid based on x = 12 or tetraploid based on x = 12) encountered, P. nicaraguensis, should be separated from the P. oleracea complex as it deviates in base chromosome number and monoploid genome size. The frequency distribution of seed size was continuous and unimodal within the wild taxa of the complex and in pairs of taxa defined by testa sculpture. Seed size of DNA hexaploids was slightly negatively correlated with sample/standard fluorescence intensities. Our results conflict with the current microspecies concept. Possible reasons underlying the discrepancy are discussed and strategies for future systematic research are suggested. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 179 , 144–156.     

A karyosystematic study of the genus Bellevalia Lapeyr. (Hyacinthaceae) in Greece

The genus Bellevalia is represented in Greece by eight taxa, three of which are endemic. Bellevalia brevipedicellata (2n = 8) and B. sitiaca (2n = 16) are restricted to the island of Kriti, while B. hyacinthoides (2n = 8, 12) is distributed in the Kiklades Islands, the central and southern mainland and the Ionian Islands. Four taxa, i.e. B. dubia subsp. boissieri (2n = 8), B. trifoliata (2n = 8), B. romana (2n = 8) and B. ciliata (2n = 8, 16) are Mediterranean elements. The presence of B. edirnensis (2n = 24) is reported as new for the Greek flora. New ploidy levels of three Bellevalia species (triplo‐, tetra‐ and hexaploids) are reported for the first time. The main morphological features, the chromosome numbers, the karyotype morphology, as well as the geographical distribution and further issues of taxonomy and conservation of all Bellevalia taxa in Greece are presented and discussed. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 157 , 723–739.     

CHROMOSOME NUMBERS IN UMBELLIFERAE. III

Chromosome numbers are reported for 156 collections representing 100 taxa of Umbelliferae. Approximately two thirds of the collections are from Mexico, Central and South America and indicate a high percentage of polyploid species in certain genera found in this area. Chromosome numbers for plants belonging to 78 taxa are published here for the first time, previously published chromosome numbers are verified for 18 taxa and chromosome numbers differing from those previously published are reported in seven instances. No chromosome counts have been previously published for nine of the genera included here. Further aneuploidy and polyploidy were found in Eryngium, and Lomatium columbianum has been found to be a high polyploid with 2n = 14x. Every chromosome count is referable to a cited herbarium specimen.     

Chromosome numbers and DNA content in Bromeliaceae: additional data and critical review

For the large Neotropical plant family Bromeliaceae, we provide new data on chromosome numbers, cytological features and genome size estimations, and combine them with data available in the literature. Root‐tip chromosome counts for 46 species representing four subfamilies and a literature review of previously published data were carried out. Propidium iodide staining and flow cytometry were used to estimate absolute genome sizes in five subfamilies of Bromeliaceae, sampling 28 species. Most species were diploid with 2n = 50 in Bromelioideae, Puyoideae and Pitcairnioideae, followed by 2n = 48 observed mainly in Tillandsioideae. Individual chromosome sizes varied more than tenfold, with the largest chromosomes observed in Tillandsioideae and the smallest in Bromelioideae. Genome sizes (2C‐values) varied from 0.85 to 2.23 pg, with the largest genomes in Tillandsioideae. Genome evolution in Bromeliaceae relies on two main mechanisms: polyploidy and dysploidy. With the exception of Tillandsioideae, polyploidy is positively correlated with genome size. Dysploidy is suggested as the mechanism responsible for the generation of the derived chromosome numbers, such as 2n = 32/34 or 2n = 48. The occurrence of B chromosomes in the dysploid genus Cryptanthus suggests ongoing speciation processes closely associated with chromosome rearrangements. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 349–368.     

Interstitial telomere‐like repeats in the monocot family Araceae

Combining molecular cytogenetics and phylogenetic modelling of chromosome number change can shed light on the types of evolutionary changes that may explain the haploid numbers observed today. Applied to the monocot family Araceae, with chromosome numbers of 2n = 8 to 2n = 160, this type of approach has suggested that descending dysploidy has played a larger role than polyploidy in the evolution of the current chromosome numbers. To test this, we carried out molecular cytogenetic analyses in 14 species from 11 genera, using probes for telomere repeats, 5S rDNA and 45S rDNA and a plastid phylogenetic tree covering the 118 genera of the family, many with multiple species. We obtained new chromosome counts for six species, modelled chromosome number evolution using all available counts for the family and carried out fluorescence in situ hybridization with three probes (5S rDNA, 45S rDNA and Arabidopsis‐like telomeres) on 14 species with 2n = 14 to 2n = 60. The ancestral state reconstruction provides support for a large role of descending dysploidy in Araceae, and interstitial telomere repeats (ITRs) were detected in Anthurium leuconerum, A. wendlingeri and Spathyphyllum tenerum, all with 2n = 30. The number of ITR signals in Anthurium (up to 12) is the highest so far reported in angiosperms, and the large repeats located in the pericentromeric regions of A. wendlingeri are of a type previously reported only from the gymnosperms Cycas and Pinus. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 15–26.     

Chromosome numbers in Pinguicula (Lentibulariaceae): survey, atlas, and taxonomic conclusions

Our study (survey, atlas of 136 microphotographs and 67 drawings) points out the actual chromosome numbers of 82 taxa of the genus Pinguicula L. They were gathered from literature and critically examined. In addition, numerous counts are published for the first time. They represent about 80% of all the taxa known. The basic chromosome numbers are x = 6, 8, 9, 11, and 14; the ploidy levels are 2n (diploid), 4n (tetraploid), 8n (octoploid) and 16n (hexadecaploid). The basic number x = 6 is a one-off, x = 8 and 11 are the most frequent in the genus; x = 14 indicates a hybridogenous differentiation process in the past. The caryological differentiation—chromosome numbers and ploidy level—is discussed with regard to distribution pattern, growth type, and infrageneric classification (at the level of sections).     

Divergent genome sizes reflect the infrafamilial subdivision of the neotropical woody Marcgraviaceae

Neotropical Marcgraviaceae comprise about seven genera and 130 species of lianas and shrubs. They predominantly occur in lowland or montane rainforests and are characterized by a variety of pollination systems. Early classifications subdivided Marcgraviaceae into subfamilies Marcgravioideae and Noranteoideae, a concept supported by molecular data. Using flow cytometry and chromosome numbers, we investigated the role of genome size and polyploidization in the evolution of Marcgraviaceae and how genome sizes are distributed between the proposed infrafamilial groups. To do this we determined genome sizes and chromosome counts for six genera and 22 species for the first time. Our study supports the subfamilial classification of the family, revealing contrasting genome sizes in Noranteoideae (2C = 5.5–21.5 pg) and Marcgravioideae (2C = 2.3–6.2 pg). Polyploidy is considered to be the main source of genome size variation as in each subfamily the higher nuclear DNA amounts were associated with higher ploidy. In addition, genome size changes independent of polyploidy were also observed in some genera, suggesting an additional role for changes in repetitive DNA abundance in the evolution of Marcgraviaceae. A high chromosome base number (x = 18; 2n = 36 to ～70) points to an undetected lower diploid level or to palaeopolyploidy. Marcgraviaceae show a remarkable (nine‐fold) variation in genome size, and several Noranteoideae have genome sizes among the highest reported for tropical woody angiosperms worldwide. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 1–14.     

2种嵩草属植物形态特征对生境干旱化的响应

该研究于西藏自治区东南部的东达山高山草甸沿生境干旱化梯度设置10个样地,采用线性回归方法分析优势种高山嵩草(Kobresia pygmaea)和矮生嵩草(K.humilis)叶片数量与其它构件数值(分株数量、茎基直径、根系数量和根系长度)之间的关系,并采用线性回归斜率测度分株功效、叶片萌生能力、根系分生功效和根系伸长功效,以探讨嵩草的分株能力、茎基生长和根系生长对生境干旱化过程的响应机制。结果显示:(1)2种嵩草植物的叶片数量与4种构件数值均为显著线性正相关关系。(2)随着生境干旱化程度增加,高山嵩草分株数量增加,矮生嵩草分株受干旱抑制程度高,分株数量呈下降趋势;2种嵩草分株功效下降,即单株叶片数量因干旱化程度增加而减少。(3)2种嵩草的茎基直径、叶片萌生能力随着生境干旱化程度增加而下降;高山嵩草叶片萌生能力的变化与生境干旱化梯度一致,具有连续性;矮生嵩草叶片萌生能力对生境干旱化的适应性弱,干旱到一定程度发生骤降。(4)随着生境干旱化,高山嵩草的根系数量和长度均增加,矮生嵩草根系长度增加,但数量却无规律变化;2种嵩草的根系分生功效和根系伸长功效均下降。研究表明:嵩草属植物分布的最适宜生境为表面稍有积水的沼生生境。为适应生境干旱化,高山嵩草降低叶片萌生率以减少蒸腾作用,增加分株数量以增强对空间的占有能力,并增加根系数量和长度来提高对土壤水分的吸收能力,因此对干旱有较强适应性且分布范围广;矮生嵩草只通过降低叶片萌生率,增加根系长度响应干旱化生境,其分布范围较窄。     

Revision of ploidy status of Dioscorea alata L. (Dioscoreaceae) by cytogenetic and microsatellite segregation analysis

Dioscorea alata is a polyploid species with several ploidy levels and its basic chromosome number has been considered by most authors to be x = 10. Standard chromosome counting and flow cytometry analysis were used to determine the chromosome number of 110 D. alata accessions of the CIRAD germplasm collection. The results revealed that 76% of accessions have 2n = 40 chromosomes, 7% have 2n = 60 chromosomes and 17% have 2n = 80 chromosomes. Progenies were produced from 2n = 40 types of D. alata and the segregation patterns of six microsatellite markers in four different progenies were analysed. The Bayesian method was used to test for diploid versus tetraploid (allo- and autotetraploid) modes of inheritance. The results provided the genetic evidence to establish the diploidy of plants with 2n = 40 chromosomes and to support the hypothesis that plants with 2n = 40, 60 and 80 chromosomes are diploids, triploids and tetraploids, respectively, and that the basic chromosome number of D. alata is x = 20. The findings obtained in the present study are significant for effective breeding programs, genetic diversity analysis and elucidation of the phylogeny and the species origin of D. alata.     

Ploidy variation in Buddleja L. (Buddlejaceae) in the Sino-Himalayan region and its biogeographical implications

The chromosome numbers of 27 populations of Buddleja , comprising 14 species, were counted. The basic chromosome number of all species was x  = 19, confirming previous reports. Different ploidy levels (2 n  = 38, 76, 114, 228) were observed in these taxa, representing diploids, tetraploids, hexaploids, and dodecaploids, respectively. The chromosome numbers of B. yunnanensis , B. brachystachya , and B. macrostachya are reported for the first time. The tetraploid 2 n  = 76 is a new ploidy level for B. myriantha . Particular attention was given to B. macrostachya , because of the variation in morphology and ploidy level between isolated populations of this species. Two types of interphase nuclei were recognized: the complex chromocentre type in B. macrostachya and the simple chromocentre type in the other species. Biogeographically, most of the polyploidy in the Asiatic species occurs in the Sino-Himalayan region. It seems to be associated with the uplift of the Himalayan Mountains, the orogeny of this region playing an important role in the evolution of polyploidy in these taxa.  © 2007 The Linnean Society of London. Botanical Journal of the Linnean Society , 2007, 154 , 305–312.     

Chromosomal evolution in Pleurothallidinae (Orchidaceae: Epidendroideae) with an emphasis on the genus Acianthera: chromosome numbers and heterochromatin

In this study, we analysed chromosome number variation and chromomycin A₃/4′,6‐diamidino‐2‐phenylindole (CMA/DAPI) banding patterns in 48 species belonging to 12 genera of subtribe Pleurothallidinae (Orchidaceae) in order to understand the chromosome evolution based on recent phylogenetic hypotheses and taxonomic treatments. All species had small chromosomes, with numbers ranging from 2n = 20 in two Specklinia spp. to 2n = 80 in an unidentified Octomeria sp. In Acianthera, the most highly represented genus in this study, a great diversity of chromosome number and pattern of fluorescent bands was observed, showing heterochromatin accumulation in Acianthera section Sicariae subsection Pectinatae. Interspecific ascending and, mainly, descending dysploidy were the main mechanisms of chromosome number evolution in subtribe Pleurothallidinae. For Pleurothallidinae, x = 20 is suggested as the basic chromosome number, the same suggested for the related subtribe Laeliinae and for the whole tribe Epidendreae. The Brazilian species of the mega‐genus Stelis had chromosomes with small amounts of heterochromatin and chromosome numbers based on x₂ = 16. These are generally divergent from those reported for Andean and Meso‐American species, but in agreement with the monophyletic hypothesis proposed for Stelis spp. with a Brazilian Atlantic distribution. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 102–120.     

CHROMOSOME MORPHOLOGY IN THE GENUS SAMBUCUS

Two basic chromosome karyotypes were found in the genus Sambucus. Chromosome numbers were observed to be 2n = 38 for S. callicarpa, S. cerulea, S. glauca, S. kamtschatica, S. melanocarpa, S. mexicana, S. miquelli, S. sibirica, and S. sieboldiana and 2n = 36 for S. simpsonii and S. williamsii. Measurements of 18 karyotypes are presented. The major differences between the two basic chromosome karyotypes can be explained as the result of a mis-division of a metacentric chromosome giving rise to two telocentric chromosomes, thus reducing the number of metacentrics from five to four and increasing the chromosome number from 2n = 36 to 2n = 38. Observed chromosome aberrations and aneuploidy may result from unstable telocentric chromosomes.     

Cytology and systematics in JapaneseArisaema (Araceae)

Chromosome numbers are determined from 37 populations attributed to 22 taxa of JapaneseArisaema. Of them, chromosome numbers ofA. limbatum var.conspicuum (2n=26),A. minus (2n=26),A. nambae (2n=28) andA. seppikoense (2n=26) are determined for the first time. New chromosome numbers, 2n=26, are reported forA. aequinoctiale, A. limbatum, A. stenophyllum, A. undulatifolium andA. yoshinagae. Three modes of basic chromosome numbers,x=14,x=13 andx=12, occur in JapaneseArisaema. Precise karyotypic comparisons of 20 taxa reveal that taxa withx=14 andx=13 share 26 major chromosome arms and have an obvious chromosomal relationship. One of two submeta-centric chromosomes inx=13 corresponds to two telo-centric chromosomes inx=14. InA. ternatipartitum with 2n=6x=72, ten out of 12 basic chromosomes are the most similar in size and arm ratio with larger ten chromosomes ofA. ringens among JapaneseArisaema examined. A basic chromosome number ofx=14 is the commonest in the genusArisaema and the remaining basic chromosome numbers,x=13 andx=12, seem to be derived through dysploidal reduction by translocating large segments of major arm of telo-centric chromosome onto other minor arm of telo-centric followed by loss of the remainings including a centromere, and by loss of two telo-centrics fromx=14, respectively. Some systematic problems of JapaneseArisaema are discussed based on new cytological data.Arisaema hatizyoense, A. minus andA. nambae are accepted as independent species.     

New chromosome numbers, meiotic behaviour and pollen fertility in American taxa of Lupinus (Leguminosae): contributions to taxonomic and evolutionary studies

Original chromosome determinations are presented for 20 American Lupinus taxa, including, for the first time, unifoliolate species, together with first data on meiotic behaviour and pollen fertility for some South American species. Most of the Brazilian multifoliolate L. lanatus, L. rubriflorus, L. multiflorus, L. paranensis, L. bracteolaris and L. reitzii and unifoliolate L. crotalarioides, L. guaraniticus and L. velutinus accessions analysed presented regular chromosome pairing. Meiotic indexes and estimations of pollen viability were higher than 90% for all species and accessions analysed, reflecting the generally regular meiotic behaviour of these plants. Chromosome numbers were determined for the first time for the eastern South‐American species L. guaraniticus, L. crotalarioides, L. paranensis, L. paraguariensis and L. velutinus (n = 18 or 2n = 36) and for the Andean L. ballianus, L. eanophyllus, L. huaronensis, L. semperflorens, plus another eight taxa (2n = 48) from Peru and Bolivia, and L. bandelierae (2n = 36) from Bolivia. Chromosome numbers were confirmed for L. lanatus, L. rubriflorus (2n = 36), L. bracteolaris (2n = 34) and L. microphyllus (2n = 48). In the three accessions of the North American unifoliolate species, L. cumulicola and L. villosus, a chromosome number (2n = 52) previously unknown among American taxa was found. The results of the study, plus published data, support the suggestions that south‐eastern South American species are a group cytologically differentiated from the Andean as well as from most other American ones, and that the Brazilian and the North American unifoliolate Lupinus had independent origins. © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society, 2006, 150 , 229–240.     

Arabidopsis S6 kinase mutants display chromosome instability and altered RBR1�CE2F pathway activity

The 40S ribosomal protein S6 kinase (S6K) is a conserved component of signalling pathways controlling growth in eukaryotes. To study S6K function in plants, we isolated single‐ and double‐knockout mutations and RNA‐interference (RNAi)‐silencing lines in the linked Arabidopsis S6K1 and S6K2 genes. Hemizygous s6k1s6k2/++ mutant and S6K1 RNAi lines show high phenotypic instability with variation in size, increased trichome branching, produce non‐viable pollen and high levels of aborted seeds. Analysis of their DNA content by flow cytometry, as well as chromosome counting using DAPI staining and fluorescence in situ hybridization, revealed an increase in ploidy and aneuploidy. In agreement with this data, we found that S6K1 associates with the Retinoblastoma‐related 1 (RBR1)–E2FB complex and this is partly mediated by its N‐terminal LVxCxE motif. Moreover, the S6K1–RBR1 association regulates RBR1 nuclear localization, as well as E2F‐dependent expression of cell cycle genes. Arabidopsis cells grown under nutrient‐limiting conditions require S6K for repression of cell proliferation. The data suggest a new function for plant S6K as a repressor of cell proliferation and required for maintenance of chromosome stability and ploidy levels.     

Cytogenetic and molecular characterization of morphologically variable Sisyrinchium micranthum (Iridaceae) in southern Brazil

Sisyrinchium micranthum is native to southern Brazil and shows a wide range of morphological variation in this region. This study was performed to compare individuals of this species in terms of traits such as morphology, chromosome number, meiotic behaviour, pollen viability and genetic diversity using inter simple sequence repeat markers. First, general morphological aspects were evaluated and plants were classified into three morphological categories (CI, CII and CIII) to analyse the cytogenetic and genetic data. Three chromosome numbers corresponding to three ploidies were found: 2n = 2x = 16, 2n = 4x = 32 and 2n = 6x = 48. All morphological types showed regular meiotic behaviour and high meiotic index values and pollen viability. CII is the most frequent in southern Brazil. The most common haploid chromosome number, n = 8, has not been reported previously in this species. The percentage of polymorphic loci ranged from 6.45 to 61.29% for each accession. Molecular and cytogenetic analyses indicate that some S. micranthum accessions may have more than one ploidy. This study represents the first effort to characterize this taxonomically complex species based on cytogenetic and genetic aspects. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169 , 350–364.