Chromosome numbers,polyploidy, and hybridization in castilleja (scrophulariaceae ) of the Great Basin and Rocky Mountains

Chromosome numbers are reported for 190 collections ofCastilleja of the Great Basin-Rocky Mountains and adjacent regions in western North America. Polyploidy has played a major role in evolu tion of this genus. Of the 35 taxa represented, 14 are exclusively diploid (n =12). The remaining 21 taxa exhibit polyploidy: eight are tetraploid only, two are octopIoid only, while 11 of the more wide-ranging species have two or more levels of polyploidy. BothC. rhexifolia andC. sulphured have diploid, tetraploid, and octoploid races while the widespreadC. miniata has four (2x, 4x, 8x, and 10x). Where appropriate, the role of polyploidy and hybridization inCastilleja evolution and their relevance to taxonomy are discussed for individual species.     

Flowering phenology of some native perennial tropical grasses from north-eastern Australia

The division of north-eastern Australia into tropical and sub-tropical zones at approximately the latitude of 20° S, as suggested by the flowering phenology of Heteropogon contortus, is supported by studies on other perennial grasses of the native pastures. A progressive evolution away from an obligate short-day flowering response which characterizes the tropical forms of Bothriochloa bladhii, perhaps Themeda australis, and the exclusive tropical species Dicanthium tenuiculum, through a quantitative short-day response, as in the more widely distributed B. decipiens var. cloncurrensis, to the day-neutral or opportunistic and largely subtropical species of B. decipiens and D. sericeum, is suggested as a sequence of flowering strategies leading to wider adaptation into the sub-tropics. There is evidence from here and elsewhere that tropical forms or species of perennial grasses are grosser than their subtropical counterparts and this is coupled with their short-day flowering behaviour. The evidence suggests that B. decipiens and D. sericeum are the evolutionary products of taxa nearer to B. decipiens var. cloncurrensis and D. tenuiculum which exhibit day-length control of flowering.     

中国姜花属十九个分类群的细胞学研究

采用压片法对中国姜花属十八个分类群进行了体细胞染色体计数,对白姜花减数分裂终变期I的染色体数目和形态进行了观察。结果显示:包括白姜花在内的十九个分类群中有六个二倍体,一个三倍体,十二个四倍体,其中十二个分类群的体染色体数目为首次报道,显示中国姜花属植物具有较高比例的多倍体类型;姜花属的染色体基数为n=17,染色体组可能是多倍体起源的。     

Chromosome evolution in the genus Ophioglossum L.

Cytological observations on eleven species of Ophioglossum revealed low gametic ( n ) chromosome numbers of 30, 34 and 60 in populations of O.eliminatum , contrasting with an earlier report of n = 90 in the same species. The rest of the species is based on n =120.Cytologically studied species of Ophioglossum exhibit a range of chromosome numbers from n = 30 in O.eliminatum to n =720 in O.reticulatum. The weighted highest common factor (HGF) from all the reported chromosome numbers in twelve species was found to be 30. This number is proposed as the palaeobasic chromosome number for the genuS. Reported chromosome numbers which are not multiples of 30 were subjected to sequential analysis, yielding three distinct ultimate base numbers, 4, 5 and 6, which can produce n = 30 in seven different ways. The neobasic number, n= 120, appears to have arisen through various combinations and permutations of these, theoretically 2401 routes; only a relatively few of these routes exist today, suggesting that extreme selection has been exerted against the majority, and further suggesting that Ophioglossum represents an evolutionary dead end through repeated cycles of polyploidy and is possibly at the verge of extinction. The stoichiometric model of evolution, which derives the various chromosome numbers possessed by the twelve species from the basic and ultimate basic chromosome numbers, is used to explain chromosomal evolution in the genus.     

Chromosome numbers in some North American species of the genus Cirsium. III. Western United States,Mexico, and Guatemala

New data are presented on chromosome numbers for 36 species, two varieties, and two hybrids ofCirsium (Compositae). These include first reports forC. rhothophilum (2n = 34),C. andrewsii (2n = 32),C. crassicaule (2n = 32),C. quercetorum (2n= 32, 112),C. pascuarense (2n= 32),C. douglasii var.canescens (2n = 30, 34),C. hydrophilum (2n = 32),C. neomexicanum (2n = 30),C. cymosum (2n = 30, 34),C. acantholepis (2n= 34),C. radians (2n = 34), C.grahami (2n = 32),C. nigriceps (2n = 36),C. andersonii (2n= 32, 64),C. anartiolepis (2n = 34), andC. subcoriaceum (2n= 34). The published data on chromosome numbers of Eurasian and AmericanCirsium are summarized. In Eurasia, speciation has taken place primarily at the diploid level but is occasionally reinforced by polyploidy. The ancestral base number of 17 has been preserved in almost all species, and there is little evidence that reduction in chromosome number has played a significant role in speciation. In America speciation has proceeded exclusively at the diploid level, but the ancestral genome of 17 chromosomes has been retained in only about half of the species examined. In the remaining species, restructuring of the genome has occurred resulting in a reduction in number from 17 to 9 in extreme cases. Polyploidy, when seen, is of no significance. It is suggested that all species with greatly reduced numbers may represent products of a single reduction series.     

Chromosomal abnormalities and developmental kinetics in in vivo-developed cattle embryos at days 2 to 5 after ovulation.

The frequency of chromosome abnormalities was investigated in cattle embryos (n = 256) derived from superovulated heifers (n = 35) on Days 2, 3, 4, and 5 postovulation (PO). Interphase nuclei (n = 4358) were analyzed for chromosome abnormalities using fluorescent in situ hybridization with chromosome 6- and chromosome 7-specific probes and the developmental rate was described by scoring cell numbers. We found that 93%, 85%, 84%, and 69% of the embryos from Days 2, 3, 4, and 5 PO, respectively, displayed a normal diploid chromosome number in all cells. Of the embryos containing abnormal cells, mixoploidy was significantly more frequent than polyploidy. The percentage of mixoploidy at Days 2, 3, 4, and 5 PO was 5%, 13%, 16%, and 31%, respectively, whereas the percentages of polyploidy were 2%, 2%, 0%, and 0%, respectively. The mean number of cells per embryo was 4.7, 8, 11.5, and 48.3, respectively, at Days 2, 3, 4, and 5 PO. Thus, in vivo-developed embryos were significantly more advanced than the in vitro-produced (IVP) embryos except for Day 2. In conclusion, a significantly lower frequency of chromosomally abnormal embryos, in particular displaying polyploidy early after fertilization, was seen in in vivo versus IVP embryos, and these chromosomal abnormalities may be inherent to the process of IVP in cattle.     

Genotypic control of the speed of development inArabidopsis thaliana (L.)Heynh. lines obtained from natural populations

Sixteen early, medium late, and late homozygote lines ofArabidopsis thaliana, obtained from three natural populations, were crossed with a common check variety S 96. The speed of development was expressed by the value log (x+y), wherex stands for the number of days after which flower primordia appear, andy for the number of leaves in the rosette. The experiments were caried out under conditions which emphasized the differences in the speed of development. We assessed the degree of dominancy, heritability on the basis of F₁ and F₂ variance, and analyzed F₂ distributions. It was established that some of the investigated lines differ from the variety S 96 in one pair of dominant genes or genes with incomplete dominancy for late flowering, other in two pairs of genes with complementary effects, and that the variety S 96 probably also contains other alleles causing late flowering inhibited by some type of epistasis. Even though the most important part is always played by one or two pairs of genes with high dfficiency, genes with lower efficiency often take part in the process; in some lines the genes with high efficiency could not be established.     

ISOZYME NUMBER IN SUBTRIBE ONCIDIINAE (ORCHIDACEAE): AN EVALUATION OF POLYPLOIDY

The Oncidiinae has attracted attention because of the variation it exhibits in chromosome number, n = 5–30, which is greater than the range in the rest of the Orchidaceae. The genus Psygmorchis, with n = 5 and 7, has been a particular focus of controversy, and many authors have suggested that 5 and 7 are the base numbers for the subtribe. The other taxa in the subtribe presumably evolved through hybridization and polyploidy. Other workers have found that the lowest counts correlate with derived morphological conditions and have hypothesized that these low numbers result from aneuploid reductions, while higher numbers are associated with ancestral morphologies and are not the result of polyploidy. These two hypotheses were evaluated by determining isozyme numbers for 13 enzymes in species that span the chromosomal range known for the Oncidiinae (n = 5–30). Isozyme number has been shown to be a reliable indicator of polyploidy in angiosperms because polyploids display isozyme multiplicity relative to diploids. This analysis revealed no differences among species in isozyme number for the enzymes examined. Therefore, our data reject the hypothesis that species with higher chromosome numbers are polyploid.     

Genetic map-based analysis of genome structure in the homosporous fern Ceratopteris richardii

Homosporous ferns have extremely high chromosome numbers relative to flowering plants, but the species with the lowest chromosome numbers show gene expression patterns typical of diploid organisms, suggesting that they may be diploidized ancient polyploids. To investigate the role of polyploidy in fern genome evolution, and to provide permanent genetic resources for this neglected group, we constructed a high-resolution genetic linkage map of the homosporous fern model species, Ceratopteris richardii (n = 39). Linkage map construction employed 488 doubled haploid lines (DHLs) that were genotyped for 368 RFLP, 358 AFLP, and 3 isozyme markers. Forty-one linkage groups were recovered, with average spacing between markers of 3.18 cM. Most loci (approximately 76%) are duplicated and most duplicates occur on different linkage groups, indicating that as in other eukaryotic genomes, gene duplication plays a prominent role in shaping the architecture of fern genomes. Although past polyploidization is a potential mechanism for the observed abundance of gene duplicates, a wide range in the number of gene duplicates as well as the absence of large syntenic regions consisting of duplicated gene copies implies that small-scale duplications may be the primary mode of gene duplication in C. richardii. Alternatively, evidence of past polyploidization(s) may be masked by extensive chromosomal rearrangements as well as smaller-scale duplications and deletions following polyploidization(s).     

Polyploidy and sterility in relation to sex in Dioscorea alata L. (Dioscoreaceae)

Chromosome numbers and fertility studies of 73 male and 30 female flowering germplasm accessions of Dioscorea alata L. were carried out. All males were tetraploids showing the same chromosome number (n=20 or 2n=40) and were pollen fertile (10.9–96.2%), most of them being highly fertile. Among the female the majority were higher ploids (hexa-and octoploids; 2n=60 and 80) and sexually completely sterile. There were only two tetraploid female accessions which were sexually fertile. Pollination studies revealed that seed sterility in D. alata was due to female sterility associated with the occurrence of higher levels of ploidy. The female sex-limited occurrence of higher polyploidy and sterility observed in D. alata is a curious situation among dioecious higher plants.     

Chromosome studies on the Bambusoideae (Gramineae)

Meiotic chromosome numbers and observations were made in eleven species belonging to nine different genera of Bambusoideae. The numbers include counts in eight species that have never been investigated cytologically:Arundinaria aff.amabilis (n=24), Chusquea bambusoides (n=ca. 20),Cryptochloa dressleri (n=11), Olyra ciliatifolia (n=11), Sucrea monophylla (n=11), Raddia brasiliensis (n=11), Strephium distichophyllum (n=11), andPariana aurita (n=22). The generaStrephium andSucrea have not been studied previously with respect to their chromosomes. The significance of these results are discussed in relation to the over 140 published counts in the subfamily, which indicates a preponderance of polyploidy in the woody members, or bamboos, but not in their herbaceous allies. Aneuploidy is rare in the former but frequent in the latter. It is postulated that the herbaceous bambusoids, which flower every year and produce recombinants regularly and in short-time cycles, could have tolerated successive reductions of the linkage groups and their genetic flexibility. These changes would not have been favored in the bamboos, which have more genetic constancy due to the long lapse (often 20–120 years) between flowering generations.     

Chromosome Numbers and Karyotypes of Six Oxytropis Species (Fabaceae) from the Qinghai Tibetan Plateau,China

Chromosome numbers and karyotypes of 13 populations of six Oxytropis species (Fabaceae) from the Qinghai Tibetan Plateau, China, were presented. The chromosome numbers and karyotypes in O.ochrocephala, O.tatarica, O.kansuensis and O.humifusa (2n=16) were reported for the first time. B chromosomes were found from O.stracheyana (2n=48). The basic chromosome number of x=8 is confirmed for the genus. The available chromosomal data indicate that polyploidy may have played an important role in the evolution of the genus, with the incidence of polyploidy in the genus reaching 58%. However, our results indicated that among the populations here examined only one was a hexaploid with 2n=48. Such a chromosomal pattern indicates that the karyotypic repatterning at the diploid level seems to be the predominant feature of chromosomal evolution in the Oxytropis species from the Qinghai Tibetan Plateau, and that sympatric speciation via hybridization and polyploidization has played a minor role in the species diversification of the genus from this area.     

New or rare data on chromosome numbers in several taxa of the genus<Emphasis Type="Italic">Artemisia (Asteraceae)</Emphasis> in Poland

Chromosome counts in 16 populations of fiveArtemisia species from Poland are presented in this paper. Those ofA. annua (2n=18) andA. dracunculus (2n=90) are reported for the first time in Polish populations. The decaploid level (2n=90) is described for the first time in non-cultivated populations ofA. dracunculus, and several cases of aneusomaty (intraindividual aneuploid variations in chromosome number: 2n=87, 88 and 89) have been detected in this species. In addition to the already known diploid number (2n=18), the tetraploid level (2n=36) has been detected inA. absinthium. The same two numbers have been recorded inA. abrotanum, which represents the first tetraploid count in populations of this taxon occurring outside botanical gardens. Finally, the chromosome number ofArtemisia campestris subsp.sericea (tetraploid, 2n=36) is reported for the first time. The relevance of polyploidy for the evolution of the genus and other cytotaxonomic or cytobiogeographical aspects are briefly discussed.     

Chromosome number variation and polyploidy in the genus Echinocereus (Cactaceae)

Analyses of meiotic and mitotic chromosomes were undertaken in 16 taxa of Echinocereus belonging to 12 species and all seven taxonomic sections (sensu Taylor). Chromosome numbers are reported for the first time for eight taxa, and previously published chromosome counts are confirmed for the remaining eight. Both diploid and polyploid counts were obtained. Eleven (69%) of the taxa surveyed were diploid (2n = 22); the five varieties of E. engelmannii were polyploid (2n = 44). Overall, chromosome counts are available for 23 of the 48 proposed species (sensu Taylor). Of these, 19 (82%) are diploid, and four (18%) are polyploid. Polyploid cytotypes are most common in the primitive sections, e.g., sections Erecti and Triglochidiatus, which suggests that polyploidy is probably a derived condition in Echinocereus. Polyploid taxa range from medium to high latitudes and elevations relative to the overall distribution of the genus. Polyploidy, hybridization, and cryptic chromosomal rearrangements are thought to be the major causes of the speciation events of the genus.     

Some pollination strategies in neotropical savannas and forests

Previously published data on flowering phenology and pollination of neotropical families are reviewed and compared with new observations, in order to evaluate some trends of pollination strategies in neotropical savannas and forests. Central American forestBignoniaceae apparently diminish competition between sympatric species with identical pollination strategies by alternating flowering. On the other hand, in theBignoniaceae of Brazilian cerrado savannas coincident flowering is more common, suggesting different pollination strategies. Bees specialized in nectar robbery are associated withBignoniaceae, particularly mass-flowering species. These nectar robbers stimulate pollinator movements between flowers and thus increase pollen-flow. The flowering phenology of theMalpighiaceae from forests and savannas apparently follows the phenology of theAnthophorinae (mainlyCentridini)-bees, on which this plant group almost exclusively depends for pollination in the Neotropics. As the flowers of different genera and species are very uniform, the bees quite indiscriminately pollinate coexistingMalpighiaceae taxa. In theMalvaceae, the more primitive tree or shrub habit and an allogamous reproduction system is quite significantly associated with an ornithophilous pollination mode. Hummingbirds in the Neotropics have probably influenced the origin of the primitive bird-pollinatedMalvaceae flower. In conjunction with the diversification of theMalvaceae and their migration into more open regions, pollination by bees has apparently become more prominent. ChiropterophilousMalvaceae seem to have developed more recently from ornithophilous ancestors within the neotropical forest regions. As a result of this ecological radiation, parallel modifications of the basic ornithophilous flower principle can be traced in different groups of theMalvaceae. Dynastinae-beetles are pollinators of South and Central American species ofAnnona, Cymbopetalum, Caladium, Talauma, Philodendron, Victoria, Nymphaea, Cyclanthus, Bactris and others. In many cases the relationship between flowers and theirDynastinae visitors is not very specific, principally reflecting differences in the faunistic spectrum of diverse regions and vegetation types. The attraction of these beetles as flower visitors in several unrelated groups of Angiosperms must have occurred repeatedly. It is suggested that the flower visiting species of this beetle group may have acquired their preference for certain pungent or aromatic flower odours by their feeding habits during the larval stage.     

Chromosome numbers in the genus Mimosa L.: cytotaxonomic and evolutionary implications

Chromosome numbers were determined for 125 accessions of 92 taxa of Mimosa from all five of Barneby??s (Mem New York Bot Gard 65:1?C835, 1991) taxonomic sections. For 69 species, 1 subspecies and 8 varieties, chromosome numbers are presented for the first time, for 6 species and 1 variety previously published data have been confirmed and for 3 species and 2 varieties different numbers were found. Results show that 74% of the accessions were diploid (2n?=?2x?=?26) and 26% polyploid, these mostly tetraploid (2n?=?4x?=?52) but with two triploid (2n?=?3x?=?39). These results double the number of Mimosa species for which the chromosome count is known from less than 10% previously reported to more than 20%, representing an important advance in the cytotaxonomy of this legume genus. These results together with literature data show that ca. 78% of Mimosa species are diploid. Polyploids are present in most of the taxonomic sections and in different lineages across the genus. No particular chromosome number is restricted to a given section or lineage. A possible relation between geography, species distribution, polyploidy and invasiveness was detected, however, further studies based on more accessions, especially from higher latitudes, are required before firm conclusions can be drawn.     

Cytotaxonomic analysis of South American species of Vernonia (Vernonieae: Asteraceae)

Chromosome numbers in 48 populations belonging to 31 species of Vernonia from South America have been determined. First chromosome counts are reported for V. propinqua var. canescens (2 n = 20), V. sceptrum (2 n = 80), V. rufogrisea (2 n = 32), V. heringeri (2 n = 32), V. hovaefolia (2 n = 64), V. hystricosa (2 n = 128), V. obtusata (2 n = 64), V. pseudoincana (2 n = 32), V. rubricaulis var.◊ australis (2 n = 64) and V. rugulosa (2 n = 30). The basic chromosome numbers x = 10, 14, 15, 16 and 17 were confirmed for New World species of Vernonia . Together with previous records, these numbers suggest that the evolution of Vernonieae has occurred through a combination of polyploidy and aneuploidy. Taxonomic implications of certain counts are also discussed.  © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 401–408.     

Cytogenetic investigation of geranium plants in tissue culture

Cytogenetic study of six cultivars and six selection lines of geranium (Pelargonium spp.), as well as of 100 plants regenerated from callus cultures has been performed. The majority of cultivars and lines had somatic chromosome numbers 2n = 7x = 56. Among regenerated plants of different cultivars (Rozovaja, Dushistaja, Krunk, Aist, Regar) obtained in vitro from various types of explants (internode, petiole) 61% of diploids and 39% aneuploids were revealed. Chromosome numbers in aneuploids varied from 46 to 82, among them 25.6% regenerated plants had 2n = 72; 10.2% -2n = 68; 5.1% -2n = = 64 and 12.8% -2n = 62. Addition of colhicine to nutrient medium increased the number of aneuploid plants.     

Karyotype studies of some species of Dalechampia Plum. (Euphorbiaceae)

Karyotype studies in eight species of Dalechampia , including 10 natural populations, revealed chromosome numbers (2 n = 36, 46, 138 and 198) differing from two numbers cited in the literature (2 n = 44 and 72). The basic number x = 6, as in the genus Acalypha , may be considered ancestral in Dalechampia. Analysis of chromosome number, haploid chromosome length and karyotype symmetry suggests that the major chromosome mechanism acting in karyotype evolution of Dalechampia is polyploidy, but differences in chromosome morphology may be caused by chromosome rearrangements.     

小花鬼针草的染色体数目及其自然多倍体类型

本文对小花鬼针草的体细胞染色体进行了观察和计数,并对其染色体倍性和有关的细胞学及分类学等问题略作讨论,旨在为药用植物的分类、品种鉴别和育种实践等工作提供必要的细胞学资料。笔者观察到的小花鬼针草的体细胞染色体除了２ｎ＝４８国外已有报道外,其中２ｎ＝２４,３６,７２,８４和９６的二倍体、三倍体、六倍体、七倍体和八倍体等多倍体系列均为首次报道,此外２ｎ＝２２,２６,４２和４７等体细胞染色体的非整倍性变异,迄今也尚未见有报道。