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Journal ArticleDOI

Cyto-genetical investigations in some common cucurbits, with special reference to fragmentation of chromosomes as a physical basis of speciation.

01 Aug 1947-Journal of Genetics (J Genet)-Vol. 48, Iss: 2, pp 237-256
TL;DR: Are sex chromosomes in higher pl,~nt~ nucleologenic?
Abstract: Introduction . M~t~rial and methods 0 bservations: Cucumis a~giz,u~ . Cucumis Memo Trichoaanth~ diolca Luffa aegyp~i~c,a . Luffa a~u~an~u~a . 6'o~iuia indica Beuincasa cerifera M~,mrdica cllarantia Cucurbita ~r~aarima Polysomaty Discussion (i) Numerica! correlation between m a~m um number ofnucleoli, sat~llltes and secondary constrictions (ii) Maximum number of nucleo]i ,lnd nucleolar constrictions of chromosomes witah reference to polyplcidy and aneuploidy . . . {iii) Variation of chromosome number in Cucm.bitaceac and R~. cytogsnetic interpretation (iv} Are sex chromosomes in higher pl,~nt~ nucleologenic? . Summary P, efsrsnces P A G ~
Citations
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Journal ArticleDOI
TL;DR: The authors of this study assume that the novel cucumber reference genes determined will enable better normalization and quantification of transcript levels in future expression studies on cucumber plants.
Abstract: It has been shown that genes considered to be valid reference genes using semi-quantitative techniques (e.g. northern blot) appear to be less reliable when highly sensitive real-time PCR (qPCR) or microarrays are used. Therefore, the validation of expression stability of reference genes has become an important component of any study using such types of assay. No reference genes have been validated for expression studies of cucumber genes to date. Since the genome of this widely cultivated crop has been recently sequenced, the availability of suitable reference genes for expression analyses of the new cucumber genes is urgently required. For the purpose of normalization in studying expression of cucumber target genes, the stability of twelve reference genes in different cucumber tissues and under various stresses and growth regulators were determined in this study. These included commonly used cucumber reference genes, such as actin, EF, cyclophilin, ubiquitin and tubulin and the newly identified candidates for reference genes that encode clathrin adaptor complex subunit (CACS), F-box protein, PPA2 activator (tonoplast intrinsic protein, TIP41), mitosis protein (YSL8), protein phosphatase 2 (PDF2), helicase (HEL) and protein homolog of At4g33380. Analyses of quantitative real-time PCR data by three commonly used Excel-based applets, BestKeeper, geNorm and NormFinder, confirmed that expression stability of reference genes depends on the experimental parameters. In addition, they revealed that, except for EF, the most stable cucumber genes included mainly the new reference genes: CACS, F-box and TIP41, whereas the commonly used internal controls demonstrated various (actin, cyclophilin, ubiquitin) or much lower stability (tubulin). Hence, the authors of this study assume that the novel cucumber reference genes will enable better normalization and quantification of transcript levels in future expression studies on cucumber plants.

141 citations


Cites background from "Cyto-genetical investigations in so..."

  • ...Biochemical, physiological and cytogenetic studies of this plant have been carried out for several decades (Bhaduri and Bose 1947; Burzyński et al. 2005; Chen et al. 1998; Janicka-Russak et al. 2008; Koo et al. 2002; Migocka and Klobus 2007; Ramachandran and Seshadri 1986), whereas the analysis of…...

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Book ChapterDOI
01 Jan 1993
TL;DR: The use of this vegetable is highlighted and its cytology, genetics, germplasm resources, and reproductive biology are reviewed and techniques applicable to the improvement of cucumber are described.
Abstract: Publisher Summary Cucumber, Cucumis sativus L., is a member of the Cucurbitaceae, which comprises 90 genera and 750 species. It is one of the oldest cultivated vegetable crops and is cultivated in nearly all countries of temperature zones. It is a thermophilic and frost-susceptible plant species, growing best at temperatures above 20 °C. This chapter highlights the use of this vegetable and reviews its cytology, genetics, germplasm resources, and reproductive biology. The taste and demands of the consumer varies according to country. Special varieties must be bred that set fruit under suboptimal temperature conditions. The demands of the processing industry concerning outer appearance—fruit shape, size, and color—also varies depending on the preservation process and the corresponding country. Therefore, cucumber breeders must consider several different breeding aims. General breeding objectives in cucumber are resistance to diseases and animal pests, maintenance of resistance in existing varieties, fruit quality, and fruit yield. Additionally, breeding aims such as parthenocarpy, constancy of femaleness, germination, and fruit set at suboptimum temperatures may be of importance in special breeding programs. Unlike many other plant species, there are different sex types in cucumber, which are of different value in breeding and concerning yield potential. By using sex inheritance and influencing sex expression, the breeding methods of self-pollinated and open-pollinated plants can be applied to cucumber. Thus, the cucumber breeder needs complete knowledge of sex inheritance and of potential ways of influencing sex expression. The chapter provides an overview of the selection of cucumber breeding methods and these methods. There have been several reports on the possibility of applying in vitro techniques in plant breeding of cucumber. The chapter describes techniques that are applicable to the improvement of cucumber.

128 citations

Journal ArticleDOI
01 Jul 2014-Genetics
TL;DR: It is shown that balancing selection is common under biologically plausible conditions and that sex differences in selection or sex-by-genotype effects of mutations can each increase opportunities for balancing selection.
Abstract: How common is balancing selection, and what fraction of phenotypic variance is attributable to balanced polymorphisms? Despite decades of research, answers to these questions remain elusive. Moreover, there is no clear theoretical prediction about the frequency with which balancing selection is expected to arise within a population. Here, we use an extension of Fisher’s geometric model of adaptation to predict the probability of balancing selection in a population with separate sexes, wherein polymorphism is potentially maintained by two forms of balancing selection: (1) heterozygote advantage, where heterozygous individuals at a locus have higher fitness than homozygous individuals, and (2) sexually antagonistic selection (a.k.a. intralocus sexual conflict), where the fitness of each sex is maximized by different genotypes at a locus. We show that balancing selection is common under biologically plausible conditions and that sex differences in selection or sex-by-genotype effects of mutations can each increase opportunities for balancing selection. Although heterozygote advantage and sexual antagonism represent alternative mechanisms for maintaining polymorphism, they mutually exist along a balancing selection continuum that depends on population and sex-specific parameters of selection and mutation. Sexual antagonism is the dominant mode of balancing selection across most of this continuum.

107 citations

Journal ArticleDOI
TL;DR: A fine-scale understanding of the mechanisms of dysploid chromosome reduction that has not been achieved previously is allowed to be achieved.
Abstract: †These authors contributed equally to this work. SUMMARY In the large Cucurbitaceae genus Cucumis, cucumber (C. sativus) is the only species with 2n = 2x = 14 chromosomes. The majority of the remaining species, including melon (C. melo) and the sister species of cucumber, C. hystrix, have 2n = 2x = 24 chromosomes, implying a reduction from n = 12 to n = 7. To understand the underlying mechanisms, we investigated chromosome synteny among cucumber, C. hystrix and melon using integrated and complementary approaches. We identified 14 inversions and a C. hystrix lineage-specific reciprocal inversion between C. hystrix and melon. The results reveal the location and orientation of 53 C. hystrix syntenic blocks on the seven cucumber chromosomes, and allow us to infer at least 59 chromosome rearrangement events that led to the seven cucumber chromosomes, including five fusions, four translocations, and 50 inversions. The 12 inferred chromosomes (AK1–AK12) of an ancestor similar to melon and C. hystrix had strikingly different evolutionary fates, with cucumber chromosome C1 apparently resulting from insertion of chromosome AK12 into the centromeric region of translocated AK2/AK8, cucumber chromosome C3 originating from a Robertsonian-like translocation between AK4 and AK6, and cucumber chromosome C5 originating from fusion of AK9 and AK10. Chromosomes C2, C4 and C6 were the result of complex reshuffling of syntenic blocks from three (AK3, AK5 and AK11), three (AK5, AK7 and AK8) and five (AK2, AK3, AK5, AK8 and AK11) ancestral chromosomes, respectively, through 33 fusion, translocation and inversion events. Previous results (Huang, S., Li, R., Zhang, Z. et al., 2009, Nat. Genet. 41, 1275‐1281; Li, D., Cuevas, H.E., Yang, L., Li, Y., Garcia-Mas, J., Zalapa, J., Staub, J.E., Luan, F., Reddy, U., He, X., Gong, Z., Weng, Y. 2011a, BMC Genomics, 12, 396) showing that cucumber C7 stayed largely intact during the entire evolution of Cucumis are supported. Results from this study allow a fine-scale understanding of the mechanisms of dysploid chromosome reduction that has not been achieved previously.

83 citations


Cites background from "Cyto-genetical investigations in so..."

  • ...…to explain it: a fragmentation hypothesis that postulated de novo regeneration of centromeres from n = 7 to n = 12 (Kozhukhow, 1930; Whitaker, 1933; Bhaduri and Bose, 1947) and a fusion hypothesis that postulated that n = 7 was derived from n = 12 via unequal translocation or fusion of…...

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  • ...The origin of the seven cucumber chromosomes has been a long-standing question, with opposite hypotheses being proposed to explain it: a fragmentation hypothesis that postulated de novo regeneration of centromeres from n = 7 to n = 12 (Kozhukhow, 1930; Whitaker, 1933; Bhaduri and Bose, 1947) and a fusion hypothesis that postulated that n = 7 was derived from n = 12 via unequal translocation or fusion of non-homologous chromosomes (Trivedi and Roy, 1970)....

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Journal ArticleDOI
TL;DR: Both centromere activation and inactivation in cucurbit species were associated with a gain/loss of a large amount of pericentromeric heterochromatin.
Abstract: The centromere of an eukaryotic chromosome can move to a new position during evolution, which may result in a major alteration of the chromosome morphology and karyotype. This centromere repositioning phenomenon has been extensively documented in mammalian species and was implicated to play an important role in mammalian genome evolution. Here we report a centromere repositioning event in plant species. Comparative fluorescence in situ hybridization mapping using common sets of fosmid clones between two pairs of cucumber (Cucumis sativus L.) and melon (Cucumis melo L.) chromosomes revealed changes in centromere positions during evolution. Pachytene chromosome analysis revealed that the current centromeres of all four cucumber and melon chromosomes are associated with distinct pericentromeric heterochromatin. Interestingly, inactivation of a centromere in the original centromeric region was associated with a loss or erosion of its affixed pericentromeric heterochromatin. Thus, both centromere activation and inactivation in cucurbit species were associated with a gain/loss of a large amount of pericentromeric heterochromatin.

83 citations


Cites background from "Cyto-genetical investigations in so..."

  • ...If the ancestor species for cucumber and melon contained 2n 14 chromosomes (24), then melon chromosome I (MeI) would be derived from a chromosomal fission event....

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References
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Journal ArticleDOI
TL;DR: The nucleolus is organized in the telophase through the activity of a distinct deep-staining body having a definite position in one chromosome (the satellited chromosome) of the monoploid complement through a reciprocal translocation which broke this body into two parts.
Abstract: 1. The nucleolus is organized in the telophase through the activity of a distinct deep-staining body having a definite position in one chromosome (the satellited chromosome) of the monoploid complement. Correlated with the number of satellited chromosomes present, the telophases of somatic tissue of haploids show one nucleolus, diploids, two nucleoli and triploids, three nucleoli. That the nucleolus develops through the activity of this body (refered to as the nucleolar-organizing body or element) was obtained from a reciprocal translocation which broke this body into two parts. Both interchanged chromosomes possessed a section. Nucleoli developed from each of these two segments. Thus, plants homozygous for the interchange developed four nucleoli in their somatic telophases; plants heterozygous for the interchange developed three nucleoli in their somatic telophases. Similarly, the telophase nucleoli resulting from the first division within the monoploid microspore of normal diploids show only one nucleolus, whereas, those of plants homozygous for the interchange are characterized by the development of two nucleoli. 2. The functional capacity to develop a nucleolus is not the same for both segments of the severed nucleolar-organizing body. This is evident when the two interchanged chromosomes are present in the same nucleus. The segment of the nucleolar-organizing body possessed by one interchanged chromosome produced a large nucleolus, whereas, the segment of the nucleolar-organizing body possessed by the other interchanged chromosome produced a small nucleolus. When this latter chromosome, with the nucleolar-organizing element of slower rate of functional capacity is present without the former (i. e. without a competing nucleolarorganizing element) it produces, in contrast, a large nucleolus. 3. The activity of the nucleolar-organizing element is hindered by certain genomic deficiencies. When this occurs, many small nucleolarlike bodies are produced and remain associated with the other chromosomes of the complement. These small nucleoli appear to develop from a swelling and later collection into droplets of the matrix substance of the chromosome.

589 citations

Journal ArticleDOI
01 Feb 1931-Planta
TL;DR: The physiological meaning of the nucleoli still remains one of the most obscure questions of the cytology as discussed by the authors, even after more than 100 years of the discovery of the Nukleolus.
Abstract: I. Einleitung. ,,Die physiologische Bedeutung des Nukleolus ist noch v611ig unbekannt, auch entbehren die bisher in Betreff derselben aufgestellten Hypothesen der genfigenden Begrfindung.\" So schreibt ZAC~ARIAS im Jahre 1885, und nicht weniger als 27 Jahre sp~ter liest man bei LCNDEGARD~ (1912): ,,l~berhaupt fehlt es nicht an Ansichten fiber die Bedeutung der Nukleolen, w~hrend die wirklich ermittelten Tatsachen ziemlich spRrlich u n d . . , auch zumeist recht unsicher sind.\" Nach weiteren 13 Jahren ist kein Fortschrit t zu verzeiehnen: ,,The physiological meaning of the nucleoli still remains one of the most obscure questions of the cytology\" (WILsO~ 1925). An Bemiihungen hat es nicht gemangelt. Das ist verst~ndlich, fehlt doch keinem tierisehen und keinem pflanzlichen Zellkern (yon ganz vereinzelten Ausnahmen abgesehen) dieser merkwfirdige K6rper. Doch bis heute sind wir fiber ,,Ansichten\" nicht hinausgekommen. Auch in der vorliegenden Arbeit wird man keine L6sung finden, im Gegenteil: Ieh habe mich bemfiht, die Frage nach der Bedeutung des Nukleolus fiberhaupt nicht aufzuwerfen. Denn es scheint, dab wir hierfiber gerade deshalb so wenig wissen, weil wir zuviel danach fragen. In wie vielen Arbeiten fiber den Kernk6rper wird die Richtigkeit des rein Ph~nomenologischen getriibt dadurch, dal3 die Frage nach der Bedeutung aufgeworfen wird. Und wieviel rein ph~nomenologisch noch unbekannt war, soll die vorliegende Untersuchung zeigen. Sie geht aus von kausaler Fragestellung. Nur mit Tatsachen wird die Antwort gegeben. Von diesen Tatsaehen aus wird man vielleicht einmal etwas fiber die Bedeutung der Nukleolen ermitteln k6nnen.

254 citations

Journal ArticleDOI

141 citations

Journal ArticleDOI
TL;DR: The chromosomes of the male plants of 17 genera, 22 species and 2 varieties of dioecious phanerogams have been investigated and the following 13 forms show each an unequal pair of chromosomes in addition to autosome pairs at the meiotic division in microsporocytes.
Abstract: 1. The chromosomes of the male plants of 17 genera, 22 species and 2 varieties of dioecious phanerogams have been investigated. Of these the following 13 forms show each an unequal pair of chromosomes in addition to autosome pairs at the meiotic division in microsporocytes. This unequal pair of chromosomes is assumed to be a sex chromosome complex of an XY-type. Consequently in these forms the male plants are heterogametic with respect to sex. The 13 forms are Salix leucopithecia, S. sachalinensis, S. japonica, S. melanostachys, S. gracilistyla, S. viminalis var. yezonensis Morus bombycis, Cannabis sativa, Datisca cannabina, Daphniphyllum macropodum, Trichosanthes japonica, Hydrilla verlicillata and Trachycarpus excelsus.2. In Cudrania triloba, Acer negundo, Trachycarpus excelsus, var. Fortunei and Ginkgo biloba, one unequal pair-like pair is found at the first meiotic metaphase in microsporocytes; but it is not safe to take this for a true unequal pair of chromosomes until a further examination has been made.3. One large chromosome pair in Morus and Trachycarpus often divides in two unequal parts at the first meiotic division. The signifi-cance of this particular behaviour, especially in relation to sex determi-nation, is not yet known.4. Although many suitable figures of metaphase and anaphase of the first and second meiotic divisions in the male of Spinacia oleracea have been examined, no evidence of the existence of sex chromosomes has been obtained. An examination of the female has still to be undertaken.In microsporocytes of Aucuba japonica, 16 chromosomes are found at the first meiotic anaphase. The zygotic numbers of chromosomes in both sexes are the same, being 32. No evidence as to the sex chromo-somes could be obtained in the male plant.5. All Salix plants studied, except one form of S. sachalinensis, have 19 as the gametic chromosome number which is a basis in Salicaceae. The meiotic division is quite normal in them.One form of S. sachalinensis from Hokkaidoo has ca. 24 chromosomes at the first meiotic metaphase and their behaviour in the meiotic stages is irregular.6. Humulus japonicus, growing wild in the vicinity of Tokyo, has a tripartite chromosome in addition to 7 autosomic gemini at the first meiotic division in microsporocytes. At the first meiotic metaphase, the tripartite chromosome divides in such a way that the two end chromosomes go to the one pole, while the middle one goes to the other. Its behaviour is strikingly similar to that of Rumex acetosa. As a result, with respect to chromosomes, two kinds of pollen grains maybe formed. These results confirm that attained by KIHARA.7. Humulus lupulus has 10 gametic and 20 zygotic chromosomes. In the first meiotic division of microsporocytes, 16 chromosomes of the 20 form 8 gemini in all, while the 4 remaining chromosomes do not form gemini, but are connected end to end to form a beaded string. This tetrapartite chromosome can be identified in several stages from early diaphase, in the first meiotic division. At metaphase each alternate chromosome of the tetrapartite goes to opposite poles respectively. Thus the daughter nuclei receive an equal number of chromosomes, i.e. 10 respectively. The two middle members of a tetrapartite chromosome are equal in size and larger than the two end ones which differ in size from each other. As a result, two kinds of gametes may be formed, one having a larger amount of chromatin volume than the other. The tetrapartite chromosome may be a sex chromosome complex in H. lupulus, a new type of sex chromosome.8. At metaphase of the first meiotic division in the microsporocytes of Xanthoxylum piperitum, 35 chromosomes are counted, one of which is not only the largest

104 citations

Journal ArticleDOI
TL;DR: The misdivision and the origin of the iso-chromosome are each likely to be important as affecting the genetic structure of the chromosome and the mechanical properties of the centromere.
Abstract: Following misdivision of the centromere at meiosis in diploid and triploidFritillaria new telocentric chromosomes are formed whose broken ends rejoin within the centromere. This type of chromosome is delayed at metaphase and anaphase in the pollen-grain mitosis. It may then, either break again at the centromere, or pass without separation to the pole as a new iso-chromosome.

98 citations

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