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  • 1
    Electronic Resource
    Electronic Resource
    Effect of Protein Depletion on Amino-acid Activating Enzymes of Rat Liver (1963)
    [s.l.] : Nature Publishing Group
    Nature 199 (1963), S. 378-379 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Protein-depleted animals exhibit, in fact, relatively less incorporation of labelled amino-acids in muscles and carcass and a greater incorporation in the viscera, particularly in the liver1-9. Two tentative hypotheses may be formulated to explain this effect in protein depletion: (1) Protein ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/199378a0
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  • 2
    Electronic Resource
    Electronic Resource
    Size analysis of inorganic particles in the alimentary tracts of Mediterranean mullet species suitable for aquaculture
    Amsterdam : Elsevier
    Aquaculture 62 (1987), S. 123-129 
    Details
    ISSN: 0044-8486
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0044-8486(87)90316-4
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  • 3
    Electronic Resource
    Electronic Resource
    A morphological basis for verticality detectors in the pigeon retina: Asymmetric amacrine cells (1983)
    Springer
    Naturwissenschaften 70 (1983), S. 368-369 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00444218
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  • 4
    Electronic Resource
    Electronic Resource
    Unreduced gametes in diploid Medicago and their importance in alfalfa breeding (1986)
    Springer
    Theoretical and applied genetics 72 (1986), S. 37-41 
    Details
    ISSN: 1432-2242
    Keywords: Alfalfa ; Medicago genus ; Polysomic polyploids ; Sporogenesis ; Unreduced gametes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In the genus Medicago, it is known that 2n gametes have been important in the evolution and breeding of cultivated alfalfa, which is a natural polysomic polyploid (2n=4x=32), however little is known on the frequency of male and female 2n gametes in diploid relatives of alfalfa. To obtain data on the frequency of 2n gametes, more than 12,000 2x–4x and 4x–2x crosses were made in 1982 at Madison (USA). Diploid parents in crosses were from four populations of M. coerulea, two of M. falcata and one diploid population of cultivated M. sativa which was derived by haploidy. The tetraploid seed parent in the crosses was a male-sterile M. sativa clone and vigorous tetraploid M. sativa plants were used as pollen parents. Each of 274 diploid plants was utilized both as male and as female. Of the 548 cross combinations, 266 crosses produced variable quantities of seeds which were sown in 1983 in a greenhouse at Perugia (Italy); the plants were subsequently space transplanted in the field in 1984. The identification of ploidy level of these genotypes was made on the basis of morphological characters, plant fertility, pollen stainability and chromosome counts. Of the 515 plants analyzed, the majority behaved as normal tetraploids indicating that many diploid plants produced 2n gametes. Diplogynous and diplandrous gamete production was not correlated with each other, which indicated a different genetic control of 2n sporogenesis in the 2 sexes. Only 4 F1 triploid plants confirmed the presence of a very effective triploid block in alfalfa. In consequence, bilateral sexual polyploidization is a more likely alternative for the origin of tetraploid alfalfa than triploid bridges. The present study showed that it is possible to efficiently identify genotypes able to produce high frequencies of 2n gametes within natural populations of diploids Medicago that are useful in alfalfa breeding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00261451
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  • 5
    Electronic Resource
    Electronic Resource
    Abnormal macrosporogenesis in five alfalfa (Medicago sativa) mutants producing 4n pollen (1993)
    Springer
    Theoretical and applied genetics 85 (1993), S. 873-881 
    Details
    ISSN: 1432-2242
    Keywords: Reproductive mutants ; Jumbo pollen ; Alfalfa ; Cytogenetics ; Sexual polyploidization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary An analysis of micro- and macrosporogenesis in five diploid alfalfa mutants was carried out using a stain-clearing technique. All plants produced tetranucleated microspores and jumbo pollen due to the complete failure of the postmeiotic cytokinesis as well as bi- and trinucleated macrospores. The latter was due to the absence of cytokinesis after the first and second meiotic division of macrosporogenesis. Only one out of the five clones analyzed formed tetranucleated macrospores as a consequence of the total lack of cytokinesis after both meiotic divisions. The fusion of nuclei within binucleated macrospores resulted in 2n macrospores of the SDR type, recognizable on the basis of nucleolus dimension, confirming the ability of jumbo pollen (jp) mutants to produce 2n eggs at a high frequency. Nuclear fusion was also observed within tri- and tetranucleated macrospores. Although having the same genetic background, the five clones showed significant variability in the expression of abnormal cytokinesis during macrosporogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00225032
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  • 6
    Electronic Resource
    Electronic Resource
    Megagametophyte organization in diploid alfalfa meiotic mutants producing 4n pollen and 2n eggs (1995)
    Springer
    Theoretical and applied genetics 90 (1995), S. 135-141 
    Details
    ISSN: 1432-2242
    Keywords: Alfalfa ; Megagametogenesis ; Supernumerary nuclei ; 2n eggs ; Meiotic mutants
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Megagametogenesis was studied in five diploid alfalfa mutants producing 4n pollen and 2n eggs, using a stain-clearing technique. All mutants produced embryo sacs with a variable number of supernumerary nuclei both at the early (bi- and tetra-nucleate) and at the late (eight-nucleate) stages of development. The presence of supernumerary nuclei is considered to be a consequence of the production of coenocytic megaspores. The production of 2n eggs was confirmed through cytological investigation by means of the diameter of the egg-cell nucleolus. The frequency of 2n eggs was lower than the frequency of binucleated macrospores as previously determined. This discrepancy may be due to environmental effects but also to the fact that binucleated macrospores may degenerate or may, after two mitotic divisions, give rise to eight-nucleated embryo sacs counted as normals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221007
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  • 7
    Electronic Resource
    Electronic Resource
    Increasing 2n gamete production in diploid alfalfa by cycles of phenotypic recurrent selection (1997)
    Springer
    Euphytica 93 (1997), S. 113-118 
    Details
    ISSN: 1573-5060
    Keywords: alfalfa ; bilateral sexual polyploidization ; Medicago sativa ; phenotypic recurrent selection ; 2n gametes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Two cycles of selection (3rd and 4th) were carried out in a diploid population of alfalfa to improve the frequency of 2n gametes. All the plants produced unreduced gametes, except one in the 2n egg population. The average seed set, used as a measure of 2n gametes production, increased significantly in the 2n pollen selection. Conversely, the increase was not significant in the case of 2n eggs. The improvement in 2n pollen production was confirmed cytologically. These results, like those of the first two cycles of selection, suggest that 2n pollen production is controlled by few major genes while 2n egg production is controlled by one recessive major gene and influenced by minor genes. The mutants selected have been utilized for producing heterotic tetraploid progenies through Bilateral Sexual Polyploidization (BSP).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1002978405500
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  • 8
    Electronic Resource
    Electronic Resource
    A statistical approach to estimate the frequency of n, 2n and 4n pollen grains in diploid alfalfa (1993)
    Springer
    Euphytica 69 (1993), S. 109-114 
    Details
    ISSN: 1573-5060
    Keywords: Medicago sativa ; lucerne ; alfalfa ; least squares ; pollen grain size ; unreduced gametes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Using pollen grain diameter, a statistical approach has been applied in order to estimate the percentage of n, 2n and 4n pollen grains produced by diploid plants of alfalfa. Pollen grain size distributions of normal diploids, normal tetraploids and jumbo pollen mutants were used as controls for n〈x, 2n〈2x and 4n〈4x pollen grains, respectively. The least squares method was used to fit the observed distributions of the plants under examination with three reference distributions. Six out of 22 plants analyzed were 2n pollen grain producers and one also produced 4n pollen grains. The results obtained indicate that the method can be efficiently applied in breeding programmes aimed at the selection of alfalfa mutants producing unreduced gametes at high frequency.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00021733
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  • 9
    Electronic Resource
    Electronic Resource
    Phenotypic recurrent selection for 2n pollen and 2n egg production in diploid alfalfa (1991)
    Springer
    Euphytica 57 (1991), S. 97-102 
    Details
    ISSN: 1573-5060
    Keywords: Medicago sativa ; lucerne ; alfalfa ; 2n gametes ; two cycle recurrent selection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Cultivated alfalfa (Medicago sativa L.) is a polysomic polyploid with tetrasomic inheritance. In this crop the hybridization of gametes with the somatic chromosome number (2n gametes) produced by diploid hybrids is a valuable method to maximize heterozygosity. For this purpose it is necessary to obtain diploids which produce high frequencies of 2n gametes. The results of the present paper indicate that phenotypic recurrent selection was efficient in increasing the production of male and female 2n gametes in diploid alfalfa. Two distinct selections were carried out, one for 2n pollen and the other for 2n egg production and two cycles of phenotypic recurrent selection were performed. The percentage of plants producing 2n gametes and the frequency of 2n gametes per plant were improved by selection. Realized heritabilities over the two cycles of recurrent selection were 39% and 60% for 2n pollen and 2n egg production, respectively; on the whole, the responses to the selection indicate that both male and female 2n gamete production are controlled by major and minor genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00023066
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  • 10
    Electronic Resource
    Electronic Resource
    Preparation of YBCO-Ag composites with low carbon contents by a wet method (1994)
    Springer
    Journal of materials science 29 (1994), S. 3113-3120 
    Details
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract YBa2Cu3O7-δ/Ag composites were prepared by a wet method, using readily available materials and a modification of the citrate method. This method allows for the addition of silver in soluble form to the YBCO soluble precursor and makes no use of nitrates, thus it allows for a smooth decomposition of the organic substance even in the presence of silver. After decomposition of the organic portion an effort was made to reduce the carbon content by using a gas flow containing N2 and O2 with 0.3% nitrogen oxide (NO). The carbon was substantially reduced by operating at high temperature. The pellets obtained from powder so formed were finally annealed at 950 °C in oxygen and then characterized. By increasing the temperature of the NO-anneal a greater spreading of the silver among the YBCO grains was observed. The results show that by this method it is possible to obtain composites in which the only phases detected are YBa2Cu3O7−δ and metallic silver. Although further work needs to be performed on the final products to obtain higher densities and so to obtain improved grain coupling, the data described here open a new way for the production of YBCO-Ag composites with low carbon contents.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00356653
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