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  • 1
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Multiplication of TMV-strains vulgare (light-green/dark-green mosaic symptoms) and flavum (severe yellow/green mosaic) had different effects on the ribosomal RNA of tobacco leaf chloroplasts. Vulgare inhibited chloroplast ribosomal RNA synthesis while having no effect on cytoplasmic ribosomal RNA synthesis (Fig. 2). Flavum inhibited chloroplast ribosomal RNA synthesis more severely than vulgare, and caused an earlier degradation of chloroplast ribosomal RNA than in control or vulgare-infected leaves (Fig. 1). Flavum also inhibited cytoplasmic ribosomal RNA synthesis. A connection between these differing effects on chloroplast ribosomal RNA metabolism and severity of visible symptoms is suggested, and discussed in relation to a possible influence on symptoms of denatured virus coat protein.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-8469
    Keywords: Nicotiana tabacum ; N-gene ; hypersensitivity ; local lesions ; virus localization ; electron microscopy ; myelinic bodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract This paper questions whether pathogenesis-related proteins (PRs) have any role in acquired systemic resistance, and whether there may be alternative explanations for the reduced number and size of lesions formed when leaves containing PRs are inoculated with virus. It is concluded that PRs may not play a direct role in acquired resistance; that altered lesion number may result from altered susceptibility of the leaf to mechanical inoculation, and that reduced lesion size could reflect a non-specific modulation of the basic localization mechanism. Preliminary experiments showing changes in ultrastructure of leaves associated with the development of acquired systemic resistance are discussed. The most striking change was development of myelinic bodies, generally between the cell wall and plasmalemma in uninoculated areas of leaf opposite halves bearing lesions.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Euphytica 63 (1992), S. 175-185 
    ISSN: 1573-5060
    Keywords: resistance ; virulence ; gene-for-gene relationships ; pathogenic fitness
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Host resistance is the main means of control of plant virus diseases. This paper reviews the genetics of resistance and matching virulence. Theoretical models of basic compatibility between plant species and their viruses, and of resistance, are described and used to predict features of resistance genetics, and mechanisms. These predictions are compared with a survey of known examples of resistance. Resistance is mainly controlled at a single genetic locus, although more complex systems are known. About half of the resistance alleles studied were dominant, the remainder were either incompletely dominant or recessive. Doubt is cast on the reliability of assessing resistance genotypes (numbers of loci and dominace relationships) from ‘distant’ phenotypic measurements such as symptom severity or plant growth. A model is proposed to reconcile apparent inconsistencies between genotype and phenotype. Dominant resistance alleles are strongly associated with virus localising mechanisms normally involving local lesions. Incompletely dominant and recessive alleles allow spread of the virus, but inhibit multiplication or symptom development. Fully recessive alleles may be associated with complete immunity. Most resistance genes in the survey had been overcome by virulent virus isolates with dominant localising resistance alleles especially vulnerable. Comparatively few resistance genes have proved exceptionally durable. Acquisition of virulence can be associated with loss of general pathogenic fitness, but in some cases this can be restored by further selection of the virus in resistant hosts. Virulence/avirulence determinants have been mapped to individual base changes in different functional regions of the viral genome. A virus may contain several virulence determinants and may develop a stable gene-for-gene relationship with a host having several resistance genes. It may be possible to design robust, oligogenic resistance systems which will be difficult for the virus to overcome.
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  • 4
    ISSN: 1573-5087
    Keywords: Plant growth regulators ; plant virus infection ; control of host-virus interaction ; resistance to virus disease ; chemotherapy of virus disease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Virus infection can severely inhibit plant growth and distort development. This article reviews changes in plant growth regulator metabolism caused by infection. In general, virus infection decreases auxin and gibberellin concentrations and increases abscisic acid concentration. Ethylene production is stimulated in necrotic or chlorotic reactions to infection, but not where the virus spreads systemically without necrosis. While these broad trends are true for most host-virus combinations studied, several situations are recorded where the virus had other effects on growth substance concentration. Cytokinin changes do not show any common pattern: both increases and decreases after infection have been reported. The extent to which virus-induced changes in growth substance concentration could be responsible for observed alterations in host growth and development is discussed. While changes in abscisic acid, gibberellin and ethylene production seem potentially important, the experimental evidence does not provide conclusive proof for control of growth by these changes. The numerous investigations of effects of exogenous regulators on virus multiplication and pathogenesis are reviewed. Different regulators, or the same regulator applied at different times or concentrations, had very diverse effects, and in some cases did significantly alter virus multiplication and pathogenesis. However, such studies seem to have yielded disappointingly little understanding of the biochemistry of the host-virus interaction, and the possible involvement of growth substances in this. Possible uses of plant growth regulators in chemotherapy of virus disease, and their possible involvement in natural or induced resistance mechanisms are discussed.
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  • 5
    ISSN: 1432-2048
    Keywords: Abscisic acid ; Nicotiana ; Ribonucleic acid synthesis ; Tobacco mosaic virus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Uptake of abscisic acid from the culture medium by discs of healthy and tobacco mosaic virus-infected tobacco leaves was measured. Small (two to five-fold) increases in abscisic acid concentration in discs caused increases in rates of [3H]uridine and [3H]adenine incorporation into total nucleic acid, virus RNA and host ribosomal RNA. Net accumulation of virus RNA was also enhanced by abscisic acid. This evidence for stimulation of RNA synthesis is compared with previous reports showing inhibition of RNA synthesis in other tissues. It is suggested that the increase in endogenous abscisic acid caused by tobacco mosaic virus infection may be at least partly responsible for observed increases in rates of RNA synthesis after infection.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Planta 148 (1980), S. 417-421 
    ISSN: 1432-2048
    Keywords: Daucus ; Germination (seeds) ; Nicotinana ; rRNA ; Seed ageing ; Seed germination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The integrity of ribosomal RNA (the percentage of complete, un-nicked molecules) in seeds was studied by electrophoresis under denaturing conditions. Two batches of carrot seed, harvested at different stages of maturity, and four batches ofNicotiana seed stored for various times were used. Within each species, there was a correlation between the integrity of the rRNA of the dry seed and the rate of germination of that seed. In carrot seed, there was extensive degradation of existing rRNA in both the embryo and endosperm during the first two days of imbibition.
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  • 7
    ISSN: 1432-2048
    Keywords: Abscisic acid and TWV ; Chloroplast (ABA in) ; Nicotiana (ABA, TMV) ; Tobacco mosaic virus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The concentrations of free and bound abscisic acid (ABA and the presumed ABA glucose ester) increased three- to fourfold in leaves of White Burley tobacco (Nicotiana tabacum L.) systemically infected with tobacco mosaic virus. Infected leaves developed a distinct mosaic of light-green and dark-green areas. The largest increases in both free and bound ABA occurred in dark-green areas. In contrast, virus accumulated to a much higher concentration in light-green tissue. Free ABA in healthy leaves was contained predominantly within the chloroplasts while the majority of bound ABA was present in non-chloroplastic fractions. Chloroplasts from light-green or dark-green tissues were able to increase stromal pH on illumination by an amount similar to chloroplasts from healthy leaf. It is unlikely therefore that any virus-induced diminution of pH gradient is responsible for increased ABA accumulation. Tobacco mosaic virus infection had little effect on free ABA concentration in chloroplasts; the virus-induced increase in free ABA occurred predominantly out-side the chloroplast. The proportional distribution of bound ABA in the cell was not changed by infection. Treatment of healthy plants with ABA or water stress increased chlorophyll concentration by an amount similar to that induced by infection in dark-green areas of leaf. A role for increased ABA concentration in the development of mosaic symptoms is suggested.
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 271 (1978), S. 726-730 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] During the fission yeast cell cycle, the rate of polyadenylated messenger RNA synthesis doubles when the cell reaches a critical size. This size-related control maintains average mRNA content in balance with total cell mass during exponential growth, even in cells growing at different absolute ...
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  • 9
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 244 (1973), S. 222-224 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] S. pombe strain 132 was grown in a minimal medium, EMM 2 (ref. 5). Cells from exponential phase cultures were collected by centrifugation and resuspended in medium containing lomofungin. Control cells were resuspended in medium alone. Measurements of RNA synthesis were made during various periods ...
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  • 10
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 215 (1967), S. 873-873 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Observations1?3 have shown the course of change in cell number with time in explants taken from tubers of the Jerusalem artichoke and cultured in contact with a medium containing 20 per cent coconut milk and 10?6 molar, 2,4-dichlorophenoxyacetic acid. It has also been shown2,3 that the first few ...
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