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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Archives of microbiology 150 (1988), S. 209-214 
    ISSN: 1432-072X
    Keywords: Carotenogenesis ; Regulation ; Phycomyces ; Retinol ; Phthalate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Wild-type Phycomyces blakesleeanus synthesizes the yellow pigment, beta-carotene. Colour mutants exhibit various alterations in the biosynthesis of beta-carotene or in its regulation. The presence of certain chemicals in the medium stimulates carotenogenesis in the wild type. We attribute different mechanisms of action to agents which stimulate or fail to stimulate different sets of mutants; this is the case of retinol and dimethyl phthalate. Dimethyl phthalate and veratrol are active on the same mutants, and therefore are likely to act in the same way. The main regulation of carotenogenesis, end-product inhibition, does not operate in the mutants of certain genes; these mutants are indifferent to retinol. By using a collection of retinoids we conclude that their action depends on their structural similarity to a part of the beta-carotene molecule. From these and other observations we propose that end-product inhibition of the pathway is mediated by a complex of beta-carotene and two gene products and that the retinoids compete with beta-carotene and prevent end-product inhibition.
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 173 (1999), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Production of bikaverin and gibberellins by Gibberella fujikuroi started after depletion of the nitrogen source, but not after depletion of phosphate. Despite this similarity, the regulation of both pathways by nitrogen involved two different mechanisms. This conclusion was supported by the fact that the production of bikaverin, in contrast to the gibberellins, was not inhibited by nitrate in a mutant that could not utilize it. The different regulation of both pathways was clearly demonstrated by a mutant that overproduced bikaverin but lacked gibberellins. An optimal bikaverin production required a low pH, with a sharp drop at about pH 5. The syntheses of fungal secondary metabolites, such as bikaverin and gibberellins, are not subject to common regulation, but respond to various combinations of signals, such as nitrogen availability, nitrate and the pH of the medium.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology reviews 25 (2001), S. 0 
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Phycomyces has been in the laboratories for about 140 years, sometimes following trends and fashions, but often anticipating them. Researchers have been attracted by the sensitive and precise responses of Phycomyces to light and other stimuli, coupled with easy manipulations and good adaptation to laboratory life. It is a simple prototype of the many organisms that use light as a source of information but not as a significant source of energy. Growth, development, genetics, and carotene production have been other subjects of pioneering research. Phycomyces was the second organism, after us, known to require a vitamin. It was one of the first organisms in the research on spontaneous mutants and the second, after Drosophila, in which mutations were induced artificially. It was used to coin the concept and the name of heterokaryosis. Phycomyces heterokaryons offer unique experimental possibilities, for instance in the study of gene function in vivo and the causes of cell death. An overall impression of parsimony and combinatorial gene usage arises from the genetic analysis of the complex functions of this fungus. The main subjects of recent attention have been the various reactions to light, gravitropism, and some aspects of metabolism, particularly the production of carotene. Interest in Phycomyces is slacking because of the repeated failures at transforming it stably with exogenous DNA.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 21 (1992), S. 67-71 
    ISSN: 1432-0983
    Keywords: Phycomyces blakesleeanus ; β-carotene ; End-product regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The regulation of carotenogenesis in the fungus Phycomyces blakesleanus is mediated by several gene products and influenced by light, retinol, and other external agents. De-regulation of the biosynthetic pathway is found in the deep-yellow carS mutants and the white carA mutants. The carA, carS recombinants are yellow; their β-carotene content is intermediate between that of strains carrying each of the two mutations. Mutagen exposure of a deep-yellow carS mutant led to the isolation of white double-mutants which become yellow in the presence of retinol. They carry two very closely linked mutations in the carS gene. When separated in different organisms, each of these mutations results in a deep-yellow phenotype. Our results support the idea that two gene products recognize the beta rings of β-carotene and shut off biosynthesis when enough β-carotene has been made. The modified gene product present in the white carS mutants stops synthesis in the absence of β-carotene.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Current genetics 11 (1987), S. 505-511 
    ISSN: 1432-0983
    Keywords: Gibberella fujikuroi ; Fusarium moniliforme ; Carotenoid mutants ; Neurosporaxanthin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The orange pigment neurosporaxanthin colours the mycelia of wild Gibberella fujijuori (Fusarium monifliforme) grown in the light, but is barely detectable in the dark. We have isolated carotenoid mutants from conidia exposed to N-methyl-N′-nitro-N-nitroso-guanidine and other mutagens. Specific blocks in the pathway are represented by white mutants accumulating phytoene and red mutants accumulating torulene; there are also mutants without carotenoids or with complex carotenoid mixtures. Regulatory mutants overproduce neurosporaxanthin, both in the light and in the dark. Other mutants contain considerable neurosporaxanthin in the dark, but less than in the light. The results bring out similarities between the carotenoid biosynthetic pathways of Gibberella and Phycomyces, and significant differences in their respective regulations.
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  • 6
    ISSN: 1432-0983
    Keywords: Nitrosoguanidine ; Comutation ; Yeast ; Chromosome replication pattern
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Contrary to what happens in bacteria, mutations induced by nitrosoguanidine in yeast are not accompanied by an excess of mutations in nearby genes. We have investigated nitrosoguanidine mutagenesis in three regions of the yeast genome: the contiguous DNA segments HIS4A, HIS4B and HIS4C, located on chromosome III; ADE1 and CDC15 separated by about 3 map units on chromosome I; and CAN1, some 50 map units away from the centromere on chromosome V. Revertants at HIS4C never suffered mutations at HIS4A or HIS4B. Reversion at CDC15 did not affect the frequency of mutation at ADE1. No tsm mutations, leading to thermonsensitivity, were found in the immediate vicinity of the locus CAN1 after selecting for canavanine resistant mutants. However, as expected from nitrosoguanidine mutagenesis of replication points and the fixed pattern of chromosome replication, the induced tsm mutations seem not to map randomly over the yeast genome; in fact, two out of the three groups of such tsm mutations studied are located in the same chromosome arm as CAN1, indicating that these two regions are replicated at the same time as CAN1. Replication synchrony is less than perfect, since the tsm mutations of each group affect many different genes.
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  • 7
    ISSN: 1432-2048
    Keywords: Blue light ; Gallic acid ; Phycomyces (uvi mutants) ; Tropism ; Ultraviolet-C radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The giant sporangiophores of Phycomyces blakesleeanus turn towards blue and away from ultraviolet C sources (wavelength under 310 nm). We have isolated fifteen mutants with normal blue tropism but defective ultraviolet tropism. Wild-type sporangiophores described a double turn when exposed successively to blue and ultraviolet beams coming from the same side; under certain conditions, the mutants turned only to the blue. The new uvi mutations modified the behaviour in heterokaryosis and were lethal in homokaryosis, i.e., they affected essential cellular components. The responses of the wild type and one of the mutants were registered and evaluated with a computer-aided device. The mutant behaved normally under blue light, but took longer than the wild type to turn away from the ultraviolet source. With very weak ultraviolet stimuli (10−8 and 10−9 W · m−2), the wild type turned towards the source, but the mutant did not respond. Calculations of absorbed-energy distributions in the sporangiophore showed that Phycomyces responds differently to similar spatial distributions of blue and ultraviolet radiations. Wild-type and mutant sporangiophores had the same high ultraviolet absorption due to gallic acid. We conclude that ultraviolet tropism is not just a modification of blue phototropism due to the high ultraviolet absorption of the sporangiophores. Phycomyces has a separate sensory system responsive to ultraviolet radiation, but not to blue light.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Planta 174 (1988), S. 309-314 
    ISSN: 1432-2048
    Keywords: Blue light ; Phorogenesis ; Photomorphogenesis ; Phycomyces ; Sporangiophore development
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The production of two kinds of vegetative reproductive structures, microphores and macrophores, byPhycomyces blakesleeanus Bgff. depends on plating density, ventilation, asparagine supply, and illumination. Quantitative determinations of these variables lead us to propose a new experimental system for developmental photobiology: standard plastic Petri plates containing 25 ml minimal medium are inoculated with 105 viable, heat-activated spores and incubated, unpiled and unsealed, at 22° C. After 4 d microphores are counted and macrophores are weighed. Both microphorogenesis and macrophorogenesis are governed by light. Photosensitivity is a developmental phenomenon which occurs 32 to 68 h after inoculation, just before the beginning of vegetative reproduction in the dark controls. The maximum photosensitivity occurs 48 h after inoculation.
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  • 9
    ISSN: 1432-2048
    Keywords: Action spectrum ; Blue-light photoreceptor ; Fluence-response relationship ; Phorogenesis ; Phycomyces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Blue light regulates vegetative reproduction inPhycomyces blakesleeanus Bgff. by inhibiting the development of microphores and stimulating that of macrophores. Fluence-response curves were obtained at twelve different wavelengths. Each response exhibits a two-step (“biphasic”) dependence on fluence, as if it resulted from the addition of two separate components with different thresholds, midpoints, and amplitudes. The absolute threshold is close to 10 photons·μm2. The threshold fluence of the low-intensity component is about 104 times smaller than that of the high-intensity component. The action spectra for each of the two components of the two responses share general similarities, but exhibit significant differences that might be taken to favour four separate photosystems. Additional complexity is indicated by the wavelength dependence of the saturation levels.
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  • 10
    ISSN: 1432-2048
    Keywords: Action spectrum ; Blue-light photoreceptor ; Mutant (Phycomyces) ; Photocarotenogenesis ; Phycomyces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Blue light stimulates the accumulation of beta-carotene (photocarotenogenesis) in the fungus Phycomyces blakesleeanus. To be effective, light must be given during a defined period of development, which immediately precedes the cessation of mycelial growth and the depletion of the glucose supply. The competence periods for photocarotenogenesis and photomorphogenesis in Phycomyces are the same when they are tested in the same mycelium. Photocarotenogenesis exhibits a two-step dependence on exposure, as if it resulted from the additon of two separate components with different thresholds and amplitudes. The low-exposure component produces a small beta-carotene accumulation, in comparison with that of dark-grown mycelia. The high-exposure component has a threshold of about 100 J· m−2 blue light and produces a large beta-carotene accumulation, which is not saturated at 2·106 J·m−2. Exposure-response curves were obtained at 12 wavelengths from 347 to 567 nm. The action spectra of the two components share general similarities with one another and with those of other Phycomyces photoresponses. The small, but significant differences in the action spectra of the two components imply that the respective photosystems are not identical. Light stimulates the carotene pathway in the carB mutants, which contain the colourless precursor phytoene, but not beta-carotene. Carotenogenesis is not photoinducible in carA mutants, independently of their carotene content. This and other observations on various car mutants indicate that light prevents the normal inhibition of the pathway by the carA and carS gene products. The chromophore(s) for photocarotenogenesis are presumably flavins, and not carotenes.
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