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  • Pisum  (3)
  • Yeast  (3)
  • Springer  (6)
  • Oxford University Press
  • 1
    Electronic Resource
    Electronic Resource
    Mechanistic differences in photoinhibition of sun and shade plants (1992)
    Springer
    Planta 188 (1992), S. 422-431 
    Details
    ISSN: 1432-2048
    Keywords: Light acclimation ; Photosynthesis ; Photoinhibition ; Photosystem II repair cycle ; Pisum ; Tradescantia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Leaf discs of the shade plant Tradescantia albiflora Kunth grown at 50 μmol · m−2 · s−1, and the facultative sun/shade plant Pisum sativum L. grown at 50 or 300 μmol · m−2, s−1, were photoinhibited for 4 h in 1700 μmol photons m−2 · s−1 at 22° C. The effects of photoinhibition on the following parameters were studied: i) photosystem II (PSII) function; ii) amount of D1 protein in the PSII reaction centre; iii) dependence of photoinhibition and its recovery on chloroplast-encoded protein synthesis; and, iv) the sensitivity of photosynthesis to photoinhibition in the presence or absence of the carotenoid zeaxanthin. We show that: i) despite different sensitivities to photoinhibition, photoinhibition in all three plants occurred at the reaction centre of PSII; ii) there was no correlation between the extent of photoinhibition and the degradation of the D1 protein; iii) the susceptibility to photoinhibition by blockage of chloroplas-tencoded protein synthesis was much less in shade plants than in plants acclimated to higher light; and iv) inhibition of zeaxanthin formation increased the sensitivity to photoinhibition in pea, but not in the shade plant Tradescantia. We suggest that there are mechanistic differences in photoinhibition of sun and shade plants. In sun plants, an active repair cycle of PSII replaces photoinhibited reaction centres with photochemically active ones, thereby conferring partial protection against photoinhibition. However, in shade plants, this repair cycle is less important for protection against photoinhibition; instead, photoinhibited PSII reaction centres may confer, as they accumulate, increased protection of the remaining connected, functional PSII centres by controlled, nonphotochemical dissipation of excess excitation energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00192810
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  • 2
    Electronic Resource
    Electronic Resource
    Light inactivation of functional photosystem II in leaves of peas grown in moderate light depends on photon exposure (1995)
    Springer
    Planta 196 (1995), S. 401-411 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; D1 protein ; Photoinhibition ; Photoprotection ; Photosystem II heterogeneity ; Pisum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To determine the dependence of in vivo photosystem (PS) II function on photon exposure and to assign the relative importance of some photoprotective strategies of PSII against excess light, the maximal photochemical efficiency of PSII (Fv/Fm) and the content of functional PSII complexes (measured by repetitive flash yield of oxygen evolution) were determined in leaves of pea (Pisum satlvum L.) grown in moderate light. The modulation of PSII functionality in vivo was induced by varying either the duration (from 0 to 3 h) of light treatment (fixed at 1200 or 1800 μmol photons · m-2 · s-1) or irradiance (from 0 to 3000 μmol photons · m-2 · s-1) at a fixed duration (1 h) after infiltration of leaves with water (control), lincomycin (an inhibitor of chloroplast-encoded protein synthesis), nigericin (an uncoupler), or dithiothreitol (an inhibitor of the xanthophyll cycle) through the cut petioles of leaves of 22 to 24-day-old plants. We observed a reciprocity of irradiance and duration of illumination for PSII function, demonstrating that inactivation of functional PSII depends on the total number of photons absorbed, not on the rate of photon absorption. The Fv/Fm ratios from photoinhibitory light-treated leaves, with or without inhibitors, declined pseudo-linearly with photon exposure. The number of functional PSII complexes declined multiphasically with increasing photon exposure, in the following decreasing order of inhibitor effect: lincomycin 〉 nigericin 〉 DTT, indicating the central role of D1 protein turnover. While functional PSII and Fv/Fm ratio showed a linear relationship under high photon exposure conditions, in inhibitor-treated leaves the Fv/Fm ratio failed to reveal the loss of up to 25% of the total functional PSII under low photon exposure. The loss of this 25% of less-stable functional PSII was accompanied by a decrease of excitation-energy trapping capacity at the reaction centre of PSII (revealed by the fluorescence parameter, 1/Fo-1/Fm, where Fo and Fm stand for chlorophyll fluorescence when PSII reaction centres are open and closed, respectively), but not by a loss of excitation energy at the antenna (revealed by the fluorescence parameter, 1/Fm). We conclude that (i) PSII is an intrinsic photon counter under photoinhibitory conditions, (ii) PSII functionality is mainly regulated by D1 protein turnover, and to a lesser extent, by events mediated via the transthylakoid pH gradient, and (iii) peas exhibit PSII heterogeneity in terms of functional stability during photon exposure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00203636
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  • 3
    Electronic Resource
    Electronic Resource
    Evidence that an endo-exonuclease controlled by the NUC2 gene functions in the induction of ‘petite’ mutations in Saccharomyces cerevisiae (1991)
    Springer
    Current genetics 20 (1991), S. 39-44 
    Details
    ISSN: 1432-0983
    Keywords: Petite mutation ; NUC2 nuclease ; Yeast ; RAD52 ; Ethidium bromide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Defects in the RAD52 gene of the yeast Saccharomyces cerevisiae reduce the levels of the NUC2 endo-exonuclease by approximately 90% compared to the levels in wild-type strains. To examine the potential role of this nuclease in the induction of mitochondrial ‘petite’ mutations, congenic RAD52 and rad52-1 haploids were subjected to treatment with ethidium bromide, a well-known inducer of these mutations. The rad52 strain showed a much higher resistance to ethidium bromide-induced petite formation than the corresponding wild-type strain. Two approaches were taken to confirm that this finding reflected the nuclease deficiency, and not some other effect attributable to the rad52-1 mutation. First, a multicopy plasmid (YEp213-10) carrying NUC2 was transformed into a RAD52 strain. This resulted in an increased fraction of spontaneous petite mutations relative to that seen for the same strain without the plasmid and sensitized the strain carrying the plasmid to peptite induction by ethidium bromide treatment. Second, a strain having a nuc2 allele that encodes a temperaturesensitive nuclease was treated with ethidium bromide at the restrictive and permissive temperatures. Petite induction was reduced under restrictive conditions. Enzyme assays revealed that the RAD52 (YEp213-10) strain had the highest level of antibody-precipitable NUC2 endo-exonuclease whereas the nuc2 and rad52 mutants had the lowest levels. Furthermore, addition of ethidium bromide to the reaction mixture stimulated the activity of the nuclease on double-stranded DNA. Peptite induction by antifolate-mediated thymine nucleotide depletion was also inhibited by inactivation of RAD52 indicating that the effect of reduced NUC2 endo-exonuclease was not restricted to ethidium bromide treatment. Taken collectively, these results indicate that the NUC2 gene product functions in the production of mitochondrial petite mutations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00312763
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  • 4
    Electronic Resource
    Electronic Resource
    In-vitro recombination in rad and rnc mutants of Saccharomyces cerevisiae (1993)
    Springer
    Current genetics 23 (1993), S. 1-8 
    Details
    ISSN: 1432-0983
    Keywords: Recombination ; Yeast ; radmutants ; Endo/exonuclease
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Extracts of S. cerevisiae cells can catalyze homologous recombination between plasmids in vitro. Extracts prepared from rad50, rad52 or rad54 disruption mutants all have reduced recombinational activity compared to wild-type. The rad52 and rad54 extracts are more impaired in the recombination of plasmids containing double-strand breaks than of intact plasmids, whereas rad50 extracts are deficient equally for both types of substrate. The nuclease RhoNuc (previously designated yNucR), encoded by the RNC1 (previously designated NUC2) gene and regulated by the RAD52 gene, is not required for recombination when one substrate is single-stranded but is essential for the majority of recombination events when both substrates are double-stranded. Furthermore, elimination of this nuclease restores recombination in rad52 extracts to levels comparable to those in wild-type extracts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00336741
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  • 5
    Electronic Resource
    Electronic Resource
    Photoinactivation of functional photosystem II and D1-protein synthesis in vivo are independent of the modulation of the photosynthetic apparatus by growth irradiance (1996)
    Springer
    Planta 198 (1996), S. 300-309 
    Details
    ISSN: 1432-2048
    Keywords: D1-protein ; Photoinhibition ; Photon exposure ; Photosystem II heterogeneity ; Light acclimation ; Pisum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To investigate whether the in-vivo photoinhibition of photosystem II (PSII) function by excess light is an intrinsic property of PSII, the maximal photochemical efficiency of PSII (Fv/Fm) and the content of functional PSII (measured by repetitive flash yield of oxygen evolution) were determined in leaves of pea (Pisum sativum L.), grown in 50 (low light), 250 (medium light), and 650 (high light) μmol photons·m−2·s−1. The modulation of PSII functionality in vivo was induced in 1.1% CO2 by varying either (i) the duration (0–2 h) of light treatment (fixed at 1800 μmol photons· m−2·s−1) or (ii) irradiance (0–3200 μmol photons·m−2·s−1) at a fixed duration (1 h), after infiltration of leaves with water (control), lincomycin (an inhibitor of chloroplast-encoded protein synthesis), or a combination of lincomycin with nigericin (an uncoupler), through the cut petioles of leaves of 22-to 24-d-old plants. The reciprocity law of irradiance and duration of illumination for PSII function in vivo (Park et al. 1995, Planta 196: 401–411) holds in all differently light-grown peas, demonstrating that inactivation of functional PSII depends on photon exposure (mol photons·m−2), not on the rate of photon absorption. In vivo, PSII acts as an intrinsic “photon counter” and at higher photon exposures is inactivated following absorption of about 3 × 107 photons. There is a functional heterogeneity of PSII in vivo with 25% less-stable PSIIs that are inactivated at low photon exposure, compared to 75% more-stable PSIIs regardless of modulation of the photosynthetic apparatus. We suggest that the less-stable PSIIs represent monomers located in the nonappressed granal margins, while the more-stable PSIIs are dimers located in the appressed grana membrane cores. The capacity for D1-protein synthesis was the same in all the light-acclimated peas and saturated at low light, indicating that D1-protein repair is also an intrinsic property of PSII. This accounts for the low intensity required for recovery of photoinhibition in sun and shade plants which is independent of light-harvesting antennae size or PSII/PSI stoichiometries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00206257
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  • 6
    Electronic Resource
    Electronic Resource
    An endo-exonuclease activity of yeast that requires a functional RAD52 gene (1988)
    Springer
    Molecular genetics and genomics 211 (1988), S. 41-48 
    Details
    ISSN: 1617-4623
    Keywords: RAD52 ; Repair ; Nuclease ; Antibody ; Yeast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Extracts of Rad+ and radiation-sensitive (rad) mutants of the yeast Saccharomyces cerevisiae were examined for total Mg2+-dependent alkaline deoxyribonuclease activity and the presence of a nuclease that crossreacts immunologically with an antiserum raised against an endoexonuclease from Neurospora crassa, an enzyme exhibiting both deoxyribo- and ribonuclease activities. No significant differences were observed in total deoxyribonuclease activity between Rad+ and rad mutants. The antibody precipitable activity, however, was found to be 30%–40% of the total alkaline deoxyribonuclease activity in logarithmically growing Rad+ cells. Extracts of stationary phase cells were lacking in antibody precipitable activity. Using immunoblot methods, a 72 kDa crossreacting protein was identified from logarithmically growing cells that was absent from stationary phase cells. In all radiation-sensitive mutants examined, except rad52, at least 20% of total activity was precipitable. Extracts from logarithmically growing rad52 mutants, including a rad52::LEU2 insertion mutant, exhibited less than 10% of the Rad+ precipitable activity; however, some crossreacting material was detected. Although, the level of endo-exonuclease activity is influenced by the RAD52 gene, it is not the product of this gene. The total deoxyribonuclease and the antibody precipitable endo-exonuclease activities were also followed during meiosis. Unlike the Rad+ strain which had previously been shown to have increased levels of total and immunoprecipitable endo-exonuclease as cells underwent meiosis, the rad52 mutant exhibited no increases in either category of nuclease activity. Given the importance of the RAD52 gene in repair, recombination and mutagenesis, the endo-exonuclease may be a significant component of these processes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00338391
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