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  • 1
    Electronic Resource
    Electronic Resource
    The effects of development at sub-optimal growth temperatures on photosynthetic capacity and susceptibility to chilling-dependent photoinhibition in Zea mays (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 85 (1992), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: When plants of Zea mays L. cv. LG11 that have been grown at optimal temperatures are transferred to chilling temperatures (0–12°C) photoinhibition of photosynthetic CO2 assimilation can occur. This study examines how growth at sub-optimal temperatures alters both photosynthetic capacity and resistance to chilling-dependent photoinhibition. Plants of Z. mays cv. LG11 were grown in controlled environments at 14, 17, 20 and 25°C. As a measure of the capacity for photosynthesis under light limiting conditions, the maximum quantum yields of CO2 assimilation (φa.c) and O2 evolution (φa.o) were determined for the laminae of the second leaves at photon fluxes of 50–150 μmol m-2s-1. To determine photosynthetic capacity at photon fluxes approaching light saturation, rates of CO2 uptake (A1500) and O2 evolution (A1500) were determined in a photon flux of 1500 μmol m-2s-1. In leaves developed at 14°C, φ and φ were 26 and 43%, respectively, of the values for leaves grown at 25°C. Leaves grown at 17°C showed intermediate reductions in φ and φ, whilst leaves developed at 20°C showed no significant differences from those grown at 25°C. Similar patterns of decrease were observed for A1500 and A1500.0 with decreasing growth temperature. Leaves developed at 25°C showed higher rates of CO2 assimilation at all light levels and measurement temperatures in comparison to leaves developed at 17 and 14°C. A greater reduction in A1500 relative to A1500.0 with decreasing growth temperature was attributed to increased stomatal limitation. Exposure of leaves to 800–1000 μmol m-2 s-1 when plant temperature was depressed to ca 6.5°C produced a photoinhibition of photosynthetic CO2 assimilation in all leaves. However, in leaves developed at 17°C the decrease in A1500 following this chilling treatment was only 25% compared to 90% in leaves developed at 25°C. Recovery following chilling was completed earlier in leaves developed at 17°C. The results suggest that growth at sub-optimal temperatures induces increased tolerance to exposure to high light at chilling temperatures. This is offset by the large loss in photosynthetic capacity imposed by leaf development at sub-optimal temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1992.tb05826.x
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  • 2
    Electronic Resource
    Electronic Resource
    Is photoinhibition of zooxanthellae photosynthesis the primary cause of thermal bleaching in corals? (2005)
    Oxford, UK : Blackwell Science Ltd
    Global change biology 11 (2005), S. 0 
    Details
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: The bleaching of corals in response to increases in temperature has resulted in significant coral reef degradation in many tropical marine ecosystems. This bleaching has frequently been attributed to photoinhibition of photosynthetic electron transport and the consequent photodamage to photosystem II (PSII) and the production of damaging reactive oxygen species (ROS) in the zooxanthellae (Symbiodinium spp.). However, these events may be because of perturbations of other processes occurring within the zooxanthellae or the host cells, and consequently constitute only secondary responses to temperature increase. The processes involved with the onset of photoinhibition of electron transport, photodamage to PSII and pigment bleaching in coral zooxanthellae are reviewed. Consideration is given to how increases in temperature might lead to perturbations of metabolic processes in the zooxanthellae and/or their host cells, which could trigger events leading to bleaching. It is concluded that production of ROS by the thylakoid photosynthetic apparatus in the zooxanthellae plays a major role in the onset of bleaching resulting from photoinhibition of photosynthesis, although it is not clear which particular ROS are involved. It is suggested that hydrogen peroxide generated in the zooxanthellae may have a signalling role in triggering the mechanisms that result in expulsion of zooxanthellae from corals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1529-8817.2003.00895.x
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  • 3
    Electronic Resource
    Electronic Resource
    Appearance of a State 1 – State 2 transition during chloroplast development in the wheat leaf: Energetic and structural considerations (1984)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 60 (1984), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The ability of developing chloroplasts to dynamically regulate the distribution of excitation energy between photosystem 1 and photosystem 2, and thus perform a State 1 – State 2 transition, was examined from analyses of chlorophyll fluorescence kinetics in 4- and 8-day-old Triticum aestivum L. cv. Maris Dove leaves grown under a diurnal light regime. Chloroplasts at all stages of development in the two leaf systems could undergo a State 1 – State 2 transition, except those found in the basal 0.5 cm of the 4-day-old leaf. The ability to physiologically modify the excitation energy distribution between the chlorophyll matrices of the two photosystems developed after the development of mature, fully photochemically competent photosystem 2 units and the appearance of excitation energy transfer between photosystem 2 and photosystem 1. Also, changes in the degree of energetic interaction between the two photosystems, in vivo rates of electron transport and the chlorophyll a/b ratio could not be correlated with the appearance of a State 1 – State 2 transition. Ultrastructural studies demonstrated a 32% increase in the degree of thylakoid appression in chloroplasts at the base of the 8-day-old leaf compared to the situation in the basal 0.5 cm of the 4-day-old leaf. This difference in thylakoid stacking can account for the differing abilities of these two tissues to perform a State 1 – State 2 transition when considered in the context of the distribution of the two photosystems within appressed and non-appressed regions of thylakoid membranes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1984.tb04560.x
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  • 4
    Electronic Resource
    Electronic Resource
    Photoinhibition of holly (Ilex aquifolium) in the field during the winter (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 83 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The distribution of holly (Ilex aquifolium) and its habitat preferences indicate a sensitivity to low temperature, particularly when exposed to high light. Experiments were conducted to determine whether photoinhibition of photosynthesis occurs in holly leaves in the field in United Kingdom during the winter. Photosynthetic efficiency was assessed in holly leaves that were exposed to or shaded from direct sunlight using measurements of photosynthetic oxygen evolution and chlorophyll fluorescence. Field measurements were conducted over 3 weeks during January and February. Correlation of the measurements of photosynthetic efficiency with weather conditions indicated that holly was suffering photoinhibition, particularly in leaves exposed to direct sunlight. Controlled environment studies demonstrated that exposure of leaves to low temperature and high light resulted in reductions in photosynthetic efficiency; however, leaves recovered rapidly when exposed to a higher temperature and reduced light level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb02472.x
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  • 5
    Electronic Resource
    Electronic Resource
    A possible role for photosystem II in environmental perturbations of photosynthesis (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 81 (1991), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Photosystem II plays an especially important role in the response of photosynthesis in higher plants to environmental perturbations and stresses. The relationship between photosystem II and photosynthetic CO2 assimilation is examined and factors identified that may modulate photosystem II activity in vivo. Particular attention is given to non-photochemical quenching of excitation energy, photoinhibition, state transitions, protein phosphorylation and biogenesis of photosystem II.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1991.tb05101.x
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  • 6
    Electronic Resource
    Electronic Resource
    Light-dependent, chilling effects on phosphorylation of thylakoid proteins and consequences for associated photochemical activities in maize (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 77 (1989), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: When maize (Zea mays L. cv. LG11) leaves are exposed to low temperatures and high light modifications to both photosystem 2 (PS2) and the light-harvesting chlorophyll a/b protein complex associated with photosystem 2 (LHC2) occur. This study examines the consequences of these modifications for phosphorylation of LHC2 and PS2 polypeptides and the associated changes in electron transport. Maize leaves were chilled at 5°C for 6 h under photon flux densities of 1 500 and 250 μmol m-2 s-1. Thylakoids were then isolated from the leaves and their abilities to phosphorylate LHC2 and PS2 polypeptides and modify electron transport activities were determined. Measurements of chlorophyll fluorescence induction in the thylakoids were also made. Thylakoids isolated from leaves chilled under high light and from leaves kept in the ambient growth environment had similar phosphoprotein profiles. However, polypeptide phosphorylation in thylakoids from the chilled leaves did not produce a decrease in PS2 electron transport. Chilling leaves under low light produced a decrease in the ability of isolated thylakoids to phosphorylate PS2, but not LHC2, polypeptides, which was not associated with any change in the phosphorylation-induced decrease in PS2 electron transport. Chilling under high, but not low, light appears to produce changes in membrane organisation that do not affect the ability of the thylakoids to phosphorylate PS2 and LHC2 polypeptides, but which do prevent the phosphorylation-induced decrease in excitation energy transfer from LHC2 to PS2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1989.tb05663.x
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  • 7
    Electronic Resource
    Electronic Resource
    Time-dependent changes in the in vitro effects of sodium chloride on photosynthetic electron transport of isolated chloroplasts (1983)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 57 (1983), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of a wide concentration range of NaCl and sorbitol on three photosynthetic electron transport reactions of Pisum sativum L. cv. Feltham First chloroplasts were examined as a function of time from thylakoid membrane isolation. Rates of electron flow from water to diaminodurene (DAD) and ferricyanide were determined polarographically, whilst photoreduction of 2,6-dichlorophenolindophenol (DCPIP) was monitored spectrophotometrically. Assay of thylakoids immediately after isolation showed that the rate of photoreduction of all three electron acceptors decreased with increasing salt concentration. However, 100 min after leaf homogenisation the response pattern of ferricyanide and DCPIP photoreduction to increasing NaCl, but not increasing sorbitol concentration, became significantly modified. This was not the case for DAD photoreduction. The results are discussed in relation to the assessment of the possible effect of salinity on photosynthetic electron transport in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1983.tb00748.x
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  • 8
    Electronic Resource
    Electronic Resource
    Light-dependent inhibition of photosynthetic electron transport by zinc (1982)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 56 (1982), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of zinc concentrations up to 400 μM were examined on three photosynthetic electron transport reactions of thylakoids isolated from Pisum sativum L. cv. Meteor. Zinc (400 μM) had no effect on photosystem I mediated electron transport from reduced N,N,N′,N′-tetramethyl-p-phenylenediamine to methyl viologen, but inhibited uncoupled electron flow from water to methyl viologen by ca 50% and to 2,6-dichlorophenol-indophenol (DCPIP) by ca 30% at saturating light levels. Zinc inhibition of DCPIP photoreduction was independent of the light intensity to which thylakoids were exposed. Decreasing the photon flux density below 400 μmol m−2 s−1 produced a logarithmic reduction in the zinc-induced inhibition of methyl viologen photoceduction; a stimulation of this reaction was observed below 80 μmol photons m−2 s−1. Increasing light intensity decreased the amount of zinc tightly bound to the thylakoid membranes, but increased the weakly associated zinc which could be removed by washing the membranes with buffer containing Mg2. The results suggest that zinc acts on the photosynthetic electron transport system at two sites. Site 1 is on the oxidizing side of photosystem 2 and the inhibition by zinc is independent of the light intensity. Site 2 is between photosystems 1 and 2 and the electron flow can be positively or negatively affected by zinc depending on the light intensity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1982.tb00328.x
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  • 9
    Electronic Resource
    Electronic Resource
    Salt induced responses of chloroplast activities in species of differing salt tolerance. Photosynthetic electron transport in Aster tripolium and Pisum sativum (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 51 (1981), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: A comparative study was made of the effects of high concentrations of NaCl, KCl and MgCl2 on two electron transport reactions of thylakoids isolated from a mesophyte, Pisum sativum and a halophyte, Aster tripolium. The rate of photosystem I mediated electron transport from reduced N, N, N′, N′-tetramethyl-p-phenylenediamine (TMPD) to methyl viologen was determined polarographically, and photosystem II mediated electron flow from water to 2,6-dichlorophenolindophenol (DCPIP) was monitored spectrophotometrically. The response of photosystem II to increasing in vitro salt concentrations was similar for thylakoids isolated from both A. tripolium and P. sativum, but differences in the response of photosystem I to salinity changes were observed for the two species. Increasing NaCl, KCl and MgCl2 concentrations produced similar patterns of response of photosystem I activity in P. sativum thylakoids, whilst for A. tripolium KCl induced a completely different response pattern compared to NaCl and MgCl2. The salinity of the culture medium in which A. tripolium was grown also had an effect on both the absolute in vitro activities of photosystems I and II and their response to changes in salt concentration of the reaction media.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1981.tb05574.x
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  • 10
    Electronic Resource
    Electronic Resource
    Analysis of immunization with DNA encoding Pseudomonas aeruginosa exotoxin A (2000)
    Oxford, UK : Blackwell Publishing Ltd
    FEMS immunology and medical microbiology 27 (2000), S. 0 
    Details
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The promising arena of DNA-based vaccines has led us to investigate possible candidates for immunization against bacterial pathogens. One such target is the opportunistic pathogen Pseudomonas aeruginosa which produces exotoxin A (PE), a well-characterized virulence factor encoded by the toxA gene. In its native protein form, PE is highly cytotoxic for susceptible eukaryotic cells through ADP-ribosylation of elongation factor-2 following internalization and processing of the toxin. To study the biologic and immunological effects of PE following in situ expression, we have constructed eukaryotic plasmid expression vectors containing either the wild-type or a mutated, non-cytotoxic toxA gene. In vitro analysis by transfection of UM449 cells suggests that expression of the wild-type toxA gene is lethal for transfected cells whereas transfection with a mutated toxA gene results in the production of inactive PE which can be readily detected by immunoblot analysis of cell lysates. To investigate the effects resulting from the intracellular expression of potentially cytotoxic gene products in DNA vaccine constructs, we immunized mice with both the wild-type and mutant toxA plasmid constructs and analyzed the resulting humoral and cellular immune responses. Immunization with the mutated toxA gene results in production of neutralizing antibodies against native PE and potentiates a TH1-type response, whereas only a minimal humoral response can be detected in mice immunized with wild-type toxA. DNA-based vaccination with the non-cytotoxic toxAmut gene confers complete protection against challenge with the wild-type PE. Therefore, genetic immunization with genes encoding potentially cytotoxic gene products raises concern with regard to the selection of feasible gene targets for DNA vaccine development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1574-695X.2000.tb01425.x
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