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  • 1
    Electronic Resource
    Electronic Resource
    Breakdown of the photosystem II reaction center D1 protein under photoinhibitory conditions: identification and localization of the C-terminal degradation products (1991)
    s.l. : American Chemical Society
    Biochemistry 30 (1991), S. 10220-10226 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00106a021
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  • 2
    Electronic Resource
    Electronic Resource
    Plastid photodamage and Cab gene expression in barley leaves (2000)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 109 (2000), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effects of norflurazon (NF) and amitrole (AM), two bleaching herbicides which inhibit carotenogenesis, were compared in leaves of 7-day-old barley (Hordeum vulgare L. cv Express) plants grown in damaging light. The herbicide effects were analysed with respect to chloroplast organization, photosynthetic functionality and nuclear photodependent expression of the Lhcb1 gene, which codes for the Lhcb1 light-harvesting chlorophyll a/b binding protein of photosystem II. Both herbicides caused dramatic photooxidation of organelles, which were photosynthetically unfunctional. Plastids of NF-treated plants lacked thylakoids and pigments. Plastids of AM-treated plants had some strikingly altered membranes and contained only very small quantities of chlorophylls. Despite the presence of severely photodamaged plastids, cells of AM-treated leaves contained high levels of Lhcb1 transcript. This transcript, on the contrary, was completely absent in the cells of NF-treated plants. These findings suggest that in order to block expression of nuclear genes coding for plastid-resident proteins, photodamage leading to the complete dismantling of thylakoids and to the total absence of any form of photosynthetic pigment is required.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.2000.100108.x
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  • 3
    Electronic Resource
    Electronic Resource
    Early degradation of photosynthetic membranes in carob and sunflower cotyledons (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 96 (1996), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The assimilatory activity of cotyledons can play an essential role in the survival of seedlings with a slow and delayed development of primary leaves. Changes in the photosynthetic activity of the cotyledon, from the onset of greening through senescence, were studied in two such plants, carob and sunflower, in order to determine its efficiency and duration, also in connection with the achievement of assimilatory autonomy by the plantlet. Chlorophyll analyses showed that the cotyledon's chloroplasts reached maximal greening in plantlets with a pair of expanded leaves. In contrast, the cotyledon's photosynthetic activity, measured as the rate of oxygen release, started to decrease early, before expansion of primary leaves. The decrease was due to the inactivation of a number of photosystem II (PSII) units, as revealed by immunodetection of breackdown products of the reaction centre's D1 and D2 thylakoid proteins. No signals of PSII alteration were noticed in the primary leaf chloroplasts that differentiated under the same environmental conditions. The damage to the cotyledon PSII, occurring in a non-photoinhibitory situation, might be due to a slower rate of turnover of D1 polypeptide than in the leaf thylakoids. The differential turnover of this protein in cotyledons and in leaves might represent an organ-specific regulation of the photosynthetic activity. The peculiarity of the cotyledon thylakoids make these organs useful objects for studying the metabolic cycle of both D1 and D2 proteins in vivo, under non-photoinhibiting conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1996.tb00466.x
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  • 4
    Electronic Resource
    Electronic Resource
    Role of phosphorylation in the repair cycle and oligomeric structure of photosystem II (1999)
    Springer
    Planta 208 (1999), S. 196-204 
    Details
    ISSN: 1432-2048
    Keywords: Key words: D1 protein ; PSII Phosphorylation ; PSII Repair cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The role of PSII protein phosphorylation in the oligomeric structure of the complex and in the repair of photodamaged PSII centers was studied with intact thylakoids and thylakoid membrane subfractions isolated from differentially light-treated pumpkin (Cucurbita pepo L.) leaves. A combination of sucrose gradient fractionation of thylakoid protein complexes and immunodetection with phosphothreonine and protein-specific antibodies was used. We report in this study that the extent of phosphorylation of PSII core proteins is equivalent in dimers and monomers, and directly depends on light intensity. Phosphorylated PSII monomers migrate to the stroma-exposed thylakoids, probably following damage of the D1 protein and the dissociation of the light-harvesting complex of PSII. Once in the stroma lamellae, monomers are gradually dephosphorylated to allow the reparation of the complex. First, CP43 is dephosphorylated and as a consequence of this modification it detaches from the PSII core. In addition to D1, D2 is also thereafter dephosphorylated. Phosphorylation of PSII core polypeptides probably ensures the integrity of the monomers until repair can proceed. Dephosphorylation, on the other hand, might serve the need for opening the complex and coordinating D1 proteolysis and the attachment of ribosomes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050550
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  • 5
    Electronic Resource
    Electronic Resource
    Inactivation of photosynthetic oxygen evolution by UV-B irradiation: A thermoluminescence study (1993)
    Springer
    Photosynthesis research 38 (1993), S. 455-462 
    Details
    ISSN: 1573-5079
    Keywords: oxygen evolution ; photodamage ; Photosystem II ; thermoluminescence ; UV-B radiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The influence of UV-B irradiation on photosynthetic oxygen evolution by isolated spinach thylakoids has been investigated using thermoluminescence measurements. The thermoluminescence bands arising from the S2QB - (B band) and S2QA − (Q band) charge recombination disappeared with increasing UV-B irradiation time. In contrast, the C band at 50°C, arising from the recombination of QA - with an accessory donor of Photosystem II, was transiently enhanced by the UV-B irradiation. The efficiency of DCMU to block QA to QB electron transfer decreased after irradiation as detected by the incomplete suppression of the B band by DCMU. The flash-induced oscillatory pattern of the B band was modified in the UV-B irradiated samples, indicating a decrease in the number of centers with reduced QB. Based on the results of this study, UV-B irradiation is suggested to damage both the donor and acceptor sides of Photosystem II. The damage of the water-oxidizing complex does not affect a specific S-state transition. Instead, charge stabilization is enhanced on an accessory donor. The acceptor-side modifications decrease the affinity of DCMU binding. This effect is assumed to reflect a structural change in the QB/DCMU binding site. The preferential loss of dark stable QB - may be related to the same structural change or could be caused by the specific destruction of reduced quinones by the UV-B light.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00046774
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  • 6
    Electronic Resource
    Electronic Resource
    Cab gene expression in bleached leaves of carotenoid-deficient maize (2000)
    Springer
    Photosynthesis research 64 (2000), S. 119-126 
    Details
    ISSN: 1573-5079
    Keywords: amitrole ; bleaching herbicides ; Cab gene expression ; carotenoid-deficient mutants ; chloroplast photodamage ; norflurazon ; ultrastructure ; Zea mays L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The chloroplast photo-oxidation and the expression of the Cab gene Lhcb1, encoding the Lhcb1 light-harvesting chlorophyll a/b-protein of PS II, have been studied in leaf cells of maize treated with the two bleaching herbicides norflurazon and amitrole and of the two carotenoid-free mutants vp9 and vp2 grown under high photodamaging light. Both herbicides and mutations caused severe photo-oxidation of organelles. However, the plastids of norflurazon-treated and vp2 leaves were totally devoid of thylakoids and did not contain any chlorophyll, while the organelles of amitrole-treated and vp9 leaves still had a few altered and photosynthetically unfunctional membranes and very small quantities of chlorophylls. Despite the dramatic photodamage undergone by the plastids over several days, the cells of amitrole-treated and vp9 leaves maintained a certain expression of the Lhcb1 gene which, on the contrary, was completely blocked in the cells of norflurazon-treated and vp2 leaves. The experimental results, obtained by integrating biochemical and molecular analyses with ultrastructural observations, show that the maintainance of Cab gene expression does not strictly depend on intact and functional chloroplasts. The transcription of these genes, still maintained in cells with greatly photo-oxidized organelles, seems to be inversely related to the degree of thylakoid demolition, which can affect the last steps of chlorophyll biosynthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1006477215572
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