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  • 1
    Electronic Resource
    Electronic Resource
    Chlorophyll Fluorescence and Photosynthesis: The Basics (1991)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Plant Physiology and Plant Molecular Biology 42 (1991), S. 313-349 
    Details
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pp.42.060191.001525
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  • 2
    Electronic Resource
    Electronic Resource
    Responses of photosystem I compared with photosystem II to high-light stress in tropical shade and sun leaves (2001)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 24 (2001), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Sun and shade leaves of several plant species from a neotropical forest were exposed to excessive light to evaluate the responses of photosystem I in comparison to those of photosystem II. Potential photosystem I activity was determined by means of the maximum P700 absorbance change around 810 nm (ΔA810max) in saturating far-red light. Leaf absorbance changes in dependence of increasing far-red light fluence rates were used to calculate a ‘saturation constant’, Ks, representing the far-red irradiance at which half of the maximal absorbance change (ΔA810max/2) was reached in the steady state. Photosystem II efficiency was assessed by measuring the ratio of variable to maximum chlorophyll fluorescence, Fv/Fm, in dark-adapted leaf samples. Strong illumination caused a high degree of photo-inhibition of photosystem II in all leaves, particularly in shade leaves. Exposure to 1800–2000 μmol photons m−2 s−1 for 75 min did not substantially affect the potential activity of photosystem I in all species tested, but caused a more than 40-fold increase of Ks in shade leaves, and a three-fold increase of Ks in sun leaves. The increase in Ks was reversible during recovery under low light, and the recovery process was much faster in sun than in shade leaves. The novel effect of high-light stress on the light saturation of P700 oxidation described here may represent a complex reversible mechanism within photosystem I that regulates light-energy dissipation and thus protects photosystem I from photo-oxidative damage. Moreover, we show that under high-light stress a high proportion of P700 accumulates in the oxidized state, P700+. Presumably, conversion of excitation energy to heat by this cation radical may efficiently contribute to photoprotection.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.2001.00673.x
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  • 3
    Electronic Resource
    Electronic Resource
    Acclimation of tropical tree seedlings to excessive light in simulated tree-fall gaps (2001)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 24 (2001), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Acclimation to periodic high-light stress was studied in tree seedlings from a neotropical forest. Seedlings of several pioneer and late-succession species were cultivated under simulated tree-fall gap conditions; they were placed under frames covered with shade cloth with apertures of different widths that permitted defined periods of daily leaf exposure to direct sunlight. During direct sun exposure, all plants exhibited a marked reversible decline in potential photosystem II (PSII) efficiency, determined by means of the ratio of variable to maximum Chl a fluorescence (Fv/Fm). The decline in Fv/Fm under full sunlight was much stronger in late-succession than in pioneer species. For each gap size, all species exhibited a similar degree of de-epoxidation of violaxanthin in direct sunlight and similar pool sizes of xanthophyll cycle pigments. Pool sizes increased with increasing gap size. Pioneer plants possessed high levels of β-carotene that also increased with gap size, whereas α-carotene decreased. In contrast to late-succession plants, pioneer plants were capable of adjusting their Chl a/b ratio to a high value in wide gaps. The content of extractable UV-B-absorbing compounds was highest in the plants acclimated to large gaps and did not depend on the successional status of the plants. The results demonstrate a better performance of pioneer species under high-light conditions as compared with late-succession plants, manifested by reduced photoinhibition of PSII in pioneer species. This was not related to increased pool size and turnover of xanthophyll cycle pigments, nor to higher contents of UV-B-absorbing substances. High β-carotene levels and increased Chl a/b ratios, i.e. reduced size of the Chl a and b binding antennae, may contribute to photoprotection in pioneer species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.0016-8025.2001.00786.x
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  • 4
    Electronic Resource
    Electronic Resource
    Relationship between photoinhibition of photosynthesis, D1 protein turnover and chloroplast structure: effects of protein synthesis inhibitors (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 17 (1994), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Irradiation of Spinach oleracea intact leaf tissue and of mesophyll protoplasts of Valerianella locusta at 20° C with strong light resulted in severe (40–80%) inhibition of photosynthesis, measured as photosystem II electron transport activity in isolated thylakoids or as fluorescence parameter FV/FM on intact leaf disks. No net degradation of the D1 protein of photosystem II was seen under these conditions. However, in the presence of streptomycin, an inhibitor of chloroplast protein synthesis, net D1 degradation (up to about 80%) did occur with a half-time of 4–6h, and photoinhibition was enhanced. Thylakoid ultrastructure remained stable during photoinhibition, even when substantial degradation of D1 took place in the presence of streptomycin. When leaf disks were irradiated at 2°C, streptomycin did not influence the degree of photoinhibition, and net Dl degradation did not occur. These results suggest that in excess (photoinhibitory) light at 20°C, turnover (coordinated degradation and synthesis) of D1 diminished the degree of photoinhibition. The observed photoinhibition is thought to be due to the accumulation of inactive photosystem II reaction centres still containing D1. In the presence of streptomycin, the Dl protein was degraded (probably in the previously inactivated centres), but restoration of active centres via D1 synthesis was blocked, leading to more severe photoinhibition. Low temperature (2°C), by restricting both degradation and resynthesis of D1, favoured the accumulation of inactive centres. Streptomycin and chloramphenicol (another inhibitor of chloroplast protein synthesis) were tested for side-effects on photosynthesis. Strong inhibitory effects of chloramphenicol, but much less severe effects of streptomycin were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1994.tb00265.x
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  • 5
    Electronic Resource
    Electronic Resource
    O2-dependent inhibition of photosynthetic capacity in intact isolated chloroplasts and isolated cells from spinach leaves illuminated in the absence of CO2 (1978)
    Springer
    Planta 142 (1978), S. 229-233 
    Details
    ISSN: 1432-2048
    Keywords: Chloroplasts ; Leaf cells ; Photoinhibition ; Photorespiration ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract When isolated intact chloroplasts or cells from spinach (Spinacia oleracea L.) leaves are incubated in the light in the absence of CO2, their capacity for subsequent CO2-dependent photosynthetic oxygen evolution is drastically decreased. This inhibition is light and oxygen-dependent and can be prevented by addition of bicarbonate. It is concluded that the normal dissipation of photosynthetic energy by carbon assimilation and in processes related to photorespiration is an essential condition for the physiological stability of illuminated intact chloroplasts and cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388218
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  • 6
    Electronic Resource
    Electronic Resource
    Simulation of in situ freezing damage of the photosynthetic apparatus by freezing in vitro of thylakoids suspended in complex media (1986)
    Springer
    Planta 168 (1986), S. 67-76 
    Details
    ISSN: 1432-2048
    Keywords: Amino acid (cryoprotective media) ; Chlorophyll fluorescence ; Freezing damage ; Photosynthesis (electron transport, photophos-phorylation) ; Spinacia (freezing damage) ; Thyllakoid, isolated
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Chloroplast thylakoid membranes were isolated from leaves of unhardened and cold-acclimated spinach (Spinacia oleracea L.). For freezethaw treatment, the membranes were suspended in complex media composed to simulate the solute concentrations in the chloroplast stroma in the unhardened and hardened states of the leaves. In particular, high concentrations of amino acids were applied for simulating the hardened state. After frost treatment, photosynthetic activities and chlorophyll fluorescence parameters of the thylakoids were tested to determine the degree of freezing damage. The results revealed a pattern of freezing injury similar to that observed upon frost treatment of thylakoids in situ. A major manifestation of damage was the inhibition of photosynthetic electron transport. Uncoupling of photophosphorylation, which is the dominating effect of freezing of thylakoids suspended in binary solutions (e.g., containing one sugar and one inorganic salt), was also visible but less pronounced in the complex media. Thylakoids obtained from cold-acclimated leaves did not exhibit an increased frost tolerance in vitro, as compared with thylakoids from unhardened plants. The results, furthermore, indicated a strong protective effect of free amino acids at the concentrations and composition found in chloroplasts of hardened leaves. The presence of inorganic salts in the complex media slightly stabilized rather than damaged the membranes during freezing. It is concluded that inactivation of thylakoids in situ may be understood as the destabilizing action of the combined solutes surrounding the thylakoids, occurring when solute concentration is raised due to freezing of water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00407011
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  • 7
    Electronic Resource
    Electronic Resource
    Oxygen dependence of photoinhibition at low temperature in intact protoplasts of Valerianella locusta L. (1991)
    Springer
    Planta 186 (1991), S. 135-142 
    Details
    ISSN: 1432-2048
    Keywords: Cold acclimation ; Photoinhibition of photosynthesis ; Photosystem II ; Protoplast ; Temperature, low ; Valerianella
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Photoinhibition of photosynthesis in vivo is shown to be considerably promoted by O2 under circumstances where energy turnover by photorespiration and photosynthetic carbon metabolism are low. Intact protoplasts of Valerianella locusta L. were photoinhibited by 30 min irradiation with 3000 μmol photons · m−2 · s−1 at 4° C in saturating [CO2] at different oxygen concentrations, corresponding to 2–40% O2 in air. The photoinhibition of light-limited CO2-dependent photosynthetic O2 evolution increased with increasing oxygen concentration. The uncoupled photochemical activity of photosystem II, measured in the presence of the electron acceptor 1,4-benzoquinone, and maximum variable fluorescence, Fv, were strongly affected and this inhibition was closely correlated to the O2 concentration. The effect of O2 did not saturate at the highest concentrations applied. An increase in photoinhibitory fluorescence quenching with [O2], although less pronounced than in protoplasts, was also observed with intact leaves irradiated at 4° C in air. Initial fluorescence, Fo, was slightly (about 10%) increased by the inhibitory treatments but not influenced by [O2]. A long-term cold acclimation of the plants did not substantially alter the O2-sensitivity of the protoplasts under the high-light treatment. From these experiments we conclude that oxygen is involved in the photoinactivation of photosystem II by excess light in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00201509
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  • 8
    Electronic Resource
    Electronic Resource
    Photoinhibition at chilling temperature (1989)
    Springer
    Planta 177 (1989), S. 409-416 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Cold acclimation ; Photoinhibition ; Photosynthesis (inhibition) ; Quantum yield ; Spinacia (cold acclimation)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of moderate light at chilling temperature on the photosynthesis of unhardened (acclimated to +18° C) and hardened (cold-acclimated) spinach (Spinacea oleracea L.) leaves were studied by means of fluorescence-induction measurements at 20° C and 77K and by determination of quantum yield of O2 evolution. Exposure to 550 μmol photons·m-2·s-1 at +4° C induced a strong photoinhibition in the unhardened leaves within a few hours. Photoinhibition manifested by a decline in quantum yield was characterized by an increase in initial fluorescence (F o) and a decrease in variable fluorescence (F v) and in the ratio of variable to maximum fluorescence (F V/F M), both at 77K and 20° C. The decline in quantum yield was more closely related to the decrease in the F V/F M ratio measured at 20° C, as compared with F V/F M at 77K. Quenching of the variable fluorescence of photosystem II was accompanied by a decline in photosystem-I fluorescence at 77K, indicating increased thermal de-excitation of pigments as the main consequence of the light treatment. All these changes detected in fluorescence parameters as well as in the quantum yield of O2 evolution were fully reversible within 1–3 h at a higher temperature in low light. The fast recovery led us to the view that this photoinhibition represents a regulatory mechanism protecting the photosynthetic apparatus from the adverse effects of excess light by increasing thermal energy dissipation. Long-term cold acclimation probably enforces other protective mechanisms, as the hardened leaves were insensitive to the same light treatment that induced strong inhibition of photosynthesis in unhardened leaves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00403600
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  • 9
    Electronic Resource
    Electronic Resource
    Inhibition of photosynthetic reactions by light (1985)
    Springer
    Planta 163 (1985), S. 218-226 
    Details
    ISSN: 1432-2048
    Keywords: Chlorophyll fluorescence ; Chloroplast, isolated ; Photoinhibition ; Photosynthesis (electron transport) ; Spinacia (photoinhibition)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Illumination of isolated intact chloroplasts of Spinacia oleracea L. for 10 min with 850 W m-2 red light in the absence of substrate levels of bicarbonate caused severe inhibition of subsequently measured photosynthetic activities. The capacity of CO2-dependent O2 evolution and of non-cyclic electron transport were impaired to similar degrees. This photoinactivation was prevented by addition of bicarbonate which allowed normal carbon metabolism to proceed during preillumination. Photoinhibition of electron transport was observed likewise upon illumination of intact or broken chloroplasts when efficient electron acceptors were absent. Addition of uncouplers did not influence the extent of inhibition. Studies of partial electron-transport reactions indicated that the activity of both photosystems was affected by light. In addition, the water-oxidation system or its connection to photosystem II seemed to be impaired. Preillumination did not cause uncoupling of photophosphorylation. Chlorophyll-fluorescence data obtained at room temperature and at 77 K are consistent with the view that photosystem-II reaction centers were altered. Addition of superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6) or 1,4-diazabicyclo(2,2,2)octane to isolated thylakoids prior to preillumination substantially diminished photoinhibition. This result shows that reactive oxygen species were involved in the damage. It is concluded that bright light, which normally does not damage the photosynthetic apparatus, may exert the described destructive effects under conditions that restrict metabolic turnover of photosynthetic energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393510
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  • 10
    Electronic Resource
    Electronic Resource
    Relative thermostability of the chloroplast envelope (1975)
    Springer
    Planta 127 (1975), S. 285-299 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Intact isolated chloroplasts from leaves of Spinacia oleracea L. were subjected to heat treatment. After heating, the integrity of the chloroplast envelopes and the activities of various light-dependent chloroplast reactions were tested. The integrity of the chloroplast envelopes, as judged from rates of ferricyanide reduction, enzyme compartmentation and visual appearance of the chloroplasts in the light microscope with phase optics, was affected much less by heat stress than the photochemical reactions of thylakoids. This indicates a comparatively high thermostability of the chloroplast envelope membranes. It is also evidence of a differential thermostability of different biomembranes. Photophosphorylation was highly susceptible to thermal stress. Heat treatment that partly inactivated phosphorylation stimulated light-dependent quenching of 9-aminoacridine fluorescence, which served as an indicator of proton transfer from stroma to thylakoids in intact chloroplasts. Drastic changes in the characteristics of chlorophyll a fluorescence emission caused by heating were probably due to structural alterations of the thylakoid system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00380726
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