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  • 1
    Digitale Medien
    Digitale Medien
    Photoinhibition, xanthophyll cycle and in vivo chlorophyll fluorescence quenching of chilling-tolerant Oxyria digyna and chilling-sensitive Zea mays (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 92 (1994), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The relationship between susceptibility to photoinhibition, zeaxanthin formation and chlorophyll fluorescence quenching at suboptimal temperatures was studied in chilling-sensitive maize and in non-acclimated and cold-acclimated Oxyria digyna, a chilling-tolerant plant of arctic and alpine habitats. In maize, zeaxanthin formation was strongly suppressed by chilling. Zeaxanthin formed during preillumination at 20°C did not protect maize leaves from photoinhibition during a subsequent high-light, low-temperature treatment, as judged from the ratios of variable to maximal fluorescence, Fv/Fm. However, such preillumination significantly increased non-photochemical quenching (qN) at low temperatures, mainly due to an enhancement of the fast-relaxing qN component (i.e., of energy-dependent quenching. qE). In O. digyna, cold-acclimation resulted in an increased zeaxanthin formation in the temperature range of 2.5–20°C. Cold-acclimation substantially decreased the susceptibility towards photoinhibition at 4°C, but qN remained nearly unchanged between 2 and 38°C, as compared to control plants. Effects of cold acclimation on photosynthesis, photochemical quenching and quantum efficiency of photosystem II were small and indicated a slight amelioration only of the function of the photosynthetic apparatus at suboptimal temperatures (2–20°Ct. I) is concluded, that the xanthophyll cycle is strongly influenced by cold acclimation, while effects on the photosynthetic carbon assimilation only play a minor role in O. digyna.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1994.tb03026.x
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  • 2
    Digitale Medien
    Digitale Medien
    Photoinhibition at chilling temperatures and effects of freezing stress on cold acclimated spinach leaves in the field. A fluorescence study (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 79 (1990), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: The role of high light stress in a natural environment was studied on spinach plants (Spinacia oleracea L. cv. Wolter) grown in the field during the winter season. Fluorescence induction (at 293 K and 77 K) of leaves was used to characterize the stress effects. Night frost with minimum temperatures between – 1.5°C and –7.5°C (i.e. above the‘frost killing point’at ca. –11.5°C) led to impaired photosynthesis. This was seen as increased initial fluorescence (Fo), decreased ratio of variable to maximum fluorescence (FV/FM) and lowered rates of O2 evolution. The freezing injury was reversible within several frostless days. Exposure to high light (about 900 mol m–2 s–1) at chilling temperatures in the field caused photoinhibition, manifested as decreased variable fluorescence (FV) and FV/FM ratio without changes in FO. The photoinhibitory fluorescence quenching was not stronger after frost than after frostless nights; synergism between light stress and preceding freezing stress was not observed. Fluorescence induction signals at 77 K showed that FV of photosystems I and II decreased to the same extent, indicating increased thermal deactivation of excited chlorophyll. Photoinhibition was fully reversible at +4°C within 1 h in low light, but only partially in moderate light. Preceding night frosts did not affect the recovery. The photoinhibition observed here is regarded as a protective system of thermal dissipation of excess light energy.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1990.tb00034.x
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  • 3
    Digitale Medien
    Digitale Medien
    Photoinhibition of photosynthesis. An evaluation of damaging and protective mechanisms (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 74 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Biologie
    Notizen: Inhibition of photosynthesis by excess excitation energy is initiated in the reaction center of photosystem II. The primary site of photoinhibition in the reaction center (components of primary charge separation or secondary electron acceptor QB) is still disputed. Photoinhibition is characterized by quenching of variable chlorophyll flurescence (Fv), resulting from increased thermal dissipation of excitation energy. Varying responses of initial fluorescence (F0), however, seem to indicate involvement of different mechanisms. As far as photoinhibition is reversible within minutes to hours, it can be viewed as a controlled protective mechanism that serves to dissipate excessive energy, Supposedly, another dissipative mechanism, distinguished by its faster kinetics (response within seconds), is related to the energy-dependent fluorescence quenching.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb02020.x
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  • 4
    Digitale Medien
    Digitale Medien
    Reversible photoinhibition of unhardened and cold-acclimated spinach leaves at chilling temperatures (1990)
    Springer
    Planta 180 (1990), S. 181-187 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Cold acclimation ; Electron transport ; Fluorescence of chlorophyll ; Photoinhibition ; Photosynthesis ; Spinacia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The photoinhibition of photosynthesis at chilling temperatures was investigated in cold-acclimated and unhardened (acclimated to +18° C) spinach (Spinacia oleracea L.) leaves. In unhardened leaves, reversible photoinhibition caused by exposure to moderate light at +4° C was based on reduced activity of photosystem (PS) II. This is shown by determination of quantum yield and capacity of electron transport in thylakoids isolated subsequent to photoinhibition and recovery treatments. The activity of PSII declined to approximately the same extent as the quantum yield of photosynthesis of photoinhibited leaves whereas PSI activity was only marginally affected. Leaves from plants acclimated to cold either in the field or in a growth chamber (+1° C), were considerably less susceptible to the light treatment. Only relatively high light levels led to photoinhibition, characterized by quenching of variable chlorophyll a fluorescence (FV) and slight inhibition of PSII-driven electron transport. Fluorescence data obtained at 77 K indicated that the photoinhibition of cold-acclimated leaves (like that of the unhardened ones) was related to increased thermal energy dissipation. But in contrast to the unhardened leaves, 77 K fluorescence of cold-acclimated leaves did not reveal a relative increase of PSI excitation. High-light-treated, cold-acclimated leaves showed increased rates of dark respiration and a higher light compensation point. The photoinhibitory fluorescence quenching was fully reversible in low light levels both at +18° C and +4° C; the recovery was much faster than in unhardened leaves. Reversible photoinhibition is discussed as a protective mechanism against excess light based on transformation of PSII reaction centers to fluorescence quenchers.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00193993
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  • 5
    Digitale Medien
    Digitale Medien
    Xanthophyll cycle and energy-dependent fluorescence quenching in leaves from pea plants grown under intermittent light (1994)
    Springer
    Planta 192 (1994), S. 176-182 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chlorophyll a/b-binding protein ; Energy-dependent fluorescence quenching ; Intermittent light ; Photosynthesis ; Pisum ; Xanthophyll cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The possible role of zeaxanthin formation and antenna proteins in energy-dependent chlorophyll fluorescence quenching (qE) has been investigated. Intermittent-light-grown pea (Pisum sativum L.) plants that lack most of the chlorophyll a/b antenna proteins exhibited a significantly reduced qE upon illumination with respect to control plants. On the other hand, the violaxanthin content related to the number of reaction centers and to xanthophyll cycle activity, i.e. the conversion of violaxanthin into zeaxanthin, was found to be increased in the antenna-protein-depleted plants. Western blot analyses indicated that, with the exception of CP 26, the content of all chlorophyll a/b-binding proteins in these plants is reduced to less than 10% of control values. The results indicate that chlorophyll a/b-binding antenna proteins are involved in the energy-dependent fluorescence quenching but that only a part of qE can be attributed to quenching by chlorophyll a/b-binding proteins. It seems very unlikely that xanthophylls are exclusively responsible for the qE mechanism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01089032
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  • 6
    Digitale Medien
    Digitale Medien
    High susceptibility to photoinhibition of young leaves of tropical forest trees (1995)
    Springer
    Planta 197 (1995), S. 583-591 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chlorophyll fluorescence ; Photoinhibition (photosynthesis) ; Photosynthetic gas exchange ; Photo-system II ; Tropical forest species ; Xanthophyll cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Photoinhibition of photosynthesis was studied in young (but almost fully expanded) and mature canopy sun leaves of several tropical forest tree species, both under controlled conditions (exposure of detached leaves to about 1.8 mmol photons·m-2·s-1) and in the field. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll (Chl) fluorescence emission (FV/FM) and also by gas-exchange measurements. For investigations in situ, young and mature leaves with similar exposure to sunlight were compared. The results show a consistently higher degree of photoinhibition in the young leaves. In low light, fast recovery was observed in both types of leaves in situ, as well as in the laboratory. The fluorescence parameter 1 — FS/F′M (where FS = stationary fluorescence and f′M = maximum fluorescence during illumination) was followed in situ during the course of the day in order to test its suitability as a measure of the photosynthetic yield of photosystem II (PSII). Electron-transport rates were calculated from these fluorescence signals and compared with rates of net CO2 assimilation. Measurements of diurnal changes in PSII ‘yield’ confirmed the increased susceptibility of young leaves to photoinhibition. Calculated electron transport qualitatively reflected net CO2 uptake in situ during the course of the day. Photosynthetic pigments were analyzed in darkened and illuminated leaves. Young and mature leaves showed the same Chl a/b ratio, but young leaves contained about 50% less Chl a + b per unit leaf area. The capacity of photosynthetic O2 evolution per unit leaf area was decreased to a similar extent in young leaves. On a Chl basis, young leaves contained more α-carotene, more xanthophyll cycle pigments and, under strong illumination, more zeaxanthin than mature leaves. The high degree of reversible photoinhibition observed in these young sun leaves probably represents a dynamic regulatory process protecting the photosynthetic apparatus from severe damage by excess light.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00191564
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  • 7
    Digitale Medien
    Digitale Medien
    Two mechanisms of recovery from photoinhibition in vivo: Reactivation of photosystem II related and unrelated to D1-protein turnover (1994)
    Springer
    Planta 194 (1994), S. 15-21 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chlorophyll fluorescence ; D1 protein ; Photoinhibition (photosynthesis) ; Photosystem II (recovery) ; Spinacia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Recovery (at 20° C) of spinach (Spinacia oleracea L.) leaf sections from photoinhibition of photosynthesis was monitored by means of the fluorescence parameter FV/FM of intact leaf tissue and of PSII-driven electron-transport activity of isolated thylakoids. Different degrees of photoinactivation of PSII were obtained by preillumination in ambient air (at 4 or 20° C), CO2-free air or at low and high O2 levels (2 or 41 %) in N2. The kinetics of recovery exhibited two distinct phases. The first phase usually was completed within about 20-60 min and was most pronounced after preillumination in low O2. The slow phase proceeded for several hours leading to almost complete reactivation of PSII. Preincubation of the leaves with streptomycin (SM), which inhibits chloroplast-encoded protein synthesis, inhibited the slow recovery phase only, indicating the dependence of this phase on resynthesis of the reaction-centre protein, D1. The fast recovery phase remained largely unaffected by SM. Both phases were strongly but not totally dependent on irradiation of the leaf with low light. When SM was absent, net degradation of the D1 protein could neither be detected upon photoinhibitory irradiation nor during following incubation of the leaf sections in low light or darkness. In the presence of SM, net D1 degradation was seen and tended to increase with O2 concentration during photoinhibition treatment. Based on these data, we suggest that photoinactivation of PSII in vivo occurs in at least two steps. From the first step, reactivation appears possible in low light without D1 turnover (fast recovery phase). Action of oxygen then may lead to a second step, in which the D1 protein is affected and reactivation requires its removal and replacement (slow phase).
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00201029
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  • 8
    Digitale Medien
    Digitale Medien
    Xanthophyll cycle and energy-dependent fluorescence quenching in leaves from pea plants grown under intermittent light (1994)
    Springer
    Planta 192 (1994), S. 176-182 
    Details
    ISSN: 1432-2048
    Schlagwort(e): Chlorophyll a/b-binding protein ; Energy-dependent fluorescence quenching ; Intermittent light ; Photosynthesis ; Pisum ; Xanthophyll cycle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The possible role of zeaxanthin formation and antenna proteins in energy-dependent chlorophyll fluorescence quenching (qE) has been investigated. Intermittent-light-grown pea (Pisum sativum L.) plants that lack most of the chlorophyll a/b antenna proteins exhibited a significantly reduced qE upon illumination with respect to control plants. On the other hand, the violaxanthin content related to the number of reaction centers and to xanthophyll cycle activity, i.e. the conversion of violaxanthin into zeaxanthin, was found to be increased in the antenna-protein-depleted plants. Western blot analyses indicated that, with the exception of CP 26, the content of all chlorophyll a/b-binding proteins in these plants is reduced to less than 10% of control values. The results indicate that chlorophyll a/b-binding antenna proteins are involved in the energy-dependent fluorescence quenching but that only a part of qE can be attributed to quenching by chlorophyll a/b-binding proteins. It seems very unlikely that xanthophylls are exclusively responsible for the qE mechanism.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00194450
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  • 9
    Digitale Medien
    Digitale Medien
    A simple model relating photoinhibitory fluorescence quenching in chloroplasts to a population of altered Photosystem II reaction centers (1991)
    Springer
    Photosynthesis research 30 (1991), S. 115-121 
    Details
    ISSN: 1573-5079
    Schlagwort(e): chlorophyll fluorescence ; electron transport ; photochemical reaction (in Photosystem II) ; photoinhibition of photosynthesis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract A model is presented describing the relationship between chlorophyll fluorescence quenching and photoinhibition of Photosystem (PS) II-dependent electron transport in chloroplasts. The model is based on the hypothesis that excess light creates a population of inhibited PS II units in the thylakoids. Those units are supposed to posses photochemically inactive reaction centers which convert excitation energy to heat and thereby quench variable fluorescence. If predominant photoinhibition of PS IIα and cooperativity in energy transfer between inhibited and active units are presumed, a quasi-linear correlation between PS II activity and the ratio of variable to maximum fluorescence, FVFM, is obtained. However, the simulation does not result in an inherent linearity of the relationship between quantum yield of PS II and FVFM ratio. The model is used to fit experimental data on photoinhibited isolated chloroplasts. Results are discussed in view of current hypotheses of photoinhibition.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00042009
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  • 10
    Digitale Medien
    Digitale Medien
    Chlorophyll fluorescence as a tool in plant physiology (1984)
    Springer
    Photosynthesis research 5 (1984), S. 139-157 
    Details
    ISSN: 1573-5079
    Schlagwort(e): Chlorophyll ; chloroplast ; fluorescence ; energy-distribution ; photochemistry, photosynthesis ; stress
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00028527
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