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  • 1
    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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  • 2
    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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  • 3
    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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    Paper (German National Licenses)
    Fulltext
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