Showing papers on "Photoinhibition published in 1992"
TL;DR: The plant survives this photoinhibition through an efficient repair system which involves an autoproteolytic activity of the photosystem II complex, D1-polypeptide synthesis and reassembly of active complexes.
987 citations
TL;DR: In this paper, a measure of the quantum yield of photosystem II, ΦII (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system.
Abstract: There is now potential to estimate photosystem II (PSII) activity in vivo from chlorophyll fluorescence measurements and thus gauge PSII activity per CO2 fixed. A measure of the quantum yield of photosystem II, ΦII (electron/photon absorbed by PSII), can be obtained in leaves under steady-state conditions in the light using a modulated fluorescence system. The rate of electron transport from PSII equals ΦII times incident light intensity times the fraction of incident light absorbed by PSII. In C4 plants, there is a linear relationship between PSII activity and CO2 fixation, since there are no other major sinks for electrons; thus measurements of quantum yield of PSII may be used to estimate rates of photosynthesis in C4 species. In C3 plants, both CO2 fixation and photorespiration are major sinks for electrons from PSII (a minimum of 4 electrons are required per CO2, or per O2 reacting with RuBP). The rates of PSII activity associated with photosynthesis in C3 plants, based on estimates of the rates of carboxylation (vo) and oxygenation (vo) at various levels of CO2 and O2, largely account for the PSII activity determined from fluorescence measurements. Thus, in C3 plants, the partitioning of electron flow between photosynthesis and photorespiration can be evaluated from analysis of fluorescence and CO2 fixation.
652 citations
TL;DR: The results are integrated into a model for the photoinhibitory process involving initial loss of bound QB followed by stable reduction and subsequent loss of QA facilitating chlorophyll P680 triplet formation, which mediates light-induced formation of highly reactive and damaging singlet oxygen.
Abstract: Photoinhibition of photosynthesis was studied in isolated photosystem II membranes by using chlorophyll fluorescence and electron paramagnetic resonance (EPR) spectroscopy combined with protein analysis. Under anaerobic conditions four sequentially intermediate steps in the photoinhibitory process were identified and characterized. These intermediates show high dark chlorophyll fluorescence (Foi) with typical decay kinetics (fast, semistable, stable, and nondecaying). The fast-decaying state has no bound QB but possesses a single reduced QA species with a 30-s decay half-time in the dark (QB, second quinone acceptor; QA, first quinone acceptor). In the semistable state, Q-A is stabilized for 2-3 min, most likely by protonation, and gives rise to the Q-A Fe2+ EPR signal in the dark. In the stable state, QA has become double reduced and is stabilized for 0.5-2 hr by protonation and a protein conformational change. The final, nondecaying state is likely to represent centers where QA H2 has left its binding site. The first three photoinhibitory states are reversible in the dark through reestablishment of QA to QB electron transfer. Significantly, illumination at 4 K of anaerobically photoinhibited centers trapped in all but the fast state gives rise to a spinpolarized triplet EPR signal from chlorophyll P680 (primary electron donor). When oxygen is introduced during anaerobic illumination, the light-inducible chlorophyll triplet is lost concomitant with induction of D1 protein degradation. The results are integrated into a model for the photoinhibitory process involving initial loss of bound QB followed by stable reduction and subsequent loss of QA facilitating chlorophyll P680 triplet formation. This in turn mediates light-induced formation of highly reactive and damaging singlet oxygen.
490 citations
01 Jan 1992
377 citations
TL;DR: The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid ΔpH gradient.
Abstract: The obligate shade plant, Tradescantia albiflora Kunth grown at 50 μmol photons · m(-2) s(-1) and Pisum sativum L. acclimated to two photon fluence rates, 50 and 300 μmol · m(-2) · s(-1), were exposed to photoinhibitory light conditions of 1700 μmol · m(-2) · s(-1) for 4 h at 22° C. Photosynthesis was assayed by measurement of CO2-saturated O2 evolution, and photosystem II (PSII) was assayed using modulated chlorophyll fluorescence and flash-yield determinations of functional reaction centres. Tradescantia was most sensitive to photoinhibition, while pea grown at 300 μmol · m(-2) · s(-1) was most resistant, with pea grown at 50 μmol · m(-2) · s(-1) showing an intermediate sensitivity. A very good correlation was found between the decrease of functional PSII reaction centres and both the inhibition of photosynthesis and PSII photochemistry. Photoinhibition caused a decline in the maximum quantum yield for PSII electron transport as determined by the product of photochemical quenching (qp) and the yield of open PSII reaction centres as given by the steady-state fluorescence ratio, F'vF'm, according to Genty et al. (1989, Biochim. Biophys. Acta 990, 81-92). The decrease in the quantum yield for PSII electron transport was fully accounted for by a decrease in F'vF'm, since qp at a given photon fluence rate was similar for photoinhibited and noninhibited plants. Under lightsaturating conditions, the quantum yield of PSII electron transport was similar in photoinhibited and noninhibited plants. The data give support for the view that photoinhibition of the reaction centres of PSII represents a stable, long-term, down-regulation of photochemistry, which occurs in plants under sustained high-light conditions, and replaces part of the regulation usually exerted by the transthylakoid ΔpH gradient. Furthermore, by investigating the susceptibility of differently lightacclimated sun and shade species to photoinhibition in relation to qp, i.e. the fraction of open-to-closed PSII reaction centres, we also show that irrespective of light acclimation, plants become susceptible to photoinhibition when the majority of their PSII reaction centres are still open (i.e. primary quinone acceptor oxidized). Photoinhibition appears to be an unavoidable consequence of PSII function when light causes sustained closure of more than 40% of PSII reaction centres.
366 citations
TL;DR: The results demonstrate the existence of a marked antagonism between physicochemical stresses, with water stress enhancing the resistance of photosystem II to constraints (heat, strong light at high temperature) that are usually associated with drought in the field.
Abstract: The in vivo photochemical activity of photosystem II was inferred from modulated chlorophyll fluorescence and photoacoustic measurements in intact leaves of several plant species (Lycopersicon esculentum Mill., Solanum tuberosum L., Solanum nigrum L.) exposed to various environmental stresses (drought, heat, strong light) applied separately or in combination. Photosystem II was shown to be highly drought-resistant: even a drastic desiccation in air of detached leaf samples only marginally affected the quantum yield for photochemistry in photosystem II. However, water stress markedly modified the responses of photosystem II to superimposed constraints. The stability of photosystem II to heat was observed to increase strongly in leaves exposed to water stress conditions: heat treatments (e.g. 42°C in the dark), which caused a complete and irreversible inhibition of photosystem II in well-watered (tomato) leaves, resulted in a small and fully reversible reduction of the photochemical efficiency of photosystem II in drought-stressed leaves. In vivo photoacoustic data indicated that photosystem I was highly resistant to both heat and water stresses. When leaves were illuminated with intense white light at 25°C, photoinhibition damage of photosystem II was more pronounced in water-stressed leaves than in undesiccated controls. However, in nondehydrated leaves, photoinhibition of photosystem II was strongly temperature dependent, being drastically stimulated at high temperatures above 38 to 40°C. As a consequence, when exposed to strong light at high temperature, photosystem II photochemistry was significantly less inhibited in dehydrated leaves than in control well-hydrated leaves. Our results demonstrate the existence of a marked antagonism between physicochemical stresses, with water stress enhancing the resistance of photosystem II to constraints (heat, strong light at high temperature) that are usually associated with drought in the field.
364 citations
Book•
01 Jan 1992
TL;DR: Porter and Porter as discussed by the authors presented an overview of plant and bacterial photosystems in their book "An Introduction to Plant and Bacterial Photosystems" (Volume 11, 2011).
Abstract: Foreword to Volume 11 by Lord Porter, OM, FRS. Preface by J. Barber. List of Contributors. Obituaries: R. Hill by F.R. Whatley. M. Avron by A. Jagendorf and Z. Gromet-Elhanan. D. DeVault by M. Seibert. Chapters 1. An Introduction to Plant and Bacterial Photosystems (R. Cogdell and R. Malkin). 2. Thermodynamics of Light Energy Conversion (L.N. Bell and N.D. Gudkov). 3. Energy Transfer and Trapping in Photosystem II (G. Renger). 4. The Molecular Biology of Photosystem II (J.M. Erickson and J-D. Rochaix). 5. Oxygen Evolution (A.W. Rutherford, J-L. Zimmermann and A. Boussac). 6. Protein Engineering of Photosystem II (H.B. Pakrasi and W.F.J. Vermaas). 7. Thermoluminescence in the Study of Photosystem II (I. Vass and Y. Inoue). 8. Dynamics of Photosystem II: Mechanism of Photoinhibition and Recovery Processes (O. Prasil, N. Adir and I. Ohad). 9. Herbicides of Photosystem II (W. Oettmeier). 10. Heat Shock Proteins in Plants: An Approach to Understanding the Function of Plastid Heat Shock Proteins (E. Kruse and K. Kloppstech). 11. Photosystem I: Composition, Organization and Structure (O. Almog, G. Shoham and R. Nechushtai). 12. Energy Transfer and Trapping in Photosystem I (P. Setif). 13. Molecular Biology of Photosystem I (Donald A. Bryant). Subject Index.
323 citations
TL;DR: Observations provide strong evidence for the proposed protective role of scytonemin, as a passive UV‐A sunscreen, in cyanobacteria.
Abstract: The proposed photoprotective role of the UV-A absorbing, extracellular pigment scytonemin was studied in the terrestrial cyanobacterium Chlorogloeopsis sp. strain O-89-Cgs(1). UV-A (315-400 nm) caused growth delay, cell growth restarting only when scytonemin had accumulated in the extracellular envelopes. Cultures with scytonemin were more resistant to photoinhibition of photosynthesis than cultures without scytonemin, the differential resistance being much greater to UV-A-caused photoinhibition than to photoinhibition caused by visible light. The presence of scytonemin in the extracellular envelopes was correlated with the inability of UV-A radiation to induce strong photopigment fluorescence (685 nm emission), regardless of the specific content os photosynthetic pigments. The physical removal of the scytonemin containing extracellular envelopes brought about the loss of UV-A resistance as measured by photobleaching rates of chlorophyll a under conditions of physiological inactivity (desiccation). These observations provide strong evidence for the proposed protective role of scytonemin, as a passive UV-A sunscreen, in cyanobacteria.
321 citations
TL;DR: Coupled cyclic electron transport is assigned a role in the protection of leaves against photoinhibition in addition to its role in ATP synthesis and avoidance of overreduction of the electron transport chain is a prerequisite for the efficient protection of the photosynthetic apparatus against photo inactivation.
Abstract: Coupled cyclic electron transport is assigned a role in the protection of leaves against photoinhibition in addition to its role in ATP synthesis. In leaves, as in reconstituted thylakoid systems, cyclic electron transport requires “poising,” i.e. availability of electrons at the reducing side of photosystem I (PSI) and the presence of some oxidized plastoquinone between photosystem II (PSII) and PSI. Under self-regulatory poising conditions that are established when carbon dioxide limits photosynthesis at high light intensities, and particularly when stomata are partially or fully closed as a result of water stress, coupled cyclic electron transport controls linear electron transport by helping to establish a proton gradient large enough to decrease PSII activity and electron flow to PSI. This brings electron donation by PSII, and electron consumption by available electron acceptors, into a balance in which PSI becomes more oxidized than it is during fast carbon assimilation. Avoidance of overreduction of the electron transport chain is a prerequisite for the efficient protection of the photosynthetic apparatus against photoinactivation.
294 citations
TL;DR: The aim of this article is to review the current state of knowledge of oxygenic photosynthesis and its related processes, and to suggest regulatory mechanisms that are designed to protect Photosystem II from photoinhibition.
Abstract: The establishment of the redox nature of oxygenic photosynthesis, in which Robin Hill's demonstration of the 'Hill reaction' played such an important role, was one of the major advances in biology this century. His subsequent delineation of the 'Z' scheme had implications, the full extent of which are only beginning to be explored some 25 years later. One such implication is the requirement for regulation of the photosystems; not only does the Z scheme require that excitation of each photosystem has to be balanced for optimal quantum efficiency, but there has to be flexibility to accommodate changes in the light environment and in the metabolic requirement for the reducing power and the protonmotive force that are its direct products (Horton 1985). Moreover, the implied stoichiometric relationship between reaction centre contents and electron transfer components means that reaction centres have to be served by large lightharvesting systems if photosynthesis is to occur at a rate sufficient for autotrophic growth. These light-harvesting structures need to contain pigments organised in such a way as to promote efficient energy transfer to the reaction centre. The advantage this confers in limiting light is shown by the increase in ratio of light-harvesting pigments per reaction centre when plants (or in fact any photosynthetic organism) are grown in shade. The result of such adaptation is, however, that photosynthesis is saturated at relatively low light intensity. As a consequence, at high light intensity, the rate of absorption exceeds to a greater or lesser extent the rate at which it can be used photosynthetically. Under such conditions the photosynthetic system will be predisposed to light-induced damage, or photoinhibition (Osmond 1981). In oxygenic photosynthesis, it is clear that Photosystem II is the more susceptible to photoinhibition-this can be attributed to the facts that trap closure in PS II is associated with an increase in exciton density in the PS II antenna, the possibility of reactive radical species forming at the QB binding site (Kyle et al. 1985) and the highly oxidising P680 + which will be formed with higher frequency as irradiance increases (Cleland 1988). Photoinhibition has been associated with damage to the antenna and the reaction centre of PS 1I (Bradbury and Baker 1986). It would be expected, therefore, that there would exist regulatory mechanisms that are designed to protect Photosystem II from photoinhibition. The aim of this article is to review the current state of knowledge of such processes.
247 citations
TL;DR: Diurnal course of A of well-watered trees exhibited sometimes important midday decreases in A related to high temperature and vapour pressure deficit, which may be considered as protective mechanisms adjusting activity of photosystem II to the electron requirement for photosynthesis.
Abstract: Adult trees of Quercus petraea were submitted to controlled water shortage in a natural stand near Nancy, France. Diurnal course of net CO2 assimilation rate (A) was measured in situ together with chlorophyll a fluorescence determined on dark adapted leaves. In 1990, trees experienced a strong water stress, with predawn and midday leaf water potentials below –2·0 and –3·0 MPa, respectively. Diurnal course of A of well-watered trees exhibited sometimes important midday decreases in A related to high temperature and vapour pressure deficit. Decreases in initial (Fo) and maximal (Fm) fluorescence and sometimes in photochemical efficiency of photosystem II (Fv/Fm) were observed and probably revealed the onset of mechanisms for thermal de-excitation. These mechanisms were shown to be sensitive to dithiothreitol. All these effects were reversible and vanished almost completely overnight. Therefore, they may be considered as protective mechanisms adjusting activity of photosystem II to the electron requirement for photosynthesis. Water stress amplified these reactions: A was strongly decreased, showing important midday depression; diurnal reductions in Fm and Fv/Fm were enhanced. The same trends were observed during summer 1991, despite a less marked drought. These protective mechanisms seemed very effective, as no photoinhibitory damage to PS II could be detected in either water stressed or control trees.
TL;DR: The effective low-temperature ranges inducing photoinactivation of catalase differed significantly for chilling-tolerant and chilling-sensitive plants and preferential and rapid declines are generally to be expected in light whenever translation is suppressed by stress actions.
Abstract: Severe photoinactivation of catalase (EC 1.11.1.6) and a decline of variable fluorescence (Fv), indicating photoinhibition of photosynthesis, were observed as rapid and specific symptoms in leaves exposed to a high heat-shock temperature of 40°C as well as in leaves exposed to low chilling temperatures in white light of only moderately high photosynthetic photon flux density of 520 μE m−2 s−1. Other parameters, such as peroxidase (EC 1.11.1.7), glycolate oxidase (EC 1.1.3.1), glutathione reductase (EC 1.6.4.2), or the chlorophyll content, were hardly affected under these conditions. At a compatible temperature of 22°C, the applied light intensity did not induce severe photoinactivations. In darkness, exposures to high or low temperatures did not affect catalase levels. Also, decline of Fv in light was not related to temperature sensitivity in darkness. The effective low-temperature ranges inducing photoinactivation of catalase differed significantly for chilling-tolerant and chilling-sensitive plants. In leaves of rye (Secale cereale L.) and pea (Pisum sativum L.), photoinactivation occurred only below 15°C, whereas inactivation occurred at 15°C in cucumber (Cucumis sativus L.) and maize (Zea mays L.). The behavior of Fv was similar, but the difference between chilling-sensitive and chilling-tolerant plants was less striking. Whereas the catalase polypeptide, although photoinactivated, was not cleaved at 0 to 4°C, the D1 protein of photosystem II was greatly degraded during the low-temperature treatment of rye leaves in light. Rye leaves did not exhibit symptoms of any major general photodamage, even when they were totally depleted of catalase after photoinactivation at 0 to 4°C, and catalase recovered rapidly at normal temperature. In cucumber leaves, the decline of catalase after exposures to bright light at 0 to 4°C was accompanied by bleaching of chlorophyll, and the recovery observed at 25°C was slow and required several days. Similar to the D1 protein of photosystem II, catalase differs greatly from other proteins by its inactivation and high turnover in light. Inasmuch as catalase and D1 protein levels depend on continuous repair synthesis, preferential and rapid declines are generally to be expected in light whenever translation is suppressed by stress actions, such as heat or chilling, and recovery will reflect the repair capacity of the plants.
TL;DR: There are mechanistic differences in photoinhibition of sun and shade plants, and an active repair cycle of PSII replaces photoinhibited reaction centres with photochemically active ones, thereby conferring partial protection against photoin inhibition.
Abstract: Leaf discs of the shade plant Tradescantia albiflora Kunth grown at 50 mumol . m-2 . s-1, and the facultative sun, shade plant Pisum sativum L. grown at 50 or 300 mumol . m-2 . s-1, were photoinhib ...
TL;DR: Short-term transfers of shade-adapted clonal tissue of the marine macroalga Ulva rotundata Blid to higher irradiances led to photoinhibition of room-temperature chlorophyll fluorescence and O2 evolution, and the ratio of variable to maximum (Fv/Fm) and variable (FV) fluorescence, and quantum yield declined with increasing irradiance and duration of exposure.
Abstract: Short-term (up to 5 h) transfers of shade-adapted (100 μmol · m−2 · s−1) clonal tissue of the marine macroalga Ulva rotundata Blid. (Chlorophyta) to higher irradiances (1700, 850, and 350 μmol · m−2 · s−1) led to photoinhibition of room-temperature chlorophyll fluorescence and O2 evolution. The ratio of variable to maximum (Fv/Fm) and variable (Fv) fluorescence, and quantum yield (ϕ) declined with increasing irradiance and duration of exposure. This decline could be resolved into two components, consistent with the separation of photoinhibition into energy-dissipative processes (photoprotection) and damage to photosystem II (PSII) by excess excitation. The first component, a rapid decrease in Fv/Fm and in Fv, corresponds to an increase in initial (Fo) fluorescence and is highly sensitive to 1 mM chloramphenicol. This component is rapidly reversible under dim (40 μmol · m−2 · s−1) light, but is less reversible with increasing duration of exposure, and may reflect damage to PSII. The second (after 1 h exposure) component, a slower decline in Fv/Fm and Fv with declining Fo, appears to be associated with the photoprotective interconversion of violaxanthin to zeaxanthin and is sensitive to dithiothreitol. The accumulation of zeaxanthin in U. rotundata is very slow, and may account for the predominance of increases in Fo at high irradiances.
TL;DR: New issues on iron deficiency, such as the possible misuse of membrane fractions, the rapid adaptation changes which are found to occur during the day in the iron deficient leaves in response to light conditions, and the comparison with other studies, are discussed.
Abstract: Iron deficiency induces changes in the structure and function of the whole photosynthetic apparatus of higher plants. The iron deficiency‐induced decrease in pigments seems to arise from the absolute requirement for iron in the formation of thylakoid membrane. Modifications found in the thylakoid composition of iron deficient leaves include changes in the photosystem II to photosystem I stoichiometry, in the xanthophylls to chlorophylls ratio and in their lipid composition. Some of these changes may result in some protection towards photoinhibition. Changes in other leaf components, such as leaf lipids and iron fractions are discussed. Changes in parameters evaluating leaf functions, including gas exchange, water status and chlorophyll fluorescence are also discussed. New issues on iron deficiency, such as the possible misuse of membrane fractions, the rapid adaptation changes which are found to occur during the day in the iron deficient leaves in response to light conditions, and the comparison ...
TL;DR: It seems likely thatlipids are required for sustaining the photosynthetic activity under environmental stress, and a loss in activity is observed as the lipids are degraded either by high light or high temperature stress.
Abstract: Effects of high light and temperature stress on the structure and function of the photosynthetic apparatus of wheat (Triticum aestivum) were studied. There was a decrease in the electron transport activity of chloroplasts isolated from photoinhibited and heat-stressed leaves. Chlorophyll fluorescence was measured in photoinhibited and heat-stressed leaves and the decrease in variable fluorescence and variable to maximum fluorescence ratio of the stressed leaves indicated a loss in the quantum yield of photosynthesis. The decrease in electron transport activity was accompanied by an increase in peroxidation of thylakoid lipids. Lipid peroxidation indicated the oxidative degradation of polyunsaturated fatty acyl residues of the thylakoid lipids. A negative correlation was observed between electron transport activity and lipid peroxidation. The electron transport activity was completely lost as the peroxidation level reached a threshold equivalent to 0.6 micromoles malondialdehyde. The threshold of lipid peroxidation for complete loss of activity was the same for both photoinhibition and heat treatment, suggesting that the nature of the environmental stress may be less important with respect to the relationship between electron transport and lipid peroxidation. Thus, it seems likely that lipids are required for sustaining the photosynthetic activity under environmental stress, and a loss in activity is observed as the lipids are degraded either by high light or high temperature stress.
TL;DR: It is reported that strong light causing photoinhibition of photosynthesis also induces ELIP transcription and accumulation of the protein in mature green pea plants and the level of blue light-induced ELIP transcript is significantly repressed by low-intensity red light.
Abstract: The early light-inducible proteins (ELIPs) are expressed in developing plants in the first hours of the greening process. Here we report that strong light causing photoinhibition of photosynthesis also induces ELIP transcription and accumulation of the protein in mature green pea plants. Accumulation of ELIP transcript is induced in plants exposed to light intensities above 500 E/m2.s (E, einstein) and is maximal at approximately 1500 E/m2.s. The ELIP mRNA level increases in correlation with the degree of photoinhibition. The increase in ELIP level in the thylakoid membranes parallels the decrease in the amount of D1 protein of the photosystem II reaction center. Examination of ELIP induction as a function of light quality demonstrates that ELIP transcription is specifically induced by blue (410-480 nm) but not by red or far-red light. The level of blue light-induced ELIP transcript is significantly repressed by low-intensity red light. However, the accumulation of ELIP translation product is related to the total amount of blue and red light energy absorbed.
TL;DR: The structural and topological stability ofThylakoid components under photoinhibitory conditions was studied on Mn depleted thylakoids isolated from spinach leaves to study the effects of photoinhibition on photosystems I and II.
Abstract: The structural and topological stability of thylakoid components under photoinhibitory conditions (4,500 microE.m-2.s-1 white light) was studied on Mn depleted thylakoids isolated from spinach leaves. After various exposures to photoinhibitory light, the chlorophyll-protein complexes of both photosystems I and II were separated by sucrose gradient centrifugation and analysed by Western blotting, using a set of polyclonals raised against various apoproteins of the photosynthetic apparatus. A series of events occurring during donor side photoinhibition are described for photosystem II, including: (a) lowering of the oligomerization state of the photosystem II core; (b) cleavage of 32-kD protein D1 at specific sites; (c) dissociation of chlorophyll-protein CP43 from the photosystem II core; and (d) migration of damaged photosystem II components from the grana to the stroma lamellae. A tentative scheme for the succession of these events is illustrated. Some effects of photoinhibition on photosystem I are also reported involving dissociation of antenna chlorophyll-proteins LHCI from the photosystem I reaction center.
TL;DR: It is suggested that the presence of diunsaturated fatty acids is important in protecting against low-temperature photoinhibition, as well as the photosynthetic transport of electrons, measured at various temperatures, was not affected by changes in extent of fatty acid unsaturation.
Abstract: Effect of the unsaturation of fatty acids in the glycerolipids of thylakoid membranes on low-temperature photoinhibition of photosynthesis was studied by mutation and transformation of the cyanobacterium Synechocystis PCC6803. When grown at 34 degrees C, the wild type contained mono-, di-, and triunsaturated lipids; a mutant, designated Fad6, contained mono- and diunsaturated lipids; and a transformant of Fad6, with a disrupted gene for desaturation and designated Fad6/desA::Kmr, contained only monounsaturated lipids. Fad6/desA::Kmr was the most susceptible among these strains to low-temperature photoinhibition of photosynthesis, whereas Fad6 and the wild type were apparently indistinguishable in terms of sensitivity to photoinhibition. This result suggests that the presence of diunsaturated fatty acids is important in protecting against low-temperature photoinhibition. The photoinhibition at room temperature, although much less significant than that at low temperature, was also affected by the unsaturation of fatty acids. By contrast, the photosynthetic transport of electrons, measured at various temperatures, was not affected by changes in extent of fatty acid unsaturation.
TL;DR: The effects of a sudden increase in irradiance and the high leaf temperatures characteristic of a canopy gap environment were studied with chlorophyll fluorescence and gas-exchange measurements on shade- and sun-acclimated leaves of Alocasia macrorrhiza.
Abstract: 1. The effects of a sudden increase in irradiance and the high leaf temperatures characteristic of a canopy gap environment were studied with chlorophyll fluorescence and gas-exchange measurements on shade- and sun-acclimated leaves of Alocasia macrorrhiza. 2. Photoinhibition occurred in both sun and shade leaves during a 2-h simulated gap treatment (1900 μmol photons m −2 s −1 ) in which leaf temperatures rose to 40°C. Dissipation of excess energy was more efficient in sun leaves, which showed rapid quenching of fluorescence. The quantum yield of photosystem II as calculated from fluorescence in low light was considerably lower for shade than sun leaves after the gap treatment
TL;DR: The decrease in susceptibility to photoinhibition exhibited following cold hardening of winter and spring cultivars is not due to an increased capacity for repair of photoinhibitory damage at 5 degrees C but reflects intrinsic properties of the cold-hardened photosynthetic apparatus.
Abstract: Photoinhibition of photosynthesis and its recovery were studied in wheat (Triticum aestivum L.) leaves grown at nonhardening (20 degrees C) and cold-hardening (5 degrees C) temperatures. Cold-hardened wheat leaves were less susceptible to photoinhibition at 5 degrees C than nonhardened leaves, and the winter cultivars, Kharkov and Monopol, were less susceptible than the spring cultivar, Glenlea. The presence of chloramphenicol, a chloroplastic protein synthesis inhibitor, increased the susceptibility to photoinhibition, but cold-hardened leaves still remained less susceptible to photoinhibition than nonhardened leaves. Recovery at 50 mumol m(-2) s(-1) photosynthetic photon flux density and 20 degrees C was at least biphasic, with a fast and a slow phase in all cultivars. Cold-hardened leaves recovered maximum fluorescence and maximum variable fluorescence in the dark-adapted state during the fast phase at a rate of 42% h(-1) compared with 22% h(-1) for nonhardened leaves. The slow phase occurred at similar rates (2% h(-1)) in cold-hardened and nonhardened leaves. Full recovery required up to 30 h. Fast-recovery phase was not reduced by either lowering the recovery temperature to 5 degrees C or by the presence of chloramphenicol. Slow-recovery phase was inhibited by both treatments. Hence, the fast phase of recovery does not require de novo chloroplast protein synthesis. In addition, only approximately 60% of the photochemical efficiency lost through photoinhibition at 5 degrees C was associated with lost [(14)C]atrazine binding and, hence, with damage to the secondary quinone electron acceptor for photosystem II-binding site. We conclude that the decrease in susceptibility to photoinhibition exhibited following cold hardening of winter and spring cultivars is not due to an increased capacity for repair of photoinhibitory damage at 5 degrees C but reflects intrinsic properties of the cold-hardened photosynthetic apparatus. A model to account for the fast component of recovery is discussed.
TL;DR: Two Spirulina platensis strains, SP-G and SP-RB, resistant and sensitive to photoinhibition of photosynthesis, respectively, were grown outdoors in dense cultures and under different photon fluxes provided by shading.
Abstract: Two Spirulina platensis strains, SP-G and SP-RB, resistant and sensitive to photoinhibition of photosynthesis, respectively, were grown outdoors in dense cultures and under different photon fluxes provided by shading. Cultures of both strains grown under full sunlight were more resistant to photoinhibition than those grown under nets with 15-50% decreases in the incident photon flux. Cultures grown outdoors were more resistant to photoinhibition than the laboratory ones. At noon, the photosynthetic activity, as expressed by O2 evolution, was higher for cultures grown under 50% shade, as compared with unshaded cultures. Productivity of the shaded cultures, in terms of biomass produced per day, was always higher when the cultures were protected from photoinhibition. Key-words: Spirulina; blue-green algae; cyanobacteria; photoadaptation; photoinhibition; photosynthesis; productivity; biomass.
TL;DR: Although both species demonstrated considerable plasticity in Amax across gap transects, P. sancti-felicis leaves had a superior capacity to track closely variation in light availability, particularly in the larger gap, and P. arieianum exhibited symptoms of chronic photoinhibition in exposed microsites within the large gap.
Abstract: Photosynthetic plasticity of two congeneric shrub species growing under natural field conditions was compared along transects spanning two canopy gaps in a Costa Rican rain forest. Piper arieianum is a shadetolerant species common in successional and mature forests, whereas P. sancti-felicis is a pioneer species abundant in abandoned clearings and large gaps. Twenty potted cuttings of each species were placed at regular intervals along two east-west transects crossing a small branch-fall gap and a large tree-fall gap. Along the transects, the percent of full sun photon flux density varied from less than 2% to 45%. After six months of growth under these conditions, leaves were monitored for incident photon flux density, photographic measures of light availability, photosynthetic capacity (Amax), leaf nitrogen content, leaf chlorophyll content, and specific leaf mass. Although both species demonstrated considerable plasticity in Amax across gap transects, P. sancti-felicis leaves had a superior capacity to track closely variation in light availability, particularly in the larger gap. For regressions of Amax on measures of light availability, P. sancti-felicis consistently showed a 3.5 to 5-fold higher coefficient of determination (R2) and a 3 to 4-fold higher slope than P. arieianum. In both species leaf nitrogen content per leaf area increased significantly with light availability, although P. sancti-felicis, again, showed a much stronger relationship between these variables. Across the transects, mean chlorophyll content per unit leaf area did not differ significantly between the species, whereas mean chlorophyll content per unit leaf dry mass was 3-times greater in leaves of P. sancti-felicis. Piper arieianum exhibited highly significant increases in chlorophyll a:b ratio with increased light availability, whereas P. sancti-felicis lacked significant variation in this trait across a gradient of light availability. Mean specific leaf mass did not vary significantly between species across the gap transects. The nature of the light acclimatory response differs quantitatively and qualitatively between these species. An important constraint on light acclimation of the shade-tolerant P. arieianum is its inability to increase photosynthetic nitrogen-use efficiency under conditions of high light availability. The lack of plasticity in chlorophyll a:b ratios does not restrict light acclimation of Amax in P. sancti-felicis. Leaves of P. arieianum exhibited symptoms of chronic photoinhibition in exposed microsites within the large gap. Species differences in the capacity to finely adjust Amax across a wide range of light conditions may be attributed to their maximum growth potential. Light acclimation in species with low maximum growth potential may be constrained at the cellular level by rates of protein and chlorophyll synthesis and at the whole-plant level by low maximum rates of uptake and supply of nutrients and water. For P. arieianum, restriction of photosynthetic plasticity is likely to limit competitive abilities of plants in high-light conditions of large gaps and clearings, whereas observed habitat restrictions for P. sancti-felicis do not appear to depend upon the highly-developed capacity for adjustment of Amax observed in this species.
TL;DR: Of these three limitations of carbon assimilation, photoinhibition was the major one at limiting light only in naturally exposed willow leaves in the field, and was the same independent of the species, the light-acclimation state of the leaf and the light intensity.
Abstract: Photoinhibition was examined in naturally exposed willow leaves in the field. In the afternoon on clear and warm days, the quantum yield of electron transport, derived from gas exchange data, was decreased by 28%. Besides this photoinhibition, decreases in the photosynthetic capacity and in the stomatal conductance were also observed. Of these three limitations of carbon assimilation, photoinhibition was the major one at limiting light only.
TL;DR: Even though the sodB mutant was more sensitive to damage by active oxygen than wild-type cells, both strains were equally sensitive to the photoinhibition of photosystem II caused by exposure to strong light.
Abstract: The enzyme superoxide dismutase is ubiquitous in aerobic organisms where it plays a major role in alleviating oxygen-radical toxicity. An insertion mutation introduced into the iron superoxide dismutase locus (designated sodB) of the cyanobacterium Synechococcus sp. PCC 7942 created a mutant strain devoid of detectable iron superoxide dismutase activity. Both wild-type and mutant strains exhibited similar photosynthetic activity and viability when grown with 17 mumol.m-2.s-1 illumination in liquid culture supplemented with 3% carbon dioxide. In contrast, the sodB mutant exhibited significantly greater damage to its photosynthetic system than the wild-type strain when grown under increased oxygen tension or with methyl viologen. Although damage occurs at both photosystems I and II, it is primarily localized at photosystem I in the sodB mutant. Growth in 100% molecular oxygen for 24 hr decreased photoacoustically measured energy storage in 3-(3,4-dichlorophenyl)-1,1-dimethylurea and abolished the fluorescence state 2 to state 1 transition in the sodB mutant, indicating interruption of cyclic electron flow around photosystem I. Analysis of the flash-induced absorption transient at 705 nm indicated that the interruption of cyclic electron flow occurred in the return part of the cycle, between the two [4 Fe-4 S] centers of photosystem I, FA and FB, and cytochrome f. Even though the sodB mutant was more sensitive to damage by active oxygen than wild-type cells, both strains were equally sensitive to the photoinhibition of photosystem II caused by exposure to strong light.
TL;DR: It is concluded that photodamage of the secondary donors of the PSII reaction center occurs by two mechanisms: a rapid superoxide and tyrosine YZ+ dependent process and a slower process in which P680+/Chl+ catalyze the damages.
Abstract: The effects of photosystem II (PSII) exogenous electron donors and acceptors on the kinetics of weak light photoinhibition of NH2OH/EDTA-extracted spinach PSII membranes were examined. Under aerobic conditions, Mn2+ (approximately 1 Mn/reaction center; Km approximately 400 nM) inhibited photoinactivation and approximately 1 Mn/reaction center plus 100 microM NH2NH2 gave almost complete protection. In the absence of electron donors, strict anaerobiosis greatly inhibited photoinactivation even in the presence of an electron acceptor. Under aerobic conditions, the addition of electron acceptors (FeCN, DCIP), oxyradical scavengers, or superoxide dismutase strongly suppressed rates of photodamages. Increase in the concentrations of superoxide above those produced by illuminated NH2OH/EDTA-photosystem II membranes increased the rates of damage in the light but gave no damage in the dark. Scavengers of hydroxyl radicals and singlet oxygen did not suppress the rates of aerobic photoinhibition. These findings, along with others, lead us to conclude that photodamage of the secondary donors of the PSII reaction center occurs by two mechanisms: (1) a rapid superoxide and tyrosine YZ+ dependent process and (2) a slower process in which P680+/Chl+ catalyze the damages.
TL;DR: The mechanism of D1 protein degradation was investigated during photoinhibitory illumination of isolated photosystem II core preparations, and it was revealed that a proteolytic activity resides within the photosSystem II core complex.
Abstract: The mechanism of D1 protein degradation was investigated during photoinhibitory illumination of isolated photosystem II core preparations. The studies revealed that a proteolytic activity resides within the photosystem II core complex. A relationship between the inhibition of D1 protein degradation and the binding of the highly specific serine protease inhibitor diisopropyl fluorophosphate to isolated complexes of photosystem II was observed, evidence that this protease is of the serine type. Using radiolabeled inhibitor, it was shown that the binding site, representing the active serine of the catalytic site, is located on a 43-kDa polypeptide, probably the chlorophyll a protein CP43. The protease is apparently active in darkness, with the initiation of breakdown being dependent on high light-induced substrate activation. The proteolysis, which has an optimum at pH 7.5, gives rise to primary degradation fragments of 23 and 16 kDa. In addition, D1 protein fragments of 14, 13, and 10 kDa were identified. Experiments with phosphate-labeled D1 protein and sequence-specific antisera showed that the 23- and 16-kDa fragments originate from the N- and C-termini, respectively, suggesting a primary cleavage of the D1 protein at the outer thylakoid surface in the region between transmembrane helices D and E.
TL;DR: The results suggest that growth at sub-optimal temperatures induces increased tolerance to exposure to high light at chilling temperatures, which is offset by the large loss in photosynthetic capacity imposed by leaf development atSub-optical temperatures.
Abstract: 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.
TL;DR: Both models, although not universal for all plants, provide useful means for the prediction of photosynthesis from fluorescence parameters, and conditions which alter one or more of the rate constants that determine the various fluorescence parameter, as well as differential light penetration in assays for oxygen evolution and fluorescence emission, may have direct effect on the relationships of the two models.
Abstract: We tested the two empirical models of the relationship between chlorophyll fluorescence and photosynthesis, previously published by Weis E and Berry JA 1987 (Biochim Biophys Acta 894: 198–208) and Genty B et al. 1989 (Biochim Biophys Acta 990: 87–92). These were applied to data from different species representing different states of light acclimation, to species with C3 or C4 photosynthesis, and to wild-type and a chlorophyll b-less chlorina mutant of barley. Photosynthesis measured as CO2-saturated O2 evolution and modulated fluorescence were simultaneously monitored over a range of photon flux densities. The quantum yields of O2 evolution (OO2) were based on absorbed photons, and the fluorescence parameters for photochemical (qp) and non-photochemical (qN) quenching, as well as the ratio of variable fluorescence to maximum fluorescence during steady-state illumination (F'v/F'm), were determined. In accordance with the Weis and Berry model, most plants studied exhibited an approximately linear relationship between OO2/qp (i.e., the yield of O2 evolution by open Photosystem II reaction centres) and qN, except for wild-type barley that showed a non-linear relationship. In contrast to the linear relationship reported by Genty et al. for qp×F'v/F'm (i.e., the quantum yield of Photosystem II electron transport) and OCO2, we found a non-linear relationship between qp×F'v/F'm and OO2 for all plants, except for the chlorina mutant of barley, which showed a largely linear relationship. The curvilinearity of wild-type barley deviated somewhat from that of other species tested. The non-linear part of the relationship was confined to low, limiting photon flux densities, whereas at higher light levels the relationship was linear. Photoinhibition did not change the overall shape of the relationship between qp×F'v/F'm and OO2 except that the maximum values of the quantum yields of Photosystem II electron transport and photosynthetic O2 evolution decreased in proportion to the degree of photoinhibition. This implies that the quantum yield of Photosystem II electron transport under high light conditions may be similar for photoinhibited and non-inhibited plants. Based on our experimental results and theoretical analyses of photochemical and non-photochemical fluoresce quenching processes, we conclude that both models, although not universal for all plants, provide useful means for the prediction of photosynthesis from fluorescence parameters. However, we also discuss that conditions which alter one or more of the rate constants that determine the various fluorescence parameters, as well as differential light penetration in assays for oxygen evolution and fluorescence emission, may have direct effect on the relationships of the two models.
TL;DR: Diurnal heliotropic leaf movements, photosynthetic gas exchange, and the ratio of variable fluorescence to maximum fluorescence (Fv/Fm) of unrestrained and horizontally restrained leaves from soybean plants grown in two different water and nitrogen treatments were measured.
Abstract: Diurnal heliotropic leaf movements, photosynthetic gas exchange, and the ratio of variable fluorescence to maximum fluorescence (Fv/Fm) of unrestrained and horizontally restrained leaves from soybean (Glycine max cv. Cumberland) plants grown in two different water and two different nitrogen treatments were measured. Leaves of plants grown in low water or low nitrogen availability treatments displayed more pronounced diaheliotropism (solar tracking) in the afternoon and a longer period of paraheliotropism (light avoiding) at midday relative to those of well-watered, high-nitrogen-grown plants. Photosaturated photosynthetic rates and the photon flux required to saturate photosynthesis were reduced by water stress and nitrogen deficiency. Compared to horizontal leaves, irradiance on orienting leaves was nearer to the breakpoint of the photosynthetic light response curve, where photosynthesis is co-limited by ribulose biphosphate regeneration and carboxylation. This would increase the carbon return on investments of nitrogen into photosynthesis. A positive linear relationship between Fv/Fm and quantum yield of photosynthesis was measured. Leaves of low-nitrogen-grown plants had earlier and more prolonged reductions in Fv/Fm at midday compared to leaves of high nitrogen grown plants of the same water treatment. Within the same water and nitrogen treatment, horizontally restrained leaves had lower midday Fv/Fm in relation to orienting leaves. Nitrogen deficiency and water stress enhanced this difference such that horizontally restrained leaves of low water and low nitrogen grown plants had earlier and longer midday depressions in Fv/Fm.