Seedlings of Lodgepole pine (Pinus contorta L.) and winter wheat (Triticum aestivum L.) were cold acclimated under controlled conditions. Both temperate conifers and winter cereals have the ability to acquire high freezing tolerance... more
Seedlings of Lodgepole pine (Pinus contorta L.) and winter wheat (Triticum aestivum L.) were cold acclimated under controlled conditions. Both temperate conifers and winter cereals have the ability to acquire high freezing tolerance during cold acclimation, and they are characterized by maintaining their green foliages during autumn and winter. Pine responds to cold acclimation by partial inhibition of photosynthesis with a low daily carbon gain, while winter wheat maintains a high activity of photosynthesis and a high daily carbon gain during cold acclimation. These different responses of photosynthesis to cold acclimation are correlated with pine reducing its need for assimilates when entering dormancy associated with termination of primary growth, while winter wheat maintains a high need for assimilates as it continues to grow and develop throughout cold acclimation. These different responses are accompanied by pine reducing its needle content of chlorophyll and developing a high...
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Iron is the most abundant transition metal on earth, but the availability of iron to aquatic photoautotrophs is often limiting due to its low solubility in aerobic ecosystems [1]. Consequently, availability of iron is an important factor... more
Iron is the most abundant transition metal on earth, but the availability of iron to aquatic photoautotrophs is often limiting due to its low solubility in aerobic ecosystems [1]. Consequently, availability of iron is an important factor determining the structure and function of the photosynthetic apparatus and hence primary productivity [2]. Among various ways for cyanobacteria to cope with iron-deficiency, some replace the Chl protein complex of PSII, CP43, with the isiA gene product, CP43’ [3]. CP43’ differs from CP43 by having a shortened lumneal loop between helices 5 and 6, although the role of CP43’ has been suggested as an alternate of CP43 and/or a Chl reservoir [4]. However, we favor the view that CP43’ has a unique role under iron-deficient conditions. In order to dissect the role of CP43’ in an iron-deficient cyanobacterium, the isiA gene was inactivated by insertion mutagenesis in Synechococcus sp. PCC 7942 cells. Understanding the role of CP43’ is of great interest wit...
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High latitude forests will experience large changes in temperature and COconcentrations this century. We evaluated the effects of future climate conditions on two dominant boreal tree species, Pinus sylvestris L. and Picea abies (L.) H.... more
High latitude forests will experience large changes in temperature and COconcentrations this century. We evaluated the effects of future climate conditions on two dominant boreal tree species, Pinus sylvestris L. and Picea abies (L.) H. Karst, exposing seedlings to three seasons of ambient (430 ppm) or elevated CO(750 ppm) and ambient temperatures, a +4 °C warming, or a +8 °C warming. Pinus sylvestris responded positively to warming: seedlings developed a larger canopy, maintained high net COassimilation rates (A) and acclimated dark respiration (R). In contrast, carbon fluxes in Picea abies were negatively impacted by warming: maximum rates of Adecreased, electron transport was redirected to alternative electron acceptors, and thermal acclimation of Rwas weak. Elevated COtended to exacerbate these effects in warm-grown Picea abies, and by the end of the experiment Picea abies from the +8 °C, high COtreatment produced fewer buds than they had three years earlier. Treatments had litt...
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Analyses of chlorophyll fluorescence and photosynthetic oxygen evolution were conducted to understand why cold-hardened winter rye (Secale cereale L.) is more resistant to photoinhibition of photosynthesis than is non-hardened winter rye.... more
Analyses of chlorophyll fluorescence and photosynthetic oxygen evolution were conducted to understand why cold-hardened winter rye (Secale cereale L.) is more resistant to photoinhibition of photosynthesis than is non-hardened winter rye. Under similar light and temperature conditions, leaves of cold-hardened rye were able to keep a larger fraction of the PS II reaction centres in an open configuration, i.e. a
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Plants from clonal cuttings of Salix sp. were subjected to a drying cycle of 10 d in a controlled environment. Gas exchange and fluorescence emission were measured on attached leaves. The light-saturated photosynthetic CO2 uptake became... more
Plants from clonal cuttings of Salix sp. were subjected to a drying cycle of 10 d in a controlled environment. Gas exchange and fluorescence emission were measured on attached leaves. The light-saturated photosynthetic CO2 uptake became progressively inhibited with decreased leaf water potential both at high, and especially, at low intercellular CO2 pressure. The maximal quantum yield of CO2 uptake was more resistant. The inhibition of light-saturated CO2 uptake at leaf water potentials around-10 bar, measured at a natural ambient CO2 concentration, was equally attributable to stomatal and non-stomatal factors, but the further inhibition below this water-stress level was caused solely by non-stomatal factors. The kinetics of fluorescence emission was changed at severe water stress; the slow secondary oscillations of the induction curve were attenuated, and this probably indicates perturbations in the carbon reduction cycle. The influence of light level during the drought period was ...
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In the Northern temperate region, and at high altitudes, conifers are exposed to quite severe climatic conditions during the winter; i.e. low temperatures below zero, often in combination with bright sunlight. This winter stress inhibits... more
In the Northern temperate region, and at high altitudes, conifers are exposed to quite severe climatic conditions during the winter; i.e. low temperatures below zero, often in combination with bright sunlight. This winter stress inhibits photosynthesis and is considered to be mediated by photo-oxidation that occurs under conditions when photosynthesis is largely inhibited by low temperatures. As briefly discussed in this communication the effects of winter stress on photosynthesis of Pinus silvestris are reflected in a number of ways in the function and organization of chloroplasts. Particular attention is paid to identifying the sites of inhibition in the photosynthetic electron transport chain. Analysis of electron transport and fluorescence kinetic studies at room temperature have shown that winter stress inhibits electron transport on both the oxidizing and on the reducing side of photosystem II. The inhibition is most pronounced on the reducing side after the primary electron acceptor. The electron transport over photosystem I seems to be relatively resistant to winter stress although a partial inhibition is also evident here. This may partly be related to the about 40% decrease of the fraction of absorbed energy (α) that is transferred directly to photosystem I, as studied at 77 °K by fluorescence kinetics.
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The effect of repeated exposure to high light (1200 μmol · m(-2) · s(-1) photosynthetic photon flux density, PPFD) at 5° C was examined in attached leaves of cold-grown spring (cv. Katepwa) and winter (cv. Kharkov) wheat (Triticum... more
The effect of repeated exposure to high light (1200 μmol · m(-2) · s(-1) photosynthetic photon flux density, PPFD) at 5° C was examined in attached leaves of cold-grown spring (cv. Katepwa) and winter (cv. Kharkov) wheat (Triticum aestivum L.) over an eight-week period. Under these conditions, Kharkov winter wheat exhibited a daily reduction of 24% in FV/FM (the ratio of variable to maximal fluorescence in the dark-adapted state), in contrast to 41% for cold-grown Katepwa spring wheat. Both cultivars were able to recover from this daily suppression of FV/FM such that the leaves exhibited an average morning FV/FM of 0.651 ± 0.004. Fluorescence measurements made under steady-state conditions as a function of irradiance from 60 to 2000 μmol · m(-2) · s(-1) indicated that the yield of photosystem II (PSII) electron transport under light-saturating conditions was the same for photoinhibited and control cold-grown plants, regardless of cultivar. Repeated daily exposure to high light at low temperature did not increase resistance to short-term photoinhibition, although zeaxanthin levels increased by three- to fourfold. In addition, both cultivars increased the rate of dry-matter accumulation, relative to control plants maintained at 5° C and 250 μmol · m(-2) · s(-1) PPFD (10% and 28% for Katepwa and Kharkov, respectively), despite exhibiting suppressed fv/fm and reduced photon yields for O2 evolution following daily high-light treatments. Thus, although photosynthetic efficiency is suppressed by a longterm, photoinhibitory treatment, light-saturated rates of photosynthesis are sufficiently high during the high-light treatment to offset any reduction in photochemical efficiency of PSII. We suggest that in these cold-tolerant plants, photoinhibition of PSII may represent a longterm, stable, down-regulation of photochemistry to match the overall photosynthetic demand for ATP and reducing equivalents.
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Research Interests: Chemistry, Photochemistry, Photosynthesis, Plant Biology, Fluorescence, and 15 moreMedicine, Chlorophyll Fluorescence, Electron Transport, Steady state, Light Acclimation, Photosystem II, Quantum Yield, Photoinhibition, Empirical Model, Oxygen evolution reaction, Gas Exchange, Fluorescence quenching, Oxygen evolution reaction (OER), high light, and Rate Constant
The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200 μmol m(-2)s(-1) on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were... more
The effects of a 60 min exposure to photosynthetic photon flux densities ranging from 300 to 2200 μmol m(-2)s(-1) on the photosynthetic light response curve and on PS II heterogeneity as reflected in chlorophyll a fluorescence were investigated using the unicellular green alga Chlamydomonas reinhardtii. It was established that exposure to high light acts at three different regulatory or inhibitory levels; 1) regulation occurs from 300 to 780 μmol m(-2)s(-1) where total amount of PS II centers and the shape of the light response curve is not significantly changed, 2) a first photoinhibitory range above 780 up to 1600 μmol m(-2)s(-1) where a progressive inhibition of the quantum yield and the rate of bending (convexity) of the light response curve can be related to the loss of QB-reducing centers and 3) a second photoinhibitory range above 1600 μmol m(-2)s(-1) where the rate of light saturated photosynthesis also decreases and convexity reaches zero. This was related to a particularly large decrease in PS IIα centers and a large increase in spill-over in energy to PS I.
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Research Interests: Biophysics, Chemistry, Photosynthesis, Fluorescence, Biology, and 15 moreCyanobacteria, Photobiology, Medicine, Biological Sciences, Mutation, Physical sciences, Light, Iron, Energy Dissipation, CHEMICAL SCIENCES, Photochemistry and Photobiology, Synechococcus, Production Function, Photosystem II, and Photoinhibition
Research Interests: Photosynthesis, Biology, Cyanobacteria, Molecular Microbiology, Medicine, and 15 moreGene expression, Biological Sciences, Molecular, Chlorophyll, Light, Genetic transformation, Iron, Spectrophotometry, Plasmids, photosystem I, Time Factors, Synechococcus, Photosystem II, Photoinhibition, and Medical and Health Sciences
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ABSTRACT
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Abstract. Chlorophyll fluorescence has been widely used in laboratory studies in understand-ing both the mechanism of photosynthesis itself and the mechanisms by which a range of environ-mental factors alter photosynthetic capacity. The... more
Abstract. Chlorophyll fluorescence has been widely used in laboratory studies in understand-ing both the mechanism of photosynthesis itself and the mechanisms by which a range of environ-mental factors alter photosynthetic capacity. The measurement of ...
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In the present study, we describe the sequential events by which the cyanobacterium Synechococcus sp. PCC 7942 adapts to iron deficiency. In doing so, we have tried to elucidate both short and long‐term acclimation to low iron stress in... more
In the present study, we describe the sequential events by which the cyanobacterium Synechococcus sp. PCC 7942 adapts to iron deficiency. In doing so, we have tried to elucidate both short and long‐term acclimation to low iron stress in order to understand how the photosynthetic apparatus adjusts to low iron conditions. Our results show that after an initial step, where CP43′ is induced and where ferredoxin is partly replaced by flavodoxin, the photosynthetic unit starts to undergo major rearrangements. All measured components of Photosystem I (PSI), PSII and cytochrome (Cyt) ƒ decrease relative to chlorophyll (Chl) a. The photochemical efficiencies of the two photosystems also decline during this phase of acclimation. The well‐known drop in phycobilisome content measured as phycocyanin (PC)/Chl was not due to an increased degradation, but rather to a decreased rate of synthesis. The largest effects of iron deficiency were observed on PSI, the most iron‐rich structure of the photosy...
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GALACTOLIPID BIOSYNTHESIS IN CHLOROPLASTS OF NONHARDENED AND FROST-HARDENED SEEDLINGS OF SCOTS PINE
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Exposure of control (non-hardened) Arabidopsis leaves to high light stress at 5° C resulted in a decrease of PSII photochemical efficiency to 55% compared to the control. This was accompanied by a parallel 65% inhibition of PSI... more
Exposure of control (non-hardened) Arabidopsis leaves to high light stress at 5° C resulted in a decrease of PSII photochemical efficiency to 55% compared to the control. This was accompanied by a parallel 65% inhibition of PSI photochemistry measured as D A820/A820, by an increase of the intersystem electron pool size as well as an acceleration of PSI-dependent cyclic electron transport. In contrast, cold acclimated leaves exhibited only 22% and 35% decrease of PSII and PSI photochemistry, respectively, under the same photoinhibitory conditions. Thermoluminescence measurements of PSII revealed that S2/S3QB- recombinations were shifted to lower temperatures in cold acclimated plants. This corresponded to lower activation energy of the S2QB- peak, thus narrowing the gap in the redox potentials between QA and QB electron acceptors. The greater resistance to high light stress will be discussed in terms of possible alternative nonradiative charge recombination pathways in cold acclimate...
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Research Interests: Chemistry, Photochemistry, Photosynthesis, Medicine, Light, and 14 moreTemperature, Thermal acclimation, Thermoluminescence, Xanthophyll Cycle, Acclimatization, Low Temperature, Photoprotection, Photosystem II, Elsevier, Recombination, Biochemistry and cell biology, Non-photochemical quenching, Charge recombination, and high light
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21 Low temperature recovery of photosynthesis in a DGDG deficient mutant of Arabidopsis Eva Selstam1, 4, Luke Hendrickson1, Marianna Krol2 ... References Dörmann P, Hoffmann-Benning S, Balbo I, Benning C (1995) Isolation and... more
21 Low temperature recovery of photosynthesis in a DGDG deficient mutant of Arabidopsis Eva Selstam1, 4, Luke Hendrickson1, Marianna Krol2 ... References Dörmann P, Hoffmann-Benning S, Balbo I, Benning C (1995) Isolation and characterisation of an Arabidopsis mutant ...
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Research Interests: Biophysics, Chemistry, Photosynthesis, Cyanobacteria, Medicine, and 15 moreElectron Transfer, Chlorophyll, Iron, Electron Transport, Heme, Photosynthetic electron transport, photosystem I, Methyl Viologen, Growth rate, Cytochromes, Intersystem Crossing, Biochemistry and cell biology, Iron stress in Cyanobacteria, Cyclic electron flow, and nadp
To finish this special issue, some friends, colleagues and students of Prof. Chow (Emeritus Professor, the Research School of Biology, the Australian National University) have written small tributes to acknowledge not only his eminent... more
To finish this special issue, some friends, colleagues and students of Prof. Chow (Emeritus Professor, the Research School of Biology, the Australian National University) have written small tributes to acknowledge not only his eminent career but to describe his wonderful personality.
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The academic research scene is rapidly changing as a consequence of the political emphasis on defining knowledge‐based societies or economies as a means to build prosperity. Most nations, both developed and less‐developed, formulate such... more
The academic research scene is rapidly changing as a consequence of the political emphasis on defining knowledge‐based societies or economies as a means to build prosperity. Most nations, both developed and less‐developed, formulate such visions today. The same vision was formulated for the European Union (EU) by the Lisbon European Council in March 2000, when Heads of Government stated that the EU should, in the next 10 years, be turned into “the most competitive and dynamic knowledge‐based economy in the world, capable of sustainable economic growth with more and better jobs and greater social cohesion”. As a consequence of this emphasis on knowledge for social development, educational programmes at undergraduate levels are now being revised with increased access, and postgraduate programmes are being reorganized into various types of graduate school arrangements to increase output. However, it is also being questioned whether quality in education and research can be maintained at...
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Research Interests: Botany, Chemistry, Horticulture, Photosynthesis, Ecology, and 15 moreCarotenoids, Medicine, Energy Metabolism, Conifers, Chlorophyll Fluorescence, Luminescence, Electron Transport, Photosynthetic electron transport, Forestry Sciences, Acclimatization, Pinus sylvestris, Cold, Photosystem II, Photoinhibition, and Cold Acclimation
Current ambient UV-B levels can significantly depress productivity in aquatic habitats, largely because UV-B inhibits several steps of photosynthesis, including the photooxidation of water catalyzed by photosystem II. We show that upon... more
Current ambient UV-B levels can significantly depress productivity in aquatic habitats, largely because UV-B inhibits several steps of photosynthesis, including the photooxidation of water catalyzed by photosystem II. We show that upon UV-B exposure the cyanobacterium Synechococcus sp. PCC 7942 rapidly changes the expression of a family of three psbA genes encoding photosystem II D1 proteins. In wild-type cells the psbAI gene is expressed constitutively, but strong accumulations of psbAII and psbAIII transcripts are induced within 15 min of moderate UV-B exposure (0.4 W/m 2 ). This transcriptional response causes an exchange of two distinct photosystem II D1 proteins. D1:1 is encoded by psbAI , but on UV-B exposure, it is largely replaced by the alternate D1:2 form, encoded by both psbAII and psbAIII . The total content of D1 and other photosystem II reaction center protein, D2, remained unchanged throughout the UV exposure, as did the content and composition of the phycobilisome. W...
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... The variations in the photosynthetic rate of synchronous green algae (Figure 6) have been shown to depend on the capacity of the ... Giese, ed,) 6: 1-46, Academic Press, New York-London, i Halldal, P, & Halldal, K, 1973,... more
... The variations in the photosynthetic rate of synchronous green algae (Figure 6) have been shown to depend on the capacity of the ... Giese, ed,) 6: 1-46, Academic Press, New York-London, i Halldal, P, & Halldal, K, 1973, Phytoplankton, chlorophyll, and submarine light conditions ...
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The definition of complexity, simultaneously introduced by Kolmogorov and Chaitin, has given a numerical measure to what was previously defined only at an intuitive level. This measure, useful as it is, becomes hard to utilise when one... more
The definition of complexity, simultaneously introduced by Kolmogorov and Chaitin, has given a numerical measure to what was previously defined only at an intuitive level. This measure, useful as it is, becomes hard to utilise when one deals with the complexity of most real systems, and biological objects in particular. We try to overcome this difficulty by discussing a possible thermodynamic definition of complexity based on energy balance. The Kolmogorov–Chaitin definition of complexity thus relates to our thermodynamic definition in a similar way as the probabilistic definition of entropy relates to the thermodynamic one. In the framework of this intuitive treatment it is discussed how the complexity of a biological system may depend on the variability of the environmental conditions. A specific illustration of this approach is given using some numerical modeling examples.
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Research Interests: Chemistry, Photochemistry, Cyanobacteria, Biological Chemistry, Medicine, and 15 moreBiological Sciences, Biological, Light, Temperature, Thermoluminescence, CHEMICAL SCIENCES, Densitometry, Protein isoforms, Photosystem II, Redox, Cold Acclimation, PSII reaction center, Charge recombinations, Immunoblotting, and Medical and Health Sciences
... Alexander G. Ivanov1,2*, Vaughan Hurry2, Prafullachandra V. Sane1,2, Gunnar Öquist2, and Norman PA Huner1 1Department of Biology and the Biotron, University of Western Ontario, 1151 Richmond Street N, London ... growth conditions (Ort... more
... Alexander G. Ivanov1,2*, Vaughan Hurry2, Prafullachandra V. Sane1,2, Gunnar Öquist2, and Norman PA Huner1 1Department of Biology and the Biotron, University of Western Ontario, 1151 Richmond Street N, London ... growth conditions (Ort and Baker, 2002; Rosso et al., 2006 ...
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ABSTRACT Anacystis nidulans was grown at two different levels of white light, 7 and50 W.m−2. The cells were disrupted through French press treatment, and phycocyanin-free photosynthetic lamellae were obtained from the homogenate by... more
ABSTRACT Anacystis nidulans was grown at two different levels of white light, 7 and50 W.m−2. The cells were disrupted through French press treatment, and phycocyanin-free photosynthetic lamellae were obtained from the homogenate by fractionated centrifugation. Comparative absorption studies of the lamellae revealed that high intensity gave an increased carotenoid content relative to chlorophyll a. The spectral characteristics of the cell-free supernatants were also analysed. The high light intensity gave increased contents of both pteridines (410 nm) and allophycocyanin (655 nm) compared with the contents in algae grown at the low light level.
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Abstract Lyophilized chloroplasts of Pisum sativum (pea) have been ex-tracted with petroleum ether of different polarity (obtained by adding varying amounts of ethanol to the petroleum ether). Ex-tracted thylakoids have then been... more
Abstract Lyophilized chloroplasts of Pisum sativum (pea) have been ex-tracted with petroleum ether of different polarity (obtained by adding varying amounts of ethanol to the petroleum ether). Ex-tracted thylakoids have then been solubilized by sodium dodecyl sulphate ...
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Subject areas: Environmental and stress responses / photosynthesis, respiration and bioenergetics. Number of black and white figures, color figures and tables: Black and white figures: 4
ABSTRACT
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To understand the mechanisms that underlie photosynthetic responses to environmental stress it is convenient to consider the model where photosynthesis is composed of a series of subprocesses beginning with the absorption of light and... more
To understand the mechanisms that underlie photosynthetic responses to environmental stress it is convenient to consider the model where photosynthesis is composed of a series of subprocesses beginning with the absorption of light and ending with the enzymatic processes related to the reduction of CO2. If we have the ambition to relate stress to photosynthetic or biomass productivity we should also consider light interception of plants at the individual plant and canopy levels. As stress may affect processes at all these levels of plant organization, we must bring together information about the function of a large number of component processes in relation to environmental stress. Furthermore, from a physiological viewpoint it is important to causally relate an observed stress effect at the levels of subprocesses to the photosynthetic performance at the leaf level.
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We have examined the molecular and photosynthetic responses of a planktonic cyanobacterium to shifts in light intensity over periods up to one generation (7 h). Synechococcus sp. PCC 7942 possesses two functionally distinct forms of the... more
We have examined the molecular and photosynthetic responses of a planktonic cyanobacterium to shifts in light intensity over periods up to one generation (7 h). Synechococcus sp. PCC 7942 possesses two functionally distinct forms of the D1 protein, ...
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Dissipation of excess absorbed light energy in eukaryotic photoautotrophs through zeaxanthin- and DeltapH-dependent photosystem II antenna quenching is considered the major mechanism for non-photochemical quenching and photoprotection.... more
Dissipation of excess absorbed light energy in eukaryotic photoautotrophs through zeaxanthin- and DeltapH-dependent photosystem II antenna quenching is considered the major mechanism for non-photochemical quenching and photoprotection. However, there is mounting evidence of a zeaxanthin-independent pathway for dissipation of excess light energy based within the PSII reaction centre that may also play a significant role in photoprotection. We summarize recent reports which indicate that this enigma can be explained, in part, by the fact that PSII reaction centres can be reversibly interconverted from photochemical energy transducers that convert light into ATP and NADPH to efficient, non-photochemical energy quenchers that protect the photosynthetic apparatus from photodamage. In our opinion, reaction centre quenching complements photoprotection through antenna quenching, and dynamic regulation of photosystem II reaction centre represents a general response to any environmental condition that predisposes the accumulation of reduced Q(A) in the photosystem II reaction centres of prokaryotic and eukaryotic photoautotrophs. Since the evolution of reaction centres preceded the evolution of light harvesting systems, reaction centre quenching may represent the oldest photoprotective mechanism.
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Plants are exposed to a large number of abiotic as well as biotic stress factors that affect the organization and function of photosynthesis, and we know of a large number of responses at different organizational levels of photosynthesis... more
Plants are exposed to a large number of abiotic as well as biotic stress factors that affect the organization and function of photosynthesis, and we know of a large number of responses at different organizational levels of photosynthesis that may be considered as adaptive responses to tolerate or avoid stress (Levitt, 1980). Because this is a congress for photobiologists I have chosen to discuss how the function of photosynthesis is inhibited by excessive excitation of plants with visible light, and how plants have acquired different mechanisms to avoid or tolerate photo- inhibition of photosynthesis. Photoinhibition of photosynthesis is a well known phenomenon and it is also established thatitmay occur under natural field conditions (Oquist et al., 1987; Neale, 1987). Photoinhibition has been studied very extensively over the last 10 years. The present status of knowledge has recently been reviewed (Powles, 1984). Mechanisms by which plants avoid or tolerate photoinhibition is much less studied and suggested protective mechanisms should at present be considered as working hypotheses.