Showing papers on "Photosynthesis published in 1998"
TL;DR: Modulation of this novel, chloroplastic redox signal either by excess light or by low temperature initiates a signal transduction pathway that appears to coordinate photosynthesis-related gene expression and to influence the nuclear expression of a specific cold-acclimation gene, plant morphology and differentiation in cyanobacteria.
944 citations
TL;DR: The pattern of fluorescence yield versus light intensity can be used to predict the acclimated light level for a cyanobacterial population, giving information valuable for both laboratory and field studies of acclimation processes.
Abstract: Cyanobacteria are ecologically important photosynthetic prokaryotes that also serve as popular model organisms for studies of photosynthesis and gene regulation. Both molecular and ecological studies of cyanobacteria benefit from real-time information on photosynthesis and acclimation. Monitoring in vivo chlorophyll fluorescence can provide noninvasive measures of photosynthetic physiology in a wide range of cyanobacteria and cyanolichens and requires only small samples. Cyanobacterial fluorescence patterns are distinct from those of plants, because of key structural and functional properties of cyanobacteria. These include significant fluorescence emission from the light-harvesting phycobiliproteins; large and rapid changes in fluorescence yield (state transitions) which depend on metabolic and environmental conditions; and flexible, overlapping respiratory and photosynthetic electron transport chains. The fluorescence parameters FV/FM, FV′/FM′,qp,qN, NPQ, and φPS II were originally developed to extract information from the fluorescence signals of higher plants. In this review, we consider how the special properties of cyanobacteria can be accommodated and used to extract biologically useful information from cyanobacterial in vivo chlorophyll fluorescence signals. We describe how the pattern of fluorescence yield versus light intensity can be used to predict the acclimated light level for a cyanobacterial population, giving information valuable for both laboratory and field studies of acclimation processes. The size of the change in fluorescence yield during dark-to-light transitions can provide information on respiration and the iron status of the cyanobacteria. Finally, fluorescence parameters can be used to estimate the electron transport rate at the acclimated growth light intensity.
754 citations
TL;DR: This review examines the potential diversity of both Rubisco and chloroplast-based CCMs across algal divisions, including both green and nongreen algae, and seeks to highlight recent advances in the understanding of the area and future areas for research.
Abstract: Algae have adopted two primary strategies to maximize the performance of Rubisco in photosynthetic CO2 fixation. This has included either the development of a CO2-concentrating mechanism (CCM), bas...
643 citations
TL;DR: A model for coral bleaching is proposed whereby the primary site of heat damage in S, pistillata is carboxylation within the Calvin cycle, as has been observed during heat damageIn higher plants, Damage to PSII and a reduction in F-v/F-m are secondary effects following the overwhelming of photoprotective mechanisms by light.
Abstract: The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tissues of a reef-building coral were examined using pulse-amplitude-modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 degrees C for 4 h resulted in (1) the development of strong non-photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (F-v/F-m) of photosystern II (PSII), Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensities were combined with elevated temperature (33 degrees C as opposed to 28 degrees C), qN collapsed in heat-stressed samples when quenching analysis was conducted in the absence of oxygen, Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O-2-dependent electron flow through the Mehler-Ascorbate-Peroxidase cycle (MAP-cycle) following the point at which the rate of light-driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in S, pistillata is carboxylation within the Calvin cycle, as has been observed during heat damage in higher plants, Damage to PSII and a reduction in F-v/F-m (i.e. photoinhibition) are secondary effects following the overwhelming of photoprotective mechanisms by light. This secondary factor increases the effect of the primary variable, temperature. Potential restrictions of electron flow in heat-stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the dinoflagellate Rubisco, Significant features of our model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, acid (2) light plays a key secondary role in the initiation of the bleaching phenomena.
641 citations
TL;DR: Differences between species in organic leaf nitrogen content per se were no longer important and higher PNUEmax of the high SLA species was due to a higher fraction of N in␣photosynthetic compounds and a higher Rubisco specific activity (for high-light grown plants).
Abstract: Factors that contribute to interspecific varia- tion in photosynthetic nitrogen-use eAciency (PNUE, the ratio of CO2 assimilation rate to leaf organic nitro- gen content) were investigated, comparing ten dicoty- ledonous species that diAer inherently in specific leaf area (SLA, leaf area:leaf dry mass). Plants were grown hydroponically in controlled environment cabinets at two irradiances (200 and 1000 lmol m -2 s -1 ). CO2 and irradiance response curves of photosynthesis were mea- sured followed by analysis of the chlorophyll, Rubisco, nitrate and total nitrogen contents of the leaves. At both irradiances, SLA ranged more than twofold across spe- cies. High-SLA species had higher in situ rates of pho- tosynthesis per unit leaf mass, but similar rates on an area basis. The organic N content per unit leaf area was lower for the high-SLA species and consequently PNUE at ambient light conditions (PNUEamb) was higher in those plants. DiAerences were somewhat smaller, but still present, when PNUE was determined at saturating irradiances (PNUEmax). An assessment was made of the relative importance of the various factors that underlay interspecific variation in PNUE. For plants grown under low irradiance, PNUEamb of high-SLA species was higher primarily due to their lower N content per unit leaf area. Low-SLA species clearly had an overinvest- ment in photosynthetic N under these conditions. In addition, high SLA-species allocated a larger fraction of organic nitrogen to thylakoids and Rubisco, which fur- ther increased PNUEamb. High-SLA species grown un- der high irradiance showed higher PNUEamb mainly due to a higher Rubisco specific activity. Other factors that contributed were again their lower contents of Norg per unit leaf area and a higher fraction of photosynthetic N in electron transport and Rubisco. For PNUEmax, dif- ferences between species in organic leaf nitrogen content per se were no longer important and higher PNUEmax of the high SLA species was due to a higher fraction of N in photosynthetic compounds (for low-light plants) and a higher Rubisco specific activity (for high-light grown plants).
520 citations
TL;DR: Measurements of the quantum efficiencies of photosynthetic electron transport through photosystem II (phiPSII) and CO2 assimilation (phiCO2) were made simultaneously on leaves of maize crops in the United Kingdom during the early growing season, when chilling conditions were experienced, supporting the hypothesis that the relative flux of photosynthesis reducing equivalents to O2 via the Mehler reaction is higher when leaves develop under chilling conditions.
Abstract: Measurements of the quantum efficiencies of photosynthetic electron transport through photosystem II (φPSII) and CO2 assimilation (φCO2) were made simultaneously on leaves of maize (Zea mays) crops in the United Kingdom during the early growing season, when chilling conditions were experienced. The activities of a range of enzymes involved with scavenging active O2 species and the levels of key antioxidants were also measured. When leaves were exposed to low temperatures during development, the ratio of φPSII/φCO2 was elevated, indicating the operation of an alternative sink to CO2 for photosynthetic reducing equivalents. The activities of ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase, glutathione reductase, and superoxide dismutase and the levels of ascorbate and α-tocopherol were also elevated during chilling periods. This supports the hypothesis that the relative flux of photosynthetic reducing equivalents to O2 via the Mehler reaction is higher when leaves develop under chilling conditions. Lipoxygenase activity and lipid peroxidation were also increased during low temperatures, suggesting that lipoxygenase-mediated peroxidation of membrane lipids contributes to the oxidative damage occurring in chill-stressed leaves.
423 citations
TL;DR: The physical structure and energetics of PSII are reviewed and a metalloradical enzyme mechanism for the water-oxidation process it catalyzes is discussed, which is based on the specifics of the chemistry in which O2 participates.
Abstract: Dioxygen is thermodynamically hot but kinetically cool, which makes it an ideal reagent for maximizing biological free energy production and for carrying out difficult chemical transformations in enzyme active sites.1 The widespread use of dioxygen in biological catalysis has led to an enzyme classification scheme s monooxygenases, dioxygenases, oxidases s that is based on the specifics of the chemistry in which O2 participates. Examples of the remarkable utility of dioxygen in biology abound and include its use in maximizing ATP production in aerobic respiration, in C-H bond activation in the P450 enzymes and methane monoxygenases, and in the degradation of important biomaterials such as lignin. Although nature has devised a multitude of mechanisms by which to activate dioxygen for useful chemistry, only one system, Photosystem II (PSII) in plants and algae, has evolved that has the capacity to lift water out of its thermodynamic well to generate dioxygen. This singular development provided photosynthetic organisms with an abundant and ubiquitous substrate for growth and diversification. The molecular mechanism by which PSII is able to strip hydrogen atoms from water and release O2 as waste is coming into view. In this article, we review the physical structure and energetics of PSII. We then discuss and analyze a metalloradical enzyme mechanism for the water-oxidation process it catalyzes.
372 citations
TL;DR: The coordination of N and C metabolism is retained during drought conditions via modulation of the activities of Suc phosphate synthase and NR commensurate with the prevailing rate of photosynthesis.
Abstract: Maize ( Zea mays L.) plants were grown to the nine-leaf stage. Despite a saturating N supply, the youngest mature leaves (seventh position on the stem) contained little NO 3 − reserve. Droughted plants (deprived of nutrient solution) showed changes in foliar enzyme activities, mRNA accumulation, photosynthesis, and carbohydrate and amino acid contents. Total leaf water potential and CO 2 assimilation rates, measured 3 h into the photoperiod, decreased 3 d after the onset of drought. Starch, glucose, fructose, and amino acids, but not sucrose (Suc), accumulated in the leaves of droughted plants. Maximal extractable phospho enol pyruvate carboxylase activities increased slightly during water deficit, whereas the sensitivity of this enzyme to the inhibitor malate decreased. Maximal extractable Suc phosphate synthase activities decreased as a result of water stress, and there was an increase in the sensitivity to the inhibitor orthophosphate. A correlation between maximal extractable foliar nitrate reductase (NR) activity and the rate of CO 2 assimilation was observed. The NR activation state and maximal extractable NR activity declined rapidly in response to drought. Photosynthesis and NR activity recovered rapidly when nutrient solution was restored at this point. The decrease in maximal extractable NR activity was accompanied by a decrease in NR transcripts, whereas Suc phosphate synthase and phospho enol pyruvate carboxylase mRNAs were much less affected. The coordination of N and C metabolism is retained during drought conditions via modulation of the activities of Suc phosphate synthase and NR commensurate with the prevailing rate of photosynthesis.
368 citations
TL;DR: The evolutionary developments that led to the ability of photosynthetic organisms to oxidize water to molecular oxygen are discussed and intermediate stages are proposed in which hydrogen peroxide was oxidized by the reaction center, and an intermediate pigment, similar to chlorophyll d, was present.
363 citations
TL;DR: Evidence indicates that moderately elevated temperatures inhibit light activation of Rubisco via a direct effect on Rubisco activase, and electron transport, as measured by Chl fluorescence, appeared to be more stable to moderate elevated temperatures than Rubisco activation.
Abstract: We tested the hypothesis that light activation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is inhibited by moderately elevated temperature through an effect on Rubisco activase. When cotton (Gossypium hirsutum L.) or wheat (Triticum aestivum L.) leaf tissue was exposed to increasing temperatures in the light, activation of Rubisco was inhibited above 35 and 30°C, respectively, and the relative inhibition was greater for wheat than for cotton. The temperature-induced inhibition of Rubisco activation was fully reversible at temperatures below 40°C. In contrast to activation state, total Rubisco activity was not affected by temperatures as high as 45°C. Nonphotochemical fluorescence quenching increased at temperatures that inhibited Rubisco activation, consistent with inhibition of Calvin cycle activity. Initial and maximal chlorophyll fluorescence were not significantly altered until temperatures exceeded 40°C. Thus, electron transport, as measured by Chl fluorescence, appeared to be more stable to moderately elevated temperatures than Rubisco activation. Western-blot analysis revealed the formation of high-molecular-weight aggregates of activase at temperatures above 40°C for both wheat and cotton when inhibition of Rubisco activation was irreversible. Physical perturbation of other soluble stromal enzymes, including Rubisco, phosphoribulokinase, and glutamine synthetase, was not detected at the elevated temperatures. Our evidence indicates that moderately elevated temperatures inhibit light activation of Rubisco via a direct effect on Rubisco activase.
TL;DR: The map suggests that redox cofactors in the D1–D2 complex are located in positions analogous to those in the bacterial reaction centre, but the distance between the chlorophylls corresponding to the bacterial ‘special pair’ is significantly larger.
Abstract: Photosystem II is a multisubunit enzyme complex involved in plant photosynthesis. It uses solar energy to catalyse the breakdown of water to reducing equivalents and molecular oxygen. Native photosystem II comprises more than 25 different subunits, and has a relative molecular mass of more than 600K. Here we report the three-dimensional structure of a photosystem II subcomplex, containing the proteins D1, D2, CP47 and cytochrome b-559, determined by electron crystallography. This CP47 reaction centre, which has a relative molecular mass of 160K, can perform light-mediated energy and electron-transfer reactions but is unable to oxidize water. The complex contains 23 transmembrane alpha-helices, of which 16 have been assigned to the D1, D2 and CP47 proteins. The arrangement of these helices is remarkably similar to that of the helices in the reaction centres of purple bacteria and of plant photosystem I, indicating a common evolutionary origin for these assemblies. The map suggests that redox cofactors in the D1-D2 complex are located in positions analogous to those in the bacterial reaction centre, but the distance between the chlorophylls corresponding to the bacterial 'special pair' is significantly larger.
TL;DR: It is concluded that O 3 depletion and the concurrent rise in UV-B irradiance is not a direct threat to photosynthetic productivity of crops and natural vegetation.
Abstract: This critical review of recent literature questions earlier predictions that photosynthetic productivity of higher plants is vulnerable to increased ultraviolet-B (UV-B) radiation as a result of stratospheric ozone (O 3 ) depletion. Direct UV-B-induced inhibition of photosynthetic competence is observed only at high UV-B irradiances and primarily involves the loss of soluble Calvin cycle enzymes and adaxial stomatal closure in amphistomatous plants. However, even under these extreme UV-B exposures, acclimation (e.g. induction of UV-B absorbing flavonoids) can protect the photosynthetic processes. In plants irradiated with UV-B throughout development a reduction in productivity is usually associated with a reduced ability to intercept light (i.e. smaller leaf area) and not an inhibition of photosynthetic competence. Finally, a review of field experiments utilizing realistic UV-B enhancement is made to evaluate whether the mechanisms involved in UV-B-induced depressions of photosynthesis are likely to impact on the photosynthetic productivity of crops and natural vegetation in the future. Predictions of plant responses to O 3 depletion are suspect from square-wave irradiance experiments in the field and controlled environments due to the increased sensitivity of plants to UV-B at relatively low photosynthetically-active photon flux densities (PPFD) and ultraviolet-A (UV-A) irradiances. Realistic modulated UV-B irradiances in the field do not appear to have any significant effects on photosynthetic competence or light-interception. It is concluded that O 3 depletion and the concurrent rise in UV-B irradiance is not a direct threat to photosynthetic productivity of crops and natural vegetation.
TL;DR: Increased C allocation to roots of M plants was associated with a stimulation of the activities of cell wall and cytoplasmic invertases and of sucrose synthase in roots colonized by VA fungi, which may provide the mechanism enabling increased partitioning of carbohydrate both to the M root system and the fungal symbiont.
Abstract: A comparative analysis of daily carbon (C) budgets and aspects of the C physiology of clover (Trifolium repens L.) colonized by vesicular-arbuscular (VA) mycorrhizal fungi was carried out over a 70 d growth period under conditions designed to ensure that shoots of mycorrhizal (M) and non-mycorrhizal (NM) plants were of similar nutrient status. C budgets did not differ on day 24 but by day 42 M plants had a significantly higher rate of photosynthesis than their NM counterparts when expressed on a whole shoot basis or unit dry weight basis. As both sets of plants were of the same size it was concluded that this greater C gain was the result of increased sink strength provided by the mycorrhizal fungus. By day 53 M plants had become larger than their uncolonized counterparts and a sink-induced stimulation in the rate of photosynthesis was no longer apparent. M plants had higher root sucrose, glucose and fructose pools from day 24. Analyses suggested that these sugars were utilized for trehalose and lipid synthesis, for the production of the large extramatrical mycelium and for the support of the respiratory demands of the M root system. Increased C allocation to roots of M plants was associated with a stimulation of the activities of cell wall and cytoplasmic invertases and of sucrose synthase in roots colonized by VA fungi. Such increases in enzyme activity may provide the mechanism enabling increased partitioning of carbohydrate both to the M root system and the fungal symbiont.
TL;DR: The present work places emphasis on the integrated nature of photosynthesis and proposes that much of the respiratory ATP necessary for whole cell photosynthesis may be generated during the production of C skeletons for N assimilation.
Abstract: The purpose of this review in reanalysing the ATP:reductant balance in illuminated leaf cells is to stress that photosynthesis in vivo does not involve CO 2 fixation alone, but embraces other processes, chief among which is N assimilation. Prior to the demonstration of CO 2 fixation and photophosphorylation by isolated chloroplasts, the mitochondria were thought likely to provide all the ATP required for CO 2 fixation (discussed in Arnon et al., 1954). During the 1960s, the development of techniques for the isolation of chloroplasts able to fix CO 2 at rates approaching those of the parent tissue induced a paradigm shift, leading to the establishment of a dominant (if not unanimous) view that chloroplasts in vivo must by themselves meet all their ATP requirements. More recent studies, however, indicate that the reality lies somewhere between these two extremes. The present work places emphasis on the integrated nature of photosynthesis and proposes that much of the respiratory ATP necessary for whole cell photosynthesis may be generated during the production of C skeletons for N assimilation. Rather than considering dissipative electron transport pathways as necessary to uncouple respiratory precursor synthesis from ATP production, the present analysis emphasizes the metabolic value of ATP produced during N-linked respiration, with cellular ATP supply being tailored to ATP demand.
TL;DR: The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to different light intensities were investigated in this paper.
Abstract: The photon use efficiencies and maximal rates of photosynthesis in Dunaliella salina (Chlorophyta) cultures acclimated to different light intensities were investigated. Batch cultures were grown to the mid-exponential phase under continuous low-light (LL: 100 μmol photon m-2 s-1) or high-light (HL: 2000 μmol photon m-2 s-1) conditions. Under LL, cells were normally pigmented (deep green) containing ∼500 chlorophyll (Chl) molecules per photosystem II (PSII) unit and ∼250 Chl molecules per photosystem I (PSI). HL-grown cells were yellow-green, contained only 60 Chl per PSII and 100 Chl per PSI and showed signs of chronic photoinhibition, i.e., accumulation of photodamaged PSII reaction centers in the chloroplast thylakoids. In LL-grown cells, photosynthesis saturated at ∼200 μmol photon m-2 s-1 with a rate (Pmax) of ∼100 mmol O2 (mol Chl)-1 s-1. In HL-grown cells, photosynthesis saturated at much higher light intensities, i.e. ∼2500 μmol photon m-2 s-1, and exhibited a three-fold higher Pmax (∼300 mmol O2 (mol Chl)-1 s-1) than the normally pigmented LL-grown cells. Recovery of the HL-grown cells from photoinhibition, occurring prior to a light-harvesting Chl antenna size increase, enhanced Pmax to ∼675 mmol O2 (mol Chl)-1 s-1. Extrapolation of these results to outdoor mass culture conditions suggested that algal strains with small Chl antenna size could exhibit 2–3 times higher productivities than currently achieved with normally pigmented cells.
01 Jan 1998
TL;DR: A genetic approach to Investigating Membrane Lipid Structure and Photosynthetic Function and its effects on the Ability of the Photosynthesis Machinery to Tolerate Temperature Stress is described.
Abstract: Preface. 1. Lipids in Photosynthesis: An Overview N. Murata, P.-A. Siegenthaler. 2. Structure, Distribution and Biosynthesis of Glycerolipids from Higher Plant Chloroplasts J. Joyard, et al. 3. Membrane Lipids in Algae J.L. Harwood. 4. Membrane Lipids in Cyanobacteria H. Wada, N. Murata. 5. Membrane Lipids in Anoxygenic Photosynthetic Bacteria C. Benning. 6. The Physical Properties of Thylakoid Membrane Lipids and Their Relation to Photosynthesis W.P. Williams. 7. Molecular Organization of Acyl Lipids in Photosynthetic Membranes of Higher Plants P.-A. Siegenthaler. 8. Role of Acyl Lipids in the Function of Photosynthetic Membranes in Higher Plants P.-A. Siegenthaler, A. Tremolieres. 9. Reconstitution of Photosynthetic Structures and Activities with Lipids A. Tremolieres, P.-A. Siegenthaler. 10. Lipid-Protein Interactions in Chloroplast Protein Import B. de Kruijff, et al. 11. Development of Thylakoid Membranes with Respect to Lipids E. Selstam. 12. Triglycerides as Products of Photosynthesis. Genetic Engineering, Fatty Acid Composition and Structure of Triglycerides D. Facciotti, V. Knauf. 13. Genetic Engineering of the Unsaturation of Membrane Glycerolipid: Effects on the Ability of the Photosynthetic Machinery to Tolerate Temperature Stress Z. Gombos, N. Murata. 14. A Genetic Approach to Investigating Membrane Lipid Structure and Photosynthetic Function P. Vijayan, et al. 15. Involvement of Chloroplast Lipids in the Reaction of Plants Submitted to Stress J.L. Harwood. Index.
TL;DR: It is hypothesised that there is a continuous vertical migration in the top layer of the sediment, where algae can avoid photoinhibition due to prolonged periods of high irradiance and lack of CO2 by migrating downwards while others migrate upwards.
Abstract: A pulse amplitude modulated fluorometer (PAM) was used to investigate photosynthetic activity of microphytobenthos on an intertidal mudflat. Spectral irradiance measurements indicate that 75% of the signal detectable by the PAM originates in the upper 150 mu m of the sediment. From the photosynthetic electron transport rate (ETR) measurements, it was concluded that the PAM could be used to observe changes in photosynthetic parameters during the day or the season. Photoacclimation to lower irradiance was indicated by changes in the maximum ETR and the saturating photon irradiance parameter I-k. When cores were exposed to a high photon irradiance for several hours, vertical migration could be followed using reflectance spectra. The data also showed that the benthic algae did not seem to experience photoinhibition or CO2 limitation. To explain this, it is hypothesised that there is a continuous vertical migration in the top layer of the sediment, where algae can avoid photoinhibition due to prolonged periods of high irradiance and lack of CO2 by migrating downwards while others migrate upwards. [KEYWORDS: microphytobenthos; chlorophyll fluorescence photosynthesis; vertical migration; C-limitation Estuary sw netherlands; photosystem-ii; marine-phytoplankton; light; photoinhibition; sediments; stabilization; respiration;communities; limitations]
TL;DR: It is shown that two components with slow and fast reaction kinetics, respectively, are involved in photoinhibition and recovery of photosynthesis, and the half-life time of the inhibition and recovery phases is clearly related to the depth distribution of the investigated species.
Abstract: The capability of several macroalgal species to protect photosynthesis from excessive irradiance by dynamic photoinhibition was investigated relative to their depth distribution in summer 1995 in the Kongsfjord (79°N; 12°E, Ny Alesund, Spitsbergen, Norway). Photoinhibition of photosynthesis was induced by exposure of algae from different water depths to a high photon fluence rate of 500 μmol m−2 s−1 for 2 h. Changes in optimal quantum yield (F
v/F
m) were measured during the inhibition phase. Recovery of photosynthesis was subsequently induced by dim white light (10 μmol m−2 s−1) and observed as changes in the variable fluorescence. With a newly developed mathematical model different parameters of the response kinetics of inhibition and recovery were calculated and related to the depth distribution of each algal species. It is shown that two components with slow and fast reaction kinetics, respectively, are involved in photoinhibition and recovery of photosynthesis. Their possible molecular bases are discussed. The half-life time (τ) of the inhibition and recovery phases, i.e. the time necessary to reach half maximal response, is clearly related to the depth distribution of the investigated species. Algae collected close to the water surface show a fast reaction of both photoinhibition and recovery and, hence, have a low τ. With increasing depth the reactions become slower and τ increases. τ was highest in deep water algae. Further analysis of the reaction kinetics in Laminaria saccharina shows that the relative proportion of the two kinetics involved change with the collection depth. In contrast, a significant difference in the reaction rates of both kinetics was not observed.
TL;DR: Although plastid aldolase catalyses a readily reversible reaction, possesses no known regulatory properties, and would appear irrelevant for the control of metabolism and growth, small changes in its activity have marked consequences for photosynthesis, carbon partitioning and growth.
Abstract: Antisense expression of a full length cDNA encoding plastid aldolase led to decreased expression of aldolase at the transcript and protein level in several 'antisense' potato transformants. To quantify the inhibition, activity was compared in corresponding leaves down a plant and in plants of different ages. Aldolase activity was decreased by 32-43%, 56-71%, 79-83% and 91-97% in A-70, A-3, A-51 and A-2. Separation on a Q-Sepharose-FF column showed the decrease was due to inhibition of plastid aldolase. The transformants showed a small increase of Rubisco activity, a small decrease of phosphoribulokinase activity, and larger but subproportional decreases of sedoheptulose-1,7-biphosphatase and plastid fructose-1,6-bisphosphatase activity. Ambient photosynthesis was inhibited by 10%, 40%, 66% and 85% in A-70, A-3, A-51 and A-2. The transformants contained increased triose phosphates, and very low ribulose-1,5-bisphosphate and glycerate-3-phosphate. Chlorophyll fluorescence indicated that photosystem II was more reduced and thylakoid energization was increased. Starch synthesis was decreased by 16% and 36% in A-70 and A-3, whereas sucrose synthesis was less strongly inhibited. Plant growth was not significantly altered in A-70, was decreased by 41% in A-3, and was severely inhibited in plants with under 20% of wild-type aldolase activity. Although plastid aldolase catalyses a readily reversible reaction, possesses no known regulatory properties, and would appear irrelevant for the control of metabolism and growth, small changes in its activity have marked consequences for photosynthesis, carbon partitioning and growth.
TL;DR: It is argued that the root/rhizome system offers a competitive advantage in nutrient-poor waters, but that it makes the plant vulnerable when changes in water quality lead to reduction of incident light.
TL;DR: Results suggest that acclimation under low N is caused by limitation of sink development rather than being a direct effect of N supply on photosynthesis.
Abstract: Acclimation of photosynthesis to elevated CO2 has previously been shown to be more pronounced when N supply is poor. Is this a direct effect of N or an indirect effect of N by limiting the development of sinks for photoassimilate? This question was tested by growing a perennial ryegrass (Lolium perenne) in the field under elevated (60 Pa) and current (36 Pa) partial pressures of CO2 (pCO2) at low and high levels of N fertilization. Cutting of this herbage crop at 4- to 8-week intervals removed about 80% of the canopy, therefore decreasing the ratio of photosynthetic area to sinks for photoassimilate. Leaf photosynthesis, in vivo carboxylation capacity, carbohydrate, N, ribulose-1,5-bisphosphate carboxylase/oxygenase, sedoheptulose-1,7-bisphosphatase, and chloroplastic fructose-1, 6-bisphosphatase levels were determined for mature lamina during two consecutive summers. Just before the cut, when the canopy was relatively large, growth at elevated pCO2 and low N resulted in significant decreases in carboxylation capacity and the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase protein. In high N there were no significant decreases in carboxylation capacity or proteins, but chloroplastic fructose-1,6-bisphosphatase protein levels increased significantly. Elevated pCO2 resulted in a marked and significant increase in leaf carbohydrate content at low N, but had no effect at high N. This acclimation at low N was absent after the harvest, when the canopy size was small. These results suggest that acclimation under low N is caused by limitation of sink development rather than being a direct effect of N supply on photosynthesis.
TL;DR: It is concluded that salinity reduces photosynthesis primarily by reducing the diffusion of CO2 to the chloroplast, both by stomatal closure and by changes in mesophyll structure which decreases the conductance to CO2 diffusion within the leaf.
Abstract: Spinach (Spinacia oleracea L.) leaves stressed by irrigation with water containing 1% (w/v) NaCl for 20 days had low conductance to CO2 diffusion both at the stomata and in the mesophyll. Mesophyll anatomy changed in salt-stressed leaves, which could have accounted for the decreased mesophyll conductance. Ribulose- 1,5-bisphosphate carboxylase/oxygenase in vitro activity and content were not affected by up to 20 days exposure to salinity but decreased when leaves were exposed to salt stress for longer than 20 days. Salt accumulation also caused a drop of Ca and Mg which might have decreased membrane stability and chlorophyll content, respectively. Measurements of chlorophyll fluorescence indicated that the 20-day-long salt stress did not directly affect photochemistry. We conclude that salinity reduces photosynthesis primarily by reducing the diffusion of CO2 to the chloroplast, both by stomatal closure and by changes in mesophyll structure which decreases the conductance to CO2 diffusion within the leaf. The capacity for carbon metabolism is eventually reduced but that occurs after substantial decreases in the conductance to CO2 diffusion.
TL;DR: It is suggested that this additional C gained by colonized plants was allocated to the mycorrhizal fungus and that it is the fungus, by acting as a sink for assimilates, that facilitated the stimulation in the rate of photosynthesis of the plant partner.
Abstract: The influence of vesicular‐arbuscular mycorrhizal (M) colonization on biomass production and photosynthesis of Trifolium repens L. was investigated in two experiments in which the foliar nitrogen and phosphorus contents of nonmycorrhizal (NM) plants were manipulated to be no lower than that of M plants. Throughout both experiments there was a stimulation in the rate of CO 2 assimilation of the youngest, fully expanded leaf of M compared with NM plants. In addition, M plants exhibited a higher specific leaf area compared with NM plants, a response that maximized the area available for CO2 assimilation per unit of carbon (C) invested. Despite the increased rate of photosynthesis in M plants there was no evidence that the additional C gained was converted to biomass production of M plants. It is suggested that this additional C gained by colonized plants was allocated to the mycorrhizal fungus and that it is the fungus, by acting as a sink for assimilates, that facilitated the stimulation in the rate of photosynthesis of the plant partner.
TL;DR: A far-red type of oxygenic photosynthesis was discovered in Acaryochloris marina, a recently found marine prokaryote that produces an atypical pigment chlorophyll d (Chl d) that might either be an acclimation to theFar-red light environments or an evolutionary intermediate between the red-absorbing oxygenic and the far- red absorbing anoxygenic photosynthesis that uses bacteriochlorophylls.
Abstract: A far-red type of oxygenic photosynthesis was discovered in Acaryochloris marina, a recently found marine prokaryote that produces an atypical pigment chlorophyll d (Chl d). The purified photosystem I reaction center complex of A. marina contained 180 Chl d per 1 Chl a with PsaA–F, -L, -K, and two extra polypeptides. Laser excitation induced absorption changes of reaction center Chl d that was named P740 after its peak wavelength. A midpoint oxidation reduction potential of P740 was determined to be +335 mV. P740 uses light of significantly low quantum energy (740 nm = 1.68 eV) but generates a reducing power almost equivalent to that produced by a special pair of Chl a (P700) that absorbs red light at 700 nm (1.77 eV) in photosystem I of plants and cyanobacteria. The oxygenic photosynthesis based on Chl d might either be an acclimation to the far-red light environments or an evolutionary intermediate between the red-absorbing oxygenic and the far-red absorbing anoxygenic photosynthesis that uses bacteriochlorophylls.
TL;DR: It is concluded that interspecific variation may be a more important determinant of photosynthetic response to CO(2) than temperature.
Abstract: Biochemical models of photosynthesis suggest that rising temperatures will increase rates of net carbon dioxide assimilation and enhance plant responses to increasing atmospheric concentrations of CO(2). We tested this hypothesis by evaluating acclimation and ontogenetic drift in net photosynthesis in seedlings of five boreal tree species grown at 370 and 580 mmol mol(-1) CO(2) in combination with day/night temperatures of 18/12, 21/15, 24/18, 27/21, and 30/24 degrees C. Leaf-area-based rates of net photosynthesis increased between 13 and 36% among species in plants grown and measured in elevated CO(2) compared to ambient CO(2). These CO(2)-induced increases in net photosynthesis were greater for slower-growing Picea mariana (Mill.) B.S.P., Pinus banksiana Lamb., and Larix laricina (Du Roi) K. Koch than for faster-growing Populus tremuloides Michx. and Betula papyrifera Marsh., paralleling longer-term growth differences between CO(2) treatments. Measures at common CO(2) concentrations revealed that net photosynthesis was down-regulated in plants grown at elevated CO(2). In situ leaf gas exchange rates varied minimally across temperature treatments and, contrary to predictions, increasing growth temperatures did not enhance the response of net photosynthesis to elevated CO(2) in four of the five species. Overall, the species exhibited declines in specific leaf area and leaf nitrogen concentration, and increases in total nonstructural carbohydrates in response to CO(2) enrichment. Consequently, the elevated CO(2) treatment enhanced rates of net photosynthesis much more when expressed on a leaf area basis (25%) than when expressed on a leaf mass basis (10%). In all species, rates of leaf net CO(2) exchange exhibited modest declines with increasing plant size through ontogeny. Among the conifers, enhancements of photosynthetic rates in elevated CO(2) were sustained through time across a wide range of plant sizes. In contrast, for Populus tremuloides and B. papyrifera, mass-based photosynthetic rates did not differ between CO(2) treatments. Overall, net photosynthetic rates were highly correlated with relative growth rate as it varied among species and treatment combinations through time. We conclude that interspecific variation may be a more important determinant of photosynthetic response to CO(2) than temperature.
TL;DR: Differences in the degree of inhibition and recovery of photosynthetic efficiency and capacity indicate that UV-radiation is one important factor affecting the vertical distribution of macroalgae in nature.
Abstract: Due to depletion of stratospheric ozone over polar regions of the Northern and Southern Hemispheres UV-B-radiation has increased at the surface of the earth. Measurements of variable chlorophyll fluorescence were conducted to document UV-induced photoinhibition of photosystem II in cultivated macroalgae with different depth distributions in Antarctica. The reactions during artificial UV-exposure were observed on a short time scale (hours) and in light–dark cycles over several days. The nine species of investigated macroalgae show great differences in UV-tolerance of the photosynthetic process. Photosynthesis of the studied green algae was inhibited to a minor degree, while the brown algae showed an intermediate inhibition of photosynthesis. The response of the studied red algae varied with species. The differences in the degree of inhibition and recovery of photosynthetic efficiency and capacity indicate that UV-radiation is one important factor affecting the vertical distribution of macroalgae in nature.
TL;DR: It is concluded that similar proportions of the aquatic and terrestrial floras have evolved CAM photosynthesis, and it is hypothesized that neotropical lacustrine species may be more ancient in origin and have given rise to terrestrial species, which have retained most of the characteristics of their aquatic ancestry.
Abstract: Crassulacean acid metabolism (CAM) is a CO2-concentrating mechanism selected in response to aridity in terrestrial habitats, and, in aquatic environments, to ambient limitations of carbon. Evidence is reviewed for its presence in five genera of aquatic vascular plants, includingIsoetes, Sagittaria, Vallisneria, Crassula, andLittorella. Initially, aquatic CAM was considered by some to be an oxymoron, but some aquatic species have been studied in sufficient detail to say definitively that they possess CAM photosynthesis. CO2-concentrating mechanisms in photosynthetic organs require a barrier to leakage; e.g., terrestrial C4 plants have suberized bundle sheath cells and terrestrial CAM plants high stomatal resistance. In aquatic CAM plants the primary barrier to CO2 leakage is the extremely high difrusional resistance of water. This, coupled with the sink provided by extensive intercellular gas space, generates daytime CO2(pi) comparable to terrestrial CAM plants. CAM contributes to the carbon budget by both net carbon gain and carbon recycling, and the magnitude of each is environmentally influenced. Aquatic CAM plants inhabit sites where photosynthesis is potentially limited by carbon. Many occupy moderately fertile shallow temporary pools that experience extreme diel fluctuations in carbon availability. CAM plants are able to take advantage of elevated nighttime CO2 levels in these habitats. This gives them a competitive advantage over non-CAM species that are carbon starved during the day and an advantage over species that expend energy in membrane transport of bicarbonate. Some aquatic CAM plants are distributed in highly infertile lakes, where extreme carbon limitation and light are important selective factors.
TL;DR: Test if general relationships exist between chlorophyll concentration, light attenuation, and gross photosynthesis across phytoplankton communities, macrophyte stands, and attached microalgal mats determines the upper limit to photosynthesis in the various communities.
Abstract: We compiled 414 studies from the literature to test if general relationships exist between chlorophyll concentration, light attenuation, and gross photosynthesis across phytoplankton communities, macrophyte stands, and attached microalgal mats. We also evaluated the upper limit to photosynthesis in the various communities. Along with increasing chlorophyll concentration, the photic zone diminishes from >100 m in sparse phytoplankton communities to centimeters-meters in macrophyte stands to
TL;DR: A high degree of co-ordination is apparent between stomatal behaviour, photosynthetic capacity and photoprotection mechanisms in trees during the summer in Portugal.
Abstract: Daily changes in photoprotective mechanisms were studied in sun leaves of Quercus suber L., Quercus ilex L., Olea europaea L. and Eucalyptus globulus Labill. trees during the summer in Portugal. Even though stomatal closure explained most of the diurnal variation in carbon assimilation along the summer, a decline in the photochemical yield of photosystem II (F′v/F′m) also occurred, as a result of an excess of intercepted solar radiation when carbon assimilation is limited by stomatal closure due to high vapour pressure deficits and/or soil water deficits. These changes were accompanied by the conversion of violaxanthin to antheraxanthin and zeaxanthin which were correlated with thermal dissipation of excess photon energy. In spite of a common general response, differences between species were observed -Olea europaea, which is a slow-growing tree, had the lowest net photosynthetic rates, the highest proportion of carotenoids in relation to chlorophyll and the highest rates of de-epoxidation of violaxanthin. This enabled a large thermal dissipation of the excess intercepted radiation but led to rather small values of light utilisation for photochemistry (ca 20%). In contrast, in E. globulus, a fast-growing tree, photosynthetic rates were the highest, thermal dissipation of absorbed radiation the lowest and maximal values of light utilisation for photochemistry reached ca 50%. The two Quercus species exhibited an intermediate response. A high degree of co-ordination is apparent between stomatal behaviour, photosynthetic capacity and photoprotection mechanisms.