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PubMed1999

Dynamics of anoxygenic photosynthesis in an experimental green sulphur bacteria biofilm.

The dynamics of sulphide oxidation in an experimental biofilm of the green sulphur bacterium, Prosthecochloris aestuarii, were studied using a newly developed light-dark cycling procedure. The biofilm was grown for 6 weeks in a benthic gradient chamber, in which gradients of light, sulphide and oxygen were imposed experimentally. The H2S concentrations and pH were measured with microsensors as a function of depth in the biofilm and of time after a change in illumination status. The sulphide oxidation rates were calculated as a function of time and depth in the biofilm using a numerical procedure to solve the non-stationary general diffusion equation. A close agreement was found between the areal rates of anoxygenic photosynthesis during the cycling procedure and the steady state before the cycling experiment. For the different layers of the biofilm, the maximum activity was observed after 10-12min of light exposure. After this maximum, sulphide oxidation decreased concomitantly with sulphide concentration, indicating sulphide limitation of anoxygenic photosynthesis. This lag time limits the application of the standard dark-light shift method with a brief light exposure of a few seconds and, therefore, the numerical procedure described in this study enables the depth distribution of anoxygenic photosynthesis rates in microbial mats to be determined more accurately.

Anaerobiosis↗
PubMed2004

Diffusive and metabolic limitations to photosynthesis under drought and salinity in C(3) plants.

Drought and salinity are two widespread environmental conditions leading to low water availability for plants. Low water availability is considered the main environmental factor limiting photosynthesis and, consequently, plant growth and yield worldwide. There has been a long-standing controversy as to whether drought and salt stresses mainly limit photosynthesis through diffusive resistances or by metabolic impairment. Reviewing in vitro and in vivo measurements, it is concluded that salt and drought stress predominantly affect diffusion of CO(2) in the leaves through a decrease of stomatal and mesophyll conductances, but not the biochemical capacity to assimilate CO(2), at mild to rather severe stress levels. The general failure of metabolism observed at more severe stress suggests the occurrence of secondary oxidative stresses, particularly under high-light conditions. Estimates of photosynthetic limitations based on the photosynthetic response to intercellular CO(2) may lead to artefactual conclusions, even if patchy stomatal closure and the relative increase of cuticular conductance are taken into account, as decreasing mesophyll conductance can cause the CO(2) concentration in chloroplasts of stressed leaves to be considerably lower than the intercellular CO(2) concentration. Measurements based on the photosynthetic response to chloroplast CO(2) often confirm that the photosynthetic capacity is preserved but photosynthesis is limited by diffusive resistances in drought and salt-stressed leaves.

Carbon Dioxide↗
PubMed2005

No down-regulation of leaf photosynthesis in mature forest trees after three years of exposure to elevated CO2.

The photosynthetic responses of six species of mature forest trees to long-term exposure to elevated CO2 (ca. 530 ppm) were determined at the Swiss Canopy Crane (SCC) site near Basel, Switzerland. In the third year of growth in elevated CO2, using web-FACE technology, net photosynthesis (As) in fully sunlit, upper canopy foliage was stimulated by ca. 40% compared to ambient controls. This enhancement did not differ from the instantaneous increase in As found in ambient-grown leaves that were temporarily measured at elevated CO2. A complete lack of down-regulation of photosynthesis was found in all species and in both the early and the late growing season. Neither was leaf nitrogen content significantly affected by long-term exposure to elevated CO2. Our results document a persistent enhancement in leaf level photosynthesis in response to elevated CO2 in mature forest trees over a period of three years. Circumstantial evidence suggests that the additional assimilates feed into large sinks other than stem and shoot growth.

Air Pollutants↗
PubMed2004

Enhanced translation of a chloroplast-expressed RbcS gene restores small subunit levels and photosynthesis in nuclear RbcS antisense plants.

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is a key enzyme that converts atmospheric carbon to food and supports life on this planet. Its low catalytic activity and specificity for oxygen leads to photorespiration, severely limiting photosynthesis and crop productivity. Consequently, Rubisco is a primary target for genetic engineering. Separate localization of the genes in the nuclear and chloroplast genomes and a complex assembly process resulting in a very low catalytic activity of hybrid Rubisco enzymes have rendered several earlier attempts of Rubisco engineering unsuccessful. Here we demonstrate that the RbcS gene, when integrated at a transcriptionally active spacer region of the chloroplast genome, in a nuclear RbcS antisense line and expressed under the regulation of heterologous (gene 10) or native (psbA) UTRs, results in the assembly of a functional holoenzyme and normal plant growth under ambient CO(2) conditions, fully shortcircuiting nuclear control of gene regulation. There was approximately 150-fold more RbcS transcript in chloroplast transgenic lines when compared with the nuclear RbcS antisense line, whereas the wild type has 7-fold more transcript. The small subunit protein levels in the gene 10/RbcS and psbA/RbcS plants were 60% and 106%, respectively, of the wild type. Photosynthesis of gene 10/RbcS plants was approximately double that of the antisense plants, whereas that of psbA/RbcS plants was restored almost completely to the wild-type rates. These results have opened an avenue for using chloroplast engineering for the evaluation of foreign Rubisco genes in planta that eventually can result in achieving efficient photosynthesis and increased crop productivity.

Carbon Dioxide↗
PubMed2000

Effect of Bradyrhizobium photosynthesis on stem nodulation of Aeschynomene sensitiva.

Some leguminous species of the genus Aeschynomene are specifically stem-nodulated by photosynthetic bradyrhizobia. To study the effect of bacterial photosynthesis during symbiosis, we generated a photosynthesis-negative mutant of the Bradyrhizobium sp. strain ORS278 symbiont of Aeschynomene sensitiva. The presence of a functional photosynthetic unit in bacteroids and the high expression of the photosynthetic genes observed in stem nodules demonstrate that the bacteria are photosynthetically active during stem symbiosis. Stem inoculation by the photosynthetic mutant gave a 50% decrease in stem-nodule number, which reduced nitrogen fixation activity and plant growth in the same proportion. These results indicate an important role of bacterial photosynthesis in the efficiency of stem nodulation.

Bacterial Proteins↗
PubMed1971

The light reactions of photosynthesis.

Historically, the role of light in photosynthesis has been ascribed either to a photolysis of carbon dioxide or to a photolysis of water and a resultant rearrangement of constituent atoms into molecules of oxygen and glucose (or formaldehyde). The discovery of photophosphorylation demonstrated that photosynthesis includes a light-induced phosphorus metabolism that precedes, and is independent from, a photolysis of water or CO(2). ATP formation could best be accounted for not by a photolytic disruption of the covalent bonds in CO(2) or water but by the operation of a light-induced electron flow that results in a release of free energy which is trapped in the pyrophosphate bonds of ATP. Photophosphorylation is now divided into (a) a non-cyclic type, in which the formation of ATP is coupled with a light-induced electron transport from water to ferredoxin and a concomitant evolution of oxygen and (b) a cyclic type which yields only ATP and produces no net change in the oxidation-reduction state of any electron donor or acceptor. Reduced ferredoxin formed in (a) serves as an electron donor for the reduction of NADP by an enzymic reaction that is independent of light. ATP, from both cyclic and noncyclic photophosphorylation, and reduced NADP jointly constitute the assimilatory power for the conversion of CO(2) to carbohydrates (3 moles of ATP and 2 moles of reduced NADP are required per mole of CO(2)).Investigations, mainly with whole cells, have shown that photosynthesis in green plants involves two photosystems, one (System II) that best uses light of "short" wavelength (lambda < 685 nm) and another (System I) that best uses light of "long" wavelength (lambda > 685 nm). Cyclic photophosphorylation in chloroplasts involves a System I photoreaction. Noncyclic photophosphorylation is widely held to involve a collaboration of two photoreactions: a short-wavelength photoreaction belonging to System II and a long-wavelength photoreaction belonging to System I. Recent findings, however, indicate that noncyclic photophosphorylation may include two short-wavelength, System II, photoreactions that operate in series and are joined by a "dark" electron-transport chain to which is coupled a phosphorylation site.

Adenosine Triphosphate↗
PubMed1994

The recovery of photosynthesis from low-temperature photoinhibition is accelerated by the unsaturation of membrane lipids: a mechanism of chilling tolerance.

In a previous study of mutants in fatty-acid desaturation of Synechocystis PCC6803, it was demonstrated that the photoinhibition of photosynthesis at low temperature in vivo is tolerated by cells as a result of the unsaturation of glycerolipids of thylakoid membranes. Since the extent of photoinhibition of photosynthesis in vivo depends on a balance between the photoinduced inactivation and the recovery from the photoinhibited state, an examination was made of the effects of the unsaturation of membrane lipids on these processes. It appears that the unsaturation of the membrane lipids does not affect the inactivation process but accelerates the recovery process and, moreover, that the apparent increase in the photoinhibition in vivo of photosynthesis at low temperature is caused by a depressed rate of recovery at low temperature.

Chloramphenicol↗
PubMed1996

A global two component signal transduction system that integrates the control of photosynthesis, carbon dioxide assimilation, and nitrogen fixation.

Photosynthesis, biological nitrogen fixation, and carbon dioxide assimilation are three fundamental biological processes catalyzed by photosynthetic bacteria. In the present study, it is shown that mutant strains of the nonsulfur purple photosynthetic bacteria Rhodospirillum rubrum and Rhodobacter sphaeroides, containing a blockage in the primary CO2 assimilatory pathway, derepress the synthesis of components of the nitrogen fixation enzyme complex and abrogate normal control mechanisms. The absence of the Calvin-Benson-Bassham (CBB) reductive pentose phosphate CO2 fixation pathway removes an important route for the dissipation of excess reducing power. Thus the mutant strains develop alternative means to remove these reducing equivalents, resulting in the synthesis of large amounts of nitrogenase even in the presence of ammonia. This response is under the control of a global two-component signal transduction system previously found to regulate photosystem biosynthesis and the transcription of genes required for CO2 fixation through the CBB pathway and alternative routes. In addition, this two-component system directly controls the ability of these bacteria to grow under nitrogen-fixing conditions. These results indicate that there is a molecular link between the CBB and nitrogen fixation process, allowing the cell to overcome powerful control mechanisms to remove excess reducing power generated by photosynthesis and carbon metabolism. Furthermore, these results suggest that the two-component system integrates the expression of genes required for the three processes of photosynthesis, nitrogen fixation, and carbon dioxide fixation.

Carbon Dioxide↗
PubMed2006

Global regulation of photosynthesis and respiration by FnrL: the first two targets in the tetrapyrrole pathway.

Fnr is a regulator that controls the expression of a variety of genes in response to oxygen limitation in bacteria. To assess the role of Fnr in photosynthesis in Rubrivivax gelatinosus, a strain carrying a null mutation in fnrL was constructed. It was unable to grow anaerobically in the light, but, intriguingly, it was able to produce photosynthetic complexes under high oxygenation conditions. The mutant lacked all c-type cytochromes normally detectable in microaerobically-grown wild type cells and accumulated coproporphyrin III. These data suggested that the pleiotropic phenotype observed in FNR is primarily due to the control at the level of the HemN oxygen-independent coproporphyrinogen III dehydrogenase. hemN expression in trans partially suppressed the FNR phenotype, as it rescued heme and cytochrome syntheses. Nevertheless, these cells were photosynthetically deficient, and pigment analyses showed that they were blocked at the level of Mg(2+)-protoporphyrin monomethyl ester. Expression of both hemN and bchE in the FNR mutant restored synthesis of Mg(2+)-protochlorophyllide. We, therefore, conclude that FnrL controls respiration by regulating hemN expression and controls photosynthesis by regulating both hemN and bchE expression. A comprehensive picture of the control points of microaerobic respiration and photosynthesis by FnrL is provided, and the prominent role of this factor in activating alternative gene programs after reduction of oxygen tension in facultative aerobes is discussed.

Bacterial Proteins↗
PubMed2002

Wild manihot species do not possess C4 photosynthesis.

Cultivated cassava (Manihot esculenta) has a higher rate of photosynthesis than is usual for C3 plants and photosynthesis is not light saturated. For these reasons it has been suggested that cultivated cassava could be derived from wild species possessing C4 photosynthesis. The natural abundance of 13C and activities of phosphoenolpyruvate carboxylase and phosphoglycolate phosphatase were measured in leaves of 20 wild cassava species to test this hypothesis. All the species studied, including M. flabellifolia the potential wild progenitor of cultivated cassava, clearly exhibited C3 not C4 characteristics.

Carbon Isotopes↗
PubMed2002

Drought-inhibition of photosynthesis in C3 plants: stomatal and non-stomatal limitations revisited.

There is a long-standing controversy as to whether drought limits photosynthetic CO2 assimilation through stomatal closure or by metabolic impairment in C3 plants. Comparing results from different studies is difficult due to interspecific differences in the response of photosynthesis to leaf water potential and/or relative water content (RWC), the most commonly used parameters to assess the severity of drought. Therefore, we have used stomatal conductance (g) as a basis for comparison of metabolic processes in different studies. The logic is that, as there is a strong link between g and photosynthesis (perhaps co-regulation between them), so different relationships between RWC or water potential and photosynthetic rate and changes in metabolism in different species and studies may be 'normalized' by relating them to g. Re-analysing data from the literature using light-saturated g as a parameter indicative of water deficits in plants shows that there is good correspondence between the onset of drought-induced inhibition of different photosynthetic sub-processes and g. Contents of ribulose bisphosphate (RuBP) and adenosine triphosphate (ATP) decrease early in drought development, at still relatively high g (higher than 150 mmol H20 m(-2) s(-1)). This suggests that RuBP regeneration and ATP synthesis are impaired. Decreased photochemistry and Rubisco activity typically occur at lower g (<100 mmol H20 m(-2) s(-1)), whereas permanent photoinhibition is only occasional, occurring at very low g (<50 mmol H20 m(-2) s(-1)). Sub-stomatal CO2 concentration decreases as g becomes smaller, but increases again at small g. The analysis suggests that stomatal closure is the earliest response to drought and the dominant limitation to photosynthesis at mild to moderate drought. However, in parallel, progressive down-regulation or inhibition of metabolic processes leads to decreased RuBP content, which becomes the dominant limitation at severe drought, and thereby inhibits photosynthetic CO2 assimilation.

Adenosine Triphosphate↗
PubMed2004

Acclimation of photosynthesis to light and canopy nitrogen distribution: an interpretation.

BACKGROUND AND AIMS: Acclimation of photosynthesis to light and its connection with canopy nitrogen (N) distribution are considered. An interpretation of a proportionality between light-saturated photosynthesis and local averaged leaf irradiance is proposed by means of a simple model. MODEL: The model assumes (a) local irradiance drives synthesis of photosynthetic protein from metabolic N; (b) photosynthetic N is slowly degraded over approx. 5-7 d; (c) metabolic N is equally available through the canopy. CONCLUSIONS: The kinetics of acclimation at different light levels may provide a way of parameterizing and testing the model. The model provides a rationale for the proportionality assumption mentioned above, which, while it is consistent with much experimental work, is valuable because it allows canopy photosynthesis to be calculated analytically.

Acclimatization↗
PubMed2005

Photosynthesis in relation to reproductive success of Cypripedium flavum.

BACKGROUND AND AIMS: Cypripedium flavum is a rare, endemic alpine slipper orchid of China, which is under threat from excessive collection and habitat changes. Conservation and re-introduction of C. flavum is restricted by lack of knowledge of the plant's photosynthesis and how that affects reproductive success. The hypothesis is tested that reproductive success is determined by photosynthetic production. * METHODS: To understand the photosynthetic characteristics and adaptation of C. flavum to alpine environments, and the relation to reproductive success, measurements were made at four field sites with varying degrees of forest cover in the Hengduan Mountains, south-west China. * KEY RESULTS: Both photosynthetic capacity and reproductive traits of C. flavum are affected by light availability. Photosynthetic rate (A) is greatest around noon, following the pattern of photosynthetically active radiation (PAR) at all sites. Cypripedium flavum has highest daily mean photosynthetic rate (A(daily)) and light-saturated photosynthetic rate (A(max)) under a half to a third of full sunlight. High radiation decreased A. However, the optimum temperature for photosynthesis was similar (18-20 degrees C) at all sites. * CONCLUSIONS: The quotient of daily mean photosynthetic rate to light saturated photosynthesis (A(daily)/A(max)) is positively correlated with the ramet number m(-2) and percentage of fruiting of C. flavum. The A(daily)/A(max) ratio is a useful proxy for evaluating reproductive success of C. flavum.

Carbon Dioxide↗
PubMed2001

Over-expression of cytosolic glutamine synthetase increases photosynthesis and growth at low nitrogen concentrations.

Nitrogen, which is a major limiting nutrient for plant growth, is assimilated as ammonium by the concerted action of glutamine synthetase (GS) and glutamate synthase (GOGAT). GS catalyses the critical incorporation of inorganic ammonium into the amino acid glutamine. Two types of GS isozymes, located in the cytosol (GS1) and in the chloroplast (GS2) have been identified in plants. Tobacco (Nicotiana tabacum) transformants, over-expressing GS1 driven by the constitutive CaMV 35S promoter were analysed. GS in leaves of GS-5 and GS-8 plants was up-regulated, at the level of RNA and proteins. These transgenic plants had six times higher leaf GS activity than controls. Under optimum nitrogen fertilization conditions there was no effect of GS over-expression on photosynthesis or growth. However, under nitrogen starvation the GS transgenics had c. 70% higher shoot and c. 100% greater root dry weight as well as 50% more leaf area than low nitrogen controls. This was achieved by the maintenance of photosynthesis at rates indistinguishable from plants under high nitrogen, while photosynthesis in control plants was inhibited by 40-50% by nitrogen deprivation. It was demonstrated that manipulation of GS activity has the potential to maintain crop photosynthetic productivity while reducing nitrogen fertilization and the concomitant pollution.

Cytosol↗
PubMed2000

Photosynthesis modulates the plant feeding of Phlebotomus papatasi (Diptera: Psychodidae).

Phlebotomus papatasi (Scopoli), the vector of Leishmania major (Yakimoff & Schokhor), feeds on plants in desert habitats in the Jordan Valley. At the end of the dry summer, the life span of sand flies is short and the amount of sugars in their guts is small. In this season the plants are under the stress of heat and dehydration. This stress arrests the photosynthesis and decreases the amounts of the main end products, sucrose and starch. We presumed that the paucity of sugars in the sand fly plant tissue diet resulted from the arrest of photosynthesis. To test this assumption, we compared the feeding of sand flies on branches of Capparis spinosa (L.) that had been kept for 24 h in darkness and on branches cut after a normal day of photosynthesis. In darkness, the branches had lost more than half of their sugar content. Afterward they were fed upon overnight by 45.2% of female and 14.3% of male sand flies. A higher proportion of 81.0% females and 38.7% males fed on branches from natural conditions and these fed flies were significantly heavier. Laboratory experiments also showed that plant tissue meals of P. papatasi often include starch grains. Such grains were found also in 50% of field-caught males and females. The nutritive potential of plant tissues was demonstrated by the 33-d median survival of P. papatasi series that had been maintained on fresh C. spinosa branches and water.

Animals↗
PubMed1997

Photomorphogenesis, photosynthesis, and seed yield of wheat plants grown under red light-emitting diodes (LEDs) with and without supplemental blue lighting.

Red light-emitting diodes (LEDs) are a potential light source for growing plants in spaceflight systems because of their safety, small mass and volume, wavelength specificity, and longevity. Despite these attractive features, red LEDs must satisfy requirements for plant photosynthesis and photomorphogenesis for successful growth and seed yield. To determine the influence of gallium aluminium arsenide (GaAlAs) red LEDs on wheat photomorphogenesis, photosynthesis, and seed yield, wheat (Triticum aestivum L., cv. 'USU-Super Dwarf') plants were grown under red LEDs and compared to plants grown under daylight fluorescent (white) lamps and red LEDs supplemented with either 1% or 10% blue light from blue fluorescent (BF) lamps. Compared to white light-grown plants, wheat grown under red LEDs alone demonstrated less main culm development during vegetative growth through preanthesis, while showing a longer flag leaf at 40 DAP and greater main culm length at final harvest (70 DAP). As supplemental BF light was increased with red LEDs, shoot dry matter and net leaf photosynthesis rate increased. At final harvest, wheat grown under red LEDs alone displayed fewer subtillers and a lower seed yield compared to plants grown under white light. Wheat grown under red LEDs+10% BF light had comparable shoot dry matter accumulation and seed yield relative to wheat grown under white light. These results indicate that wheat can complete its life cycle under red LEDs alone, but larger plants and greater amounts of seed are produced in the presence of red LEDs supplemented with a quantity of blue light.

Biomass↗
PubMed2003

Contrasting effects of N and P deprivation on the regulation of photosynthesis in tomato plants in relation to feedback limitation.

The effects were studied of both nitrogen and phosphorus limitation and irradiance on the performance and operation of photosynthesis in tomato leaves (Lycopersicon esculentum Mill.). Plants were grown at low N, high N, low P or high P supply and at two irradiances. Using mature leaves, measurements were made of the irradiance dependencies of the relative quantum efficiencies of photosystems I and II, and of the rate of carbon dioxide fixation. Measurements were also made of foliar starch and chlorophyll concentrations. The results showed that photosynthetic light-harvesting and electron-transport activity acclimate to nutrient stress and growth irradiance such that the internal relationships between electron transport by photosystems I and II do not change; the linear relationship between PhiPSII, and PhiPSI was not affected. It was also evident that under N stress photosynthesis was reduced by a decreased light absorption and by the decreased utilization of assimilates, while P stress mainly affected the carboxylation capacity. Under N stress foliar starch levels increased and the oxygen sensitivity of CO2 fixation decreased, whereas P stress resulted in decreased starch levels and increased oxygen sensitivity of CO2 fixation. The relationship between starch accumulation and oxygen sensitivity (increased starch correlated with decreased oxygen sensitivity) was always the same across the nutrient treatments. These results are consistent with N deprivation producing an increasing limitation of photosynthesis, possibly by feedback from the leaf carbohydrate pool, whereas, although P deprivation produces a decreased rate of CO2 fixation, this is accompanied by a increase in oxygen sensitivity, suggesting that feedback limitation is decreased under P stress.

Acclimatization↗
PubMed2004

Seasonal change in the balance between capacities of RuBP carboxylation and RuBP regeneration affects CO2 response of photosynthesis in Polygonum cuspidatum.

The balance between the capacities of RuBP (ribulose-1,5-bisphosphate) carboxylation (V(cmax)) and RuBP regeneration (expressed as the maximum electron transport rate, J(max)) determines the CO(2) dependence of the photosynthetic rate. As it has been suggested that this balance changes depending on the growth temperature, the hypothesis that the seasonal change in air temperature affects the balance and modulates the CO(2) response of photosynthesis was tested. V(cmax) and J(max) were determined in summer and autumn for young and old leaves of Polygonum cuspidatum grown at two CO(2) concentrations (370 and 700 micromol mol(-1)). Elevated CO(2) concentration tended to reduce both V(cmax) and J(max) without changing the J(max):V(cmax) ratio. The seasonal environment, on the other hand, altered the ratio such that the J(max):V(cmax) ratio was higher in autumn leaves than summer leaves. This alternation made the photosynthetic rate more dependent on CO(2) concentration in autumn. Therefore, when photosynthetic rates were compared at growth CO(2) concentration, the stimulation in photosynthetic rate was higher in young-autumn than in young-summer leaves. In old-autumn leaves, the stimulation of photosynthesis brought by a change in the J(max):V(cmax) ratio was partly offset by accelerated leaf senescence under elevated CO(2). Across the two seasons and the two CO(2) concentrations, V(cmax) was strongly correlated with Rubisco and J(max) with cytochrome f content. These results suggest that seasonal change in climate affects the relative amounts of photosynthetic proteins, which in turn affect the CO(2) response of photosynthesis.

Carbon Dioxide↗