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At least 721 records · Page 40Linked to original sources
PubMed2005

Responses of antioxidant enzyme and photosynthesis in rape seedling to the combined stresses of acid rain and ultraviolet-B radiation.

Effects of the simulated acid rain (AR) and ultraviolet-B (UV-B, 280-320 nm) radiation with a single or two ways simultaneously (AR + UV-B) on the antioxidant enzyme and photosynthesis of the rape seedlings were investigated by the hydroponic culture. The results of static experiment indicated that the tolerance of rape seedling to single stress (AR or UV-B) is stronger than that to dual stresses (AR + UV-B). Furthermore, the dual stresses had additive effect on catalase activity, and a synergistic effect on MDA content, net photosynthesis rate, water use efficiency as well as intercellular CO2 concentration. Meanwhile, it has an independent effect on chlorophyll content, stomatal conductance, and transpiration rate as well as membrane permeability. During 64 h restoration course, the dynamic change in the curves of physiological and biochemical indices were not identical, and none of them show a simple linear variation. According to the static and dynamic experiments, it was found that a responsive sequence of catalase activity, membrane permeability, MDA content and photosynthetic characteristics to the above-mentioned stresses was as follows: AR + UV-B > UV-B > AR.

Acid Rain↗
PubMed2006

[Light response curve of dominant tree species photosynthesis in broadleaved Korean pine forest of Changbai mountain].

Based on the measurements of leaf photosynthesis, the light response curves of Pinus koraiensis, Tilia amurensis, Quercus mongolica and Fraxinus mandshurica photosynthesis in broadleaved Korean pine forest of Changbai Mountains were fitted with rectangle and non-rectangle hyperbolae. The results showed that rectangle hyperbola was simpler for fitting, while non-rectangle hyperbola was more reasomable because of its fitted results better matched physiological meanings. The values of intrinsic quantum efficiency for CO2 uptake (alpha), light-saturated net photosynthetic rate (Pmax), and dark respiration rate (Rd) of the four tree species were higher when fitted with rectangle hyperbola than with non-rectangle hyperbola, while that of light compensation point (Lcp) varied with tree species. The values of alpha and Rd obtained from the two hyperholae had the same sequences, i.e., F. mandshurica > T. amurensis > Q. mongolica > P. koraiensis for alpha, and F. mandshurica > Q. mongolica > T. amurensis > P. koraiensis for Rd, but for Pmax and Lcp, the sequences were not the same.

China↗
PubMed2006

[Effects of two kinds of allelochemicals on photosynthesis and chlorophyll fluorescence parameters of Solanum melongena L. seedlings].

In a culture experiment, the effects of different concentration 2,6-bis (1, 1-dimethylethyl) phenol and 1,2-benzodicarboxylic dimethyl ester on the photosynthesis and chlorophyll fluorescence characteristics of eggplant seedlings were studied, and the results showed that these two allelochemicals were the barriers of chlorophyll content, net photosynthetic rate (Pn), and stomatal conductance (Gs). The intercellular CO2 concentration (Ci) decreased in the former period, and then increased. The allelochemicals increased initial fluorescence (Fo), but decreased maximum photochemical efficiency of PS II (Fv/Fm), quantum efficiency of non-cyclic electron transport of PS II (phi(PSII)), photochemical quenching ((qP) and antenna conversion efficiency (Fv'/Fm' ). 2,6-bis (1,1-dimethylethyl) phenol made non-photochemical quenching (qN) increase first and decrease then, while 1,2-benzodicarboxylic dimethyl ester decreased qN, which was harmful to the photosynthesis structure.

Butylated Hydroxytoluene↗
PubMedDate not supplied

[Role of phycobilin pigments in photosynthesis].

Experimental data on possible role of phicobilliprotein (PhBP) in photosynthesis are analysed. It is concluded that the widely spread notion about PhBP only as the light-gathering pigments which transfer the energy to chlorophyll, turned to be insufficiently substantiated experimentally until recently. At the same time the discovered ability of PhBP for reversible redox transformations together with the new data on the nature of fluorescence of blue-green algae and PhBP localization in the cell allowed a suggestion that PhBP can independently of chlorophyll or together with it directly participate in photochemical reactions of photosynthesis. A suggestion is advanced concerning possible existence of the reaction centres of PhBP in phicobillisomes.

Hydrogen-Ion Concentration↗
PubMed1989

DNA methylation and the differential expression of C4 photosynthesis genes in mesophyll and bundle sheath cells of greening maize leaves.

The methylation of nuclear and chloroplast DNAs has been examined in relation to the known differential expression of C4 photosynthesis genes in the bundle sheath and mesophyll cells of etiolated, greening, and fully green maize leaves. We have focused our research on phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (RBUp2Case) which are coded by nuclear genes, and on the large subunit of RBUp2Case which is coded by a plastid gene. Reversed-phase high performance liquid chromatography revealed several kinds of methylated bases in DNAs of both photosynthetic cell types, with the largest amounts in fully green leaves. The occurrence of selective DNA methylation was investigated by employing an isoschizomeric pair of methyl-sensitive and -insensitive endonucleases followed by Southern hybridizations with specific DNA probes. Notably, there was an inverse correlation between the relative abundance of specific transcripts in a given cell type during greening and the methylation status of the corresponding nuclear or chloroplast gene. Furthermore, a heterologous in vitro transcription system using Escherichia coli RNA polymerase revealed that the plastid gene encoding the RBUp2Case large subunit in both cell types was active as a template in the unmethylated state, whereas it was inactive when methylated. Thus, the selective methylation of both chloroplast and nuclear DNA is likely one component of a multilevel control mechanism for the differential regulation of cell-specific C4 photosynthesis gene expression in greening maize leaves.

Cell Nucleus↗
PubMedDate not supplied

[Evaluation of the effect of a single dose of ammonia on lettuce photosynthesis in a hermetically sealed phytotron].

The threshold of the phytotoxic effect (PTE) of ammonia at a concentration of 10 to 20 mg/m3 on 28-day lettuce plants was evaluated during a single 2-hour exposure. The rate of Hill's reaction, level of energization of chloroplast membranes during leaf illumination as well as visible photosynthesis of lettuce plants from the beginning of fumigation to vegetation day 31 were recorded. Similar changes in the above parameters induced by ammonia were seen. This suggests that photosynthesis was inhibited already at light stages. As a measure of PTE, 10 per cent decrease of the photosynthetic productivity of plants exposed to fumigation was recommended in comparison with controls during the vegetation period. According to this measure, the PTE of ammonia amounted to 20 mg/m3 in the above experimental conditions.

Ammonia↗
PubMedDate not supplied

[Radiation entropy and its role in the process of photosynthesis].

The paper deals with the following problems: 1) radiation entropy and the value of maximum performance coefficient of photosynthesizing systems eta m; 2) problem of physical meaning of eta m and on its association with real processes in photosynthesis. It has been shown that for calculating entropy of nonequilibrium radiation its origin should be known and that the value eta m does not practically limit the processes which proceed in photosynthesis.

Mathematics↗
PubMedDate not supplied

[Analysis of photosynthesis light curves under continuous illumination].

A mathematical description of the photosynthesis light curve is proposed taking into account the type of photosynthetic unit (PSU) organization (unicentral or multicentral), energy migration between the PSU, and the nonlinear character of the dark process limiting the rate. In the case of unicentral PSU the light curve is described by the expression: I = v (1--yv)/(1--v) where I is light intensity; v is relative rate of photosynthesis (relative to the maximal rate); y is the parameter which determines the shape of the curve. Its value depends on the efficiency of energy migration between PSU and on the ratio of the limiting dark reactions rates. The variations of the value from 1 to 0 give different known types of light curves. Coordinates are proposed in which the curves for multicentral and unicentral PSU are distinguished and parameter is estimated. Experimental light curves for a number of marine algae correspond to the supposition of the PSU unicentral organization, with y = 0.9.

Darkness↗
PubMedDate not supplied

[Effect of adaptation to light of different spectral composition on photosynthesis of Chlorella cells].

Dependence of cell photosynthesis in different spectral regions on illumination conditions of chlorella culture during growing (blue, green and red light) was studied. Change in the shape of action spectra of photosynthesis (measured with interference light filters) was discovered. This change is mostly pronounced in relation to the red and blue maxima. The largest relative value of the blue maximum was observed for the cells grown in the red light.

Adaptation, Physiological↗
PubMed1993

Magnesium, potassium flux and photosynthesis.

Photosynthetic capacity of chloroplasts is regulated by stromal pH. The pH of the stroma must be maintained higher than external pH during illumination in order to optimize photosynthetic carbon reduction cycle activity. Stromal pH is affected by K+/H+ counterexchange across the chloroplast envelope. Magnesium ion external to the chloroplast affects K+/H+ counterfluxes and hence stromal pH and photosynthesis. K+/H+ counterfluxes across the envelope are facilitated by K+ and H+ conducting ion channels, and an H+ pumping envelope ATPase. External magnesium affects K+/H+ exchange by binding to negative surface charges on the envelope membrane. Magnesium binding restricts currents through K+ channels. Magnesium block of K+ uptake through this channel impairs H+ efflux, inhibiting photosynthesis. Under conditions which lead to net K+ efflux through the channel, envelope-bound magnesium restricts K+ efflux, reducing the driving force for electroneutral H+ uptake. External magnesium has a profound effect on chloroplast photosynthetic capacity by an indirect control of H+ movement across the envelope and hence of stromal pH.

Chloroplasts↗
PubMedDate not supplied

[The principle of instantaneous action in photosynthesis].

The principle of instant action for photosynthesis is grounded. According to this principle, all primary photophysical events of energy delivery from light harvesting Chl molecules to reaction centres proceed at time intervals not exceeding critical value approximating 10(-10) seconds. This provides: a) high quantum yield (more then 90%) of primary photosynthesis: b) Chl protection from irreversible photodestruction. Original experimental data obtained by V.I. Godik and the author support the above principle at least for purple bacteria, green bacteria and photosystem I of plants.

Chlorophyll↗
PubMed2000

Bio-optical Characteristics and the Vertical Distribution of Photosynthetic Pigments and Photosynthesis in an Artificial Cyanobacterial Mat.

Zonations of photosynthesis and photopigments in artificial cyanobacterial mats were studied with (i) oxygen and pH microsensors, (ii) fiber-optic microprobes for field radiance, scalar irradiance, and PSII fluorescence, and (iii) a light microscope equipped with a spectrometer for spectral absorbance and fluorescence measurements. Our analysis revealed the presence of several distinct 1-2 mm thick cyanobacterial layers mixed with patches of anoxygenic photosynthetic bacteria. Strong attenuation of visible light confined the euphotic zone to the uppermost 3 mm of the mat, where oxygen levels of 3-4 times air saturation and a pH peak of up to pH 8.8 were observed under saturating irradiance (413 µmol photon m(-2) s(-1)). Oxygen penetration was 5 mm in light and decreased to 1 mm in darkness. Volumetric oxygen consumption in the photic and aphotic zones of illuminated mat was 5.5 and 2.9 times higher, respectively, than oxygen consumption in dark incubated mats. Scalar irradiance reached 100-150% of incident irradiance in the upper 0.5 mm of the mat due to intense scattering in the matrix of cells, exopolymers, and carbonate precipitates. In deeper mat layers scalar irradiance decreased nearly exponentially, and highest attenuation coefficients of 6-7 mm(-1) were found in cyanobacterial layers, where photosynthesis and photopigment fluorescence also peaked. Visible light was attenuated >100 times more strongly than near infrared light. Microscope spectrometry on thin sections of mats allowed detailed spectral absorbance and fluorescence measurements at defined positions relative to the mat surface. Besides strong spectral signals of cyanobacterial photopigments (Chl a and phycobiliproteins), the presence of both green and purple photosynthetic bacteria was evident from spectral signals of Bchl a and Bchl c. Microprofiles of photopigment absorbance correlated well with microdistributions of phototrophs determined in an accompanying study.

Journal Article↗
PubMed1998

Oxygenic photosynthesis and respiratory activity in microbial mats of the ebro delta, spain, by oxygen exchange method

Photosynthetic and respiratory activities at low light intensities (300 &mgr;E m-2 s-1) in the microbial mats of the Ebro Delta were measured by the oxygen exchange method in the laboratory. The response to H2S concentration, a significant factor in the dynamics of that ecosystem, was assessed. Total photosynthesis reached 23. 78-28.17 &mgr;g O2 cm-2 h-1. Photosynthetic activity was not significantly different at the two temperatures tested. Respiratory activity reached a consumption of 6.95-8.56 &mgr;g O2 cm-2 h-1 at 25 degreesC and 11.42-11.70 &mgr;g O2 cm-2 h-1 at 35 degreesC. The Q10 value for respiration was 1.37-1.64. Oxygen production in Microcoleus chthonoplastes, the most abundant cyanobacterium in those microbial mats, was highly resistant to sulfide inhibition. Concentrations less than 0.02 mM sulfide did not affect the rate of photosynthesis. Concentrations up to 0.1 mM sulfide caused different degrees of partially reversible inhibition, with a maximum of 67% at 0.78 mM sulfide. Primary production (g C assimilated/m2/year) in those microbial mats was also assessed and compared with data from other ecosystems.

Journal Article↗
PubMed2003

Heterologous expression of a ketohexokinase in potato plants leads to inhibited rates of photosynthesis, severe growth retardation and abnormal leaf development.

In the present paper we investigated the effect of heterologous expression of a rat liver ketohexokinase in potato (Solanum tuberosum L.) plants with the aim of investigating the role of fructose 1-phosphate in plant metabolism. Plants were generated that contained appreciable activity of ketohexokinase but did not accumulate fructose 1-phosphate. They were, however, characterised by a severe growth retardation and abnormal leaf development. Studies of (14)CO(2) assimilation and metabolism, and of the levels of photosynthetic pigments, revealed that these lines exhibited restricted photosynthesis. Despite this fact, the levels of starch and soluble sugars remained relatively constant. Analysis of intermediates of starch and sucrose biosynthesis revealed large increases in the triose phosphate and fructose 1,6-bisphosphate pools but relatively unaltered levels of inorganic phosphate and 3-phosphoglycerate, and these lines were also characterised by an accumulation of glyceraldehyde. The transformants neither displayed consistent changes in the activities of Calvin cycle enzymes nor in enzymes of sucrose synthesis but displayed a metabolic profile partially reminiscent of that brought about by end-product limitation, but most likely caused by an inhibition of photosynthesis brought about by the accumulation of glyceraldehyde. Analysis of the metabolite contents in lamina and vein fractions of the leaf, and of the enzymes of carbohydrate oxidation indicate that the phloem-enriched veins of ketohexokinase-expressing leaves tend toward hypoxia and indicate a problem of phloem transport.

Animals↗
PubMed1999

Heterogeneous inhibition of photosynthesis over the leaf surface of rosa rubiginosa L. during water stress and abscisic acid treatment: induction of a metabolic component by limitation of CO(2) diffusion

The contribution of changes in stomatal conductance and metabolism in determining heterogeneous photosynthesis inhibition during dehydration and abscisic acid (ABA) feeding was investigated using detached leaves of Rosa rubiginosa L. The steady-state and maximal rates of electron transport under a transient high CO(2) concentration were monitored using chlorophyll fluorescence imaging. The decrease in electron transport rate induced by dehydration and ABA treatment almost reverted to the control rate under transient high CO(2) availability. Therefore, inhibition of photosynthesis was mainly mediated through stomatal closure. However, since reversion was not complete, a metabolic inhibition was also identified as a decrease in the maximal electron transport rate driven by carboxylation. Under dehydration or ABA feeding, as under low ambient CO(2) treatment, in 21% or 0.4% O(2), the lower the steady-state electron transport was, the lower was the maximal electron transport rate during transient high CO(2) availability. We conclude that low CO(2) availability reduced the capacity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) to drive electron transport. The potential contribution of Rubisco deactivation mediated by stomatal closure is discussed.

Journal Article↗
PubMed1987

Effect of ozone on net photosynthesis in oat (Avena sativa) and duckweed (Lemna gibba).

Short exposure to ozone depressed photosynthesis in both oat and duckweed at concentrations above 140 microg m(-3) and 300 microg m(-3), respectively. The effect on exposed oat flag leaves was age-dependent, with maximum susceptibility to ozone 10-20 days after emergence of the panicle. In duckweed, photosynthesis was more sensitive to differences in ozone concentration than to differences in duration of exposure.

Journal Article↗
PubMed1991

Photosynthesis inhibition of soybean leaves by insecticides.

Field grown soybean cv. Williams-82 plants were sprayed with malathion or carbaryl formulations at 30, 60 and 90 days after planting. Net photosynthesis (PN) was measured in the control (water-sprayed) and pesticide-treated plants, 1, 3 and 7 days after treatment, with a LICOR 6200 Portable Photosynthesis System. The pesticide-treated plants showed a significant reduction (24% with malathion and 20% with carbaryl) in PN after the first application. After the 60-day spray treatment PN suppression on day 1 and day 3 after treatment was the same as after the first application; but PN reached the same level as that of the water-sprayed control 7 days after treatment. After the 90-day treatment no change in PN was observed with the pesticide-treated plants compared to the control. These data indicate that malathion and carbaryl formulations may exert a detrimental influence on soybean physiology.

Journal Article↗
PubMed1996

Effect of UVB phototherapy and oral calcitriol (1,25-dihydroxyvitamin D3) on vitamin D photosynthesis in patients with psoriasis.

BACKGROUND: Phototherapy and activated froms of vitamin D help clear psoriasis. OBJECTIVE: The influence of UVB phototherapy and oral calcitriol (1,25-dihydroxyvitamin D3) on vitamin D photosynthesis was assessed in 16 patients. METHODS: Patients were randomly selected to receive orally either placebo or calcitriol (0.5 to 2 micrograms daily) for the duration of the 8-week study; all patients received approximately 21 UVB treatments. Before and after treatment, serum levels of 25-hydroxyvitamin D and calcitriol were measured by high-pressure liquid chromatography. RESULTS: Although calcitriol had no additive effect on phototherapy as a treatment modality, a significant increase in serum 25-hydroxyvitamin D levels occurred in both groups; in three patients extraordinarily high levels developed (> 120 ng/ml). Oral calcitriol significantly increased calcitriol serum levels. Increased serum calcitriol did not inhibit cutaneous synthesis of vitamin D or its hepatic conversion to serum 25-hydroxyvitamin D. CONCLUSION: UVB induces high levels of vitamin D photosynthesis. Because oral or topical calcitriol alone helps clear psoriasis, studies to explore the possible influence of UVB phototherapy on its production should be considered. If UVB phototherapy induces cutaneous calcitriol synthesis this could explain the lack of added benefit to treatment when oral calcitriol is administered with phototherapy.

Administration, Oral↗