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N-Terminus Conservation in the Terminal Pigment of Phycobilisomes from a Prokaryotic and Eukaryotic Alga 1

Gantt, Elisabeth; Cunningham, Francis X.; Lipschultz, Claudia A.; Mimuro, Mamoru
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1988 EN
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High molecular weight polypeptides from phycobilisomes, believed to be involved in facilitating the energy flow from phycobilisomes to thylakoids, are conserved in the prokaryote Nostoc sp. and the eukaryote Porphyridium cruentum. Partial N-terminal sequence analysis of the phycobilisome-polypeptides of Nostoc (94 kilodalton) and Porphyridium (92 kilodalton) revealed 55% identity in the first 20 residues, but no significant homology with sequences of other phycobiliproteins or phycobilisome-linkers. Polypeptides (94 and 92 kilodalton) from Nostoc thylakoids free of phycobilisomes, previously presumed to be involved in the phycobilisome-thylakoid linkage (M Mimuro, CA Lipschultz, E Gantt 1986 Biochim Biophys Acta 852: 126) exhibit the same immunocrossreactivity but are different from the 94 kilodalton-phycobilisome polypeptide by having blocked N-termini and a different amino acid composition.

Spectral, Photophysical, and Stability Properties of Isolated Photosystem II Reaction Center 1

Seibert, Michael; Picorel, Rafael; Rubin, Andrew B.; Connolly, John S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1988 EN
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565.39938%
Photosystem II reaction center (RC) preparations isolated from spinach (Spinacea oleracea) by the Nanba-Satoh procedure (O Nanba, K Satoh 1987 Proc Natl Acad Sci USA 84: 109-112) are quite labile, even at 4°C in the dark. Simple spectroscopic criteria were developed to characterize the native state of the material. Degradation of the RC results in (a) blue-shifting of the red-most absorption maximum, (b) a shift of the 77 K fluorescence maximum from ∼682 nm to ∼670 nm, and (c) a shift of fluorescence lifetime components from 1.3-4 nanoseconds and >25 nanoseconds to ∼6-7 nanoseconds. Fluorescence properties at 77 K seem to be a more sensitive spectral indicator of the integrity of the material. The >25 nanosecond lifetime component is assigned to P680+ Pheophytin− recombination luminescence, which suggests a correlation between the observed spectral shifts and the photochemical competence of the preparation. Substitution of lauryl maltoside for Triton X-100 immediately after RC isolation stabilizes the RCs and suggests that Triton may be responsible for the instability.

Carbon Dioxide-Induced Oscillations in Fluorescence and Photosynthesis: Role of Thylakoid Membrane Energization in Regulation of Photosystem II Activity

Peterson, Richard B.; Sivak, Mirta N.; Walker, David A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1988 EN
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565.39938%
The response of CO2 fixation to a sudden increase in ambient CO2 concentration has been investigated in intact leaf tissue from spinach (Spinacia oleracea) using a dual channel infrared gas analyzer. Simultaneous with these measurements, changes in fluorescence emission associated with a weak, modulated measuring beam were recorded. Application of brief (2-3 seconds) dark intervals enabled estimation of the dark fluorescence level (Fo) under both steady state and transient conditions. The degree of suppression of Fo level fluorescence in the light was strongly correlated with nonphotochemical quenching under all conditions. During CO2-induced oscillations in photosynthesis under 2% O2 the changes in nonphotochemical quenching anticipate changes in the rate of uptake of CO2. At such low levels of O2 and constant illumination, changes in the relative quantum efficiency of open photosystem II units were estimated as the ratio of the rate of CO2 uptake and the photochemical quenching coefficient. Under the same conditions the relative quantum efficiency of photosystem II was found to vary inversely with the degree of nonphotochemical quenching. The relationship between changes in the rate of CO2 uptake: photochemical quenching coefficient and nonphotochemical quenching was altered somewhat when the same experiment was conducted under 20% O2. The results suggest that electron transport coupled to reduction of O2 occurs to varying degrees with time during oscillations...

Purification and Identification of the Fusicoccin Binding Protein from Oat Root Plasma Membrane 1

de Boer, Albertus H.; Watson, Bruce A.; Cleland, Robert E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1989 EN
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565.39938%
Fusicoccin (FC), a fungal phytotoxin, stimulates the H+-ATPase located in the plasma membrane (PM) of higher plants. The first event in the reaction chain leading to enhanced H+-efflux seems to be the binding of FC to a FC-binding protein (FCBP) in the PM. We solubilized 90% of the FCBP from oat (Avena sativa L. cv Victory) root PM in an active form with 1% octyl-glucoside. The FCBP was stabilized by the presence of protease inhibitors. The FCBP was purified by affinity chromatography using FC-linked adipic acid dihydrazide agarose (FC-AADA). Upon elution with 8 molar urea, two major protein bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with molecular weights of 29,700 and 31,000 were obtained. Successive chromatography on DEAE Bio-Gel A, hexyl agarose, and FC-AADA resulted in the same two bands when the FC-AADA was eluted with sodium dodecyl sulfate. A direct correlation was made between 3H-FC-binding activity and the presence of the two protein bands. The stoichiometry of the 29,700 and 31,000 molecular weight bands was 1:2. This suggests that the FCBP occurs in the native form as a heterotrimer with an apparent molecular weight of approximately 92,000.

The Simultaneous Determination of Carbon Dioxide Release and Oxygen Uptake in Suspensions of Plant Leaf Mitochondria Oxidizing Glycine 1

Lilley, Ross McC.; Ebbighausen, Holger; Heldt, Hans W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1987 EN
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565.39938%
The construction and operation of a device for continuous measurement of CO2 release by suspensions of respiring mitochondria is described. A combination of this device with a Clark-type O2 electrode was used for simultaneous measurement of respiration and of CO2 release by spinach and pea leaf mitochondria with glycine as substrate. Both mitochondrial preparations showed high rates of respiration and high respiratory control ratios. The addition of oxaloacetate not only inhibited O2 uptake substantially, but also greatly stimulated glycine oxidation as monitored by CO2 release. In spinach leaf mitochondria, the maximal rates of glycine oxidation thus obtained, were two times higher than the rate of glycine oxidation required at average rates of photorespiration. It is concluded from these results that under saturating conditions the capacity of glycine oxidation by intact mitochondria exceeds the capacity of glycine-dependent respiration.

Membrane Transport in Isolated Vesicles from Sugarbeet Taproot: III. Effects of Fluoride on ATPase Activity and Transport

Giannini, John L.; Miller, Gene W.; Briskin, Donald P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1987 EN
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565.39938%
The effects of fluoride on the tonoplast type ATPase and transport activities associated with sealed membrane vesicles isolated from sugarbeet (Beta vulgaris L.) storage tissue were examined. This anion had two distinct effects upon the proton-pumping vesicles. When ATP hydrolysis was measured in the presence of gramicidin D, significant inhibition (approximately 50%) only occurred when the fluoride concentration approached 50 millimolar. In contrast, the same degree of inhibition of proton transport occurred when the fluoride concentration was about 24 millimolar. Effects on proton pumping at this concentration of fluoride could be attributed to an inhibition of chloride movement which serves to dissipate the vesicle membrane potential. Valinomycin could partially restore ATPase activity in sealed vesicles which were inhibited by fluoride and this restoration occurred with a reduction in the membrane potential. Fluoride demonstrated a competitive interaction with chloride-stimulation of proton transport and inhibited the uptake of radioactive chloride into sealed vesicles. When the vesicles were allowed to develop a pH gradient in the absence of KCl, and KCl was subsequently added, fluoride reduced enhancement of the existing pH gradient by KCl. The results are consistent with a chloride carrier that is inhibited by fluoride.

Interaction of Herbicides and Quinone with the QB-Protein of the Diuron-Resistant Chlamydomonas reinhardtii Mutant Dr2

Haworth, Philip; Steinback, Katherine E.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1987 EN
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565.39938%
We have used the diuron-resistant Dr2 mutant of Chlamydomonas reinhardtii which is altered in the 32 kilodalton QB-protein at amino acid 219 (valine to isoleucine), to investigate the interactions of herbicides and plastoquinone with the 32 kilodalton QB-protein. The data contained in this report demonstrate that the effects of this mutation are different from those of the more completely characterized mutant which confers extreme resistance to triazines in higher plants. The mutation in C. reinhardtii Dr2 confers only slight resistance to a number of inhibitors of photosynthetic electron transport. Extreme triazine resistance results from an increase in the binding constant of the herbicide with the 32 kilodalton QB-protein, in contrast the diuron binding constant for chloroplasts isolated from wild-type (sensitive) Chlamydomonas and the resistant Dr2 are indistinguishable. We conclude that the altered structure in the 32 kilodalton QB-protein of Dr2 does not directly affect the diuron binding site. This mutation appears to alter the steric properties of the binding protein in such a way that diuron and plastoquinone do not directly compete for binding. This steric perturbation confers mild resistance to other herbicidal inhibitors of photosynthesis and alters the kinetics of QA to QB electron transfer.

Partitioning of Noncyclic Photosynthetic Electron Transport to O2-Dependent Dissipative Processes as Probed by Fluorescence and CO2 Exchange

Peterson, Richard B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1989 EN
Relevância na Pesquisa
565.39938%
The partitioning of noncyclic photosynthetic electron transport between net fixation of CO2 and collective O2-dependent, dissipative processes such as photorespiration has been examined in intact leaf tissue from Nicotiana tabacum. The method involves simultaneous application of CO2 exchange and pulse modulated fluorescence measurements. As either irradiance or CO2 concentration is varied at 1% O2 (i.e. absence of significant O2-dependent electron flow), the quantum efficiency of PSII electron transport (φse) with CO2 as the terminal acceptor is a linear function of the ratio of photochemical:nonphotochemical fluorescence quenching coefficients (i.e. qQ:qNP). When the ambient O2 concentration is raised to 20.5% or 42% the qQ:qNP is assumed to predict the quantum efficiency of total noncyclic electron transport (φ′se). A factor which represents the proportion of electron flow diverted to the aforementioned dissipative processes is calculated as (φ′se − φse)/φ′se where φse is now the observed quantum efficiency of electron transport in support of net fixation of CO2. Examination of changes in electron allocation with CO2 and O2 concentration and irradiance at 25°C provides a test of the applicability of the Rubisco model to photosynthesis in vivo.

Identification and Characterization of the Ca2+-ATPase which Drives Active Transport of Ca2+ at the Plasma Membrane of Radish Seedlings

Rasi-Caldogno, Franca; Pugliarello, Maria Chiara; Olivari, Claudio; De Michelis, Maria Ida
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1989 EN
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565.39938%
In microsomes from 24-hour-old radish (Raphanus sativus L.) seedlings ATP-dependent Ca2+ uptake occurs only in inside-out plasma membrane vesicles (F Rasi-Caldogno, MC Pugliarello, MI De Michelis [1987] Plant Physiol 83: 994-1000). A Ca2+-dependent ATPase activity can be shown in the same microsomes, when assays are performed at pH 7.5. The Ca2+-dependent ATPase is stimulated by the Ca2+ ionophore A23187 and is localized at the plasma membrane. Ca2+-dependent ATPase activity and ATP-dependent Ca2+ uptake present very similar saturation kinetics with erythrosin B (50% inhibition at about 0.1 micromolar), free Ca2+ (half-maximal rate at about 70 nanomolar), and MgATP (Km 15-20 micromolar). Ca2+ uptake can be sustained by GTP or ITP at about 60% the rate measured in the presence of ATP; only very low Ca2+ uptake is sustained by CTP or UTP and none by ADP. These results indicate that the Ca2+-ATPase described in this paper is the enzyme which drives active transport of Ca2+ at the plasma membrane of higher plants.

Oxidation of Proline and Glutamate by Mitochondria of the Inflorescence of Voodoo Lily (Sauromatum guttatum) 1

Skubatz, Hanna; Meeuse, Bastiaan J. D.; Bendich, Arnold J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1989 EN
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565.39938%
In appendices of Sauromatum guttatum that are developing thermogenicity, mitochondria isolated from successive developmental stages of the inflorescence show an increase in the oxidation rates of proline and glutamate. A similar rise in the oxidation rates of these compounds is observed in mitochondria obtained from the spathe, a nonthermogenic organ of the inflorescence. Changes in oxidative metabolism were also observed in mitochondria isolated from sections of immature appendix treated with salicylic acid (SA) at 0.69 microgram per gram fresh weight indicating that they are induced by SA. At that concentration, however, SA has no effect on oxygen consumption by mitochondria in the presence of glutamate, proline, or malate. Furthermore, oxygen uptake by mitochondria in the presence of proline or glutamate is partially sensitive to salicylhydroxamic acid (SHAM) at concentrations greater than 2 millimolar when in the presence of 1 millimolar KCN. For NADH, succinate, and malate a high capacity of the alternative (cyanide-resistant) pathway is found that is completely sensitive to SHAM at 1.5 to 4 millimolar. The increase in the mitochondrial capacity to oxidize either amino acid is also found in four other Araceae species including both thermogenic and nonthermogenic ones. After anthesis...

Isolation and Characterization of the Tricarboxylate Transporter from Pea Mitochondria 1

McIntosh, Cecilia A.; Oliver, David J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1992 EN
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565.5068%
The tricarboxylate transporter was solubilized from pea (Pisum sativum) mitochondria with Triton X-114, partially purified over a hydroxylapatite column, and reconstituted in phospholipid vesicles. The proteoliposomes exchanged external [14C]citrate for internal citrate or malate but not for preloaded d,l-isocitrate. Similarly, although external malate, succinate, and citrate competed with [14C]citrate in the exchange reaction, d,l-isocitrate and phosphoenolpyruvate did not. This tricarboxylate transporter differed from the equivalent activity from animal tissues in that it did not transport isocitrate and phosphoenolpyruvate. In addition, tricarboxylate transport in isolated plant mitochondria, as well as that measured with the partially purified and reconstituted transporter, was less active than the transporter isolated from animal tissues.

Effects of Diclofop and Diclofop-Methyl on Membrane Potentials in Roots of Intact Oat, Maize, and Pea Seedlings

DiTomaso, Joseph M.; Brown, Patrick H.; Stowe, Amy E.; Linscott, Dean L.; Kochian, Leon V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1991 EN
Relevância na Pesquisa
565.5068%
Growth and electrophysiological studies in roots of intact diclofop-methyl susceptible and resistant seedlings were conducted to test the hypothesis that the herbicide acts primarily as a proton ionophore. The ester formulation of diclofop, at 0.2 micromolar, completely inhibited root growth in herbicide-susceptible oat (Avena sativa L.) after a 96 hour treatment, but induced only a delayed transient depolarization of the membrane potential in oat root cortical cells. Root growth in susceptible maize (Zea mays L.) seedlings was dramatically reduced by exposure to 0.8 micromolar diclofop-methyl, while the same diclofop-methyl exposure hyperpolarized the membrane potential within 48 hours after treatment. Furthermore, exposure of maize roots to the protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP) (50 nanomolar), inhibited growth by only 31%, 96 hours after treatment, while the same CCCP exposure depolarized the resting potential by an average of 32 millivolts. Thus, the protonophore hypothesis cannot account for a differential membrane response to phytotoxic levels of diclofop-methyl in two susceptible species. From the results of others, much of the evidence to support the protonophore hypothesis was obtained using high concentrations of diclofop acid (100 micromolar). At a similar concentration...

Analysis of Changes in Minimal and Maximal Fluorescence Yields with Irradiance and O2 Level in Tobacco Leaf Tissue

Peterson, Richard B.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1991 EN
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565.5068%
The responses of minimal and maximal fluorescence yields of chlorophyll a to irradiance of actinic white light were determined by pulse modulated fluorimetry in leaf discs from tobacco, Nicotiana tabacum, at 1.6, 20.5, and 42.0% (v/v) O2. Steady-state maximal fluorescence yield (Fm′, measured during a saturating light pulse) declined with increasing irradiance at all O2 levels. In contrast, the steady-state minimal fluorescence yield (Fo′, measured during a brief dark interval) increased with irradiance relative to that recorded for the fully dark-adapted leaf (Fo) or that observed after 5 minutes of darkness (Fo*). The relative magnitude of this increase was somewhat greater and extended to higher irradiances at the elevated O2 levels compared with 1.6% O2. Suppression of Fo′ was only observed consistently at saturating irradiance. The results are interpreted in terms of the occurrence of photosystem II units possessing exceedingly slow turnover times (i.e. “inactive” units). Inactive units play an important role, along with thermal deactivation of excited chlorophyll, in determining the response of in vivo fluorescence yield to changes in irradiance. Also, a significant interactive effect of O2 concentration and the presence or absence of far red light on oxidation of photosystem II acceptors in the dark was noted.

Solubilization and Reconstitution of Ca2+ Pump from Corn Leaf Plasma Membrane 1

Kasai, Minobu; Muto, Shoshi
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1991 EN
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565.5068%
The Ca2+ transport system of corn (Zea mays) leaf plasma membrane is composed of Ca2+ pump and Ca2+/H+ antiporter driven by H+ gradient imposed by a H+ pump (M Kasai, S Muto [1990] J Membr Biol 114: 133-142). It is necessary for characterization of these Ca2+ transporters to establish the procedure for their solubilization, isolation, and reconstitution into liposomes. We attempted to solubilize and reconstitute the Ca2+ pump in the present study. A nonionic detergent octaethyleneglycol monododecyl ether (C12E8) was the most effective detergent for a series of extraction and functional reconstitution of the Ca2+ pump among seven detergents examined. This was judged from activities of ATP-dependent 45Ca2+ uptake into liposomes reconstituted with the respective detergent-extract of the plasma membrane by the detergent dilution method. C12E8-extract of the plasma membrane was subjected to high performance liquid chromatography using a DEAE anion exchange column. Ca2+-ATPase was separated from VO43−-sensitive Mg2+-ATPase. These ATPases were separately reconstituted into liposomes, and their ATP-dependent Ca2+ uptake was measured. The liposomes reconstituted with the Ca2+-ATPase, but not with the VO43−-sensitive Mg2+-ATPase, showed ATP-dependent Ca2+ uptake. Nigericin-induced pH gradient (acid inside) caused only a little Ca2+ uptake into liposomes reconstituted with the Ca2+-ATPase...

Partial Purification and Reconstitution of the α-Ketoglutarate Carrier from Corn (Zea mays L.) Mitochondria 1

Genchi, Giuseppe; De Santis, Aurelio; Ponzone, Carmela; Palmieri, Ferdinando
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1991 EN
Relevância na Pesquisa
565.5068%
The α-ketoglutarate carrier from corn shoot mitochondria (Zea mays L., B 73) was solubilized in Triton X-114 and partially purified by chromatography on hydroxyapatite and celite in the presence of cardiolipin. On SDS-gel electrophoresis, the hydroxyapatite/celite eluate showed various protein bands between 12 and 70 kilodaltons. When reconstituted into liposomes, the α-ketoglutarate transport protein catalyzed a phthalonate-sensitive α-ketoglutarate/α-ketoglutarate exchange. The protein was purified 60-fold with a recovery of 88% with respect to the mitochondrial extract. The protein yield was 0.6%. The properties of the reconstituted carrier, i.e. requirement for a counter-anion, substrate specificity, and inhibitor sensitivity, were similar to those of the α-ketoglutarate transport system as characterized in plant and animal mitochondria.

Alternative Respiration and Heat Evolution in Plants 1

Ordentlich, Arie; Linzer, Rebecca A.; Raskin, Ilya
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1991 EN
Relevância na Pesquisa
565.5068%
The alternative respiratory pathway dissipates most of the chemical energy of respiratory substrates as heat. We have shown that this heat can be quantified by microcalorimetry and is a measure of alternative pathway activity in vivo. The alternative pathway is known to increase in aged potato (Solanum tuberosum) slices and in chill-stressed leaves. Aging of potato slices for 24 hours was accompanied by an almost fourfold increase in the rate of heat evolution. This heat increase was resistant to KCN but could be blocked by an alternative pathway inhibitor, salicylhydroxamic acid (SHAM). In cucumber (Cucumis sativus) leaves subjected to chilling stress (between 4 and 16°C), the rate of heat evolution was inversely related to temperature. As in aged potato slices, the increased rate of heat evolution in cucumber leaves was blocked by SHAM, but not by KCN. Nitrogen or the combination of SHAM and KCN blocked most of the heat evolution in both aged potato slices and chill-stressed cucumber leaves. Calorimetric measurements of the alternative pathway corresponded to respiration measurements performed using an oxygen electrode.

Physiological Characterization of a Single-Gene Mutant of Pisum sativum Exhibiting Excess Iron Accumulation: I. Root Iron Reduction and Iron Uptake

Grusak, Michael A.; Welch, Ross M.; Kochian, Leon V.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1990 EN
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565.5068%
Root systems of mutant (E107) and parental (cv `Sparkle') Pisum sativum genotypes were studied to determine the basis for excess Fe accumulation in E107. Plants were grown with (+Fe-treated) or without (−Fe-treated) added Fe(III)-N,N'-ethylenebis[2-(2-hydroxyphenyl)glycine] in aerated nutrient solutions. Daily measurements of Fe(III) reduction indicated a four-to seven-fold higher reduction rate in +Fe- or −Fe-treated E107, and −Fe-treated Sparkle, when compared with +Fe-treated Sparkle. An agarose-based staining technique used to localize Fe(III) reduction, revealed Fe(III) reduction over most of the length of the roots (but not at the root apices) in both E107 treatments and −Fe-treated Sparkle. In +Fe-treated Sparkle, Fe(III) reduction was either nonexistent or localized to central regions of the roots. Measurements of short-term Fe influx (with 0.1 millimolar 59Fe(III)-ethylenediaminetetraacetic acid) was also enhanced (threefold) in +Fe- or −Fe-treated E107 and −Fe-treated Sparkle, relative to +Fe-treated Sparkle. The physiological characteristics of E107 root systems, which are similar to those seen in Fe-deficient Sparkle, have led us to conclude that the mutation causes E107 to act functionally as an Fe-deficient plant...

Measurement of Heme Efflux and Heme Content in Isolated Developing Chloroplasts 1

Thomas, Jim; Weinstein, Jon D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1990 EN
Relevância na Pesquisa
565.5068%
Hemes destined for cytosolic hemoproteins must originate in one of the cellular compartments which have the capacity for heme synthesis, namely the chloroplast or the mitochondria. Since developing chloroplasts from greening cucumber (Cucumis sativus, cv. Sumter) cotyledons are known to contain complete heme and chlorophyll biosynthetic pathways, they were tested for their capacity export hemes. Picomole quantities of heme were measured by reconstitution of the heme with apo-peroxidase and subsequent determination of peroxidase activity. The assay method was sensitive (as little as 0.7 picomole of heme could be detected in a volume of 100 microliters) and was linear with heme concentration. When intact plastids were incubated with apo-peroxidase, a steady-state rate of efflux between 0.12 and 0.45 picomole heme/minute/milligram plastid protein was measured. The efflux rate was not due to plastid breakage and could be enhanced by incubating with the heme precursor, δ-aminolevulinic acid. Cold acetone extraction removed 47 ± 17 picomoles heme/milligram plastid protein from the total b-type heme pool in the chloroplasts (166 ± 9 picomoles heme/milligram protein, by acid-acetone extraction). The reconstitution technique provided a similar estimate of readily exchangeable heme in the plastid...

Al3+ and Ca2+ Alteration of Membrane Permeability of Quercus rubra Root Cortex Cells 1

Zhao, Xiao-Jun; Sucoff, Edward; Stadelmann, Eduard J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1987 EN
Relevância na Pesquisa
565.5068%
This study was undertaken to quantify the effect of aluminum and calcium on membrane permeability. The influence of Ca2+ (0.2-3.7 millimolar) and Al3+ (0-3.7 millimolar) on the permeability of root cortical cells of Quercus rubra was measured using three nonelectrolytes (urea, methyl urea, and ethyl urea) as permeators of progressively increasing lipid solubility. Water permeability was also measured. Al3+ (a) increased membrane permeability to the nonelectrolytes, (b) decreased the membrane's partiality for lipid permeators, and (c) decreased membrane permeability to water. Ca2+ had effects on permeability that were opposite to those of Al3+. When Al3+ and Ca2+ were tested in combination, these opposite effects counteracted each other. The results suggest that Al3+ altered the architecture of membrane lipids.

Photorespiration and Internal CO2 Accumulation in Chara corallina as Inferred from the Influence of DIC and O2 on Photosynthesis 1

Brechignac, François; Lucas, William J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1987 EN
Relevância na Pesquisa
565.5068%
An O2 electrode system with a specially designed chamber for `whorl' cell complexes of Chara corallina was used to study the combined effects of inorganic carbon and O2 concentrations on photosynthetic O2 evolution. At pH = 5.5 and 20% O2, cells grown in HCO3− medium (low CO2, pH ≥ 9.0) exhibited a higher affinity for external CO2 (K½(CO2) = 40 ± 6 micromolar) than the cells grown for at least 24 hours in high-CO2 medium (pH = 6.5), (K½(CO2) = 94 ± 16 micromolar). With O2 ≤ 2% in contrast, both types of cells showed a high apparent affinity (K½(CO2) = 50 − 52 micromolar). A Warburg effect was detectable only in the low affinity cells previously cultivated in high-CO2 medium (pH = 6.5). The high-pH, HCO3−-grown cells, when exposed to low pH (5.5) conditions, exhibited a response indicating an ability to fix CO2 which exceeded the CO2 externally supplied, and the reverse situation has been observed in high-CO2-grown cells. At pH 8.2, the apparent photosynthetic affinity for external HCO3− (K½[HCO3−]) was 0.6 ± 0.2 millimolar, at 20% O2. But under low O2 concentrations (≤2%), surprisingly, an inhibition of net O2 evolution was elicited, which was maximal at low HCO3− concentrations. These results indicate that: (a) photorespiration occurs in this alga and can be revealed by cultivation in high-CO2 medium...