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Dynamics of Photosystem II and Its Light Harvesting System in Response to Light Changes in the Halotolerant Alga Dunaliella salina1

Pick, Uri; Gounaris, Kleoniki; Barber, James
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1987 EN
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A photosystem two (PSII) core complex consisting of five major polypeptides (47, 40, 32, 30, and 10 kilodaltons) and a light harvesting chlorophyll a/b complex (LHC-2) have been isolated from the halotolerant alga Dunaliella salina. The chlorophyll and polypeptide composition of both complexes were compared in illuminated and dark-adapted cultures. Dark adaptation is accompanied by a decrease in the chlorophyll a to chlorophyll b (Chl a/Chl b) ratio of intact thylakoids without any change in total chlorophyll. These changes occur with a half-time of 3 hours and are reversed upon reillumination. Analyses of PSII enriched membrane fragments suggest that the decrease in the Chl a/Chl b is due partly to an increase in the Chl b content of LHC-2 and partly to changes in the relative levels of the two complexes. Apparently during dark adaptation there is: (a) a net synthesis of chlorophyll b, (b) removal of PSII core complexes resulting in a 2-fold drop in the PSII cores to LHC-2 chlorophyll ratio. These changes should dramatically increase the light harvesting capacity of the remaining PSII reaction centers. Presumably this adjustment of antenna size and composition is a physiological mechanism necessary for responding to shade conditions. Also detected...

Properties of Single K+ and Cl− Channels in Asclepias tuberosa Protoplasts 1

Schauf, Charles L.; Wilson, Kathryn J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1987 EN
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Potassium and chloride channels were characterized in Asclepias tuberosa suspension cell derived protoplasts by patch voltage-clamp. Whole-cell currents and single channels in excised patches had linear instantaneous current-voltage relations, reversing at the Nernst potentials for K+ and Cl−, respectively. Whole cell K+ currents activated exponentially during step depolarizations, while voltage-dependent Cl− channels were activated by hyperpolarizations. Single K+ channel conductance was 40 ± 5 pS with a mean open time of 4.5 milliseconds at 100 millivolts. Potassium channels were blocked by Cs+ and tetraethylammonium, but were insensitive to 4-aminopyridine. Chloride channels had a single-channel conductance of 100 ± 17 picosiemens, mean open time of 8.8 milliseconds, and were blocked by Zn2+ and ethacrynic acid. Whole-cell Cl− currents were inhibited by abscisic acid, and were unaffected by indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid. Since internal and external composition can be controlled, patch-clamped protoplasts are ideal systems for studying the role of ion channels in plant physiology and development.

Nitrogen Utilization in Lemna1: I. Relations between Net Nitrate Flux, Nitrate Reduction, and in Vitro Activity and Stability of Nitrate Reductase

Ingemarsson, Björn
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1987 EN
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Cultures of Lemna gibba L. G3 were maintained at a constant, N-limited growth rate by adding nitrate daily in amounts calculated to sustain a rate of culture N increment of 0.20 day−1. Nitrate added to the culture was consumed within 8 to 10 hours and the partitioning to reduction and accumulation during this phase corresponded to, on the average, 75 and 25% of net uptake, respectively. The calculated rate of nitrate reduction was stimulated by onset of net uptake without delay and decreased when net uptake ceased. NADH-nitrate reductase (NR) activity measured in vitro without inclusion of antiproteolytic agents more than doubled during the first hour after nitrate addition and then gradually fell to its original level over the rest of the 24 hour interval. In the presence of the proteinase inhibitor leupeptin during extraction, however, NR activity was in general much higher and without any apparent cycles. The relative stabilizing effect of leupeptin was greatest on NADH-NR and reduced flavin adenine mononucleotide-NR activities whereas the effect was less on NADH-cytochrome c reductase activity (diaphorase) and reduced methylviologen-NR activity. The constant nitrate reductase activity measured in the presence of proteinase inhibitors is assumed to reflect the physiological situation. It thus appeares that short-term changes in nitrate assimilation by N-limited Lemna is related to the flux of nitrate to the reducing site and not to changes in nitrate reductase activity.

Influence of Nitrate and Ammonium Nutrition on the Uptake, Assimilation, and Distribution of Nutrients in Ricinus communis

Van Beusichem, Marinus L.; Kirkby, Ernest A.; Baas, Robert
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1988 EN
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Ricinus communis L. plants were grown in nutrient solutions in which N was supplied as NO3− or NH4+, the solutions being maintained at pH 5.5. In NO3−-fed plants excess nutrient anion over cation uptake was equivalent to net OH− efflux, and the total charge from NO3− and SO42− reduction equated to the sum of organic anion accumulation plus net OH− efflux. In NH4+-fed plants a large H+ efflux was recorded in close agreement with excess cation over anion uptake. This H+ efflux equated to the sum of net cation (NH4+ minus SO42−) assimilation plus organic anion accumulation. In vivo nitrate reductase assays revealed that the roots may have the capacity to reduce just under half of the total NO3− that is taken up and reduced in NO3−-fed plants. Organic anion concentration in these plants was much higher in the shoots than in the roots. In NH4+-fed plants absorbed NH4+ was almost exclusively assimilated in the roots. These plants were considerably lower in organic anions than NO3−-fed plants, but had equal concentrations in shoots and roots. Xylem and phloem saps were collected from plants exposed to both N sources and analyzed for all major contributing ionic and nitrogenous compounds. The results obtained were used to assist in interpreting the ion uptake...

Effects of La3+ on Surface Charges, Dielectrophoresis, and Electrofusion of Barley Protoplasts 1

Abe, Shunnosuke; Takeda, Junko
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1988 EN
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565.83367%
When dielectrophoresis and electrofusion of barley (Hordeum vulgare var Moor) leaf protoplasts were assayed in the presence of 0.1 to 1 millimolar lanthanum ion (La3+) in the basal medium (0.7 molar mannitol, 1 millimolar piperazine-N, N-bis[2-ethanesulfonic acid]-Na [pH 6.7], 0.1 millimolar CaCl2), dielectrophoresis and induction of electrofusion were strongly inhibited. The latter remained inhibited and the former recovered by about 60% after washing the La3+ -treated protoplasts without EDTA. These inhibitions were almost completely abolished by washing the La3+ -treated protoplasts with 1 millimolar EDTA. Inductively coupled plasma atomic emission spectroscopic analysis revealed that protoplasts retained a considerable amount of La3+ after washing without EDTA and released most of the bound La3+ by washing with 1 millimolar EDTA. This tightly bound La3+ seemed responsible for the inhibition of electrofusion and dielectrophoresis that was observed in the La3+ -treated protoplasts after washing. ζ-potentials of protoplasts were -39.0±3.2 millivolts, -16.7 ± 2.6 millivolts, and virtually zero in media containing 0, 0.1, and 0.3 millimolar La3+ (I = 7.2 millimolar), respectively, and had a positive value (+ 14.2 ± 2.2 millivolts) in the presence of 1 millimolar La3+. These effects of La3+ on ζ-potentials were easily abolished by washing without EDTA. This indicates that charged species located at the surface of plasma membrane of protoplasts cannot account for the sites at which La3+ exerts its inhibition of dielectrophoresis and electrofusion. In contrast...

Phosphorylation and Dephosphorylation Reactions of the Red Beet Plasma Membrane ATPase Studied in the Transient State 1

Briskin, Donald P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1988 EN
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565.76043%
The reaction mechanism of the solubilized red beet (Beta vulgaris L.) plasma membrane ATPase was studied with a rapid quenching apparatus. Using a dual-labeled substrate ([γ-32P]ATP and [5′,8-3H]ATP), the presteady-state time course of phosphoenzyme formation, phosphate liberation and ADP liberation was examined. The time course for both phosphoenzyme formation and ADP liberation showed a rapid, initial rise while the timecourse for phosphate liberation showed an initial lag. This indicated that ADP was released with formation of the phosphoenzyme while phosphate was released with phosphoenzyme breakdown. Phosphoenzyme formation was Mg2+-dependent and preincubation of the enzyme with free ATP followed by the addition of Mg2+ increased the rate of phosphoenzyme formation 2.3-fold. This implied that phosphoenzyme formation could result from a slow reaction of ATP binding followed by a more rapid reaction of phosphate group transfer. Phosphoenzyme formation was accelerated as the pH was decreased, and the relationship between pH and the apparent first-order rate constants for phosphoenzyme formation suggested the role of a histidyl residue in this process. Transient kinetics of phosphoenzyme breakdown confirmed the presence of two phosphoenzyme forms...

Regulation of Vacuolar pH of Plant Cells: II. A 31P NMR Study of the Modifications of Vacuolar pH in Isolated Vacuoles Induced by Proton Pumping and Cation/H+ Exchanges

Guern, Jean; Mathieu, Yves; Kurkdjian, Armen; Manigault, Pierre; Manigault, Jeanne; Gillet, Brigitte; Beloeil, Jean-Claude; Lallemand, Jean-Yves
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1989 EN
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The vacuolar pH and the trans-tonoplast ΔpH modifications induced by the activity of the two proton pumps H+-ATPase and H+-PPase and by the proton exchanges catalyzed by the Na+/H+ and Ca2+/H+ antiports at the tonoplast of isolated intact vacuoles prepared from Catharanthus roseus cells enriched in inorganic phosphate (Y Mathieu et al 1988 Plant Physiol [in press]) were measured using the 31P NMR technique. The H+-ATPase induced an intravacuolar acidification as large as 0.8 pH unit, building a trans-tonoplast ΔpH up to 2.2 pH units. The hydrolysis of the phosphorylated substrate and the vacuolar acidification were monitored simultaneously to estimate kinetically the apparent stoichiometry between the vectorial proton pumping and the hydrolytic activity of the H+-ATPase. A ratio of H+ translocated/ATP hydrolyzed of 1.97 ± 0.06 (mean ± standard error) was calculated. Pyrophosphate-treated vacuoles were also acidified to a significant extent. The H+-PPase at 2 millimolar PPi displayed hydrolytic and vectorial activities comparable to those of the H+-ATPase, building a steady state ΔpH of 2.1 pH units. Vacuoles incubated in the presence of 10 millimolar Na+ were alkalinized by 0.4 to 0.8 pH unit. It has been shown by using 23Na NMR that sodium uptake was coupled to the H+ efflux and occurred against rather large concentration gradients. For the first time...

Amino Acid and Peptide Uptake in the Scutella of Germinating Grains of Barley, Wheat, Rice, and Maize 1

Salmenkallio, Marjatta; Sopanen, Tuomas
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1989 EN
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565.76043%
Scutella separated from germinating grains of barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), rice (Oryza sativa L.), and maize (Zea mays L.) took up the four amino acids and the three peptides tested from incubation media. The uptake of amino acids by wheat scutella was similar to that of barley scutella and was via at least four uptake systems: two nonspecific amino acid uptake systems, one system specific for proline, and another system specific for basic amino acids. The scutellum of rice apparently has two nonspecific systems and a system specific for the basic amino acids, but the proline-specific system is lacking. The scutellum of maize seems to have the same systems as the scutellum of rice, but one (or both) of the nonspecific systems differs from that of the other species studied in taking up arginine only slowly. No great differences were observed in the uptake of peptides in the four species studied. The rates of uptake of different amino acids and peptides were of the same order of magnitude in the four cereals. The fact that carboxypeptidase activities in the endosperms of wheat and barley are 20-to 100-fold higher than those in rice and maize, does thus not seem to be reflected in the uptake properties of the scutella.

The Role of Phospholipids in Plasma Membrane ATPase Activity in Vigna radiata L. (Mung Bean) Roots and Hypocotyls 1

Kasamo, Kunihiro; Nouchi, Isamu
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1987 EN
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565.79984%
Root and hypocotyl plasma membrane H+-ATPases were partially purified from deoxycholate-solubilized fractions of microsomes in mung bean (Vigna radiata L.) plants in the presence of glycerol. Certain properties of the ATPases and the manner in which phospholipids affect their activity were compared. Root ATPase was similar to hypocotyl ATPase with respect to substrate specificity, salt stimulation, pH dependence, Km for ATP·Mg2+ and inhibitor sensitivity, except for inhibition by vanadate. Both purified ATPases required phospholipids for their activation. Optimum concentrations of exogenously added phospholipid mixture (asolectin) to hypocotyl and root ATPase mixture were 0.03% and 1.0%, respectively. Root ATPase activation did not decrease if more than 1.0% asolectin was added. Qualitatively, phosphatidylserine and phosphatidylcholine brought about greater ATPase activation than other phospholipids. The hypocotyl ATPase was activated by phosphatidylinositol, phosphatidylserine and phosphatidylglycerol to a greater extent than the root ATPase. Root, but not hypocotyl ATPase, was slightly inhibited by the addition of phosphatidylinositol, phosphatidylethanolamine, and phosphatidic acid. The hypocotyl plasma membrane contained phosphatidylinositol + phosphatidylserine...

Effects of Prostaglandins E2 and F2α on the Electrofusion of Pea Mesophyll Protoplasts

Christov, Alexander M.; Vaklinova, Stanka G.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1987 EN
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565.76043%
The effects of prostaglandins E2 and F2α on the electrofusion of pea (Pisum sativum cv Ran 1) mesophyll protoplasts were examined. Prostaglandins E2 and F2α influenced electrofusion by lowering the threshold voltage necessary for fusion of dielectrophoretically arranged pairs of protoplasts. The direct current voltage threshold decreased with increasing Ca2+ concentration up to 0.1 millimolar CaCl2 and the effects of prostaglandins E2 and F2α were more pronounced when CaCl2 was present in the medium. Treatment with calcium channel blocker methoxy verapamil did not change the prostaglandin effects, while the addition of ethyleneglycol-bis (β-aminoethyl either)-N,N,N′,N′-tetraacetic acid, which binds free Ca2+, increased the threshold voltage. Influence of prostaglandins E2 and F2α and Ca2+ on the membrane fluidity was investigated by analysis of pyrene fluorescence spectra. The values of the ratio between the maximum fluorescence emission intensities of the excimer and the monomer forms (Iex/Imon) indicated that prostaglandins and Ca2+ decrease the membrane fluidity. It is proposed that electrically evoked displacement of plasmalemma components takes part in the fusion process (U Zimmermann 1982 Biochim Biophys Acta 694: 227-277). We suggest that prostaglandins E2 and F2α facilitate the electrofusion of pea mesophyll protoplasts by changing the fluidity of plasmalemma.

Proton Transport in Plasma Membrane and Tonoplast Vesicles from Red Beet (Beta vulgaris L.) Storage Tissue 1: A Comparative Study of Ion Effects on ΔpH and ΔΨ

Giannini, John L.; Briskin, Donald P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1987 EN
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565.83367%
The proton transport properties of plasma membrane and tonoplast vesicles isolated from red beet (Beta vulgaris L.) storage tissue were examined and compared. Membrane vesicles isolated with 250 millimolar KCl in the homogenization media and recovered at low density following sucrose density gradient centrifugation displayed characteristics of proton transport (nitrate inhibition, no inhibition by orthovanadate, pH optimum of 7.75, pyrophosphate-driven proton transport) which were consistent with a tonoplast origin. When the KCl in the homogenization medium was replaced by 250 millimolar KI, sealed membrane vesicles were recovered at higher densities in sucrose gradients and displayed properties (orthovanadate sensitivity, no inhibition by nitrate, pH optimum of 6.5) consistent with a plasma membrane origin. A comparison of anion effects (potassium salts) upon ΔpH and ΔΨ revealed a direct correspondence between the relative ability of anions to stimulate proton transport and reduce ΔΨ. For tonoplast vesicles, the relative order for this effect was KI > KBr ≥ KCl > KClO3 > K2SO4 while for plasma membrane vesicles, a different order KI > KNO3 ≥ KBr ≥ KClO3 > KCl > K2SO4 was observed. Proton transport in plasma membrane and tonoplast vesicles was inhibited by fluoride; however...

Water Transport in Maize Roots 1: Measurement of Hydraulic Conductivity, Solute Permeability, and of Reflection Coefficients of Excised Roots Using the Root Pressure Probe

Steudle, Ernst; Oren, Ram; Schulze, Ernst-Detlef
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1987 EN
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565.76043%
A root pressure probe has been used to measure the root pressure (Pr) exerted by excised main roots of young maize plants (Zea Mays L.). Defined gradients of hydrostatic and osmotic pressure could be set up between root xylem and medium to induce radial water flows across the root cylinder in both directions. The hydraulic conductivity of the root (Lpr) was evaluated from root pressure relaxations. When permeating solutes were added to the medium, biphasic root pressure relaxations were observed with water and solute phases and root pressure minima (maxima) which allowed the estimation of permeability (PSr) and reflection coefficients (σsr) of roots. Reflection coefficients were: ethanol, 0.27; mannitol, 0.74; sucrose, 0.54; PEG 1000, 0.82; NaCl, 0.64; KNO3, 0.67, and permeability coefficients (in 10−8 meters per second): ethanol, 4.7; sucrose, 1.6; and NaCl, 5.7. Lpr was very different for osmotic and hydrostatic gradients. For hydrostatic gradients Lpr was 1·10−7 meters per second per megapascal, whereas in osmotic experiments the hydraulic conductivity was found to be an order of magnitude lower. For hydrostatic gradients, the exosmotic Lpr was about 15% larger than the endosmotic, whereas in osmotic experiments the polarity in the water movement was reversed. These results either suggest effects of unstirred layers at the osmotic barrier in the root...

Spectral Properties and Composition of Reaction Center and Ancillary Polypeptide Complexes of Photosystem II Deficient Mutants of Synechocystis 6803 1

Dzelzkalns, Valdis A.; Bogorad, Lawrence
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1989 EN
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565.76043%
The polypeptide composition and spectral properties of three photosystem II (PSII) deficient mutants of the cyanobacterium Synechocystis 6803 have been determined. The levels of the 43 and 47 kilodalton chlorophyll-binding proteins and the reaction center component D2 are affected differently in each mutant; the 33 kD polypeptide of the oxygen-evolving complex is found at wild-type levels in all three. The 43 and 47 kilodalton proteins are implicated as important elements in the assembly and/or stability of the PSII reaction center, although the loss of one of these polypeptides does not lead to the loss of all PSII proteins. Low temperature fluorescence emission spectra of wild-type cells reveal chlorophyll-attributable peaks at 687 (PSII), 696 (PSII), and 725 (photosystem I) nanometers. All three mutants retain the 725 nanometer fluorescence but lack the 696 nanometer peak. This suggests that the latter fluorescence arises from PSII reaction center chlorophyll or results from interactions among functional PSII components in vivo. Cells that contain the 43 kilodalton and lack the 47 kilodalton protein, retain the 687 fluorescence; furthermore, in as much as this fluorescence is absent from cells without the 43 kilodalton protein, the 687 nanometer peak is judged to emanate from the 43 kilodalton chlorophyll-protein. A new peak...

Distribution of Thylakoid Proteins between Stromal and Granal Lamellae in Spirodela 1: Dual Location of Photosystem II Components

Callahan, Franklin E.; Wergin, William P.; Nelson, Nathan; Edelman, Marvin; Mattoo, Autar K.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1989 EN
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565.76043%
We have quantified the lateral distribution of 12 thylakoid proteins of Spirodela oligorrhiza by immunoblot analysis of detergent-derived granal and stromal lamellae. The immunological, ultrastructural, cytochemical, and biophysical measurements each indicated the expected overall separation of photosystem II (PSII) and photosystem I (PSI) components; however, certain proteins were not completely localized to one lamellar fraction. The apoproteins of the light harvesting chlorophyll a/b complex, subunit 1 of PSI and the components of the PSII reaction center (the 32 kilodalton, D2, and cytochrome b559 proteins) were dually located between granal and stromal lamellae. Proteins associated exclusively with one of the membrane types were: in granal lamellae, the 43 and 51 kilodalton PSII proteins, and in stromal lamellae, the α and β subunits of the proton ATPase.

Calcium and Proton Transport in Membrane Vesicles from Barley Roots 1

DuPont, Frances M.; Bush, Douglas S.; Windle, John J.; Jones, Russell L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1990 EN
Relevância na Pesquisa
565.76043%
Ca2+ uptake by membrane fractions from barley (Hordeum vulgare L. cv CM72) roots was characterized. Uptake of 45Ca2+ was measured in membrane vesicles obtained from continuous and discontinuous sucrose gradients. A single, large peak of Ca2+ uptake coincided with the peak of proton transport by the tonoplast H+-ATPase. Depending on the concentration of Ca2+ in the assay, Ca2+ uptake was inhibited 50 to 75% by those combinations of ionophores and solutes that eliminated the pH gradient and membrane potential. However, 25 to 50% of the Ca2+ uptake in the tonoplast-enriched fraction was not sensitive to ionophores but was inhibited by vanadate. The results suggest that 45Ca uptake was driven by the low affinity, high capacity tonoplast Ca2+/nH+ antiporter and also by a high affinity, lower capacity Ca2+-ATPase. The Ca2+-ATPase may be associated with tonoplast, Golgi or contaminating vesicles of unknown origin. No Ca2+ transport was specifically associated with the distinct peak of endoplasmic reticulum that was identified by NADH cytochrome c reductase, choline phosphotransferase, and dolichol-P-man-nosyl synthase activities. A small shoulder of Ca2+ uptake in the plasma membrane region of the gradient was inhibited by vanadate and erythrosin B and may represent the activity of a separate plasma membrane Ca2+-ATPase. Vesicle volumes were estimated using electron spin resonance techniques...

Distinction between Hypoxanthine and Xanthine Transport in Chlamydomonas reinhardtii1

Pérez-Vicente, Rafael; Cárdenas, Jacobo; Pineda, Manuel
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1991 EN
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565.83367%
Chlamydomonas reinhardtii cells consumed hypoxanthine and xanthine by means of active systems which promoted purine intracellular accumulation against a high concentration gradient. Both uptake and accumulation were also observed in mutant strains lacking xanthine dehydrogenase activity. Xanthine and hypoxanthine uptake systems exhibited very similar Michaelis constants for transport and pH values, and both systems were induced by either hypoxanthine or xanthine. However, they differed greatly in the length of the lag phase before uptake induction, which was longer for hypoxanthine than for xanthine. Cells grown on ammonium and transferred to hypoxanthine media consumed xanthine before hypoxanthine, whereas cells transferred to xanthine media did not take up hypoxanthine until 2 hours after commencing xanthine consumption. Metabolic and photosynthetic inhibitors such as 2,4-dinitrophenol, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea, and carbonylcyanide m-chlorophenylhydrazone inhibited to a different extent the hypoxanthine and xanthine uptake. Similarly, N-ethylmaleimide abolished xanthine uptake but slightly affected that of hypoxanthine. Hypoxanthine consumption was inhibited by adenine and guanine whereas that of xanthine was inhibited only by urate. We conclude that hypoxanthine and xanthine in C. reinhardtii are taken up by different active transport systems which work independently of the intracellular enzymatic oxidation of these purines.

Biosynthesis and Desaturation of Prokaryotic Galactolipids in Leaves and Isolated Chloroplasts from Spinach 1

Heemskerk, Johan W. M.; Schmidt, Hermann; Hammer, Ute; Heinz, Ernst
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1991 EN
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565.83367%
Mono- and digalactosyldiacylglycerol (MGDG and DGDG) were isolated from the leaves of sixteen 16:3 plants. In all of these plant species, the sn-2 position of MGDG was more enriched in C16 fatty acids than sn-2 of DGDG. The molar ratios of prokaryotic MGDG to prokaryotic DGDG ranged from 4 to 10. This suggests that 16:3 plants synthesize more prokaryotic MGDG than prokaryotic DGDG. In the 16:3 plant Spinacia oleracea L. (spinach), the formation of prokaryotic galactolipids was studied both in vivo and in vitro. In intact spinach leaves as well as in chloroplasts isolated from these leaves, radioactivity from [1-14C]acetate accumulated 10 times faster in MGDG than in DGDG. After 2 hours of incorporation, most labeled galactolipids from leaves and all labeled galactolipids from isolated chloroplasts were in the prokaryotic configuration. Both in vivo and in vitro, the desaturation of labeled palmitate and oleate to trienoic fatty acids was higher in MGDG than in DGDG. In leaves, palmitate at the sn-2 position was desaturated in MGDG but not in DGDG. In isolated chloroplasts, palmitate at sn-2 similarly was desaturated only in MGDG, but palmitate and oleate at the sn-1 position were desaturated in MGDG as well as in DGDG. Apparently, palmitate desaturase reacts with sn-1 palmitate in either galactolipid...

Oxidation of External NAD(P)H by Purified Mitochondria from Fresh and Aged Red Beetroots (Beta vulgaris L.) 1

Fredlund, Kenneth M.; Rasmusson, Allan G.; Møller, Ian M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1991 EN
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565.79984%
Mitochondria were isolated from fresh beetroots (Beta vulgaris L. cvs Rubria and Nina) by differential centrifugation followed by Percoll gradient centrifugation. These purified mitochondria oxidized external NADH, although relatively slowly (20-40 versus 100-120 nanomoles oxygen per minute times milligram protein for NADH and succinate oxidation, respectively), with respiratory control ratios of two to three and ADP/O ratios of 1.2 to 1.6. NADPH was also oxidized, but even more slowly and with little or no coupling. The optimum for both NADH and NADPH oxidation by fresh beetroot mitochondria was pH 6. The rate of external NADH oxidation by isolated mitochondria was enhanced threefold during storage of the intact tubers at 10°C for 12 weeks. The optimum of the induced NADH oxidation was approximately pH 6.8. Succinate and malate oxidation only increased by 30% during the same period and NADPH oxidation was constant. This is strong evidence that NADH and NADPH oxidation are catalyzed by different enzymes at least in beetroots. Activity staining of nondenaturing polyacrylamide gels with NADH and Nitro Blue Tetrazolium did not show differences in banding pattern between mitochondria isolated from fresh and stored beetroots. The induction is discussed in relation to physiological aging processes.

Membrane Potential and Proton Cotransport of Alanine and Phosphate as Affected by Permeant Weak Acids in Lemna gibba1

Basso, Barbara; Ullrich-Eberius, Cornelia I.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1987 EN
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565.79984%
The treatment of Lemna gibba plants with the weak acids (trimethylacetic acid and butyric acid), used as tools to decrease intracellular pH, induced a hyperpolarization of membrane potential, dependent on the concentration of the undissociated permeant form of the weak acid and on the value of the resting potential. Measurements were carried out both with `high potential' and `low potential' plants and the maximum values af acid induced hyperpolarizations were about 35 and 71 millivolts, respectively. Weak acids influenced also the transient light-dark membrane potential changes, typical for photosynthesizing material, suggesting a dependence of these changes on an acidification of cytoplasm. In the presence of the weak acids, the membrane depolarization induced by the cotransport of alanine and phosphate with protons was reduced; the maximum reduction (about 90%) was obtained with alanine during 2 millimolar trimethylacetic acid perfusion at pH 5. A strong inhibition of the uptake rates (up to 48% for [14C]alanine and 68% for 32P-phosphate) was obtained in the presence of the weak acids, both by decreasing the pH of the medium and by increasing the concentration of the acid. In these experimental conditions, the ATP level and O2 uptake rates did not change significantly. These results constitute good evidence that H+/solute cotransport in Lemna...

Inhibition of Zeaxanthin Formation and of Rapid Changes in Radiationless Energy Dissipation by Dithiothreitol in Spinach Leaves and Chloroplasts 1

Demmig-Adams, Barbara; Adams, William W.; Heber, Ulrich; Neimanis, Spidola; Winter, Klaus; Krüger, Almuth; Czygan, Franz-Christian; Bilger, Wolfgang; Björkman, Olle
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1990 EN
Relevância na Pesquisa
565.83367%
Dithiothreitol, which completely inhibits the de-epoxidation of violaxanthin to zeaxanthin, was used to obtain evidence for a causal relationship between zeaxanthin and the dissipation of excess excitation energy in the photochemical apparatus in Spinicia oleracea L. In both leaves and chloroplasts, inhibition of zeaxanthin formation by dithiothreitol was accompanied by inhibition of a component of nonphotochemical fluorescence quenching. This component was characterized by a quenching of instantaneous fluorescence (Fo) and a linear relationship between the calculated rate constant for radiationless energy dissipation in the antenna chlorophyll and the zeaxanthin content. In leaves, this zeaxanthin-associated quenching, which relaxed within a few minutes upon darkening, was the major component of nonphotochemical fluorescence quenching determined in the light, i.e. it represented the `high-energy-state' quenching. In isolated chloroplasts, the zeaxanthin-associated quenching was a smaller component of total nonphotochemical quenching and there was a second, rapidly reversible high-energy-state component of fluorescence quenching which occurred in the absence of zeaxanthin and was not accompanied by Fo quenching. Leaves, but not chloroplasts...