Light-stimulated Electrogenic Uptake of Neutral Amino Acids by Leaf Cells of Egeria densa and Vicia faba

Petzold, U.; Dahse, I.; Müller, Eberhard

doi:10.1016/s0015-3796(85)80027-5

Cited by 14 publications

(8 citation statements)

References 23 publications

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“…A plasma membrane-located, ATP-driven, H+-efflux process establishes a H+ electrochemical gradient across the membrane of plant cells (22 an alkalinization of the suspension medium (7,12,13,16,18,19,25). However, alkalinization may also arise from metabolism of the transported amino acid (18).…”

Section: Introductionmentioning

confidence: 99%

“…Its addition to the cell suspension did not result in medium alkalinization and evidence indicates that it is lost from the cell to the medium. The data suggest that the origin of medium alkalinization is co-transport not metabolism, and that the loss of labeled CO2 and -y-aminobutyric acid from the cell result in an overestimation of the stoichiometry of the H'/L-glutamate uptake process.A plasma membrane-located, ATP-driven, H+-efflux process establishes a H+ electrochemical gradient across the membrane of plant cells (22 an alkalinization of the suspension medium (7,12,13,16,18,19,25). However, alkalinization may also arise from metabolism of the transported amino acid (18).…”

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confidence: 99%

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l-Glutamate-Dependent Medium Alkalinization by Asparagus Mesophyll Cells

McCutcheon¹,

Ciccarelli²,

Chung³

et al. 1988

Plant Physiol.

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Mechanically isolated Asparagus sprengeri Regel mesophyll cells cause alkalinization of the suspension medium on the addition of Lglutamate or its analog L-methionine-D,L-sulfoximine. Using a radiolabeled pH probe, it was found that both compounds caused internal acidification whereas L-aspartate did not. Fusicoccin stimulated Ho efflux from the cells by 111% and the uptake of L-[U-'4Cjglutamate by 55%.Manometric experiments demonstrated that, unlike L-methionine-D,Lsulfoximine, L-glutamate stimulated CO2 evolution from nonilluminated cells. Simultaneous measurements of medium alkalinization and "CO2 evolution upon the addition of labeled L-glutamate showed that alkalinization was immediate and reached a maximum value after 45 minutes whereas "CO2 evolution exhibited a lag before its appearance and continued in a linear manner for at least 100 minutes. Rates of alkalinization and uptake of L-IU-'4Cjglutamate were higher in the light while rates of '4CO2 evolution were higher in the dark. The major labeled product of glutamate decarboxylation, y-aminobutyric acid, was found in the cells and the suspension medium. Its addition to the cell suspension did not result in medium alkalinization and evidence indicates that it is lost from the cell to the medium. The data suggest that the origin of medium alkalinization is co-transport not metabolism, and that the loss of labeled CO2 and -y-aminobutyric acid from the cell result in an overestimation of the stoichiometry of the H'/L-glutamate uptake process.A plasma membrane-located, ATP-driven, H+-efflux process establishes a H+ electrochemical gradient across the membrane of plant cells (22 an alkalinization of the suspension medium (7,12,13,16,18,19,25). However, alkalinization may also arise from metabolism of the transported amino acid (18). Protonation of a basic metabolite will result in alkalinization as will a decarboxylation process:RCOO-+ H+--RH + CO2 On the basis of medium alkalinization and uptake studies, an H+ cotransport system specific for L-Glu3 and L-MSO has been proposed for photosynthetically competent Asparagus mesophyll cells (12). However, the apparent H+ uptake rate was 5 to 8 times faster than the uptake of L-["4C]Glu indicating a large molar excess of H+ associated with the L-Glu uptake process. This investigation also demonstrated that addition of L-Glu results in the rapid release of CO2 (12). These findings indicate that the consumption of H+ may result from a metabolic process. Medium alkalinization would occur if L-Glu was decarboxylated by an extracellular enzyme prior to the entry of the decarboxylated product into the cell. This model is analogous to the hydrolysis of sucrose by an extracellular invertase prior to hexose cotransport into sugarcane cells (8). Medium alkalinization would also occur if glutamate cotransport into the cell resulted in the export and protonation of a basic product of L-Glu metabolism. Alternatively, the high H+ to L-Glu ratio could arise from the loss of labeled CO2 or other metabolites from the cell an...

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Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

l-Glutamate-Dependent Medium Alkalinization by Asparagus Mesophyll Cells

McCutcheon¹,

Ciccarelli²,

Chung³

et al. 1988

Plant Physiol.

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“…Amino acid influx into Egeria leaves was measured as reported previously (12 DHS hyperpolarized the membrane in the same way as SSHB (by 4-39 mV, eight cells from different leaves). In contrast to FC (5), the effects ofall three steroids were reversed after washing the leaves with the x solution.…”

Section: Amino Acid and Sucrose Uptake Experimentsmentioning

confidence: 99%

“…Egeria leaves (10)(11)(12)(13)(14)(15) were incubated for 1 h in 2 mL of a solution containing 4 nm (reference 500 nm). The experiments were peformed at least three times with five replicates.…”

Section: Reduction Of Fecnmentioning

confidence: 99%

“…In order to characterize further the role of the steroid structure in modifying transport on the cellular level, we here describe the effects of another potent synthetic analog, SSHB (1 in Fig. 1), on the membrane potential and on proton and solute transport of Egeria densa, a submerged aquatic weed well characterized in this respect (5,6,12), and we compare the SSHB effect with those induced by related substances and FC.…”

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Effects of (22S,23S)-Homobrassinolide and Related Compounds on Membrane Potential and Transport of Egeria Leaf Cells

Dahse¹,

Sack²,

Bernstein³

et al. 1990

Plant Physiol.

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ABSTRACT(22S,23S)-Homobrassinolide was tested for its effect on the electric cell potential, proton extrusion, ferricyanide reduction, and amino acid and sucrose uptake of leaves of Egeria densa Planchon. In the light, (22S,23S)-homobrassinolide and its derivative, 2a-3a-dihydroxy-5a-stigmast-22-en-6-one, were similar to each other and similar to fusicoccin in causing hyperpolarization and proton extrusion, whereas stigmasterol was less effective. In darkness, the three sterols showed comparable effects.(22S,23S)-Homobrassinolide slightly stimulated ferricyanide reduction and promoted uptake of sucrose and a-aminoisobutyric acid. The results are compatible with a stimulation of an electrogenic proton pump mechanism at the plasmalemma by (22S,23S)-homobrassinolide.behavior to auxin in corn roots (14) suggests an FC3-like mechanism of action for this compound. Unfortunately, the structural requirements of the steroid backbone, responsible for the stimulation of transport by brassinosteroids, is not yet clear, although some work was dedicated to this issue (10). In order to characterize further the role of the steroid structure in modifying transport on the cellular level, we here describe the effects of another potent synthetic analog, SSHB (1 in Fig. 1), on the membrane potential and on proton and solute transport of Egeria densa, a submerged aquatic weed well characterized in this respect (5, 6, 12), and we compare the SSHB effect with those induced by related substances and FC. MATERIALS AND METHODS Plant CultivationBrassinosteroids are a new class of growth regulators found in many plants (1, 10). Among them brassinolide, (22R,23R,24S)-2a,3a,22,23-tetrahydroxy-24-methyl-Bhomo-7-oxa-5a-cholestan-6-one, is the best characterized and causes the highest growth promotion. The comparison with other plant hormones in a series of bioassays revealed auxinlike properties, albeit a powerful synergism between brassinolide and IAA was reported (1 1, 15

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Brassinosteroide ?eine neue Phytohormon-Gruppe?

Adam

Petzold

1994

Naturwissenschaften

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Light-stimulated Electrogenic Uptake of Neutral Amino Acids by Leaf Cells of Egeria densa and Vicia faba

Cited by 14 publications

References 23 publications

l-Glutamate-Dependent Medium Alkalinization by Asparagus Mesophyll Cells

l-Glutamate-Dependent Medium Alkalinization by Asparagus Mesophyll Cells

Effects of (22S,23S)-Homobrassinolide and Related Compounds on Membrane Potential and Transport of Egeria Leaf Cells

Brassinosteroide ?eine neue Phytohormon-Gruppe?

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