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C Grignon

Publications and source records attributed to C Grignon.

27 records · Page 2Linked to original sources
PubMed1988

H Cotransports in Corn Roots as Related to the Surface pH Shift Induced by Active H Excretion.

The surface pH shift induced by active H(+) excretion in corn (Zea mays L.) roots was estimated using acetic acid influx as a pH probe (H Sentenac, C Grignon 1987 Plant Physiol 84: 1367-1372). At constant bulk pH, buffering the medium strongly reduced the magnitude of the surface pH shift. This was used to study the effect of surface pH shift on H(+) cotransports. In the absence of buffers, the surface pH shift increased with the bulk pH. Buffers decreased (32)Pi influx and this effect was stronger at pH 7.2 than at pH 5.8, and stronger in the absence than in the presence of an inhibitor of the proton pump (vanadate). Buffers exerted a similar depressive and pH-dependent effect on net NO(3) (-) uptake. They hyperpolarized the cell membrane, and stimulated (86)Rb(+) influx, K(+):H(+) net exchange, and malate accumulation. These results are consistent with the hypothesis that H(+) accumulation at the cell surface is effective in driving H(+) reentry. We concluded that the surface pH shift due to proton pump activity is involved in the energetic coupling of H(+) cotransports.

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PubMed1987

Effect of H Excretion on the Surface pH of Corn Root Cells Evaluated by Using Weak Acid Influx as a pH Probe.

The initial rate of (2-(14)C)acetic acid (AA) uptake by corn roots was used for probing the dependency of the root cell surface pH on H(+) excretion. AA influx was linearly related to AA concentration, dependent on the concentration of the undissociated form (AH), unaffected by variations of the membrane potential, and was thus assumed to result mainly from the free diffusion of AH across the membrane. Various treatments (vanadate, dicyclohexylcarbodiimide, hypoxia, nitrate, root ageing, fusicoccin) were used to vary H(+) flux while the medium pH was maintained constant. There was a positive relation between AA influx and the net H(+) efflux. This relation disappeared when the proton buffering strength of the absorption medium was increased. These results indicate that the pH at the membrane surface was lowered by H(+) excretion, even in situations where the bulk (pH) was unaffected. The depressive effect of vanadate on AA influx was counteracted by acidifying the medium in order to estimate this pH shift: -1.2 pH units in 12.5 millimolar K(2)SO(4) (pH 6.8). Substituting AA by butyric acid showed that this estimation was not dependent of the probe used.

Journal Article↗
PubMed1986

H and k electrogenic exchanges in corn roots.

The membrane potential difference, the net H(+) exchange rate, the K(+) net flux, and the K(+) ((86)Rb(+)) influx were measured in excised corn roots as functions of the K(+) concentration in the medium at various pH values, in the presence of poorly permeant anions. The roots behaved as a K(+)/H(+) exchange system. By comparing the results in normal or hypoxic conditions, or in the presence of vanadate, it was possible to distinguish the active components of membrane potential and transports from the passive ones. The magnitude of the electrogenic potential was not related to the active H(+) extrusion rate. At pH 6, the variations of the electrogenic potential resulted from variations of the stoichiometry of the active H(+)/K(+) exchange. The same relationship between this stoichiometry and the K(+) concentration was observed in conditions ensuring different membrane polarizations (pH 6, pH 4, or pH 6 with fusicoccin). Both metabolic and Mg-ATPase specific inhibitors stopped the active H(+) transport and the net K(+) influx. Nevertheless, the tracer influx in the presence of vanadate remained higher than the passive influx calculated from the permeability coefficient determined in hypoxia. It is proposed that vanadate uncouples the K(+) moiety of the H(+)/K(+) antiport and allows it to mediate isotopic exchanges.

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PubMed1985

Effect of pH on Orthophosphate Uptake by Corn Roots.

Orthophosphate (Pi) influx in washed corn roots was studied with experimental conditions allowing a distinction of pH effects on Pi ionization in the medium and on the transport system itself. There appeared to be no relationship between the pH dependencies of membrane potential, H(+) secretion, and (32)Pi influx. The Pi uptake versus pH curves were compared to the calculated ones describing the concentrations of the different ionized Pi forms in the medium and in the cell walls; the latter were obtained using the theoretical model described by Sentenac and Grignon (1981) Plant Physiol 68: 415-419). The conclusion was that the transported form is H(2)PO(4) (-) and the concentration sensed by the transport system is the local one. The ionic compositions of experimental media were manipulated to ensure constant pH and various H(2)PO(4) (-) concentrations, or constant H(2)PO(4) (-) concentration and various pH values in the walls. The kinetic analysis of the results in the micromolar range showed that the transport system has an intrinsic sensitivity to pH, and is switched from a low activity state at pH > 6 to a high activity one at pH < 4 (pH in the walls). This change could be triggered by the protonation of a group with pK 5.5.

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PubMed1983

A procedure for estimating the surface potential of charged or neutral membranes with 8-anilino-1-naphthalenesulphonate probe. Adequacy of the Gouy-Chapman model.

Using the fluorescent anion 8-anilino-1-naphthalenesulphonate (ANS) for determining the membrane surface potential necessitates that the intrinsic affinity constant Ki for the ANS sites be known. Two methods are presented which do not rely on a determination of Ki at high ionic strength. They are respectively applied to neutral membranes (egg phosphatidylcholine liposomes) and highly charged natural ones (horse bean microsomes and liposomes from their phospholipids). The value of Ki appears to be insensitive to the level of occupancy of the sites, the KCl concentration and the pH in large ranges. Furthermore, the classical Gouy-Chapman model seems to describe correctly the whole set of data, provided apparent mean molecular areas larger than the published crystallographic ones are admitted.

Anilino Naphthalenesulfonates↗
PubMed1982

Proton permeability of liposomes from natural phospholipid mixtures.

A method to determine the proton permeability coefficient of phospholipid membrane with the fluorescent probe pyranine is described. Very high proton permeability coefficients of liposomes from natural extracts are measured with great accuracy. The proton permeability appears to be linearly related to the fluidity of the bilayers. This relation as well as the comparison of the activation energies of proton permeability and fluidity support the hypothesis (Nichols J.W. and Deamer D.W. (1980) Proc. Natl. Acad. Sci. USA 77, 2038--2042) of a transfer process along a network of hydrogen bonded water molecules. It is suggested that the common lipid characteristics of biological membranes (net surface charge and unsaturation) favor a high proton permeability.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1982

Effect of temperature and ions on the microviscosity of bilayers from natural phospholipid mixtures.

The thermotropic behaviour of two natural extracts of phospholipids differing by their content in saturated fatty acids and acidic polar heads were studied with the aid of the fluorescent probes : perylene and diphenylhexatriene. The main results are that the bilayers are in a fluid state in the range from -- 5 to 50 degrees C, in the presence as well as in the absence of calcium, and that misleading conclusions may be derived with the perylene probe. The effects of pH and Ca2+/H+ interaction on the microviscosity were studied. In the absence of calcium pH increase fluidizes the bilayers ; when Ca2+ is present the microviscosity is constant over a large pH range. Calculations using the Gouy-Chapman theory suggest that the pH-induced microviscosity changes are controlled by the content in phosphadidylserine, diphosphatidylglycerol and phosphatidic acid of the extracts. Similarly the rigidifying effect of Ca2+ seems to be related to the content in these phospholipids. These hypothesis were confirmed by modifying the content of the extracts in these phospholipids. It is proposed that the behaviour of the two studied extracts results from the high insaturation of their fatty acids, which is typical of biological membranes.

Calcium↗
PubMed1981

A model for predicting ionic equilibrium concentrations in cell walls.

Purified cell walls were prepared from roots of Horse bean (Vicia faba L., var. minor) and Yellow Lupine (Lupinus luteus L.). Two methods were used: (a) grinding and (b) lysis of the endocellular contents by Triton X-100. The Ca(2+), Mg(2+), and K(+) contents were determined after incubation in various solutions in such a manner that the measurements gave access to the undisturbed equilibrium contents. The results were used to test a model which describes the ionic atmosphere in the cell walls as a result of simultaneous electrostatic interactions between free ions (Donnan effect) and specific association equilibria, including acido-basic ones. This model correctly accounted for the whole set of experimental results and predicted the values of the unmeasurable local concentrations and pH.

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