Titration of Isolated Cell Walls of <i>Lemna minor</i> L

Morvan, C.; Demarty, Mauríce; Thellier, Michel

doi:10.1104/pp.63.6.1117

Cited by 52 publications

(20 citation statements)

References 10 publications

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“…However, the apparent pKas for these sites cannot be determined in the pH range of the titration shown. According to Morvan et al (16), these sites are probably dominated by uronic acids.…”

Section: Methodsmentioning

confidence: 99%

“…On the other hand, the second apparent pKa, determined by the midpoint between the two apparent equivalence points (pH 5.7 and 8.6), is approximately 7.1. We hypothesize that the first apparent pKa (below 5) represents carboxyl groups of uronic acids, and the second pKa represents a combination of ionizable groups and hydrolysis of methyl esters of the pectic substance (16).…”

Section: Methodsmentioning

confidence: 99%

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Surface Chemical Properties of Purified Root Cell Walls from Two Tobacco Genotypes Exhibiting Different Tolerance to Manganese Toxicity

Wang¹,

Evangelou²,

Nielsen³

1992

Plant Physiol.

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Surface chemical characteristics of root cell walls extracted from two tobacco genotypes exhibiting differential tolerance to Mn toxicity were studied using potentiometric pH titration and Fourier transform infrared spectroscopy. The Mn-sensitive genotype KY 14 showed a stronger interaction of its cell wall surface with metal ions than did the Mn-tolerant genotype Tobacco Introduction (T.l.) 1112. This observation may be attributed to the relatively higher ratio of COO to COOH in KY 14 cell walls than that found in the cell walls of T.I. 1 1 12 in the pH range of 4 to 10. For both genotypes, the strength of binding between metal ions and cell wall surface was in the order of Cu > Ca > Mn > Mg > Na. However, a slightly higher preference of Ca over Mn was observed with the T.l. 1112 cell wall. This may explain the high accumulation of Mn in the leaves of Mn-tolerant genotype T.l. 1112 rather than the high accumulation of Mn in roots, as occurred in Mn-sensitive KY 14. It is concluded that surface chemical characteristics of cell walls may play an important role in plant metal ion uptake and tolerance.Recently, more evidence has suggested that cell wall exchange properties may well affect ion availability for uptake, diffusion rates in the apoplast, the chemical and electrical environment of the membrane and its transporters, growth of the cell wall, and function of cell wall enzymes (1). Therefore, an evaluation of the role of the root cell wall in the processes of metal ion uptake and tolerance is indeed necessary.In this study, purified cell wall materials from two tobacco (Nicotiana tabacum L.) genotypes demonstrating different tolerance to Mn toxicity were investigated. The study examined the intrinsic surface chemical characteristics of root cell walls and related these characteristics to genotypic differences in Mn uptake and tolerance. MATERIALS AND METHODSMn toxicity has been a significant growth-limiting factor for many crops in various regions, especially where crops are grown in relatively low pH soils (e.g. pH < 5.5 (14,19,20) and trichomes (3). The Mn trapped in plant vacuoles has been speculated to be complexed with organic acids (14). This hypothesis is supported by thermodynamic predictions using computer simulation models (24,25 Plant Physiol. Vol. 100, 1992 equilibrated for a relatively long period (e.g. 20 h). The titration curves shown in Figure 2 obtained with a 30-min equilibration period imply that the neutralization reaction between OH-and the H-form of the cell wall of KY 14 genotype in the Na solution background may be faster than that of T.I. 1112. This result indicates that the architecture and/or composition of the cell walls of the two genotypes are different.The shape of the titration curve of KY 14 in Figure 2 suggests that there are at least two apparent pKas in the cell wall material. However, the pKas obtained from such a titration plot cannot be considered as intrinsic pKas because the latter require additional information on ionic strength effect and residue ...

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“…However, the apparent pKas for these sites cannot be determined in the pH range of the titration shown. According to Morvan et al (16), these sites are probably dominated by uronic acids.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Surface Chemical Properties of Purified Root Cell Walls from Two Tobacco Genotypes Exhibiting Different Tolerance to Manganese Toxicity

Wang¹,

Evangelou²,

Nielsen³

1992

Plant Physiol.

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“…Due to the presence of polygalacturonic acids, plant cell walls behave as polyanions with a pK a around 3 [21]. Depending on the sign of the charge of the substrate, either attraction or repulsion may occur.…”

Section: Kinetic Properties Of the Enzyme Bound To The Cell Walls (Rementioning

confidence: 99%

“…the electrostatic partition coefficient will tend to unity [21]. Clearly, the two enzyme populations will not be kinetically differentiated anymore, and $1 will tend to equal $2 (at---) 1).…”

Section: The Effect Of the Ionic Strength (Reaction-diffusion)mentioning

confidence: 99%

Combined effects of diffusional hindrances, electrostatic repulsion and product inhibition on the kinetic properties of a bound acid phosphatase

Thiébart‐Fassy

Hervagault

1993

FEBS Letters

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The kinetic properties of a soybean cell wall phosphatase were studied and compared under different environmental conditions. The native enzyme isolated from the wall exhibits classical Michaelis Menten kinetics. When buried into the cell wall, its natural environment, the enzyme mimics an apparent negative cooperativity. This deviation from hyperbolic dependence of the activity vs. the substrate concentration may result from an heterogeneous distribution of the enzyme molecules between the surface and the inside of the wall, where an electrostatic partition effect takes place. Cell wall fragments compacted on a Millipore-type membrane allow the study of the dual effects of diffusional hindrances and electrostatic interactions on the global kinetic behavior. By increasing the ionic strength, partition effects can be suppressed and therefore diffusional effects alone can be taken into account. On the one hand, diffusion and partition act individually and synergetically to decrease the apparent global affinity of phosphatase with respect to glucose 6-phosphate. On the other hand, product inhibition by inorganic phosphate is subjected to dual effects from diffusion through accumulation and partition through repulsion. A simple diffusion partition reaction model accounts qualitatively and quantitatively for the experimental observations.

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“…Above this value, the additional saturation of the -COO-groups leads to such a lowering of the surface charge density in the exchanger that the preferential attraction of the bivalent cations (the electroselectivity) vanishes. The progressive disappearance of the electrostatic interactions results in the tendency of the global equilibrium constants to ultimately reach the intrinsic pK value: 3.36 of the a-D-galacturonic acid monomer (6), the main building block of the constitutive pectin of the cell wall. LITERATURE CITlE;D…”

mentioning

confidence: 99%

Proton-Metal Cation Exchange in the Cell Wall of Nitella flexilis

Cutsem¹,

Gillet²

1983

Plant Physiol.

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When protons are exchanging for bivalent cations (Cu2", Zn2+, or Ca2+) on the carboxylic groups of Nitella flexilis cell wall, the values of the respective global equilibrium constants do not change up to a protonation degree of 80%. These values drastically increase at higher proton concentrations and tend to =3.4, which is the intrinsic pK value of the constitutive a-D-galacturonic acid monomer. These data suggest that the electric field in the matricial polymer and the cation bridges between pairs of negative sites have disappeared.Plant cells are surrounded by a rigid cell wall usually of a pecto-cellulosic type. Fixed negative charges arise from the ionization at natural pH of the constitutive pectins. They can protonate under the influence of the ionic force, the pH, and the ionic composition of the bathing medium, or as a consequence of a significant proton excretion by the plasmalemma (3).The protonation of the carboxylate groups lowers the amount ofcations fixed in the cell wall, affects the ion exchange selectivity and the ion activity in the cell wall. This can alter the solute transfer from the external medium to the plasmalemma as well as the membrane resting potential (10).On the other hand, the auxin-enhanced excretion of high amounts of pectic acids from the cytoplasm to the cell wall and their ionization could act as a metabolic way of regulating the cytoplasmic pH in plants. Moreover, the neutralization by bivalent cations of the excreted pectic acids, particularly in the inner part of the cell wall (8, 9), could be a critical factor in the growth mechanisms of the plant cell.In this study, we have measured the uronic acid protonation in the Nitella cell wall in equilibrium with metal cations and verified a global equilibrium equation describing the proton cation exchange. A 1-cm cell wall section has a mean dry weight of 40 ug. It has a width of 0. 1 16 cm and is 5.14 um thick (values measured in a 0.5 mN CuCl2 solution at 25°C using a Zeiss micrometer). The fresh volume of the cell wall section being thus 5.96 10-5 cm3 and the density of the pectro-cellulosic matrix being 1.75 (measured in a CsCl gradient), the cell wall has a water content of 62% (v/v). In other words, 1 kg dry cell walls absorbs 0.933 L of water. A cation exchange capacity of 1.35 eq kg-' dry matter is thus equivalent to a concentration of 1.45 eq l' in the wall water.Experimental Procedure. Calcium, zinc, or

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Titration of Isolated Cell Walls of Lemna minor L

Cited by 52 publications

References 10 publications

Surface Chemical Properties of Purified Root Cell Walls from Two Tobacco Genotypes Exhibiting Different Tolerance to Manganese Toxicity

Surface Chemical Properties of Purified Root Cell Walls from Two Tobacco Genotypes Exhibiting Different Tolerance to Manganese Toxicity

Combined effects of diffusional hindrances, electrostatic repulsion and product inhibition on the kinetic properties of a bound acid phosphatase

Proton-Metal Cation Exchange in the Cell Wall of Nitella flexilis

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