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

Abstract

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 ...

Is There a Positive Synergistic Effect of Biochar and Compost Soil Amendments on Plant Growth and Physiological Performance?

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Plant Responses to Heavy Metal Toxicity

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Phytoextraction of Metals: Modeling Root Metal Uptake and Associated Processes

“…The Langmuir isotherm (see below) has generally been used to represent solute sorption to a finite number of exchange sites in the root and to provide a good fit for metal sorption to plant biomass (Chen et al 1996;Sun and Shi 1998;Villaescusa et al 2004;Vijayaraghavan et al 2006) and to root tissue (Bhainsa and D'Souza 2001). Mobilized metals are able to bind to sites in the root cell walls (Wang et al 1992) and plasma membranes (Briat and Lebrun 1999).…”