Effects of cadmium on the behaviour of citric acid in isolated tomato xylem cell walls

Abstract

Effects of cadmium on the sorption of citric acid in isolated xylem cell walls were Investigated. 2.5 nM to 9.5 mM [1.5-14 C]citric acid solutions were perfused through columns of xylem cell wall material, isolated from tomato plants (Lycoperslcon esculentum Mill, cv. Tiny Tim).The anion exchange potential of the column was estimated by amino acid analysis as approximately 46 meq dm" 3 , whereas the apparent anion exchange capacity (A£C) was estimated as 1.65 + 0.18 10 "M (citric acid units). This low AEC was attributed to a 'zipper' effect, a mutual screening of fixed R" and A + charges.Pre-loading with 11s Cd 2+ did not affect citric acid sorption, indicating the absence of Cd-effects on the availability of fixed A + charges, and the absence of the formation of effective R~-Cd 2+ and Donnan free space (DFS) [Cd(cit)HJ + complexes.Simultaneous application of both citric acid and 11B Cd 2+ , ""Ca^, or ^Mg 2 * resulted in increased sorption of citric acid, probably due to capacityimprovement rather than changes in valence-dependent anion sorption; this may be due to the presence of bulk [M(cit)]", held in the column as [M(cit)HJ + after protonation in the DFS. Sorption of citric acid was greatest in the presence of Ca 2+ , which was discussed in the light of the differences between Ca, Cd and Mg in their characteristics as co-ordinative M-complexes of citric acid. The overall results indicate the potential importance of the presence of metal ions for the xylem transport behaviour of organic acids in plants.

Cadmium uptake by durum wheat in presence of citrate

“…the same order of magnitude as previously reported fluxes (0.30-2.67 nmol mg −1 dw roots h −1 ) for plants grown in close experimental conditions (Jones and Darrah 1995;Bell et al 2003). Citrate adsorption on roots was significantly higher in presence of Cd, which is consistent with results from Senden et al (1994) who have observed an increase of adsorbed citrate on tomato xylem cell walls when Cd was present in solution. Cadmium was also adsorbed on roots and internalized, with a Cd internalization flux ranging between 0.020 and 0.054 nmol mg −1 dw roots h −1 , which is in the range of previous observed values in similar growing conditions (Hart et al 1998;Berkelaar and Hale 2003).…”

Effects of cadmium on the longitudinal and lateral xylem movement of citric acid through tomato stem internodes

“…Obviously, Cd additions resulted in an about 2-fold increase in AEC values for citric acid, for both citric acid concentrations. The order of magnitude of AEC values agrees with values found in experiments with columns of isolated xylem cell walls as reported by Senden et al (1994). The 2-fold increase in response to Cd perfusion corresponds to predictions distilled from earlier column experiments (Senden et al 1994) for 0·05 mM citric acid perfusions.…”

“…Remarkably, hardly any information exists on the effects of metals on the behaviour of xylem organic solutes. Effects of metals on the behaviour of organic solutes are described and used in various ways in chemistry, most especially in ligand-exchange chromatography (Helfferich 1961(Helfferich , 1962Navratil et al 1975;Davankov & Senechkin 1977;Matejka & Weber 1990;Sud et al 1992), but in plant transport physiology the only information available is reported by Senden et al (1992bSenden et al ( , 1994. In the latter papers, cadmium, calcium and magnesium were shown to affect the sorption of citric acid into columns of isolated tomato xylem cell walls: the total citric acid sorption increased up to 7-fold the control values by metal treatments.…”

“…Tiny Tim). The experiments were set up to investigate the persistence of effects of Cd on citric acid sorption in isolated xylem cell walls (see Senden et al 1994), in a plant system which also allows lateral escape. The data indicate the effects of cadmium on both longitudinal movement (expressed by values on apparent anion exchange capacity, AEC) and lateral escape (expressed by the lateral escape rate constant) of citric acid during its transport through the xylem.…”

Root uptake and translocation of nickel in wheat as affected by histidine

“…On the other hand, a number of possible ligands i.e., organic acids, amino acids, peptides and proteins, stimulate the root to shoot transport of mineral ions (Callahan et al, 2006). The transport rate of di-or trivalent cations has been reported to be enhanced significantly by complexation with organic acids (Senden et al, 1994;Yang et al, 1997), amino acids, or peptides (Mullins et al, 1986;Senden et al, 1994;Stephan et al, 1996;Clark et al, 1986). Only a small fraction of the metal content in plants is present in the form of free aqua ions.…”