Cadmium — citric acid — xylem cell wall interactions in tomato plants

Abstract

Mutual interactions between cadmium ions, citric acid and xylem cell walls were examined. Cadmium and citric acid were measured as "^Cd and [1,5-^*'C] citric acid, respectively. Xylem cell walls were obtained by bacterial degradation of tomato stem sections {Lycopersicon esculentum Mill, cv. Tiny Tim), and applied as ion-exchange columns. The xylem column material carried 2 4dm3 HzO kg "^ dry weight, and was temporarily capable of buffering perfusates at pH 5 7, Sorbed cadmium and citric acid were determined from H2O and HCI rinses after perfusion periods. In all experiments, total cadmium and/or citric acid recoveries were better than 98%, indicating both the effectiveness of the rinses applied and the possibility of full regeneration of the xylem column. The results indicate that the presence of 2 45 mol m"^ citric acid causes an approximately 50% reduction of adsorbed cadmium levels, irrespective of the applied total cadmium concentrations (004-04 mol m"Ĉ d(NO3)2.4H2O). This reduction is probably related to a corresponding reduction to approximately 2% of the control applied free Cd^^ concentration, the latter also independent of the total cadmium concentrations. Furthermore, without inducing positively charged citrate complexes in the applied solution, the presence of cadmium resulted in increased levels of citric acid absorbed in the xylem column. The Donnan Free Space accumulation of citric acid in the presence of Cd(NO3)2.4H2O, observed in the experiments described, could be expressed by its distribution coefficient, as approximately 15 times the control accumulation. These data indicate that the xylem column may operate as a ligand exchanger, suggesting the importance of metal ions for the longitudinal and lateral movement of organic complexing compounds in the xylem.

The role of organic acids in heavy metal tolerance in plants

“…The efficiency of metals transfer in the xylem in the form of a complex with organic acids is attributed to the lower adsorption of uncharged or negatively charged chelated forms of metals by the negatively charged cell walls of xylem, as well as to a decrease in lateral removal of metals from the vessel, which was noted in particular for Zn and Cd (Senden, van Paassen, Van der Meer, and Wolterbeek, 1992). The role of organic acids in the intracellular detoxification of metals has been studied most intensively in heavy metal hyperaccumulators (Rauser, 1999;Küpper, Mijovilovich, Meyer-Klaucke, and Kroneck, 2004;Sun, Zhou, and Jin, 2006;Yang et al, 2006), and primarily for Zn/Cd hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri (Cosio, Martinoia, and Keller, 2004).…”

Citric acid in tomato plant roots and its effect on cadmium uptake and distribution

“…In previous experiments with plant sub-systems (Senden and Wolterbeek, 1990;Senden et al, 1992a), effects of citrate on Cd xylem transport characteristics were observed. The present experiments were performed to get more insight in the effects of citric acid on Cd accumulation and mobility in whole plants.…”

Tracing Cadmium from Culture to Spikelet: Noninvasive Imaging and Quantitative Characterization of Absorption, Transport, and Accumulation of Cadmium in an Intact Rice Plant

“…Interestingly, Tsukamoto et al (2006) reported that the velocity of transport of 52 Mn in the shoot from the shoot base was 3.6 cm h 21 in a 3-week-old manganesedeficient barley plant, which was very similar to our results with Cd. It is known that interactions take place between cationic solutes and negatively charged groups in the cell walls of the xylem vessels along the pathway from the roots to the leaves (Marschner, 1995), and organic chelating compounds including citrate affect these interactions (Senden et al, 1992). We speculated that Cd (and probably manganese as well) bound to organic compounds in the xylem flow interacts with the cell walls of the xylem vessels, and this makes the transport velocity slower than that of the bulk flow, for which the mechanism is similar to chromatography.…”