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

Abstract

Experiments were carried out to investigate the effects of root citric acid on uptake and initial distribution of cadmium (Cd) in tomato plants (Lycopersicon esculentum, cv. Tiny Tim). Cd was measured by "y-spectrometry, using 115Cd spikes. Citric acid was measured by UV-detection, and, after spiking with lac-citric acid, by ~-spectrometry. Cd was applied for 48 h periods, in control experiments, in the presence of citric acid, and after 24 h plant pre-incubation with citric acid.Pre-incubation resulted in two-fold increases in fast-exchangeable amounts of root citric acid, as measured by the presence of citric acid in xylem exudates of decapitated and pressurized roots.Simultaneous application of Cd and citric acid did not change Cd accumulation in total plants and in the roots, nor did any significant change occur with respect to Cd root-to-shoot transport, and Cd concentrations in shoot tissues and xylem fluid. After citric acid pre-incubation, total plant uptake of Cd increased twofold, without any significant change in Cd accumulation in the roots. Cd root-to-shoot transport was increased 5-6 fold, and Cd concentrations in shoot tissues and xylem fluid were increased 6-8 fold. Speciation calculations indicated that, under the conditions applied, xylem Cd may be, at least partly, complexed in citric acid.

The symbiosis between Nicotiana tabacum and the endomycorrhizal fungus Funneliformis mosseae increases the plant glutathione level and decreases leaf cadmium and root arsenic contents

“…In non-hyperaccumulator plants [i.e., plants which are not able to translocate and accumulate very high concentrations of one or more metal(loid)s in the shoots without showing severe toxicity symptoms (Baker et al, 2000)], the main Abbreviations: AM, arbuscular mycorrhiza; Fm, Funneliformis mosseae; GSH, reduced glutathione; PC, phytochelatin.detoxification mechanism of Cd is the complexation with thiolpeptides and the subsequent sequestration in the vacuoles of root cells (Verbruggen et al, 2009). Acropetal Cd translocation from root to shoot takes place through the xylem vascular elements, following the transpiration-driven water flow, possibly both in free and complexed form, such as Cd-organic acids or Cdphytochelatins, as suggested by Senden et al (1995) in tomato, and by Gong et al (2003) in Arabidopsis thaliana, respectively.…”

Cadmium accumulation in crops

“…At subtoxic shoot Cd concentrations, tomato plants not previously exposed to Cd and preincubated (24 h) with 2.5 × 10 -4 M citrate increased root-to-shoot transport of 5 × 10 -6 M Cd six-to eightfold compared to no citrate addition or to the simultaneous addition of citrate and Cd (Senden et al 1995). Pre-incubation with citrate also doubled the amount of citrate collected from xylem exudates (Senden et al 1995). In another study, citrate was shown to decrease the lateral escape of Cd from xylem vessels and to reduce adsorption of Cd to xylem cell walls (Senden and Wolterbeek 1990).…”

Organic acids enhance the uptake of lead by wheat roots

“…For example, organic acids in pot experiments triggered uranium accumulation in Indian mustard and Chinese cabbage , and increased chromium accumulation in tomato (Srivastava et al 1999). Under hydroponic conditions, organic acids furthermore increased the uptake of cadmium by tomato and durum wheat (Senden et al 1995;Berkelaar and Hale 2003), and of lanthanum by wheat and barley (Wang et al 2004;Han et al 2005).…”