Reduced translocation of cadmium from roots is associated with increased production of phytochelatins and their precursors

Abstract

SummaryCadmium (Cd) is a non-essential trace element and its environmental concentrations are approaching toxic levels, especially in some agricultural soils. Understanding how and where Cd is stored in plants is important for ensuring food safety. In this study, we examined two plant species that differ in the distribution of Cd among roots and leaves. Lettuce and barley were grown in nutrient solution under two conditions: chronic (4 week) exposure to a low, environmentally relevant concentration (1.0 µM) of Cd and acute (1 h) exposure to a high concentration (5.0 mM) of Cd. Seedlings grown in solution containing 1.0 µM CdCl 2 did not show symptoms of toxicity and, at this concentration, 77% of the total Cd was translocated to leaves of lettuce, whereas only 24% of the total Cd was translocated to barley leaves. We tested the hypothesis that differential accumulation of Cd in roots and leaves is related to differential concentrations of phytochelatins (PCs), and its precursor peptides. The amounts of PCs and their precursor peptides in the roots and shoots were measured using HPLC. Each of PC 2-4 was synthesized in the barley root upon chronic exposure to Cd and did not increase further upon acute exposure. In the case of lettuce, no PCs were detected in the root given either Cd treatment.The high amounts of PCs produced in barley root could have contributed to preferential retention of Cd in barley roots.

Effects of sulfur supply and hydrogen peroxide pretreatment on the responses by rice under cadmium stress

“…This finding was similar with the report by Aina et al (2007), where a significant induction of PC 3 was detected in the roots of plants exposed to 100 lmolÁL -1 Cd. In contrast to our results, Akhter et al (2012) reported that PC 2 being 1-2 orders of magnitude higher than those of PC 3 and PC 4 in barley roots upon chronic exposure to 1.0 lmolÁL -1 CdCl 2 . The discrepancy indicates crop-specific responses of PCs to Cd toxicity.…”

“…and Cu 2? in the nutrient solution (Akhter et al 2012). Recent studies have shown that PCs could undergo long-distance transport in the root-to-shoot and shoot-to-root directions (Chen et al 2006).…”

“…Complexation of Cd 2? with PCs, GSH or Cys in roots could contribute to reduced xylem loading and Cd translocation (Akhter et al 2012). According to Wong and Cobbett (2009), PCs promoted Cd retention in roots, thereby reducing the translocation of this toxic metal to shoots of Arabidopsis.…”

Cadmium Bioavailability, Uptake, Toxicity and Detoxification in Soil-Plant System

“…Phytochelatins (PCs) are a family of peptides with the structure (c-Glu-Cys)n-Gly, where n represents the repetition of g-Glu-Cys, which tends to vary from 2 to 11 (Akhter et al 2012). As with other metals, PCs play an important role in Cd detoxification (Márquez-García et al 2011;Choppala et al 2014).…”

“…Phytochelatins are reported to neutralize harmful effects by chelating metals with their SH groups. Of all the heavy metals, Cd 2+ has been observed to invoke the strongest activation of the phytochelatin synthase (PCS) and thus PC production (Akhter et al 2012) due to the high affinity of the thiol groups for Cd on the cysteine residues (Chekmeneva et al 2011). Chen et al (2007) studied Cd-PC complexes in Brassica chinensis and observed binding stoichiometries of 1:1 to 3:1 depending on the availability of thiol groups and Cd 2+ in the cytosol.…”