Abstract
To investigate the possible role of EDTA in mitigating cadmium (Cd) toxicity, we treated mustard (<em>Brassica juncea</em> L.) seedlings with CdCl<sub>2</sub> (0.5 mM and 1.0 mM, 3 days) alone and in combination with 0.5 mM EDTA in a semihydroponic medium. In the absence of EDTA, mustard seedlings accumulated Cd in their roots and shoots in a concentration dependent manner. Overaccumulation of Cd boosted generation of hydrogen peroxide (H<sub>2</sub>O<sub>2</sub>) and superoxide anions (O<sub>2</sub><sup>•−</sup>), increased lipoxygenase (LOX) activity, lipid peroxidation, and cytotoxic methylglyoxal (MG) content. It also disturbed components of the antioxidant defense and glyoxalase systems. Furthermore, Cd stress decreased growth, leaf relative water content (RWC) and chlorophyll (chl) content but augmented the proline (Pro) content. On the other hand, EDTA supplemented Cd-stressed seedlings improved the constituents of the AsA-GSH cycle with the upregulated activities of ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT). Moreover, addition of EDTA to the Cd-stressed seedlings notably enhanced Gly I activity in contrast to the stress treatment. Ethylenediaminetetraacetic acid decreased Cd accumulation in the both shoots and roots, as well as increased other nonprotein thiols (NPTs) in leaves, including the phytochelatin (PC) content. It also decreased H<sub>2</sub>O<sub>2</sub> and O<sub>2</sub><sup>•−</sup> generation, lipid peroxidation and MG content but enhanced RWC, chl and Pro contents in the leaves, which confirmed the improved growth of seedlings. The findings of the study suggest that exogenous application of EDTA to the Cd-treated seedlings reduces Cd-induced oxidative injuries by restricting Cd uptake, increasing NPTs concentration and upregulating most of the components of their antioxidant defense and glyoxalase systems.
Highlights
As a result of anthropogenic activities, heavy metal pollution is gradually becoming an increasing problem for world agriculture
The rise in H2O2 content and activity of LOX was accountable for the enhancement of thiobarbituric acid reactive substances (TBARS) content or lipid peroxidation under Cd stress
Tab. 1 TBARS and H2O2 content, LOX activity, and chl content of B. juncea L. seedlings induced by exogenous EDTA under Cd stress
Summary
As a result of anthropogenic activities, heavy metal pollution is gradually becoming an increasing problem for world agriculture. As a redox-inactive metal, Cd indirectly produces more reactive oxygen species (ROS) which include singlet oxygen (1O2) and superoxide anion (O2−), hydrogen peroxide (H2O2), and the hydroxyl radical (OH). Cellular macromolecules such as lipids, proteins, and nucleic acids are oxidized by the elevated level of ROS [6,7]. To diminish ROS-induced oxidative stress, plant cells have well organized antioxidant defense systems which comprise nonenzymatic components including ascorbic acid (AsA), glutathione (GSH), phenolic compounds, alkaloids, α-tocopherol, nonprotein amino acids, etc., and enzymatic components including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione peroxidase (GPX), and glutathione S-transferase (GST) [6,10]
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