EDTA-enhanced Cr detoxification and its potential toxicity in rice (Oryza sativa L.)

Abstract

Ethylenediamine tetraacetic acid (EDTA) is a chelating agent used worldwide for the phytoextraction of heavy metals using hyperaccumulating plants as well as in household and industrial purposes and persists in cultivated land for a long time without any known impact on nonhyperaccumulating plants. In this study, the effects of EDTA in the presence and absence of chromium on the hydroponic solution were evaluated at the cellular and molecular levels in nonhyperaccumulating rice plants (Oryza sativa L.). EDTA application enhanced phytochelatin (PC) and metallothionein (MT) synthesis, which was confirmed by the upregulation of phytochelatin and metallothionein genes in rice roots. However, a lower quantity of EDTA (25 µM) along with chromium enhanced chromium uptake (22.5%) in the root but inhibited its translocation to the shoot, indicating vacuolar sequestration of excessive chromium in the root. Conversely, in the absence of chromium, the H2O2 concentration was found to be increased, which significantly enhanced electrolyte leakage (98.5%) and lipid peroxidation (33.3%) compared with control plants. Our data indicate that excessive PCs and MTs without vacuolar sequestration enhance reactive oxygen species (ROS) generation. The findings of this investigation show that enhanced PCs and MTs owing to EDTA sequester excessive chromium in root vacuoles but, in the absence of sequestration due to a lack of chromium, enhance reactive oxygen species generation, resulting in toxicity. The outcomes of this investigation will open a new avenue of research in phytoextraction or phytoremediation activities.