Effects of malic acid and EDTA on oxidative stress and antioxidant enzymes of okra (Abelmoschus esculentus L.) exposed to cadmium stress

Environmental stresses, including heavy metal pollution, are increasing at a growing rate and influencing arable lands. Chelators play an essential role in several biochemical pathways in the cells of plants treated with heavy metals. This research evaluated the modifying effect of malic acid (MA) and ethylenediaminetetraacetic acid (EDTA) on the physiological and biochemical parameters of okra plants exposed to Cd stress in which the okra plants were cultivated in hydroponic conditions. At the 4-leaf stage, they were applied with the treatments of cadmium nitrate at three levels (0, 50, and 100 mg/L), EDTA and MA at two levels (0.5 and 1 mM), and Cd + EDTA + MA at different rates for one month. The harvested plants were subjected to the measurement of the physico-biochemical factors. The results revealed that the application of Cd alone reduced leaf area (up to 21.57 %), and dissolved sugars (up to 40.51 % in the shoot and 45.19 % in the root) and increased MDA (up to 66.37 % and 76.43 % in the shoot and root, respectively), H2O2 (up to 67.14 % and 53.28 % in the shoot and root, respectively), proline (up to 52.04 % and 40.93 % in the shoot and root, respectively), and dissolved proteins (up to 14.59 % and 21.90 % in the shoot and root, respectively) contents in both shoots and roots whereas the application of MA and EDTA to the Cd-treated plants increased their leaf area and dissolved sugars and reduced MDA, H2O2, proline, and dissolved proteins content. The antioxidant enzymes, e.g., superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), were significantly higher in the plants treated with MA, EDTA, and Cd, but the application of MA and EDTA to the Cd-treated plants reduced the activity of all these antioxidant enzymes versus the plants only treated with Cd. MA and EDTA are likely to prevent the accumulation of Cd in the cytosol by binding to it and transferring it into vacuoles, thereby mitigating Cd toxicity in the okra plants.