The effect of the exogenous application of EDTA and maleic acid on tolerance, phenolic compounds, and cadmium phytoremediation by okra (Abelmoschus esculentus L.) exposed to Cd stress

Abstract

The effects of Cd application alone or along with ethylenediaminetetraacetic acid (EDTA) and maleic acid (MA) were explored in okra (Abelmoschus esculentus.L.). Okra plants were planted in hydroponic conditions and in the 4-leaf stage, they were exposed to cadmium nitrate at three levels (0, 50, and 100 mg/L) and/or EDTA and MA at two levels (0.5 and 1.0 mM) and the combined application of different Cd concentrations with EDTA and MA for one month. The results showed a decrease in shoot and root dry weight and length and an increase in malondialdehyde (MDA), cell death, Cd accumulation, anthocyanins, and phenol and total flavonoid contents in the Cd-treated plants. The application of EDTA and MA alleviated the detrimental impacts of Cd on the okra plants by the improved management of translocation, compartmentation, and tolerance index. HPLC method revealed that rosmaric and coumaric acids were the most abundant phenolic compounds among the studied compounds. The variations of the phenolic compounds in the Cd-treated plants versus the control showed that the greatest increase was in chlorogenic acid (101.91%) and the greatest decline in coumaric acid (60.90%). The highest increase and decrease in the plants exposed to Cd with EDTA or MA versus the plants only exposed to Cd were related to coumaric acid (106.60%) and chlorogenic acid (43.45%) related to the treatment of 100 mg/L Cd +1 mM MA, respectively. In conclusion, okra has good potential for the phytoremediation of Cd and the EDTA and MA increased the phytoextraction efficiency.