Exogenous plant growth regulators improved phytoextraction efficiency by Amaranths hypochondriacus L. in cadmium contaminated soil

Phytoextraction assisted by plant growth regulators (PGRs) is gaining popularity in phytoremediation applications. A pot experiment was conducted to compare the effects of foliar applications of 11 PGRs, including Indole-3-acetic acid (IAA), Indole-3-butyric acid (IBA), diethyl aminoethyl hexanoate (DA-6), 6-Benzylaminopurine (6-BA), 1-naphthylacetic acid (NAA), Abscisic acid (ABA), 2,4-Dichlorophenoxyacetic acid (2,4-D), Ethrel (ETH), Brassinolide (BR), Gibberellin (GA(3)), and Compound sodium nitrophenolate (CSN) on plant development, chlorophyll content, antioxidant enzyme activities, Cd phytoextraction capacity and micro-distribution of Amaranthus hypochondriacus L. grown in Cd contaminated soil. The effect on biomass yield was dependent on the PGRs type, with IBA being the most efficient. The addition of PGRs increased Cd extraction efficiency, with their effect decreasing in the order: IAA > DA-6 > IBA > 2,4-D > 6-BA > NAA > BR > CSN > ETH > GA(3) > ABA. Application of PGRs increased Cd concentrations in leaves and stems but reduction was found in roots (except for 2,4-D). Exogenous PGRs increased the activities of stress ameliorating enzymes (SOD and CAT) and led to a reduction in MDA (malondialdehyde) concentration. In leaves, scanning electron microscope-Energy dispersive spectrometer (SEM-EDS) confirmed that application of IBA or DA-6 further fixed more Cd in upper and lower epidermal cells, which might relate to more Cd migration from roots to shoots in Amaranthus hypochondriacus L. These findings suggest that the treatment with IBA or DA-6 appears to be optimal for enhancing the phytoextraction efficiency of Amaranthus hypochondriacus L. in Cd contaminated soil.