Synergistic effects of EDDS and ALA on phytoextraction of cadmium as revealed by biochemical and ultrastructural changes in sunflower (Helianthus annuus L.) tissues.

This study explored the phytoremediation potential of sunflower on cadmium (Cd) contaminated soils. We also studied the mechanisms through which a plant growth regulator, 5-aminolevolinic acid (ALA) protected sunflower plants from Cd-induced cellular injury. Six-leaf old sunflower plants were exposed to 0.3 g kg Cd for one week and then treated with chelating agents i.e. trisodium (S,S)-ethylenediamine-N,N'-disuccinic acid (EDDS, 5 mmol kg) and citric acid (CA,10 mmol kg), and 10 mg L ALA. One week after chelators and ALA application, plants were harvested for further analyses. Results suggested that chelators EDDS/CA significantly increased Cd accumulation but inhibited plant growth of sunflower. In contrast, ALA promoted both Cd absorption and biomass accumulation, especially when applied in combination with EDDS. Bioaccumulation quantity and remove efficiency of Cd + EDDS + ALA treated plants was increased by 21.00% and 20.93% as compared with Cd + EDDS treatment. The qRT-PCR results revealed that increased Cd uptake by chelators EDDS/CA and ALA was associated with an increased expression of Cd transport genes e.g. OPT6, HMA3 and Nramp1 in sunflower leaves and roots. Our study suggested that ALA protects sunflower plants from Cd-induced cellular injury by immobilizing Cd ions, modulating activities of antioxidative enzymes and capturing reactive oxygen species.