Cadmium tolerance and detoxification inMyriophyllum aquaticum: physiological responses, chemical forms, and subcellular distribution

Abstract

Submerged macrophytes have been found to be promising in removing cadmium (Cd) from aquatic ecosystems; however, the mechanism of Cd detoxification in these plants is still poorly understood. In the present study, Cd chemical forms and subcellular distributing behaviors inMyriophyllum aquaticumand the physiological mechanism underlyingM. aquaticumin response to Cd stress were explored. During the study,M. aquaticumwas grown in a hydroponic system and was treated under different concentrations of Cd (0, 0.01, 0.05, 0.25, and 1.25 mg/L) for 14 days. The differential centrifugation suggested that most Cd was split in the soluble fraction (57.40-66.25%) and bound to the cell wall (24.92-38.57%). Furthermore, Cd inM. aquaticumwas primarily present in NaCl-extractable Cd (51.76-91.15% in leaves and 58.71-84.76% in stems), followed by acetic acid-extractable Cd (5.17-22.42% in leaves and 9.54-16.56% in stems) and HCl-extractable Cd (0.80-12.23% in leaves and 3.56-18.87% in stems). The malondialdehyde (MDA) and hydrogen peroxide (H2O2) concentrations inM. aquaticumwere noticeably increased under each Cd concentration. The activities of catalase (CAT), guaiacol peroxidase (POD), and superoxide dismutase (SOD) in leaves were initially increased under relatively low concentrations of Cd but were decreased further with the increasing concentrations of Cd. The ascorbate (AsA), glutathione (GSH), and nitric oxide (NO) concentrations in stems increased with increasing Cd concentrations. Taken together, our results indicate thatM. aquaticumcan be used successfully for phytoremediation of Cd-contaminated water, and the detoxification mechanisms inM. aquaticuminclude enzymatic and non-enzymatic antioxidants, subcellular partitioning, and the formation of different chemical forms of Cd.