Assessment of physiological and biochemical responses of Amaranthus retroflexus seedlings to the accumulation of heavy metals with regards to phytoremediation potential

Abstract

The aim of this research was to assess, under laboratory conditions, how the accumulation of four heavy metals (HMs) (lead (Pb), copper (Cu), nickel (Ni), and zinc (Zn)), prepared as aqueous solutions from 1 μM to 1 mM, affected biochemical and physiological parameters of Amaranthus retroflexus seedlings. Seedlings showed considerably high resistance to all investigated HMs and no significant oxidative stress in leaves. After chronic exposure to high doses of any of the HMs, seedlings remained viable, but with slightly slower axial growth. We propose the use of biochemical indices (lipid peroxidation (LPO) intensity; level of total peroxides) as criteria to assess the adaptive potential of amaranth plants to HMs. These indices had very high correlation coefficients (r) with the accumulation of HMs in A. retroflexus roots, stems and leaves: 0.86–0.89 for malone dialdehyde (MDA) content for Ni and Zn, and 0.79–0.94 for total peroxides (for Cu, Pb, and maximum in Ni). At 1 mM of any HM, seedlings accumulated Pb and Ni at levels of HM-hyperaccumulating species. If soil is contaminated (in terms of maximum permissible concentration, MPC) by Pb (8.2 ± 2.2 MPC) or Ni (3.5 ± 1.0 MPC) (equivalent to 1 mM of the HM in solution), A. retroflexus is a strong candidate for the phytoremediation of Pb- and Ni-contaminated soils.

Keywords:

• Amaranthus retroflexus L.
• heavy metal accumulation
• LPO
• metal tolerance
• superoxide generation
• total peroxides