Mitigation of peroxidative stress for a barley exposed to cadmium in the presence of water-extractable organic matter from compost-like materials

Abstract

Lipoxygenase (LOX) activity and levels of malondialdehyde (MDA), a decomposition product of lipid peroxides, have been reported to be increased when uptaking Cd into plants. Thus, these parameters can be employed as indices of the stress for plants that are exposed to Cd. On the other hand, complexation of Cd with soil organic matter, such as humic matter, can affect Cd toxicity to plants. In the present study, LOX activity and levels of MDA in barley exposed to Cd in the absence and presence of humic matter were analyzed to evaluate its effect on stress of the barley. The water-extractable organic matter (WEOM) from a compost-like material (CLM) that was prepared by a thermal treatment of rice bran was used as humic matter. Barley was hydroponically cultured for 30 days in the MS culture solution containing 5 μM Cd in the absence and presence of WEOM (100 mg C L-1). Although wet weights and chlorophyll levels were significantly reduced when exposed to Cd, the addition of WEOM resulted in the increases of those parameters. In addition, the LOX activity and MDA levels were also significantly decreased in the presence of WEOM, showing the alleviation of stress by exposing to Cd. Levels of the Cd uptake into the barley after a 30-day cultivation period were decreased to 50-70% in the presence of WEOM, compared to that in its absence. Thus, adding WEOM is effective in the mitigation of stress for the barley that is exposed to Cd, because the uptake of Cd into the plant is suppressed.