Reactive oxygen species production and antioxidative defense system in pea root tissues treated with lead ions: the whole roots level

Abstract

The lead absorbed by the roots induce oxidative stress conditions through the Reactive oxygen species (ROS) production for the pea plants cultivated hydroponically for 96 h on a Hoagland medium with the addition of 0.1 and 0.5 mM of Pb(NO3)2. The alterations in \( {\text{O}}_{2}^{ - \cdot } \) and H2O2 concentrations were monitored spectrophotometrically which show a rapid increase in \( {\text{O}}_{2}^{ - \cdot } \) production during the initial 2 h, and in case of H2O2, during the eighth hour of cultivation. The level of ROS remained higher at all the time points for the roots of the plants cultivated with Pb2+ and it was proportional to metal concentration. The production of \( {\text{O}}_{2}^{ - \cdot } \) and H2O2 was visualized by means of fluorescence microscope technique. They are produced in nonenzymatic membrane lipid peroxidation and its final product is Malondialdehyde, the level of which increased together with the level of H2O2. As stress intensity raised (duration of treatment and Pb2+ concentration), so did the activities of superoxide dismutases, catalase and ascorbate peroxidase antioxidative enzymes and of low-molecular antioxidants, particularly glutathione (GSH), homoglutathione (h-GSH) and cysteine substrate toward their synthesis. The root cells redox state (GSH/GSSG) dropped proportionally to lead stress intensity.