Lead (Pb) bioaccumulation and antioxidative responses in Tetraena qataranse

Abstract

Lead (Pb) is the second most toxic metal on Earth and is toxic to humans and other living things. In plants, Pb commonly inhibits growth when it is at a concentration in the soil of 30�mg/kg or more but several Pb tolerant plants have been reported. However, few studies have focused on plant response to Pb exposure, particularly at concentrations higher than 30�mg/kg. The assessment and evaluation of metal dose-dependent plant responses will assist in future phytoremediation studies. Therefore, this work documents the Pb concentration-dependent antioxidative response in Tetraena qataranse. Young seedlings were irrigated with 0, 25, 50, and 100�mg/L Pb every 48�h for seven weeks under greenhouse conditions. A phytotoxicity test showed that at the lowest treatment concentration, Pb stimulates growth. However, at 100�mg/L (1600�mg/kg Pb in the growth medium at harvest), the metal disrupted healthy growth in T. qataranse, particularly root development. Metal accumulation in the root was higher (up to 2784�mg/kg) than that of the shoot (1141.6�mg/kg). Activity assays of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GPX), and glutathione reductase (GR) showed a progressive increase in enzymatic activities due to Pb treatment. Together, the results of this study suggest that T. qataranse is a Pb hyperaccumulator. Increased antioxidant enzyme activity was essential to maintaining cellular homeostasis and assisted in the arid plant?s tolerance to Pb stress.