| Divalent heavy metal cation cadmium (Cd2+) causes phytotoxicity in plants. The high bioaccumulation index in plants and soil will also threat human health through food chain. It has been shown that Cd will inhibit germination of seeds and exert a wide range of adverse effects on growth and metabolism of plants. It was reported that high concentration of Fe2+ in paddy soil could exert some impacts on plant growth and Cd2+ accumulation. Cadmium and ferrous cation with high concentration in soil, are known to cause oxidative damage to plants either directly or indirectly by triggering an increased level of production of reactive oxygen species (ROS). Plants have antioxidative enzymes, such as superoxide dismutase (SOD), catalase and peroxidase (POD), which can scavenge ROS to avoid oxidative damage. Malondialdehyde (MDA) level is used as an index of lipid peroxidation under stressful conditions in plants. Therefore activity of antioxidative enzymes (SOD and POD) and MDA level can be used to monitor the oxidative stress of plants. In anaerobic waterlogged environment, rice can form iron plaque around root surface and screen metals by adsorption and co-precipitation. Thus, the availability and balance of Fe/Cd in the rhizosphere of rice will be influenced. Many researchers investigated the impacts of ferrous and cadmium respectively on rice growth, while few efforts were made on the interaction of these two metal ions, which exist in production conditions.In order to investigate mechanisms of Fe and Cd stress on rice in real production condition, the pot experiment with 4 soil Fe2+ levels (577,677,777 and 977 mg/kg) and 2 soil Cd2+ concentrations (0.413 and 5.413 mg/kg) was conducted. The rice cultivar used in the experiment was Hang43. Shoots of rice collected at tillering, booting and mature stages were ground with liquid nitrogen and were homogenized in phosphate buffer (pH 7.8). The extracted supernatant was used to assay SOD activity, POD activity and MDA level, by NBT method, guaiacol colorimetric method and the thiobarbituric acid method, respectively. Fe and Cd concentrations in shoots and roots were determined by flame atomic absorption spectrophotometer (FAAS) after digestion procedures. Fe and Cd contents in iron plaque on the roots were extracted using dithionite-citrate-bicarbonate (DCB) method, and were measured by AAS.The experimental results showed that ferrous and cadmium in soil had interaction on the activities of lipid peroxidation, antioxidative enzymes and uptakes of these two metals.1?There is no evidence that Fe2+ and Cd2+ affect the value of SPAD and appearance of rice clearly, which means under the circumstance of the experiment the danger of these two mental can be concealed.2?The physiological and biochemical status of rice changed along with the growth period. At booting stage, rice is heavily hurt by oxidative stress caused by the metals. At this time activities of SOD and POD are restricted causing the increase of MDA in leaves. Cd2+ remarkably decreased MDA and depressed activities of SOD and POD, but those adverse effects were mediated by increasing Fe2+ concentration in soil.3?The amount of cadmium in rice roots, shoots and iron plaque are positively correlated. It can be concluded that rice uptake Cd mainly from iron plaque, which helps to screen in the rhizosphere and inhibit the uptake of Cd2+ in rice.4?It can be conclude that iron and cadmium affect each other on absorption and enrichment of rice. Fe2+ in soil can alleviate the stress of Cd2+by restraining the accumulation of Cd2+ in shoots. The accumulation of Cd and Fe in roots changed along with the growth period:booting stage> maturing stage> tillering stage. Metals distribution in the tissue of rice is roots> shoots. |
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