| As a toxic heavy metal, cadmium (Cd) is harmful to plants, animals and humans in the current environment. Hydroponic experiments were performed to investigate the ameliorating effects and mitigation mechanisms of selenium and silicon on Cd toxicity in ramie (Boehmeria nivea (L.) Gaud.), which is a local plant in Hunan Province. The toxic effects of Cd on ramie growth and development and the distribution of Cd in ramie seedlings were also analyzed. Ramie growth, the accumulation and translocation of Cd in ramie tissues, photosynthesis and the antioxidant systems were evaluated to elaborate the mechanisms of selenium and silicon on enhancing Cd tolerance, so as to provide bases for ramie remediation to heavy metals. The main results are presented in follows:1、Ramie is tolerant to Cd stress and can accumulate it in bodies. In ramie tissues, Cd is more accumulated in roots, then the stems, and the leaves. Cd is mainly accumulated in the roots, and a portion was transferred to aerial parts, which alleviated the toxic effects of shoots efficiently. However, Cd induced damages to the normal growth and metabolism in ramie. The growth of ramie seedlings was inhibited and the biomasses of roots and aboveground parts were reduced, and the MDA content was increased. Additionally, the levels of protein and chlorophyll were reduced while the proline content was evaluated, which might be an adaption strategy of ramie to Cd stress.2、Under Cd stress, low concentrations of selenium (0.5,1.0,1.5μM) alleviated the toxic effects of ramie, remitted the Cd-induced inhibition, and reduced the absorption of Cd. In this situation, selenium exhibited antagonism against Cd. Oppositely, high concentrations of selenium (2,5,10μM) magnified the toxic effects to plants, and improved the accumulation of Cd. In this situation, selenium cooperated with Cd and caused damages to plants.3、Under Cd stress, both selenium and silicon are benefit for ramie growth. Both promoted ramie biomasses and chlorophyll content, inhibited the uptake of Cd and the translocation of Cd to aerial parts. Besides, the addition of selenium or silicon to plants decreased the levels of MDA and H2O2, which suggested that both selenium and silicon could alleviate Cd-induces peroxidation damages in ramie seedings.4、Selenium or silicon may alleviate the peroxidation damages via the following ways. One is to improve the activities of antioxidant enzyme such as SOD and POD, and exceed the removal of excess free radicals. The other is to stimulate the efficiency of ascorbate-glutathione cycle. This cycle is helpful to eliminate reactive oxygen and protect plants from oxidative injures. In addition, GSH, AsA and vitamin E cooperated in scavenging oxygen radicals and protecting cell metabolism, which might be an important tolerant and detoxication mechanism against Cd stress. Moreover, the effects of combination of Se and Si appeared to be more superior compared to addition separately in response to Cd stress. |
