| With the acceleration of industrialization process, heavy metal pollution has become one of the world’s focus on environmental issues, especially the soil heavy metal pollution. Heavy metals can be harmful to human through food chain enrichment. Cd and Cu are more heavy metal pollutants in heavy metal pollution, which exist in nature by the form of compound pollution and the governance are difficult. In this study, ryegrass(Lolium perenne L.) is regarded as test material, we using the combining method of pot experiment and hydroponic system to study the mechanism of Cd and/or Cu toxicity on ryegrass and explore the effect of supplying exogenous NO and SA. The main researvh results are as follows:1. 100 and 150μM Cd stress had a detrimental effect on ryegrass seedlings, especially under the 150μM Cd stress. 100 and 150μM Cd inhibited plant growth, decreased chlorophyll concentration, and reduced the absorption of Fe, Cu and Zn. Excess Cd also altered the activities of antioxidant enzymes, and increased the accumulation of reactive oxygen species(ROS). Exogenous NO alleviated Cd toxicity of ryegrass plants, especially under the 150μM Cd stress, as evidenced by improved plant growth and increased concentrations of chlorophyll and mineral nutrients.These indicated that the photosynthesis was improved and ion equilibrium was revealed. Exogenous NO also mitigated oxidative stress by regulating the activities of antioxidant enzymes and the accumulation of O2?-, H2O2 and MDA. Moreover, the applications of NO also reduced the translocation of Cd from roots to the leaves. These results indicated that the mechanisms of NO for mitigating Cd toxicity may be associated with reduced root-to-shoot translocation of Cd and enhanced capacity of antioxidative systems to protect plants from oxidative stress.2. Addition of 100, 200, 300μM SA considerably increased chlorophyll content and the activities of antioxidant enzymes, increased the uptake and translocation of mineral elements, and decreased H2O2 and MDA accumulation in both shoots and roots of Cd-stressed plants. Addition of 200μM SA not only decreased the Cd uptake in ryegrass, but also decreased the root-to-shoot translocation of Cd and changed its subcellular distribution in plants. Addition of 200μM SA increased Cd concentrations in soluble fraction and cell wall in both shoots and roots markedly, with the majority of Cd associated with the cell wall and the soluble fraction and a minor part of Cd present in the cell organelle. Based on these results, we conclude that the optimal concentrations of exogenous SA could alleviate Cd induced stress and promote ryegrass plant growth.3. Cd, Cu, and especially Cd+Cu caused serious chlorosis, inhibited the growth of ryegrass seedlings, and increased dramatically the accumulation of Cd and/or Cu in both shoots and roots. However, the addition of 100μM SNP alleviated significantly the toxic effects induced by Cd or Cu, and especially by Cd+Cu, which was manifested in the increased plant growth, chlorophyll content, and the activation of antioxidant enzymes. Moreover, exogenous NO improved effectively the absorption of mineral elements. In addition, exogenous NO inhibited the translocation of Cd and Cu from roots to shoots. These data also suggested that the alleviating effect of NO may be better when the metal stresses are more serious.4. In a pot experiment, different concentrations of SNP solution was poured into Cd-contaminated soil every seven days to study the toxicity of cadmium to perennial ryegrass and exogenous NO relief effect and its mechanism by means of the continuous stubble. The relief effect of the different concentrations of SNP is different. 50-300μM SNP treatment can improve the chlorophyll content, improve the antioxidant enzyme activity and promote the absorption of mineral elements, especially 300μM SNP. In addition, exogenous NO reduced root-to-shoot translocation of Cd. However, addition of 500μM SNP had no significant effect with Cd treatment. |
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