| Tomato is one of the most important vegetables,and it is a model plant for the study of fruit development in Solanaceae plants.Mercury,which is a toxic element,can be harmful to human health when it exists in farmland and agricultural products.In order to develop the technique which decreased the mercury content in tomato,bacterial mercuric ion reductase(merA)and organomercurial lyase(merB)genes were expressed in tomato plants for these abilities that can convert toxic organic mercury to less toxic and volatility elemental mercury.These transgenic tomato plant can produce fruit vegetable with safe mercury content from mercury-contaminated soil and it can be used for phytoremediation of mercury polluted soil.Results show that transgenic plants with merA and merB expressed have high resistance to inorganic and organic mercury,and transgenic plants have drastically lower mercury levels in their fruits,seeds,and leaves than wild-type plants.In soil with high HgCl2 contamination(1600 ?g/kg),mercury concentration in fruits of WT tomato was 62.66 ?g/kg,exceeded the maximum allowable mercury level in vegetables(10 ?g/kg);mercury concentration in transgenic tomato was 9.66 ?g/kg,and it was lower than the maximum allowable mercury level.In soil with 260 ?g/kg HgC12,mercury content in WT tomato fruits was 33.54 ?g/kg,and it was 4.01 ?g/kg in transgenic tomato fruits.This result show that merA/merB transgenic tomato plants can produced fruits with acceptable levels of mercury of the food safety standard in mercury polluted soil.In contaminated soil,the yield loss of transgenic plants was lower than that of WT plants because of the higher mercury resistance of transgenic plants.These results show that transgenic tomato plant decreased the mercury content of fruit from mercury-contaminated soil,and the capability of merA/merB genes to decrease the mercury content in plants were veriflcated in rice,tobacoo and Arabidophsis.For the feasibility verification of the application of merA/merB transgenic plants in mercury pollution sources such as coal-fired power plant,in this study the total mercury concentration in vegetables and grain crops collected from farms located near two coal-fired power plants were measured to assess the current state of mercury pollution.We found that the mercury concentration in soil was correlated with distance from the two power plants,and this result showed that the coal-fired power plants were the direct source of mercury pollution in farmland soil.79%of vegetable samples and 67%of grain samples exceeded the food safety standard.The risk assessment showed that probable daily intake of mercury for local residents exceeded the toxicologically tolerable values.Data show that merA/merB transgenic tomato and other plants produced agricultural products with mercury content complied with the food safety standard in the same mercury levels as coal-fired power plant region.MerA/merB transgenic tomato was planted in soil with the same mercury pollution level as coal-fired power plant region,and the mercury concentration in soil was significantly decreased.In the presence of 260 ?g/kg Hg(?),transgenic tomato decreased the soil mercury concentration to 43.0±5.4 ?g/kg after 3 months of plant growth,whereas WT tomato reduced it to 196.6±8.2 ?g/kg.The capability of merA/merB genes of improving the Hg-phytoremediation of contaminated soils was also verificated in rice.Due to the small cultivated area per capita and the shortage of farmland resources in China,it is objectively not allowed to abandon cultivation of large-scale farmland for the phytoremediation of mercury.Therefore,in the farmland with mercury pollution,merA/merB transgenic tomato and other plants with low-mercury content in edible organs and Hg-phytoremediation ability would be a technic approach to reduce the mercury pollution problems in vegetables,grains and farmlands. |
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