| Nowadays, heavy metal pollution occur in soil seriously. Phytoremediation technology has attracted wide attention for its advantages, such as low cost, environmentally friendly and no secondary pollution. Phytoremediation technology has broad application prospects, but due to the lack of understanding to the mechanism of hyperaccumulator limit its improvement and application. Sedum alfredii Hance as a kind of Zn/Cd/Pb hyperaccumulating plant species native to China, is considered to be a good material for phytoremediation. The root exudates of plants is the most direct response to external environmental stress, so the research on root exudates of hyperaccumulator has great significance for improving the efficiency of phytoremediation. In this research, two ecotypes of Sedum alfredii Hance are used as research material. We use some analytical techniques such as high performance liquid chromatography, ion chromatography, inductively coupled plasma mass spectrometry to set a analytical testing methods for the root exudates of Sedum alfredii Hance. We systematically study the characteristics of the Sedum alfredii Hance root exudates and the major results are summarized as follows:1. We set up an analytical testing methods for organic acids and amino acids in the root exudates of Sedum alfredii Hance. Two ecotypes of Sedum alfredii Hance are used in this research through nutrient solution culture. Root exudates are collected in0.5mM CaCl2solution, then use anion and cation exchange column chromatography to separate and purify the organic acids, and use solid phase extraction to purify the amino acid. Integrated use of reversed-phase chromatography, ion-pair reversed-phase chromatography and ion exchange chromatography to qualitative and quantitative analysis the organic acids and amino acids in root exudates, while expanding the methods used to root, stem and leaf of Sedum alfredii Hance. The kind of organic acids and amino acids in root exudates of two ecotypes of Sedum alfredii Hance are nearly the same, but there are significant differences in the content. The organic acids in root exudates of Sedum alfredii Hance are constituted by a large number oxalic acid, tartaric acid, lactic acid, and a small amount of malic acid, citric acid, fumaric acid. And the amino acids in root exudates are constituted by18kinds of protein amino acid,γ-aminobutyric acid and other non-protein amino acids. Similarly, the organic acids of two ecotypes of Sedum alfredii Hance in root, stem and leaf are nearly the same, but there are significant differences in the content. The organic acids are constituted by oxalic acid, tartaric acid, malic acid, lactic acid, citric acid, fumaric acid, as well as a small amount of acetic acid, succinic acid, propionic acid.2. The root exudates of two ecotypes of Sedum alfredii Hance were significantly lower pH values (P<0.05), when treated with three different heavy metals (Zn/Cd/Pb). Universal, the acidic of root exudates of HE is larger than NHE. Compared with three different heavy metals, the pH of root exudates is lowest when treated with Pb, and the pH of root exudates is highest when treated with Cd. It has a great relationship with the form of three different heavy metals in nutrient solution as well as their toxicity.3. Although the kind of organic acids and amino acids in root exudates of two ecotypes of Sedum alfredii Hance are nearly the same when treated with three different heavy metals, there are significant differences in the content. The oxalic acid, tartaric acid, glutamic acid, γ-aminobutyric acid in root exudates of two ecotypes of Sedum alfredii Hance are significantly increased when treated with Zn, while the secretion of tartaric acid, glutamic acid, y-aminobutyric acid, HE was significantly higher than NHE (P<0.05). The oxalic acid, citric acid, glutamic acid, γ-aminobutyric acid in root exudates of two ecotypes of Sedumalfredii Hance are significantly increased when treated with Pb, while oxalic acid, citric acid, glutamic acid, Y-aminobutyric acid in secretion, HE was significantly higher than NHE (P<0.05). Under different heavy metal stress, the oxalic acid increase in secretion for two ecotypes of Sedum alfredii Hance, while malic acid, fumaric acid in secretion is low.4. The response to heavy metal stress and the rate to increase the secretion of organic acids and amino acids of Two ecotypes of Sedum alfredii Hance are quite different (P<0.05). Generally, HE faster than NHE. At12h treatment, the secretion of HE will make a great increase, while NHE will be later. At12h treatment, the secretion of NHE increase slowly, even decreased sometimes, and its secretion will make a great increase at36h treatment. This rapid response mechanism is unique to HE, and it is also shows that HE can tolerance and accumulate more heavy metal than NHE.5. Adding oxalic acid and γ-aminobutyric acid to nutrient solution can increase biomass of two ecotypes of Sedum alfredii Hance when treated with Zn. Further, γ-aminobutyric acid also can increase the Zn accumulation aboveground of two ecotypes of Sedum alfredii Hance, but oxalic acid can not. For the plant treated with Pb, adding oxalic acid and γ-aminobutyric acid to nutrient solution not only increase biomass of HE, but also increase the Pb enrichment underground. And it is contrary for NHE, adding oxalic acid and γ-aminobutyric acid to nutrient solution rduce the biomass of NHE, and also lower the Pb enrichment underground. |
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