| Taking the aquatic plant Spirodela polyrrhiza as the materials in the experiment, we reasearch accumulation, distribution, physiological and biochemical effects of the rare earth elements Ce and Y, and target sites in S. polyrrhiza after a 15 days stressing by different concentrations (0,10,20,40,60 μmol·L-1) light rare earth Cerium (Ce) and the heavy rare earth Yttrium (Y). Furthermore, the adaptative strategies of plants under rare earth stressing are also studied. Meanwhile, some theoretical supports for the resistance mechanism of plant are provided.1. The distributions of Ce and Y in S. polyrrhiza and the change of ionomic are measured by ICP-AES. The results are obtained as follows, (1) Ce and Y are mainly combined in cellulose and pectin, but the contents of each component are different. In the Ce treatment group, the contents are in the following order of highest to least, cellulose and pectin (83-85%), crude protein (8-12%), crude polysaccharide (4-6%), crude fat (1%). In the Y treatment group, they are:cellulose and pectin (60-80%), crude protein (11-24%), crude polysaccharide (8-14%), crude fat(1-2%). (2) After the treatments of Ce and Y, the ionomics of S. polyrrhiza will change. In the Ce treatment group:The contents of Ca, K and Cu increase at first and then decrease, but the levels in the highest concentration group (60 μmol·L-1) are 83%,89%,86% of these in controls (0 μmol·L-1), respectively. The contents of Mg, P, S and Mn firstly decrease and then increase, but the contents in the highest concentration are higher than these in the control group. In the Y treatment group: the contents of Ca, K, P and S firstly increase and decrease afterwards, but the contents in the highest concentration group are 114% and 115% compared with in the control, respectively; the content of Mg raise first and then decline, but the content in the highest concentration is higher than the level seen in the control group; The contents of Cu, Zn and B increase, the contents in the highest concentration group account are 213% and 164% of these in the control, respectively.2. The morphological changes of S. polyrrhiza are analysed by using the scanner(Epson Perfection V700). PLAD results show that the damage degree of leaf become more serious with the increasing concentration of rare earth Ce and Y. The control group damage rate is 3%, and the highest concentration group is 77%, and there is no significant difference between Ce treatment and Y treatment. Either Ce or Y will reduce the relative growth of S. polyrrhiza, the qualitility in the highest concentration group are 36% and 27% compared with the control group, respectively. At the same time, the rate of cell death also rise up, and the rates in the highest concentration group are 1.3 and 1.4 times higher than these in the control group.3. The changes of fatty acid content and composition are measured by gas chromatography/mass spectrometry. The research results show that the unsaturated fatty acid decreased significantly after Ce and Y treatment. In the Ce treatment group:the contents of palm oleic acid (16:1), oleic acid (18:1), linoleic acid (18:2) and linolenic (18:3) in the highest concentration are 37%,98%,79% and 60% compred with the control group, respectively. In the Y treatment group, they are 37%,98%,68% and 52%. The saturated fatty acid myristic acid (14:0) content increases, but palmitic acid (16:0) and stearic acid (18:0) content decrease. MDA accumulates gradually in S. polyrrhiza, the level in the highest concentration group are 2.3 times and 2.9 times higher than the control group. The effects of Ce and Y on the O2- producing rate and H2O2 content are similar, and they reach the peak at the highest concentration group. In the Ce treatment group they increase 83% and 47%, In the Y treatment group they are 99% and 46% respectively.4. After treatments of Ce and Y, both superoxide dismutase (SOD) and catalase (CAT) activity decrease, which will reduce the ability of eliminating active oxygen. In the highest concentration Ce and Y group they make the SOD activity decrease by 82% and 88%, CAT activity decrease by 25% and 27% respectively. But peroxidase (POD) activity are induced to raise, the levels in the highest concentration group are 1.5 times and 1.9 times higher than the controls. So we can conclude that the POD play a leading role in removing oxide. The soluble protein content decreased significantly with the increasing concentration of Ce and Y, the contents in the highest concentration group are 41% and 25% of these in the controls respectively.5. After treatment of Ce, glutathione reductase (GR) activity is observed to be a rising trend after the first drop, but the contents in highest concentration group is still lower than the controls, account for 89%. In the Y group it shows a decrease trend, the highest concentration group account for 44% in the controls. Both ascorbate peroxidase (APx) activity decreases, the levels in the highest concentration group account for 51% and 43% in the control respectively. These show that the ability of removing oxide decrease with the increase of Ce and Y concentration. The content of reduced glutathione (GSH) and ascorbic acid (AsA) increase, and the ability of removing oxide increase. The GSH content of the highest concentration group increase by 62% and 36%, AsA increase by 24% and 39% respectively.6. Rare earth Ce and Y change chloroplast photosynthetic capacity obviously. (1) chlorophyll a, b and carotenoid content decrease rapidly with the increase of Ce and Y concentration. They all reach the lowest value in the highest concentration group, account for 46% and 40% (Chla),57% and 49% (Chlb),72% and 57% (Car) respectively. (2) Fv/Fm decreases by 11% and 20%, and Fv/Fo also decreases by 27% and 49%. But Fo/Fm increases by 47% and 84%. NPQ and qP decrease with the increase of Ce. The levels in the highest concentration group account for 63% and 28% of in the control. In the Y treatment group they account for 57% and 28%. (3) both photosynthetic phosphorylation and ATP content decline. In the Ce treatment group the contents decrease by 49% and 72%, In the Y treatment they are 65% and 84%. The changes of Ca2+-ATPase and Mg2+-ATPase activity are similar. In Ce treatment group they account for 54% and 45%, and in the Y treatment they are 47% and 40%. (4) In the Ce and Y treatment group, rare earth with granular aggregation deposite in the cell wall by observing chloroplast ultrastructure, while in the control group the phonomenon is not observed. The chloroplasts of control are oval, double envelope and thylakoid stucture can be observed clearly. But with the increase of rare earth concentration, the chloroplast structure appears to be in different degree damage. The chloroplast volume is expanded gradually to double membrane rupture, grana lamellae severely damage, material content loss, and chloroplast structure disintegrate. But in Y treatment group they are more seriously. (5) The results of SDS-PAGE show that polypepitide components degrade gradually with the increase of Ce and Y concentration. Through the western-blot analysis, CP43 and CP47 are degraded gradually, but Dl and D2 are not significant. |
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