| As farmland cadmium(Cd) pollution situation in China is stressing increasing, the grain security issues in Cd contaminated area are becoming increasingly conspicuous. It is of great significance to food production safety in mild or low Cd contaminated area to reduce the Cd accumulation in grain by means of fertilization and so on. Solution culture and pot experiments were performed to study the effects of phosphate levels on Cd uptake and transportion in high Cd accumulation variety “T you705”(T705) and low Cd accumulation variety “Xiangzaoxian 24”(X24). The main results were summarized as follows:1. The Cd uptake rates in rice seedlings increased with the increasing concentrations of Cd in environment, and the Cd uptake rates of root and shoot in T705 were higher than those of X24. The Michaelis-Menten equation fitting the Cd absorption kinetics of rice seedlings shows that the roots of T705 have higher Cd-affinity(1/Km = 1.20) than the roots of X24(1/Km = 0.94). The maximum rate of Cd uptake(Fmax) of T705 roots was 2.7 times that of X24 roots, and the Cd transport efficiency between root and shoot of T705 was also significantly higher than that of X24. The deposition rate of root cell wall in T705 is much higher than that in X24, and the deposition rate of root cell wall in X24 is higher than that in T705.2. Subcellular distribution results shows that the distribution of Cd was cell cytoplasm > cell wall > organelles in root and cell wall > cell cytoplasm > organelles in shoot. A part of the Cd absorbed from the rhizosphere was deposited on the cell wall of the root system, and the other part of the Cd transported across the cell membrane into the protoplasts, a tinny fraction of which is located in the organelles. The Cd transported to shoots from roots was mostly deposited on the cell wall, and secondly cytoplasm fraction and only a small fraction of Cd was stored in the organelles.3. The solution culture experiment results shows that 1 ~ 30 mmol·L-1 of phosphate in rhizosphere environment significantly reduced the Cd accumulation in rice roots and the transport rate to the shoot. When the Cd content was 4.4 μmol·L-1, adding 5 mmol·L-1 phosphate into solution reduced the Cd content of root by 80.63% and of shoot by 30.13% and declined the Cd transport rate by 63.43% in T705 and reduced the Cd content of root by 79.21% and of shoot by 48.06% and declined the Cd transport rate by 48.06% in X24.4. The results of pot experiment for the whole growth period showed that foliar application of phosphate did not significantly influence the Cd content in grain. But adding 0.5 to 2.5 g·kg-1 of calcium magnesium phosphate fertilizer(CMP) into soil can significantly reduce the Cd content of roots, leaves, rachis and grains of X24 in mature stage. Adding 2.0 g·kg-1 CMP, the Cd content in grain decreased by 38.3 % compared with that of the control, and reached the upper limit of the national food safety standards(0.20 mg·kg-1, GB2762-2012).5. Adding CMP did not significantly influence the pH of neutral soil, but significantly increased the content of iron and manganese oxides deposited on root surface. Subcellular distribution results shows that CMP has significantly decreased the contents of cell wall and protoplast in root. The percentage of the Cd content in protoplast to the Cd content in root was decreased by the application of CMP feterlizer. X-ray photoelectron spectroscopy(XPS) analysis results show that the application of CMP did not significantly affected the binding energy and peak area of carbon(C), nitrogen(N) and oxygen(O), silicon(Si) in root, but significantly increased the relative proportions of the phosphorus(P) and the iron(Fe) elements in root. Adding the application of CMP in soil, the Cd content in cell wall and protoplasts of root was significantly decreased, but the distribution ratio of the cell wall in root was significantly increased. Therefore, the application of CMP improved the interception effect of iron plaque and cell wall on Cd. |
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