Characterization And Analysis Of Chelates Involved In Compartmentation Of Cadimium In Rice Plants

Rice is one of the most important cereal crops in China and it plays the key role in food security and guarantee system in our country. Cadimium (Cd) pollution is a main problem impacts on rice quality security. Consequently, quantification and speciation analysis of Cd in rice plant are closely linked to food security. At present, most related researches focus on Cadimium concentration testing and distribution in different organs. However, few of them involving analysis of distribution and formation in subcellular fraction at home and abroad. In this dissertation ,we chose two rice species with different Cd tolerance, Zhenshan 97B and Miyang 46, as our materials. Detections of Cd concentration and forms in various parts and subcellular fractions under 5 tested concentrations were studied. Furthermore, Cd tolerant mechanism in rice was discussed. Results of the studies are as follows:1. It was found that the Cd tolerance of Zhenshan 97B differed from that of Miyang 46. Judging from some important physical signs, such as apparence, height and chlorophyll content, the effect of Cd on Zhenshan 97B was less than that of Miyang 46. Accumulation of Cd in the roots was more than that in the leaves, and it increased significantly with the rise of tested concentration. What's more, Zhenshan 97B was less sensitive on Cd than Miyang 46.2. In principle, regularities of distribution of Cd in rice subcellular fractions is cell wall>cytolymph>organelle. Cell wall and vacuole are important compartmental organizations of Cd. Mechanisms of Cd tolerance of the two materials are different. The cell wall of Zhenshan 97B has a stronger sequestrated effection on Cd than Miyang 46, but when Miyang 46 confronts Cd stress , it seemed that the vacuoles detoxification was more important in its root cells. In leaves, contents of Cd in the whole cell and that in each subcellular fractions of Miyang 46 are significantly higher than that of Zhenshan 97B.3. SEC-ICP-MS was used to analyse the Cd-binding complex in rice plants. Chromatographic separation was performed on a Superdex Peptide 10/300 GL column using a solvent contained 50 mmol/L ammonium acetate (pH 7.5), furthermore, 114Cd as the monitoring ion. As a result, No Cd-binding complexes was found in cell walls and organelles, and the binding of Cd to the cell walls mainly depends on cation exchange sites and plenty of substances with affinity to Cd. Also, cytolymph abounds in compounds which can bind to Cd, and, especially, vacuoles are the critical position that Cd-binding complexes exsist in. There are 8 peaks marked different induced molecular weights in rice roots. The retention time of the main Cd-binding complexes is between 1100s and 1700s, and the range of molecular weight is 8000~ 14000 Da.. While 3 peaks with different molecular weights were found in rice leaves, and the retention time was from 800s to 1200s with 17388Da, approximately, which was far below that in roots. 4. Another method was developed for structural analysis of freedom phytochelatin(PC) released by Couplnt Sodium Dimercaptosulphonate(DMPS) using the Orbitrap with high resolution. It was found that the essential chelates in roots are PC2 and PC3, There are also some iso-PC2(ser) and des-Gly-PC2., Otherwise, important chelates in leaves are PC2 , iso-PC2(ser) , des-Gly-PC and Glutathione (GSH).