Research On Influnce Of Silicon And Sulfur On Arsenic Uptake And Accumulation Of Rice (Oryza Sativa L.)

With the continuing development of industrial technology, more and more people are becoming to concern the social and environmental problems which due to the heavy metal pollution. Arsenic is a widespread environmental contaminant. Nowadays, China has become one of the most serious contamination countries in the list of World Health Organization(WHO). What's more, the health risk of arsenic in human beings through food-chain is becoming worse. Therefore, seeking an effec-tive method for reducing the arsenic risk to human health through food chain is im-minent. On the one hand, Rice is one of China's three major food crops, which is also a typical crop of silicon. Silicon can promote rice growth and high yield, besides it can significantly reduce arsenate and arsenite uptake by rice. On the other hand, the formation of PCs in response to the stress caused by heavy metals was one of the truly adaptive responses occurred commonly in higher plants.Sulfur is an important component of rice protein and phytochelatins(PCs). What is the possible mechanism of sulfur affecting arsenic absorption by rice? The research about this field is not much at home and abroad, which is the main research in this issues. Hydroponic experiment and pot experiment were conducted to study the differences and mechanisms about arsenic uptake and accumulation among four rice genotypes, in which rice cultivars TN1 and Baixiangjing with high silicon uptake efficiency and Juanyejing and Hitomebore with low silicon efficiency. The influence of sulfur on plant antioxidant system, phytochelatins synthesis and arsenic accumulation was in-vestigated through different concentration of sulfur under arsenic stress. Meanwhile, molecular biology techniques was used to get a cloned phytochelatins synthase(PCS) gene, which was the basis for next study of gene function.The main research of this paper is as follows:(1) Research on influnce of silicon on arsenic accumulation of rice.Through the research of arsenic absorption,transportation,accumulation and related physiological of different rice genotypes, we found arsenic uptake, translocation and accumulation was different among the rice genotypes which uptaking silicon differ-ently at seedings and mature under hydroponics and soil culture. At the seedings stage with low arsenic supply, the capability of arsenic transportation from root to shoot was higher of low silicon uptake efficiency genotype than that of high silicon uptake efficiency genotype, the same as ATPase activity and non-protein thiol(NPT) content of low silicon uptake efficiency genotype. The influence on arsenic accumu-lation of genotypes with high silicon uptake efficiency was higher than that with silicon supply under arsenic conditions. While, Silicon had no influence on iron plaque amount on the root surface significantly. Arsenic was reduced in grains, husks, stems leaves and roots of rice with silicon supply, besides, arsenic concentrations in husk was significantly difference between genotypes.(2) Research on influnce of sulfur on arsenic accumulation of rice.Sulfur is a major component of polypeptide mercapto, which is very important for the synthesis of phytochelatins(PCs) and GSH.Through the study of different arsenic concentration, supplying sulfur could promote the arsenic of root transfer to shoot under low arsenic condition. Sulfur can reduce arsenic concentration in rice plant significantly with high arsenic concentration. Moreover, the content of non-protein thiol, GSH, phytochelatins(PCs) was increase with sulfur supply under high arsenic concentration stress, which noted that sulfur could increase the resistance of rice for heavy metal stress by increasing phytochelatins under high arsenic concentrations. Further tests showed that rice seedlings were grown in nutrient solutions with low sulphate (1.8μM SO42?) or high sulphate (0.7 mM SO42?) for 12 or 14 d, before be-ing exposed to 10μM arsenite or arsenate for 2 or 1 d, respectively. Arsenite is the main form of arsenic in rice roots with all treatments except for the plants are ex-posed to arsenate pretreated with the low sulphate nutrient solution. In the arsenite exposure treatment, low sulphate-pretreated rice accumulated less arsenite than high sulphate pretreated plants, but the arsenite concentrations in shoots of low sulphate pretreated rice were higher than those of high sulphate pretreated. In the arsenate exposure treatment, the low sulphate pre-treatments also resulted in less arsenite ac-cumulation in rice roots. The low sulphate-pretreated plants had a higher arsenic transfer factor than the high sulphatepretreated plants.Besides, sulphur deprivation in nutrient solution decreased the concentrations of non-protein thiols in rice roots ex-posed to either arsenite or arsenate. The results suggest that arsenite is the main form of arsenic in rice root and rice sulphate nutrition plays an important role in regulating arsenic translocation from roots to shoots, possibly through the complexation of ar-senite-phytochelatins. (3)cloning of phytochelatins synthase(PCS)gene from rice and construction of plant expression vector.Phytochelatins synthase(PCS) gene was cloned by reverse transcription polymerase chain reaction(RT-PCR) from the total RNA of rice. Sequence analysis revealed that the PCS gene was located on chromosome 6, and has the highest nucleotide se-quence homology with rice which landed NO.is NM₀01063069.1, but not with sorghum, maize. Meanwhile, the plasmid vector pET-28a,pCam2335 were used to construct the prokaryotic expression vector and nonspecific expression vector of this gene for the further research on physiological and biochemical characterization of PCS.