Effects Of Zinc And Copper On Growth And The Synthesis Of Phytochelatins Under Cadmium Stress In Seedlings Of Rice

Rice is one of the most important cereal crops in China and readily absorbs and accumulates Cadimium(Cd), what is more, Cd can enter human body through the food chain, and cause great harm to the human. Therefore, the Cd toxicity of rice has posed a potential threat to both safe food production and human health. To reduce Cd accumulation and alleviate its toxicity in rice h ave arisen increasing public concern. The synthesis of phytochelatins(PCs) is an adaptive response to stress, and it can alleviate heavy metal poisoning. The research of phytoremediation which use PCs ease heavy metal is becoming a new hot point recently. Zinc(Zn) and Cd located in the same main group of the periodic table and had similar chemical properties; Copper(Cu) is an essential nutrient element under normal growth conditions of the plants. It plays an important role in plants growth and in plant defense response. There are mutual impacts between Cd and many nutrient elements. Research for mutual impacts between Cd and elements about the synthesis of PCs in alleviating heavy metal toxicity are still far from clear.Paddy rice(Oryza sativa ssp. indica cv. 9311) were used as experimental materials to determine the root length, the content of biomass, heavy metals, phytochelatins(PCs) and glutathione(GSH) under combined pollution of Zn/Cd, Cu/Cd. The aim of this study is to provide a theoretical basis for Zn/Cd, Cu/Cd competitive absorption mechanism and a scientific basis on the use of Zn and Cu relieveing heavy metal poision in terms of generating PCs. The main findings are about the followings:1. By using liquid chromatography tandem mass spectrometry, the condition of mass spectrometry, chromatographic column, mobile phase in the chromatographic conditions and the purification steps of sample pretreatment were investigated, we established a detection method for PCs. Chromatography was performed on a polymeric column with acetonitrile and water containing 0.1% formic acid as the mobile phase. These polymeric materials not only make it possible to overcome a sharp decline in column efficiency of the conventional silica-based C18 columns used for analysis of rice samples, but also greatly reduce matrix effects via adsorption of potential interferences through PAX cartridges. We developed a sensitive and robust method for reliable identification and subsequent quantification of thiols by HPLC-MS/MS. This validated method was applied successfully for the analysis of rice exposed to three different Cd concentrations(0, 50 and 100 μM); what is more, the research provided a new method and basis for the evaluation of the accumulation and detoxification of heavy metal Cd in rice.2. Rice seeds(Oryza sativa spp. Indica cv. 9311) were cultivated in complete Yoshida’s rice nutrient solution in 2015. In the presence of Cd, Zn, Cu and the binary mixtures of Cd-Zn, Cd-Cu, the effects of Zn and Cu on growth in seedlings on the low and high concentration of Cd stress. The results show that the increasing Cd level will inhibit the growth of rice, resulting in rice seedling dry weight accumulation decline. Zn treatment has a mitigation effect for Cd stress in dry weight. Regardless of the concentration of Cd treatment, Zn addition makes the dry weight of the shoot and root of rice increased. When the concentration of Zn was 10μM, the dry weight of root was significantly higher than that of the single Cd treatment, which was 1.1 times of the Cd treatment alone. In root length, under Cd stress, with the increase of Zn level, the length of rice first increased and then decreased, but the root length was longer than that of rice under Cd stress. When the concentration of Cu was 1μM, it has a mitigation effect for low Cd stress. The biomass of root and shoot of rice seedling was promoted, the content of Cd in root and shoot of rice was decreased, what is more, the root growth was promoted. Cu could not alleviate the toxic effect of high concentration of Cd, and the growth of rice was significantly inhibited with increase concentration of Cu.3. Rice seeds(Oryza sativa spp. Indica cv. 9311) were cultivated in complete Yoshida’s rice nutrient solution in 2015. In the presence of Cd, Zn, Cu and the binary mixtures of Cd-Zn, Cd-Cu, the effects of Zn and Cu on the synthesis of phytochelatins in seedlings on the low and high concentration of Cd stress. The results show that the increasing Cd level can increase PCs content. Compared with the single Cd treatment, the addition of Zn decreased the PCs content of rice roots and the effect decreased more significantly with the increase of Zn level. Under low concentration Cd treatment, Zn promoted the synthesis of GSH. Under the high concentration Cd treatment, the GSH content showed a trend of first increase and then decreased with the increase of Zn concentration. When the concentration of Zn was 10μM, the content of GSH reached maximum. Regardless of the concentration of Cd treatment, the addition of Cu makes the content of PCs in the rice roots and shoots increased first and then decreased. In low Cd condition, the content of GSH in the shoot and root of rice was gradually decreased with the increase of Cu concentration. In high Cd condition, the case was opposite. The experiment explained that the concentration of Zn and Cu was 1-10μM was beneficial to produce biothiols and alleviate Cd stress on seedlings of rice seedlings.