Effect Of Rare Earth La (Ⅲ) On Calcium Ion Exchange Capacity Of Horseradish Cell Membrane

There was a special biological effect and good chemical properties of rare earth elements (REEs). Therefore, REEs have been widely and successfully used in many fields, such as agriculture, forestry, stell, energy, and medicine. With the increase in the usage of the rare earth, REEs would inevitably enter into the rural environment and transfer through the food chain to human. Thus, REEs would influence the food safety and the human health. However, it is difficult to understand the effect mechanism of REEs especially heavy REEs on organism correctly. Rare earth elements, especially lanthanum (La) are named "super-calcium", which showed the similar function as that of Ca2+in organism. Most of the biological effects of Rare earth ions are relevant to that the similarity with calcium ion. Calcium (Ca) is essential for living organisms. But, the doctrine of "super-calcium" is still a hypothesis. It was reported that appropriate concentration of REEs could play a positive effect on plants, and high concentration of REEs play a negative effect. The above effect was called the "hormesis effect". However, the barrier effect of plant cell wall, it is difficult to understand the effect of REEs on Ca2+. Thus, the effect mechanism was still unclear. Study on the relationship between REEs and Ca2+has become a controversial issue in bio-inorganic chemistry of REEs. It may explain the biological effect of REEs. Therefore, in this thesis, the effect of La(Ⅲ) on ability of Ca2+exchange in the membrane of horseradish cell was investigated by using fluorescence microscope, conductance instrument, BAS100B electrochemical working station, flow cytometry, confocal laser scanning microscope, polyacrylamide gel electrophoresis, circular dichroism (CD), UV-vis absorption spectra, fluorescence microscope (FL), the method of the molecular dynamics simulation (Discovery Studio, Version2.1, Accelrys Inc.:San Diego, CA,2008) and quantum chemical calculation in order to further reveal the chemical process of REEs action on cell in living organisms and its effect mechanism.The main results are as follows:1) The horseradish treated with the low concentration of La(Ⅲ), cell proliferation were increased and the membrane permeability were decreased. While, the horseradish treated with the high concentration of La(Ⅲ), cell proliferation and differentiation were decreased, but the membrane permeability were increased.2) For the first time, a new method for detecting Ca2+on the surface of plant cell was investigated. We constructed a new system for the detection of the "living" cells of plant and then achieved the detection of the exchange ability of Ca2+in the membrane of the plant "living" cell. In the thesis, the content of Ca+on the surface of horseradish cell in the present of rare earth metal ion was detected using the new method. It was found that the low concentration of La(Ⅲ) promotes the concentration of Ca2+on the surface of horseradish cell decreased, leading to the extracellular Ca2+into the horseradish cell. The amount of calcium entry into the horseradish cell was decreased, as the lanthanum ions concentration increased. Combined with the data of quantum chemical calculation, we knew that the high concentration of La(Ⅲ) can complex with Ca2+channel protein, and then made some impairment to the structure of Ca+channel protein. The growth and development of horseradish cell was inhibited.3) CLSM and FCM system can accurately reflect cytosolic concentration of free Ca2+labeled by Fluo-3AM. The low concentration of La(Ⅲ) increased [Ca2+] in the cytosolic, and the high concentration of La(Ⅲ) decreased [Ca2+] in the cytosolic.4) The results from the investigation indicated that La(Ⅲ) could change the calmodulin (CaM) activity in the simulated physiological solution. It showed the "hormesis effect" with increasing the concentration of La(Ⅲ). Besides, La(Ⅲ) can complex with CaM, and then affect the structure and function of CaM.The results mentioned above demonstrated that La(Ⅲ) could affect the ability of Ca2+exchange in the membrane of horseradish cell, and then affect the growth and development of horseradish cell. It is one of the cellular mechanisms of REEs action on living organisms.