Chemical Mechanisms For Alleviation Of Cadmium And Arsenic Toxicities On Rice (Oryza Sativa) Cell Walls By Inorganic Mineral

Plant cell walls usually contain various inorganic mineral elements,such as silicon（Si）,iron（Fe）and Zinc（Zn）.A large number of studies have shown that silicon can improve the ability of rice to resist cadmium stress,while the iron plaque on the surface of rice root can reduce the absorption of arsenic by rice root.We adopt a simple system of rice suspension cells,and use biophysical chemistry method to analyze that how silicon and zinc resist cadmium into cells jointly.Meanwhile,we coated the rice cells with an iron plaque artificially,and analyzed how the iron plaque blocks the five-valent arsenic into the cells at the cellular level.As a whole,we mainly have the following conclusions:1 、In the presence of Si,Zn²⁺ binds to ligands formation of the[Si-hemicellulose matrix]-Zn in the cell walls,these complexes can inhibit the rice suspension cell from absorbing Cd²⁺ ions.Synergistic effects between nutrient elements may enhance tolerance for Cd stress in plant.In the presence of zinc in the cell culture medium,Si-accumulating cells can reduce cadmium ion toxicity.We investigated cells using noninvasive microtest technology（NMT）,inductively coupled plasma mass spectroscopy（ICP-MS）,atomic force microscopy（AFM）and Polymerase chain reaction（PCR）.After Zn²⁺ and Cd²⁺ competition adsorption,the [Si-hemicellulose matrix] ligand and Zn²⁺on the cell wall formed [Si-hemicellulose matrix]-Zn complex.These complexes can be converted into surface precipitation after the concentration of Zn²⁺ was increased,which can effectively inhibit the uptake of cadmium ions by cells.This,in turn,induced the lower expression of Cd-related transporters.This synergistic effect could be decisive for the survival of cells under conditions of high Cd concentrations.2 、Rice cell surfaces coated by iron plaque can improve the mechanical performance of the cell wall.Iron plaque coating can significantly increase the surface potential of cell walls to induce the formation of Fe As O4·2H2O on the walls by electrostatic adsorption,inhibiting the uptake of As O43-ions into the cells.To understand the biological function of iron plaque in rice root,the suspension cells of rice were reacted with the hydroxide gel in acidic conditions to coated iron plaque on Individual cell artificially.The mechanical strength of the cell surface was significantly improved due to the iron plaque by the measurement in AFM mechanicalmodel.Field emission scanning electron microscopy（FE-SEM）and AFM-KPFM analysis found that the nano-particles of the iron plaque were about 12 nm and provided more positive charge to absorb the negatively charged arsenic ions.Transmission electron microscopy（TEM）and X-ray photoelectron spectroscopy（XPS）showed that the composition of the iron was ferric oxide.Finally,iron plaque can combine with arsenic ion to form two hydration arsenic acid irons to inhibit arsenic ion absorption by rice cell.