The Study Of Organosilicon Regulates Nutrients Transport And Cell Wall-induced Depostition Of Silicon In Rice

Silicon（Si）is the second most abundant element in soil,and is beneficial to plant growth.Rice（Oryza sativa）is a typical silicophilic plant,with the huge accumulation of Si in plant,the over-ground parts of rice is able to accumulate Si to up to 10% of their dry weight.These Si mostly deposites in specialized cells or on cell walls as amorphous silica,only a little Si could covalently crosslink cell wall components in form of Si-cell wall complexes（organosilicone）.Numerous studies have shown that Si plays key roles in alleviating environmental stress and regulating transportation of nutrients,however,the functions of Si and its corresponding mechanisms are poorly understood.In order to rule out biological complexity,we used the rice suspension cells as research materials,which is under the same developmental stages and genetic background.Using the noninvasive micro-test technology（NMT）,isobaric tags for relative and absolute quantitation（iTRAQ）method and other chemical or biological methods,we minutely investigated the differences of nutrient transport and protein expression in Si-and non-modified rice cells.Meanwhile,different cell wall components induced deposition of silica was imitated by atomic force microscope（AFM）.The main results are summarized as following: 1.Cell wall-bound form of silicon could improve the mechanical properties of cell walls,in turn,improves the membrane stability,thereby promoting uptake of ammonium（NH₄⁺）.Under the normal and PEG-treated（1% PEG 6000）conditions,the mean rates of NH₄⁺ influx were measured by NMT,and the influxes of Si-modified cells are greater than those non-modified cells in two conditions.The measurements of total RAN and protein shown that the cells cultured in medium with silicon contained higher concentrations of RAN and protein than that without,suggesting that application of Si can improve N metabolic level in whole single-cell.X-ray photoelectron spectroscopy（XPS）and AFM results revealed that Si covalently crosslink cell wall components in form of Si-cell wall complexes,these Si could increase the tightness of cell wall and improve its mechanical properties.The mechanical properties of cell wall are related to cell membrane stability.Ion fluxes,electrolyte leakage and change of fluorescent dye DiBAC4（3）-labelled membrane potential（MP）determined in different conditions,shown that plasma membrane of Si-treated cells is more stable.2.Si nutrion results in different expression of proteins in rice cells.In the environment without stresses,iTRAQ results shown that 74 proteins were regulated by Si,they are 51 down-regulated and 23 up-regulated proteins.Through analysis,Si-limiting cells suffer from various environmental stresses because of defective cell wall.Therefore,Si nutrion results in different expression of proteins in rice cells,especially expression of proteins related to biosynthesis of cell wall and stress response.3.Different constituents of cell wall have different ability to induce deposition of silica in rice plant and hemicelluloses are major factors.The substrate is mica modified by constituents of cell wall,the deposition of amorphous silica in rice plant was imitated in vitro by AFM.The study has shown that the xylan,a main component of hemicellulose,is more conducive to the deposition of silica than pectin.