| After the plant body absorbs silicic acid,most of it is deposited on the cell wall surface to form inorganic silica,while a very small part is covalently cross-linked with cell wall hemicellulose compoment to form organosilicon complex.These two different forms of silicon interact closely with the plant cell wall,which must affect the expression of cell wall proteins and the interaction with the cell wall polysaccharide components.However,the effect of silicon nutrition on rice suspension cell wall protein contents and the microscopic mechanism of silica-cell wall polysaccharides interaction are still poorly understood.For this purpose,we suspended and cultured rice cells with the same genetic background under the condition of silicon（+Si）and without silicon（-Si）,the influence of silicon nutiition on the secondary structures of the cell wall proteins was preliminarily investigated by laser confocal Raman spectroscopy;The change of the cell wall protein contents was analyzed by Tandem Mass Tag（TMT）relative quantitative proteomics.In addition,in order to simulate the interaction between silica deposited in the apoplast and cell wall polysaccharides,we prepared silica colloidal probes of different sizes,modified the two main cell wall polysaccharides,cellulose and pectin on mica,then measured the interaction forces of silica and different cell wall polysaccharides by Atomic Force Microscopy（AFM）force spectra technology.The main results of this study are described as following:1.The addition of silicon nutrition changed the composition of the secondary structure of rice suspension cell wall proteins and affected the contents of cell wall protein;cell wall proteins with varying contents involved in a variety of biochemical functional pathways.After the suspension cells of rice were cultured with silicon（+Si）,silicon mainly existed in the cell wall and formed organosilicon complex with hemicellulose.Raman spectra showed that the composition of secondary structures of cell wall proteins was changed in the presence of silicon.After further purification of the cell wall,0.2 M Ca Cl2,2 M Li Cl and SDS were used to extract cell wall proteins with silicon（+Si）and without silicon（-Si）,276 differentially expressed proteins were identified by TMT relative quantitative proteomics.Through bioinformatics screening,33 classical cell wall proteins and 98 non-classical cell wall proteins were identified,of which 40 were up-regulated and 91 were down-regulated.The differentially expressed cell wall proteins were found to be distributed in various molecular biochemical functional pathways such as catalysis,binding,hydrolysis,oxidoreductase,transfer and protease activity.Cell wall proteins related to the formation or decomposition of polysaccharides,iron ion homeostasis,metal ion transport,alpha-amylase activity and aspartic-type peptidase activity were inhibited.Cell wall proteins related to nutrient reservoir activity and chitinase activity were accumulated.For the functional annotation of classical cell wall proteins,the proteins are mainly distributed in three functional pathways that proteins acting on cell wall polysaccharides,proteases and oxido-reductases.A detailed analysis of the function of differentially expressed rice cell wall proteins revealed silicon nutrition affect the contents of many stress-related cell wall proteins（peroxidases,aspartic-type endopeptidase and cysteine proteases and xylanase inhibitors）,it also affect the contents of some cell wall proteins related to cell wall polysaccharide metabolism（xyloglucan-xyloglucosyltransferases,α-amylase）.2.The colloidal probes of different sizes of silica microparticles were successfully prepared,and the forces between the different sizes of silica microparticles and the main polysaccharides of the cell wall were measured by AFM.It was found that silica and pectin have greater binding force.Except for the organosilicon is found on cell wall,most of the silicon is deposited on the surface of the cell wall to form inorganic silica.The silica microparticles with 1μm sizes and 4μm sizes were successfully modified on AFM probes,through Scanning Electron Microscopy（SEM）and AFM inspection,it was found that the silica colloidal probes can be used to obtain the force-distance curves by interacting with substrate.The main polysaccharides of the cell wall-cellulose and pectin were modified on new cleaved mica,and AFM imaging and Raman spectra were performed on it.The forces between the silica microparticles of different silica sizes and substrates were measered based on the force-distance curves,it was found that the silica partices exhibited the greater binding force with pectin compared with the celluose and mica,indicating that the silica was preferred to combine with the pectin.Moreover,the silica particles with the size of 1μm exhibited the greater force with cell wall polysaccharides at per unit area,which is demonstrated that the silica preferred to deposite on the cell wall polysacchrides at smaller size,and then the silica particles could aggregate to form larger micropartices. |
