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Silicon (Si) plays a large number of diverse roles in plants, but the structural and chemical mechanisms operating at the single-cell level remain unclear., We isolate the cell walls from suspension-cultured individual cells of rice ( Oryza sativa) and fractionate them into three main fractions including cellulose (C), hemicellulose (HC) and pectin (P)., We find that most of the Si is in HC as determined by inductively coupled plasma-mass spectrometry ( ICP- MS), where Si may covalently crosslink the HC polysacchrides confirmed by X-ray photoelectron spectroscopy ( XPS). The HC-bound form of Si could improve both the mechanical property and regeneration of the cell walls investigated by a combination of atomic force microscopy ( AFM) and confocal laser scanning microscopy ( CLSM)., This study provides further evidence that HC could be the major ligand bound to Si, which broadens our understanding of the chemical nature of 'anomalous' Si in plant cell walls. [ABSTRACT FROM AUTHOR]

Silicon ( Si) alleviates cadmium ( Cd) toxicity in rice ( Oryza sativa). However, the chemical mechanisms at the single-cell level are poorly understood., Here, a suspension of rice cells exposed to Cd and/or Si treatments was investigated using a combination of plant cell nutritional, molecular biological, and physical techniques including in situ noninvasive microtest technology ( NMT), polymerase chain reaction ( PCR), inductively coupled plasma mass spectroscopy ( ICP- MS), and atomic force microscopy ( AFM) in Kelvin probe mode ( KPFM)., We found that Si-accumulating cells had a significantly reduced net Cd2+ influx, compared with that in Si-limited cells. PCR analyses of the expression levels of Cd and Si transporters in rice cells showed that, when the Si concentration in the medium was increased, expression of the Si transporter gene Low silicon rice 1 ( Lsi1) was up-regulated, whereas expression of the gene encoding the transporter involved in the transport of Cd, Natural resistance-associated macrophage protein 5 ( Nramp5), was down-regulated. ICP- MS results revealed that 64% of the total Si in the cell walls was bound to hemicellulose constituents following the fractionation of the cell walls, and consequently inhibited Cd uptake. Furthermore, AFM in KPFM demonstrated that the heterogeneity of the wall surface potential was higher in cells cultured in the presence of Si than in those cultured in its absence, and was homogenized after the addition of Cd., These results suggest that a hemicellulose-bound form of Si with net negative charges is responsible for inhibition of Cd uptake in rice cells by a mechanism of [ Si-hemicellulose matrix] Cd complexation and subsequent co-deposition. [ABSTRACT FROM AUTHOR]

Despite the ubiquity and beneficial role of silicon (Si) in plant biology, structural and chemical mechanisms operating at the single-cell level have not been extensively studied., To obtain insights regarding the effect of Si on individual cells, we cultivated suspended rice ( Oryza sativa) cells in the absence and presence of Si and analyzed single cells using a combination of physical techniques including atomic force microscopy ( AFM)., Si is naturally present as a constituent of the cell walls, where it is firmly bound to the cell wall matrix rather than occurring within intra- or extracellular silica deposition, as determined by using inductively coupled plasma mass spectrometry ( ICP- MS) and X-ray photoelectron spectroscopy ( XPS). This species of Si, linked with the cell wall matrix, improves the structural stability of cell walls during their expansion and subsequent cell division. Maintaining cell shape is thereby enhanced, which may be crucial for the function and survival of cells., This study provides further evidence that organosilicon is present in plant cell walls, which broadens our understanding of the chemical nature of 'anomalous Si' in plant biology. [ABSTRACT FROM AUTHOR]

The stresses acting on plants that are alleviated by silicon (Si) range from biotic to abiotic stresses, such as heavy metal toxicity. However, the mechanism of stress alleviation by Si at the single-cell level is poorly understood., We cultivated suspended rice ( Oryza sativa) cells and protoplasts and investigated them using a combination of plant nutritional and physical techniques including inductively coupled plasma mass spectrometry ( ICP- MS), the scanning ion-selective electrode technique ( SIET) and X-ray photoelectron spectroscopy ( XPS)., We found that most Si accumulated in the cell walls in a wall-bound organosilicon compound. Total cadmium (Cd) concentrations in protoplasts from Si-accumulating (+Si) cells were significantly reduced at moderate concentrations of Cd in the culture medium compared with those from Si-limiting (−Si) cells. In situ measurement of cellular fluxes of the cadmium ion (Cd2+) in suspension cells and root cells of rice exposed to Cd2+ and/or Si treatments showed that +Si cells significantly inhibited the net Cd2+ influx, compared with that in −Si cells. Furthermore, a net negative charge (charge density) within the +Si cell walls could be neutralized by an increase in the Cd2+ concentration in the measuring solution., A mechanism of co-deposition of Si and Cd in the cell walls via a [Si-wall matrix]Cd co-complexation may explain the inhibition of Cd ion uptake, and may offer a plausible explanation for the in vivo detoxification of Cd in rice. [ABSTRACT FROM AUTHOR]