Silicon-containing granules of rat liver,kidney and spleen mitochondria

Summary Isolated rat liver mitochondria containing granule aggregates (25–75 nm in diameter) and small (5–10 nm) electron opaque granules were examined by electron probe X-ray microanalysis. The granule aggregates gave an intense Si signal, while the small granules gave both Si and P signals. Isolated mitochondria of rat liver, spleen and kidney, subjected to detergent solubilization and differential centrifugation, produced two granule fractions: (1) a 10,000g fraction consisting predominantly of granule aggregates (25–75 nm) composed of smaller granules (5–10 nm in diameter), and (2) a 10,000–30,000 g fraction of non-aggregated small granules (5–10 nm). Thin sections of isolated granule aggregates gave Si X-ray signals similar to those obtained from in situ granules. In addition S, Cl, Mg, Cr and Fe X-ray signals were observed. Cr occurred only in the large kidney granules, while Fe occurred in both fractions of the spleen and kidney granules. The presence of Si in the granules was confirmed by chemical analysis of the isolated granules and in vivo radiolabeling of the granules with ³¹Si and ⁶⁸Ge. Contamination within the electron microscope was eliminated by a liquid nitrogen anticontamination device.Supported by Grant GM-08229-13-15 from the National Institutes of Health, USPHSWe are grateful to the Perkin-Elmer Corporation and to their Western Branch Manager, Mr. Michael E. Mullen and Microscopist, Mr. Minoru Saito, for use of and assistance with the Hitachi H 500 transmission electron microscope with the scanning attachment, and to the Kevex Corporation for the use of the Kevex X-ray Spectrometer. We also wish to acknowledge Mary Louise Chiappino for her technical assistance in preparing the thin sections, the final micrographs and X-ray spectra photographs and Darlene Lum for technical assistance in the laboratory     

The mechanism of two-photon photochemical laser-induced deposition of silicon thin films from silane

We have investigated the mechanism of silicon thin film deposition by ArF excimer laser irradiation of silane gas diluted with argon. The Si films were deposited by a focused laser beam irradiating in parallel to silicon and silicon dioxide substrates at a gas flow rate of 20 SCCM, total pressure of 60 Torr and repetition rate of 15 Hz. At laser energy fluences higher than 160 mJ/cm² the deposition rate was almost independent of the incident laser energy, while at a lower energy the deposition rate depended strongly on the laser energy. A 3/2 power law was found for absorption measurements carried out at the same pressure under flow conditions and for several repetition rates at average laser power above 300 mW, regardless of the laser repetition rate. This kind of behavior is typical of a multiphoton absorption process involving saturation effects caused by focusing of the laser beam. Below 300 mW the power dependence indicated a two-photon absorption process. From the observed photochemical yield we found the value 5.7×10^-44 cm⁴ s molec^-1 for the two-photon absorption cross section.A Gaussian-shaped transverse thickness distribution of the deposited layer was obtained with a maximum value corresponding to the center of the laser beam spatial profile. This distribution depended on the deposition parameters, and was attributed to the diffusion process of silane decomposition products in the gas phase in the substrate. Analysis of the adsorption features of the process showed that the major product adsorbed on the substrate surface is silicon.An Arrhenius plot of the deposition rate versus the substrate temperature exhibits two regimes, each associated with a different activation energy. Between 340°C and 460°C the activation energy is 0.25–0.3 e. V, while between 500°C and 560°C it is 1.1 e. V. The activation energy in the higher temperature regime is similar to that found for thermal nonlaser assisted chemical vapor deposition. However, in the lower temperature regime the deposition process is mainly laser induced, and the value of the activation energy is due to the process of adsorption of the gas species on the substrate.     

Functionalized silicon quantum dots tailored for targeted siRNA delivery

For RNA interference (RNAi) mediated silencing of the ABCB1 gene in Caco-2 cells biocompatible luminescent silicon quantum dots (SiQDs) were developed to serve as self-tracking transfection tool for ABCB1 siRNA. While the 2-3 nm sized SiQD core exhibits green luminescence, the QD surfaces are completely saturated with covalently linked 2-vinylpyridine that may electrostatically bind siRNA. For down-regulating P-glycoprotein (Pgp) expression of the ABCB1 gene the SiQDs were complexed with siRNA. The cellular uptake and allocation of SiQD-siRNA complexes in Caco-2 cells were monitored using confocal laser scanning microscopy and transmission electron microscopy. The release of siRNA to the cytoplasm was verified through real-time PCR quantification of the reduced ABCB1 mRNA level. Additional evidence was obtained from time-resolved in situ fluorescence spectroscopic monitoring of the Pgp efflux dynamics in transfected Caco-2 cells which yielded significantly reduced transporter efficiencies for the Pgp substrate Rhodamine 123.     

A novel silicon complex is as effective as sodium metasilicate in enhancing the collagen-induced inflammatory response of silicon-deprived rats

An experiment was conducted with rats to determine whether silicon deprivation affects the inflammatory response to the injection of type II collagen, and to compare the effectiveness of the organic complex arginine silicate inositol (ASI) with inorganic silicon (NaSiO₃) in mitigating any observed change in response. Dark Agouti rats were fed a ground corn–casein–safflower-based diet containing about 2.8 mg Si/kg. The experimental variables were supplemental 0 and 35 mg Si/kg as either ASI or NaSiO₃. After five weeks on their respective treatments, each rat was injected with type II collagen and euthanized four weeks later. Urine was collected before injection during week five and week nine before euthanasia. The silicon-supplemented rats generally exhibited a more marked inflammatory response than the silicon-deprived rats. The circulating number of lymphocytes was higher (p<0.003) and number of neutrophils was lower (p<0.008) in silicon-deprived than silicon-supplemented rats. ASI and NaSiO₃ were about equally effective in enhancing these changes. Post-injection of tibial release of prostaglandin E₂ (PGE₂) (p<0.04), urinary excretion of magnesium (p<0.03) and deoxypyridinoline (p<0.009), and plasma osteopontin (p<0.009), magnesium (p<0.0007) and copper (p<0.004) were higher in silicon-supplemented than silicon-deprived rats. The increases in plasma magnesium (Si×sex, p<0.04) and copper (Si×sex, p<0.02) were more marked in male than female rats. One but not the other silicon supplement when compared to silicon deprivation significantly affected the tibial release of PGE₂, and plasma copper and iron concentrations. However, with the exception of the pre-injection urinary excretion of helical peptide, no other of the variables determined was significantly different between rats fed ASI and those fed NaSiO₃. The findings suggest that, in rodents, physiological amounts of silicon promote the immune response, sex may influence the response to dietary silicon, and that both organic silicon complexes and inorganic silicon are similarly effective in preventing changes in inflammation induced by silicon deprivation.     

Silicon isotope fractionation in rice plants, an experimental study on rice growth under hydroponic conditions

Silicon (Si) isotope composition and Si distribution among different rice plant organs and different parts of rice leaf at maturity were studied, which may provide new insights into the mechanism of Si accumulation in plants and biogeochemical Si cycle. An isotope ratio mass spectrometer (IRMS) was used to examine Si isotope fractionation by rice plant grown in a hydroponic system. The observed ³⁰Si-depletion (about 0.3‰) of whole plant relative to external nutrient solutions suggested biologically mediated Si isotope fractionation occurred during uptake. However, it was not possible to judge the Si uptake mechanism with the data. For δ³⁰Si variation within plant, there was a consistent increasing trend from lower to upper tissues (stem < leaf < husk < grain; leaf sheath < leaf blade base <leaf blade middle < leaf blade top). The phenomenon, reflecting kinetic isotope effects, could be explained that isotope fractionation during Si deposition in rice plant was a Rayleigh-like behavior. The range (−2.7‰ to 2.3‰) of δ³⁰Si variation among rice plant tissues in present experiment exceeded that (−1.7‰ to 2.5‰) of phytoliths observed previously in continents, which would enhance understanding the role of phytoliths on globe Si isotope balance.     

Critical Role of Silicon in Directing the Bio-inspired Mineralization of Gelatin in the Presence of Hydroxyapatite

Significant progress has been made on understanding the critical role of organic components in directing the collagen mineralization.We hypothesize that the inorganic trace elements might also play important role in the mineralization of collagenous matrix.To this aim,we systematically compared the in-vitro biomineralization behaviors of gelatin,gelatin-HA and gelatin-SiHA electrospun membranes.The results indicated that the presence of Si ions played a striking influence on the nucleation behaviors and mineralized structures.The gelatin-SiHA samples demonstrated more homogeneous nucleation within the gelatin fiber and growth along the fiber direction,in comparison with the heterogeneous nucleation and growth of spherulitic clusters on top of the nanofiber surface,i.e.extrafibrillar mineralization.The likely shift of the nucleation mode to the intrafibrillar mineralization in the presence of Si ions led to good alignment of apatite c-axis with the long axis of the nanofiber,resulting in a mineralization process and microstructure that were closer to those in natural bone.Cellular response analysis indicated that Si incorporation improved the MSC attachment and cytoskeleton organization.Such findings might have important implication in both understanding the complex mechanisms involved in collagen mineralization and optimal designing of advanced bio-inspired materials with potential superior mechanical and biological properties.     

Silicon Supplementation Improves the Bone Mineral Density of Calcium-Deficient Ovariectomized Rats by Reducing Bone Resorption

The purpose of this study was to investigate the effect of silicon (Si) supplementation on bone mineral density (BMD) and bone metabolism parameters relative to calcium (Ca) intake levels in ovariectomized rats. A total of 72 female Wistar rats (6 weeks) were ovariectomized (OVX) and divided into six groups, and Si (500 mg of Si per kilogram of feed) was or was not administered with diets containing various levels of Ca (0.1%, 0.5%, and 1.5%) for 10 weeks. The groups were as follows: (1) Ca-deficient group (0.1% Ca), (2) Ca-deficient with Si supplementation group, (3) adequate Ca group (0.5% Ca), (4) adequate Ca with Si supplementation group, (5) high Ca group (1.5% Ca), and (6) high Ca with Si supplementation group. Si supplementation significantly increased the BMD of the femur and tibia in Ca-deficient OVX rats, while no change was observed with Si supplementation in the BMD of the spine, femur, and tibia in the adequate and high Ca groups. Serum alkaline phosphatase and osteocalcin levels were not affected by Si supplementation or Ca intake levels. C-telopeptide type I collagen levels were significantly decreased as a result of Si supplementation in Ca-deficient OVX rats. In summary, Si supplementation produced positive effects on bone mineral density in Ca-deficient OVX rats by reducing bone resorption. Therefore, Si supplementation may also prove to be helpful in preventing osteoporosis in postmenopausal women whose calcium intake is insufficient.     

The myth of plant transformation

Technology development is innovative to many aspects of basic and applied plant transgenic science. Plant genetic engineering has opened new avenues to modify crops, and provided new solutions to solve specific needs. Development of procedures in cell biology to regenerate plants from single cells or organized tissue, and the discovery of novel techniques to transfer genes to plant cells provided the prerequisite for the practical use of genetic engineering in crop modification and improvement. Plant transformation technology has become an adaptable platform for cultivar improvement as well as for studying gene function in plants. This success represents the climax of years of efforts in tissue culture improvement, in transformation techniques and in genetic engineering. Plant transformation vectors and methodologies have been improved to increase the efficiency of transformation and to achieve stable expression of transgenes in plants. This review provides a comprehensive discussion of important issues related to plant transformation as well as advances made in transformation techniques during three decades.