Silicon Uptake Research Articles

Interannual variability of Si and N cycles at the time-series station KERFIX between 1990 and 1995 – a 1-D modelling study

Interannual variability of nutrients and plankton cycles were studied at the time-series station KERFIX (50°40′S, 68°25′E) using a 1-D coupled physical-biogeochemical model that is descended from that of Pondaven et al. (1998). At KERFIX, a high half saturation constant for silicic acid uptake ( K Si ) and a high Si/ N uptake ratio are required to reproduce the Si and N cycles. Although very high in comparison with most data from temperate systems, these values are consistent with K Si and Si/ N uptake ratios measured in the Indian sector of the Southern Ocean. Past and recent finding on the role of light and iron limitation on nutrient consumption ratios might explain these “unusual” silicon uptake kinetic parameters. Comparison of model results with observations show that the model correctly reproduces the observed interannual variability of nutrients and plankton cycles at KERFIX between 1992 and 1995. Characteristic features of this region are a spring phytoplankton bloom of 1.0–1.5 mg Chlorophyll a m −3 and a net excess of silicic acid utilisation over that of nitrate. This high silicic acid utilisation leads to low Si concentrations in late summer and subsequent Si limitation of diatom growth. The interannual variability of production of silicon and nitrogen predicted by the model is 1.93±0.04 mol Si m −2 yr −1 and 1.35±0.07 mol N m −2 yr −1 (±SD). In parallel, the predicted export is 1.12±0.04 mol Si m −2 yr −1 and 0.06±0.01 mol N m −2 yr −1. It is shown that diatoms may contribute significantly to export if diatom sinking is taken into account. An interannual variability of the predicted Si and N cycles is detected. This variability is associated with changes in the mixed layer properties, which have been documented to be linked to the Pacific El Niño Southern Oscillation or displacement of the Polar Front.

Stable five- and six-coordinated silicate anions in aqueous solution.

Addition of aliphatic polyols to aqueous silicate solutions is shown to yield high concentrations of stable polyolate complexes containing five- or six-coordinated silicon. Coordinating polyols require at least four hydroxy groups, two of which must be in threo configuration, and coordinate to silicon via hydroxy oxygens at chain positions on either side of the threo pair. The remarkable ease by which these simple sugar-like molecules react to form hypervalent silicon complexes in aqueous solution supports a long-standing supposition that such species play a significant role in the biological uptake and transport of silicon and in mineral diagenesis.

Bioavailability of silicon from food and food supplements

The bioavailability of silicon from three different silicon sources was studied. A diet rich in silicon, a tablet containing a dry extract of horsetail and a solution of silicon in a choline-glycerol matrix were compared. Blood and urine of one healthy test person were sampled to monitor the silicon uptake. The silicon content of blood and serum samples was determined by graphite furnace atomic absorption spectrometry. Strongly diverging results were obtained for the three different silicon sources. Neither an increase in urinary silicon excretion nor in serum silicon content was observed when feeding the silicon rich diet. Urinary silicon excretion did significantly (P < 0.05) rise during supplementation with tablets containing dry extract of horsetail. Intake of a solution of silicon in a choline-glycerol matrix resulted in a significantly (P < 0.05) increased urinary silicon excretion and serum silicon content. From these results it can be concluded that speciation (chemical form, matrix) strongly influences the bioavailability of silicon.

Characterization of a silicon transporter gene family in Cylindrotheca fusiformis: sequences, expression analysis, and identification of homologs in other diatoms.

The transport of silicon is an integral part of the synthesis of the silicified cell wall of diatoms, yet knowledge of the number, features, and regulation of silicon transporters is lacking. We report the isolation and sequence determination of five silicon transporter (SIT) genes from Cylindrotheca fusiformis, and examine their expression patterns during cell wall synthesis. The encoded SIT amino acid sequences are highly conserved in their putative transmembrane domains. Nine conserved cysteines in this domain may account for the sensitivity of silicon uptake to sulfhydryl blocking agents. A less conserved C-terminal domain is predicted to form coiled-coil structures, suggesting that the SITs interact with other proteins. We show that SIT gene expression is induced just prior to, and during, cell wall synthesis. The genes are expressed at very different levels, and SIT1 is expressed in a different pattern from SIT 2-5. Hybridization experiments show that multiple SIT gene copies are present in all diatom species tested. From the data we infer that individual transporters play specific roles in silicon uptake, and propose that the cell regulates uptake by controlling the amount or location of each. The identification of all SIT genes in C. fusiformis will enhance our understanding of the mechanism and control of silicon transport in diatoms.

Kinetics of uptake and elimination of silicic acid by a human subject: A novel application of 32Si and accelerator mass spectrometry

Silicon is possibly important in human physiology in protecting against the toxic effects of aluminium, but the kinetics of uptake and excretion of silicic acid, the bioavailable form, are not well characterised. We have used 32Si as a tracer in a human uptake experiment to determine a gastrointestinal uptake factor for silicic acid, and to elucidate the kinetics of renal elimination. Urine collections were made for extending intervals from 2 to 12 h over 2 days following ingestion by a single human subject of a neutral silicic acid solution containing tracer levels of 32Si (t 1/2 ≈ 150 y). Silicon was isolated as SiO 2 and the 32Si content determined by accelerator mass spectrometry (AMS), using a gas-filled magnet technique to eliminate a prolific isobaric interference from 32S. Silicon uptake appears to have been essentially complete within 2 h of ingestion. Elimination occurred by two simultaneous first-order processes with half-lives of 2.7 and 11.3 h, representing around 90% and 10%, respectively, of the total output. The rapidly eliminated 32Si was probably retained in the extracellular fluid volume, whilst the slower component may represent intracellular uptake and release. Elimination of absorbed 32Si was essentially complete after 48 h and was equivalent to 36% of the ingested dose. This establishes only a lower limit for gastrointestinal absorption as, although there was no evidence for longer term retention of additional 32Si, the possibility could not be excluded by these results.

Plasma-deposited silylation resist for 193 nm lithography

Plasma-enhanced chemical-vapor-deposited carbon-based polymer films are examined for use as an all-dry positive-tone photoresist for 193 nm lithography. These films are designed to crosslink upon exposure to 193 nm radiation, enabling selective silicon uptake via reaction with hydroxyl groups. After oxygen plasma pattern transfer, features with resolution below 0.25 μm have been obtained.

CHANGES IN DOMOIC ACID PRODUCTION AND CELLULAR CHEMICAL COMPOSITION OF THE TOXIGENIC DIATOM PSEUDO‐NITZSCHIA MULTISERIES UNDER PHOSPHATE LIMITATION1

ABSTRACTProduction of domoic acid (DA), a neurotoxin, by the diatom Pseudo‐nitzschia multiseries (previously Nitzschia pungens f. multiseries) Hasle and its cellular chemical composition were studied in phosphate‐limited chemostat continuous cultures and in subsequent batch cultures. Under steady‐state chemostat conditions, DA production increased from 0.01 to 0.26 pg DA · cell−1· d−1 as the growth rate decreased. When the nutrient supply was discontinued (to produce a batch culture), DA production was enhanced by a factor of ca. 3. DA production was temporarily suspended upon addition of phosphate to the batch cultures but resumed 1 d later at a higher rate coincident with the decline of phosphate uptake. In both steady‐state continuous culture and batch culture, more DA was produced when alkaline phosphatase activity (APA) was high. The association of high DA production with high levels of APA and high cellular N:P ratios strongly suggests that phosphate limitation enhances DA production. Also, DA production was high when other primary metabolism (e.g. uptake of carbon, nitrogen, phosphorus and silicon, and cell division) was low, but chlorophyll a and adenosine triphosphate were generally high. This suggests that the synthesis of DA requires a substantial amount of biogenic energy.

Plasma-deposited silylation resist for 193 nm lithography

Plasma-deposited carbon-based polymer films are examined for use as an all-dry positive-tone photoresist for 193 nm lithography. These films are designed to crosslink upon exposure to 193 nm radiation, enabling selective silicon uptake via reaction of silylamine gas with hydroxyl in the film. After oxygen plasma pattern transfer, features with resolution below 0.50 μm have been obtained with a 0.35 numerical aperture projection system.

The Detection of the Accumulation of Silicon in Phalaenopsis (Orchidaceae)

Small particles along the veins of leaves in Phalaenopsis contain silicon. The silica bodies are spherical in shape and 5-20 μm in diameter. In the in vitro cultured plantlets, they grow differently in size, depending on the developmental stage of the plantlets and the concentration of silicon added to the medium. The growth of the silica body was increased by increasing the concentration of CaSiO 3 from 0·01 to 0·5 mg l -1 and was maximized from 0·5 to 1·0 mg l -1. In the medium with 1·0 mg l -1 CaSiO 3, they grew to a size larger than that of the greenhouse plants after 6 months in culture. The sensitivity of the growth of the silica bodies to the environmental concentration of silicon was then suggested to be a useful indicator for studying the uptake of silicon in plants.

Silicon Supplying Capacity of Paddy Soils and Characteristics of Silicon Uptake by Rice Plants in Cool Regions in Japan

Silicon Supplying Capacity of Paddy Soils and Characteristics of Silicon Uptake by Rice Plants in Cool Regions in Japan

Silicon accumulation and water uptake by wheat

Silicon (Si) content in cereal plants and soil-Si solubility may be used to estimate transpiration, assuming passive Si uptake. The hypothesis for passive-Si uptake by the transpiration stream was tested in wheat (Triticum aestivum cv. Stephens) grown on the irrigated Portneuf silt loam soil (Durixerollic calciorthid) near Twin Falls, Idaho. Treatments consisted of 5 levels of plant-available soil water ranging from 244 to 776 mm provided primarily by a line-source sprinkler irrigation system. Evapotranspiration was determined by the water-balance method and water uptake was calculated from evapotranspiration, shading, and duration of wet-surface soil. Water extraction occurred from the 0 to 150-cm zone in which equilibrium Si solubility (20°C) was 15 mg Si L−1 in the Ap and Bk (0–58 cm depth) and 23 mg Si L−1 in the Bkq (58–165 cm depth). At plant maturity, total Si uptake ranged from 10 to 32 g m−2, above-ground dry matter from 1200 to 2100 g m−2 and transpiration from 227 to 546 kg m−2. Silicon uptake was correlated with transpiration (Siup=−07+06T, r2=0.85) and dry matter yield with evapotranspiration (Y=119+303ET, r2=0.96). Actual Si uptake was 2.4 to 4.7 times that accounted for by passive uptake, supporting designation of wheat as a Si accumulator. The ratio of Si uptake to water uptake increased with soil moisture. The confirmation of active Si uptake precludes using Si uptake to estimate water use by wheat.

Uptake of Boron and Silicon by Barley Genotypes with Differing Susceptibilities to Boron Toxicity

We investigate in more detail the boron resistance mechanism by comparing boron uptake in three barley genotypes with differing susceptibilities to boron toxicity-whether differences in boron uptake were controlled by an active or a passive process were also examined. Furthermore because of several similarities in the transport characteristics of B(OH) 3 and Si(OH) 4 , the uptake of silicon by the genotypes was also compared

Silicon Uptake and Distribution in Agropyron smithii as Related to Grazing History and Defoliation

Silicon Uptake and Distribution in Agropyron smithii as Related to Grazing History and Defoliation

Effect of silicon on the growth of rice plant at different growth stages

Rice plants (Oryza sativa L. cv. Akebono) were cultured in Kimura B solution. The effect of silicon on plant growth and the characteristics of the uptake and distribution of silicon at different growth stages were studied from both aspects: the addition and removal of silicon during the vegetative, reproductive and ripening stages. When silicon was removed during the reproductive stage, the dry weights of straw (stem+leaf blade) and grain decreased by 20 and 50% respectively, compared with those of the plants cultured in the solution with silicon throughout the growth period. Conversely, when silicon was added during the reproductive stage, the dry weights of straw and grain increased by 243 and 30%, respectively, over those of the plants cultured in a solution devoid of silicon throughout the growth period. The effect of silicon on the dry weights of straw and grain was small when silicon was either added or removed during the vegetative and ripening stages. The percentage of filled spikelets remarkably increased or decreased when silicon was added or removed during the reproductive stage. The 1,000-grain weight was hardly influenced by the addition or removal of silicon regardless of the growth stage. About 66% of silicon in the whole plant and 70 to 75% of silicon in the leaf blades were absorbed during the reproductive stage. About 75% of silicon in the panicle was absorbed during the ripening stage although no beneficial effect was detected in this experiment. Forty to 50% of the silicon absorbed during the vegetative and reproductive stages was present in the leaf blades, whereas only 20 to 30% of silicon absorbed during the ripening stage was present in the leaf blades. Based on these results, it is concluded that the supply of silicon during the reproductive stage is most important for plant growth.

RELATIONSHIPS AMONG NITROGEN, SILICON, AND HEAVY METAL UPTAKE BY PLANTS

Because vegetative parts of grass species are generally high in Si, monocot and dicot plants were grown in steam-sterilized soil to further test the hypothesis that there is competition between N and Si for plant uptake. Silicon uptake by dicots is low, so the species tested in this study was not se

The uptake and transport of silicon by perennial ryegrass and wheat

In experiments with perennial ryegrass and wheat, silicon (Si) concentration in flowing solution culture was maintained constant at 0, 10 and 20 mgl−1 (ryegrass) or 0, 20 and 40 mgl−1 (wheat). Uptake and transport were measured in both species at frequent harvests over periods of up to 80 days. By the final harvests the initial differences in concentration between plants grown at high or low Si were largely eliminated. Much more Si was taken up by both species from the culture solution than was present in the transpiration stream. With ryegrass, the calculated cumulative amounts taken up through mass flow by plants grown at 10 or 20mgl−1 Si, represented less than 40 and 70 per cent, respectively, of the total Si uptake. Up to 94 per cent of the Si taken up by wheat was transported rapidly to the shoots; older leaves contained up to 11.8 per cent Si.

Physiological responses of Vaccinium vitis-idaea to high tissue concentrations of manganese

Photosynthetic rates, dry moss accumulation, leaf number per shoot, stem length, and tissue element concentrations were measured in Vaccinium vitis-idaea growing in tussock tundra at Toolik Lake, Alaska. Manganese concentrations of 6 800 – 12 300 μg/g dry mass in leaf tissue of V. vitis-idaea did not affect photosynthetic rates, dry mass, or leaf number when compared with plants containing 18–1500 μg manganese/g dry mass. Tissue analysis indicated possible substitution of manganese for magnesium and inhibition of uptake and (or) translocation of calcium, iron, manganese, silicon, and aluminum. High concentrations of calcium and the high correlation between manganese and silicon concentrations suggest that these elements may play a role in manganese tolerance observed in V. vitis-idaea.

The formation of titanium silicide by arsenic ion beam mixing and rapid thermal annealing

The reaction of titanium thin films with n+ doped single crystal silicon induced by As+ ion beam irradiation and subsequent rapid thermal annealing has been studied. Arsenic doping in the silicon substrate retards the thermal growth of silicide resulting in an incomplete conversion of the titanium into titanium disilicide during low temperature (∼600 °C) rapid thermal annealing under a nitrogen ambient. High energy As+ion beam irradiation (90–170 keV) prior to the rapid thermal annealing leads to intermixing of the titanium and silicon which, at sufficiently high energy and dosage, results in complete conversion of titanium to a silicide phase. Subsequent rapid thermal annealing of the ion beam irradiated samples induces further uptake of silicon into the silicide phase leading to the formation of the stable C-54 titanium disilicide phase. However, very little additional titanium consumption occurs during the thermal annealing. The silicide formed by the ion beam mixing process shows superior sheet resistance uniformity and has a smoother morphology compared to thermally grown silicide. The uniformity of the silicidation reaction by ion beam mixing also leads to superior n+p junction characteristics.

The population and production dynamics of benthic algae in an artificial recirculating hard-water stream

An artificial stream has been used to examine the population and production dynamics of benthic algae that grow in the hard-water, nutrient-rich streams of southern England. The channel, made of glass-reinforced plastic is 60 m in circumference and filled with flintsca. 40 mm in diameter. Water 0.3 m deep above the gravel was recirculated at 0.4 m s-1by an archimedean screw pump. Water was supplied from the aquifer at a rate of 4.2 m3h-1and left the channel from an overflow notch. The chemical composition of the inflow water was relatively constant so that differences between inflow and outflow could be directly related to biological and non-biological changes in the channel. Experiments in the dark showed that calcium carbonate precipitated, reducing calcium concentration and alkalinity to 80% of inflow values. Reactive phosphate precipitated to 28% of inflow concentrations. Preliminary experiments were done in the light between April and December 1976 and detailed experiments between April 1977 and July 1978. The initial colonization phase, in both 1976 and 1977, was dominated by diatoms. Chlorophyll densities increased by over 300-fold in 14 days in 1977. The change in cell numbers of four dominant species, over a 7 day period, confirmed doubling times of less than 2 days. Maximum densities of 500-600 mg chlam-2were reached 5 weeks after the dark covers had been removed. The biomass remained constant for the next 14 days and during this phase the rate of silicon uptake was 4.5 g m-2day-1. Substantial uptake was also recorded, while the biomass was declining, between the seventh and ninth weeks. Over a period of 60 days, 107 gSi m-2were taken up and photosynthetic studies indicated that 137 gC m-2has also been taken up. In terms of biomass this would correspond to 2.3-4.6 g chlam-2, whereas the maximum observed biomass was 0.5-0.6 g m-2. Loss of fine particulate material over 60 days was 0.0558 g of pigment per square metre and sedimentation into the lower layers of the gravel was 0.735 g of pigment per square metre. During weeks 10, 11 and 12 substantial quantities of silicon and phosphorus were released into the water and for a brief period calcium bicarbonate concentrations in the channel approached inflow concentrations. The diatoms of the initial colonization phase were succeeded by a lime-encrusted growth of blue-green and green algae (Lyngbya kützingii,Chamaesiphon polymorphusandGongrosira incrustans) with densities through the winter of 1977 of 200 mg chi a m -2.Cladophora glomeratadeveloped in the autumn of 1977 and its epiphytic algal flora was substantially different from the epilithic flora. Diatoms recurred in large numbers in the spring of 1978. In terms of biomass the principal diatoms wereAchnanthes minutissima,Fragilaria virescens,Gomphonema rhombicum,Meridion circulare,Nitzschia fonticolaandSynedra ulna. Regression analysis showed that suspended chlorophyll a concentration was not related to benthic algal biomass (estimated as chlorophyll a) but more closely related to benthic diatom volume or dissolved silicon concentration. The seasonal succession of algae in the channel was very similar to that which occurs in local streams. The initial colonization phase by diatoms bears a striking resemblance to the spring outburst of benthic diatoms in local streams. In the channel (and in natural streams, by inference) this succession cannot be controlled by changes in discharge, water velocity or chemical composition of the water. The onset of diatom growth in the spring in streams is probably largely controlled by light intensity. The absence of large numbers of insect larvae, until mid-April, probably allows the biomass-to develop. After April the impact of insect larvae on diatom populations may be considerable.

Effect of Nutritional Conditions on the Silicon Uptake by Rice Plants : Comparative Studies on the Silica Nutrition in Plants (Part 21)

Effect of Nutritional Conditions on the Silicon Uptake by Rice Plants : Comparative Studies on the Silica Nutrition in Plants (Part 21)