Auswahl der wissenschaftlichen Literatur zum Thema „Si-transporter“

Silicon (Si) has long been known to play a major physiological and structural role in certain organisms, including diatoms, sponges, and many higher plants, leading to the recent identification of multiple proteins responsible for Si transport in a range of algal and plant species. In mammals, despite several convincing studies suggesting that silicon is an important factor in bone development and connective tissue health, there is a critical lack of understanding about the biochemical pathways that enable Si homeostasis. Here we report the identification of a mammalian efflux Si transporter, namely Slc34a2 (also termed NaPiIIb), a known sodium-phosphate cotransporter, which was upregulated in rat kidney following chronic dietary Si deprivation. Normal rat renal epithelium demonstrated punctate expression of Slc34a2, and when the protein was heterologously expressed in Xenopus laevis oocytes, Si efflux activity (i.e., movement of Si out of cells) was induced and was quantitatively similar to that induced by the known plant Si transporter OsLsi2 in the same expression system. Interestingly, Si efflux appeared saturable over time, but it did not vary as a function of extracellular [Formula: see text] or Na+ concentration, suggesting that Slc34a2 harbors a functionally independent transport site for Si operating in the reverse direction to the site for phosphate. Indeed, in rats with dietary Si depletion-induced upregulation of transporter expression, there was increased urinary phosphate excretion. This is the first evidence of an active Si transport protein in mammals and points towards an important role for Si in vertebrates and explains interactions between dietary phosphate and silicon.

Silicon (Si) is known to alleviate many nutritional stresses. However, in Brassica napus, which is a highly S-demanding species, the Si effect on S deficiency remains undocumented. The aim of this study was to assess whether Si alleviates the negative effects of S deficiency on Brassica napus and modulates root sulfate uptake capacity and S accumulation. For this, Brassica napus plants were cultivated with or without S and supplied or not supplied with Si. The effects of Si on S content, growth, expression of sulfate transporter genes (BnaSultr1.1; BnaSultr1.2) and sulfate transporters activity in roots were monitored. Si supply did not mitigate growth or S status alterations due to S deprivation but moderated the expression of BnaSultr1.1 in S-deprived plants without affecting the activity of root sulfate transporters. The effects of Si on the amount of S taken-up and on S transporter gene expression were also evaluated after 72 h of S resupply. In S-deprived plants, S re-feeding led to a strong decrease in the expression of both S transporter genes as expected, except in Si-treated plants where BnaSultr1.1 expression was maintained over time. This result is discussed in relation to the similar amount of S accumulated regardless of the Si treatment.

Silicon (Si) is the second most abundant element in the earth crust constituting 27.7 per cent. The beneficial effects of Si includes mitigation of various forms of abiotic and biotic stresses. Rice (Oryza sativa), a typical Si accumulator, takes up Si actively in the form of silicic acid. There are three transporters involved in the uptake of Si viz, LSi1, LSi2 and LSi3. Influx transporter (LSi1) takes up silicic acid from soil solution and mediates its transport upto the exodermal layer of root system, followed by the efflux transporter (LSi2), which transports it across the aerenchyma. Further movement of Si to the aerial parts of the plant is mediated by another influx transporter, LSi6 and finally gets deposited as silica in the plant parts. Silicon present in soil solution as well as its deposition in plants helps in mitigating various stresses in rice. Si application during drought stress prevents compression of xylem vessels and thereby resulting in reduction of transpiration rate. Sufficient supply of Si stabilises the culms and serves to decrease the risk of lodging. Rice is sensitive to metal toxicities like Iron (Fe), Manganese (Mn) and Aluminium (Al). Si complexation with these metal ions decreases their translocation rate and reduces the toxic effects. Heavy metal toxicity due to accumulation of cadmium (Cd) and arsenic (As) can be alleviated through supplementation of Si. Si also ameliorates salt stress by decreasing Na uptake and its root-to-shoot translocation. Silicon deposition in plant parts provides a mechanical barrier against pathogens and pests. The plants supplied with Si produce phenolics and phytoalexins in response to fungal infection and cuticle-Si double layer act as a defence mechanism preventing pests. The key mechanisms of Si-mediated alleviation of stresses in rice include stimulation of antioxidants, complexation of toxic metal ions with Si, immobilization of toxic metal ions and compartmentation of metal ions within plants.

Copper (Cu) is an essential micronutrient for plants and is the a.i. in pesticides for some pathogens and algae. Elevated doses of Cu can cause toxicity in plants. While silicon (Si) is reported to alleviate the toxicity of some heavy metals, its role in reducing the symptoms induced by excess Cu is unclear. Therefore, the role of Si in plant response to Cu stress was investigated in arabidopsis [Arabidopsis thaliana (L.) Heyn.]. Based on plant symptoms (a reduction of leaf chlorosis as well as increased shoot and root biomass) and a reduction of phenylalanine ammonia lyase [PAL (EC 4.3.1.5), a stress-induced enzyme] activity in the shoot, Si was found to alleviate copper stress. Real-time reverse transcriptase-polymerase chain reaction analyses indicated that the RNA levels of two arabidopsis copper transporter genes, copper transporter 1 (COPT1) and heavy metal ATPase subunit 5 (HMA5) were induced by high levels of Cu, but were significantly decreased when Si levels were also elevated. Taken together, our findings indicate that Si addition can improve the resistance of arabidopsis to Cu stress, and this improvement operates on multiple levels, ranging from physiological changes to alterations of gene expression.

Background/Aims: Hyperuricemia is an independent risk factor for chronic kidney disease and cardiovascular disease. Here, we examined the combined protective effects of Chinese herbal formula Si-Wu-Tang and Er-Miao-San on hyperuricemia and renal impairment in rats. Methods: Rats were randomly divided into normal rats, hyperuricemic rats, and hyperuricemic rats orally administrated with benzbromarone (4.5 mg·kg-1·d-1), Si-Wu-Tang (3.78 g·kg-1·d-1) and Si-Wu-Tang plus Er-Miao-San (6.48 g·kg-1·d-1) for 4 weeks. Hyperuricemic rats were orally gavaged with adenine (0.1 g·kg-1·d-1) and potassium oxonate (1.5 g·kg-1·d-1) daily for 4 weeks. Serum uric acid, creatinine, total cholesterol (TCH), triglyceride and blood urea nitrogen (BUN) concentrations, as well as urinary uric acid and microalbuminuria were measured weekly. Serum xanthine oxidase (XOD) activity and renal histopathology were also evaluated. The renal expression of organic anion transporter 1 (OAT1) and organic anion transporter 3 (OAT3) was detected by western blot. Results: Si-Wu-Tang plus Er-Miao-San lowered serum uric acid, creatinine, triglyceride and BUN levels to a greater degree than did Si-Wu-Tang alone. Si-Wu-Tang plus Er-Miao-San ameliorated microalbuminuria and renal histopathology, as well as decreased serum TCH concentration and XOD activity in hyperuricemic rats. Combination of Si-Wu-Tang and Er-Miao-San also led to a greater increase in OAT1 and OAT3 expression than did Siwutang alone. Conclusion: Si-Wu-Tang and Er-Miao-San synergistically ameliorated hyperuricemia and renal impairment in rats through upregulation of OAT1 and OAT3.

Luminal glucose (Glc) concentrations in the small intestine (SI) are widely assumed to be 50-500 mM. These values have posed problems for interpreting SI luminal osmolality and absorptive capacity, Glc transporter Michaelis-Menten constants (Km), and the physiological role of active Glc transport and its regulation. Hence we measured luminal contents, osmolality, and Glc, Na+, and K+ concentrations in normally feeding rats, rabbits, and dogs. Measured Glc concentrations were compatible with the portion of measured osmolality not accounted for by Na+ and K+ salts, amino acids, and peptides. Mean SI luminal osmolalities were less than or equal to 100 mosmol/kg hypertonic. For animals on the most nearly physiological diets, SI Glc concentrations averaged 0.4-24 mM and ranged with time and SI region from 0.2 to a maximum of 48 mM. The older published very high values are artifacts of direct infusion of concentrated Glc solutions into the gut, nonspecific Glc assays, and failure to test for quantitative recovery or to centrifuge samples in the cold. By storing food after meals and releasing it between meals, rat stomach greatly damps diurnal fluctuations in quantity and osmolality of food reaching the SI and hence also damps fluctuations in absorption rates. These new values for luminal Glc have five important physiological implications: the problem of accounting for apparently very hypertonic SI contents in the face of high osmotic water permeability disappears; the effective Km of the SI Glc transporter is now comparable to prevailing Glc concentrations; the SI no longer appears to have enormous excess absorptive capacity for Glc; regulation of Glc transport by dietary intake now makes functional sense; and the claim that high luminal Glc concentrations permit solvent drag to become the major mode of Glc absorption under normal conditions is undermined.

Silicon is, besides oxygen, the most abundant element on earth. Only two taxa use this element as a major constituent of their skeleton, namely sponges (phylum Porifera) and unicellular diatoms. Results from combined cytobiological and molecularbiological techniques suggest that, in the demosponge Suberites domuncula, silicic acid is taken up by a transporter. Incubation of cells with the fluorescent silica tracer PDMPO [2-(4-pyridyl)-5-{[4-(2-dimethylaminoethylaminocarbamoyl)methoxy]phenyl}-oxazole] showed a response to silicic acid by an increase in fluorescence; this process is temperature-dependent and can be blocked by DIDS (4,4-di-isothiocyanatostilbene-2,2-disulphonic acid). The putative NBC (Na+/HCO3−) transporter was identified, cloned and analysed. The deduced protein comprises all signatures characteristic of those molecules, and phylogenetic analysis also classifies it to the NBC transporter family. This cDNA was used to demonstrate that the expression of the gene is strongly up-regulated after treatment of cells with silicic acid. In situ hybridization demonstrated that the expression of the sponge transporter occurs in those cells that are located adjacent to the spicules (the skeletal element of the animal) or in areas in which spicule formation occurs. We conclude that this transporter is involved in silica uptake and have therefore termed it the NBCSA {Na+/HCO3−[Si(OH)4]} co-transporter.

The effects of silicon (Si) on root development, mineral content, and expression of Si transporter genes in Euphorbia pulcherrima Willd. ‘Flame’, ‘Mable Bell’, ‘Green Star’, ‘Pink Bell’, and ‘Peach Bowl’ cultivars were investigated in this study. Stem cuttings in a propagation bench were drenched regularly with a solution containing either 0 (control) or 50 ppm of silicon (Si treatment) from potassium silicate (K2SiO3), with a 25 °C mean air temperature and 80% relative humidity (RH) under 70% shading. The results showed that the ‘Flame’ treated with Si had a significantly higher survival ratio as compared with that of the control (P ≤ 0.05) and that the Si treatment improved number of roots, length of longest root, fresh root weight, and dry root weight in all cultivars except ‘Mable Bell’. Supplementary Si increased the content of magnesium (Mg) and decreased the content of boron (B) and zinc (Zn) in the roots. The content of sulfur (S) in the shoots was increased by supplementary Si. The relative expression of Lsi1 and Lsi2 was higher in ‘Peach Bowl’, while it was lower in ‘Mable Bell’ and ‘Green Star’, which may be caused by the differing accumulation of Si in the shoot. Overall, supplementary Si had beneficial effects during cutting propagation of poinsettia cultivars, although these effects were cultivar-dependent.

Ingestion of carbohydrates from the small intestine is the major route of energy supply in animals. In mammals these functions develop both pre- and postnatally and are coordinated for the sucking period. In birds, the physiological requirements are different and hatchlings ingest diets rich in complex carbohydrates soon after hatching. The present study examined the ontogeny of intestinal carbohydrate uptake in the chicken. The expression of mRNA for a brush border enzyme, sucrase–isomaltase (SI), which is critical in disaccharide digestion, was determined, together with that of the Na–glucose transporter (SGLT)-1, which is the major apical glucose transporter, In addition, the homeobox gene cdx, which is involved in inducing SI expression in mammals was examined. It was found that the expression of cdxA mRNA and cdxA protein increased from day 15 of incubation until hatch, after which further changes were small. CdxA protein was shown to bind to the promoter region of SI in the chick indicating that cdxA is similar to the mammalian cdx2. The mRNA of SI was observed at 15 d incubation, increased from 17 d of incubation to a peak on day 19, decreased at hatch and had a further peak of expression 2 d post-hatch. In contrast, the mRNA of SGLT-1 was not detected until 19 d of incubation when a major peak of expression was observed followed by a decrease to low levels at hatch and small increases post-hatch. It appears that both SI and SGLT-1 mRNA are expressed before hatch in the chick, but the ontogeny of expression is controlled by different mechanisms.

Les effets du silicium (Si) et/ou de la proline sur l’amélioration de la tolérance à la contrainte saline ont été étudiés chez deux espèces de luzerne, Medicago sativa L. et M. truncatula Gaertn. Deux variétés marocaines de M. sativa L., Oued Lmalah (OL) et Demnate 201 (Dm) et une variété européenne NS Mediana ZMS V (NS Med) originaire de la Serbie ont été utilisées. Les expériences ont été menées aux différents stades de développement sous conditions contrôlées. Les résultats ont montré que la salinité réduit le taux de germination et la viabilité de l’embryon et inhibe la mobilisation des réserves des embryons en particulier chez la variété NS Med. Cette restriction de la germination est concomitante à un stress oxydant reflété par des fortes accumulations en malonyldialdehyde (MDA) et en peroxyde d’hydrogène (H2O2) et une toxicité ionique manifestée par un rapport K+/Na+ très réduit. Cependant, le traitement des graines par le Si induit une forte accumulation de la proline et améliore la germination, la viabilité des embryons et la mobilisation des réserves. Le Si induit également une forte activité de la catalase (CAT) et du superoxyde dismutase (SOD) et réduit la teneur en MDA et en H2O2. Au stade plante, la salinité réduit la croissance des plantes et la nodulation chez toutes les variétés étudiées. Cette restriction de la croissance est associée à une diminution significative de la teneur des feuilles en chlorophylles, de la fluorescence chlorophyllienne (Fv/Fm) et de la conductance stomatique. La salinité réduit la teneur des plantes en azote et en K+ et augmente celle en Na+. La comparaison entre les trois variétés ciblées montre que la variété européenne NS Med est significativement la plus affectée. L’apport exogène de Si ou de proline induit une accumulation significative des solutés compatibles telles que la proline, la glycine betaïne et les sucres solubles et améliore l’activité antioxydante de la SOD, la CAT, l’ascorbate peroxydase et la glutathionne réductase. Par rapport aux plantes non traitées, le Si améliore aussi la teneur relative en eau, réduit le niveau de stress oxydant et rétablit par conséquent la croissance ainsi que l’activité photosynthétique des plantes stressées. De même, chez la plante modèle M. truncatula, l’application de la proline et de Si module l’expression des gènes codant des enzymes du métabolisme de la proline telles que la Pyroline-5-carboxylate synthétase 1 (P5CS1), la P5CS2, l’Ornithine aminotransférase, la Proline déshydrogénase 1 et la P5C déshydrogénase ainsi que le gène Low silicon 2 codant un transporteur du Si. L’apport exogène de Si et/ou de proline montre des effets améliorateurs plus importants quand ces deux molécules sont appliquées séparément chez M. sativa, alors que l’application combinée des deux molécules est plus bénéfique pour M. truncatula. Nos résultats démontrent que l’apport exogène de proline et/ou du Si présente un intérêt évident pour le développement d’une agriculture durable. Le développement de fertilisants enrichis en proline ou Si est fortement recommandé pour améliorer la productivité des cultures sous contraintes environnementales
The effects of silicon (Si) and/or proline on the tolerance to salt stress were investigated in alfalfa Medicago sativa L. and Medicago truncatula Gaertn. Two Moroccan M. sativa varieties, Oued Lmalah (OL) and Demnate 201 (Dm), and a European M. sativa variety NS Mediana ZMS V (NS Med) originating from Serbia were used. Experiments were carried out at different stages of development. Results showed that salt stress reduced seed germination and embryo viability and inhibited reserve mobilization, particularly in the NS Med variety. The restricted germination is concomitant with an oxidative stress reflected by high levels of malonyldialdehyde (MDA) and hydrogen peroxide (H2O2) and ionic toxicity indicated by lower K+/Na+ ratio. However, Si supply induces a significant accumulation of proline and improves seed germination, embryo viability and reserve mobilization. Si also triggers high catalase (CAT) and superoxide dismutase (SOD) activities and reduces MDA and H2O2 contents. During plant growth, salinity reduces plant growth and nodulation in all of the varieties. Growth restriction is accompanied by a significant decrease in leaf chlorophyll content, chlorophyll fluorescence (Fv/Fm) and stomatal conductance. Salinity also reduces plant nitrogen and K+ and increases Na+. Among the three alfalfa varieties, the European variety NS Med is the most affected. Exogenous supply of Si and proline results in a considerable accumulation of some compatible solutes, such as proline, glycine betaine and soluble sugars together with an enhanced antioxidant enzyme activity, such as SOD, CAT, ascorbate peroxidase and glutathione reductase. This improved leaf relative water content, reduced oxidative stress and therefore restores growth and photosynthetic activity of salt-stressed plants. Similarly, using the model legume M. truncatula, the application of proline and Si modulates the expression of genes encoding enzymes of proline metabolism, such as Pyroline-5-carboxylate synthetase 1 (P5CS1), P5CS2, Ornithine aminotransferase, Proline dehydrogenase 1, and P5C dehydrogenase as well as Low silicon 2 gene encoding a silicon transporter. In conclusion, separate application of proline and Si is more beneficial for improving M. sativa salt tolerance while the combined application of the two molecules is beneficial for M. truncatula

The second-most common element in the crust of the earth is silicon, performs a variety of beneficial roles in soils and plants. It helps to reduce a variety of biotic (diseases and pest insects) and abiotic pressures (salt, drought and heavy metals).Si influences the heavy metal and metalloid uptake by plants through different mechanisms including (1) Si bioavailability in soil is influenced by biological factors, (2) by altering the soil's properties, (3) heavy metal co-precipitation, (4) heavy metals being changed into less solubility forms, (5) root architecturemodification, (6) controlling antioxidant enzymes, (7) gene expression that controls how wellheavy metals are absorbed by and transported to plants is regulated both up and down. In this chapter it is discussed about the various mechanisms involved in heavy metal and metalloid uptake by Silicon. The application of industrial by products (fly ash, steel slag etc.) decreased the conversion of soluble metals into insoluble metal silicates, phosphates, and hydroxides reduces the intake of heavy metals. Si application can reduce heavy metal bioavailability in soil. Silicon nanoparticles along with Pb-resistant microbes significantly reduced the Pb concentration in plants. Si application changes mineral composition of Fe plaque in rice root which decreases both shoot As and grain As. A significant decrease in Cd and Pb toxicity of wheat along with increased grain yield can be possible by the application of organic and inorganic silicon fertilisers. By preventing the production of low affinity cation transporter, silicon nanoparticles can decrease the uptake of Cd into rice grains and phloem (OsLCT1). Through decreased electrolytic leakage, lower levels of malondialdehyde and hydrogen peroxide, and increased antioxidant enzyme activity, si treatment reduces Cd toxicity in cotton. To assess the viability of using Si for the remediation of metalcontaminated soils, extensive field tests are needed

We have examined the developmental changes in composition, amount, and uptake of yolk nutrients (fat, protein, water and carbohydrates) and the expression ofnutrient transporters in the yolk sac membrane (YSM) from embryonic day 11 (Ell) to 21 (E21) and small intestine from embryonic day 15 (E15) to E21 in embryos from young (22-25 wk) and old (45-50 wk) Cobb and Leghorn breeder flocks. The developmental expression profiles for the peptide transporter 1 (PepTl), the amino acid transporters, EAAT3, CAT-1 and BOAT, the sodium glucose transporter (SGLTl), the fructose transporter (GLUT5), the digestive enzymes aminopeptidase N (APN) and sucraseisomaltase (SI) were assayed by the absolute quantification real time PCR method in the YSM and embryonic intestine. Different temporal patterns of expression were observed for these genes. The effect of in ovo injection of peptides (the dipeptide Gly-Sar, purified peptides, trypsin hydrolysate) on transporter gene expression has been examined in the embryonic intestine. Injection of a partial protein hydrolysate resulted in an increase in expression of the peptide transporter PepT2. We have initiated a transcriptome analysis of genes expressed in the YSM at different developmental ages to better understand the function of the YSM.