Growth promotion and an increase in cell wall extensibility by silicon in rice and some other Poaceae seedlings

The effect of silicon on organ growth and its mechanisms of action were studied in rice (Oryza sativa L. cv. Koshihikari), oat (Avena sativa L. cv. Victory), and wheat (Triticum aestivum L. cv. Daichino-Minori) seedlings grown in the dark. Applying silicon in the form of silicic acid to these seedlings via culture solution resulted in growth promotion of third (rice) or second (oat and wheat) leaves. The optimal concentration of silicon was 5–10 mM. No growth promotion was observed in early organs, such as coleoptiles or first leaves. In silicon-treated rice third leaves, the epidermal cell length increased, especially in the basal regions, without any effect on the number of cells, showing that silicon promoted cell elongation but not cell division. Silicon also increased the cell wall extensibility significantly in the basal regions of rice third leaves. These results indicate that silicon stimulates growth of rice and some other Poaceae leaves by increasing cell wall extensibility. Received: July 31, 2001 / Accepted: September 18, 2001     

碳/碳材料含硅羟基磷灰石涂层体外成骨细胞相容性研究

目的:成骨细胞在碳/碳复合材料表面羟基磷灰石涂层上有良好的长入,该实验在羟基磷灰石(hydroxyapatite HA)涂层中掺入硅后,研究成骨细胞对该涂层的生物活性,为临床骨科应用提供实验基础。方法:本研究采用化学液相气化沉积/水热法在碳/碳材料表面制备了含硅羟基磷灰石(silicon-hydroxyapatite Si-HA)涂层。在体外成骨细胞相容性的研究中,以HA涂层为对照,通过甲基噻唑基四唑(methylthiazolyl tetrazolium MTT)法测定细胞增殖反应和对细胞毒性反应,碱性磷酸酶(alkaline phosphatase ALP)测定细胞的分化,扫描电镜观察细胞生长形态,免疫荧光显影技术测定细胞的长入。结果:在HA涂层中引入硅后,Si-HA涂层和HA涂层在第2天、第4天的成骨细胞增殖实验表明前者的细胞长入数较后者多,两者的差异有统计学意义,而Si-HA涂层浸泡液中的ALP活性下降较HA涂层而言更明显,两者的差异有统计学意义,电镜扫描及荧光染色均提示在Si-HA涂层中成骨细胞的增值数更多。结论:在HA涂层中引入硅后,改变了涂层自身的晶体结构及表面电荷,同时诱导成骨细胞分泌胶原,使得成骨细胞更好的贴壁生长和增殖,成骨能力增加。在临床骨科植入物表面涂层改性上有很好的应用前景。     

Engineered Si(1 0 0) surfaces for the gas-phase anchoring of metal β-diketonate complexes

A synthetic strategy for the covalent anchoring of nickel β-diketonate complexes on Si(1 0 0) has been examined. Engineered Si(1 0 0) surfaces were prepared by the Si-grafting of 10-undecylenic acid methyl ester followed by hydrolysis of the ester to free the carboxylic functions suited for the anchoring of the Ni complex. Bis(pentane-2,4-dionate)Ni(II) was bonded to the functionalized surface from the gas phase by the exchange of the acetylacetonate ligand with the grafted acid. The surface density of the anchored Ni complex was controlled by tuning the surface concentration of carboxylic groups adopting a mixed monolayer of undecylenic acid and 1-decene used as a spectator spacer. The nickel decorated silicon surfaces were characterized by attenuate total reflectance infrared absorption spectroscopy (ATR-IRAS) and angle resolved X-ray photoelectron spectroscopy (AR-XPS).     

Silicon supplementation modulates antioxidant system and osmolyte accumulation to balance salt stress in Acacia gerrardii Benth

Experiments were conducted to investigate the role of silicon (Si, 2 mM potassium silicate - K₂SiO₃) in ameliorating the salinity (200 mM NaCl) triggered growth retardation, photosynthetic inhibition and the oxidative damage in Talh trees (Acacia gerrardii Benth). Salinity stress reduced length and dry biomass accumulation of root and shoot which were significantly improved by Si supplementation. Application of Si enhanced the synthesis of photosynthetic pigments including chlorophyll a, chlorophyll b, total chlorophylls and carotenoids resulting in greater photosynthetic activity measured in terms of net CO₂ assimilation. Stomatal conductance and transpiration rate were declined due to NaCl treatment and supplementation of Si ameliorated the negative impact of NaCl on these attributes and was significantly improved when applied to normal grown plants. Further, lipid peroxidation was more in NaCl stressed plants without Si as compared to those supplemented with Si. Si protected Talh trees from NaCl induced oxidative damage by improving the activity of antioxidant enzymes (SOD, POD, CAT, APX and GR) and the content of ascorbic acid. Accumulation of compatible osmolytes including proline and glycine betaine was increased due to Si supplementation leading to improved growth under saline conditions in addition Si supplementation mitigated the deleterious effects of NaCl on flavonoid content. More importantly Si supplementation prevented excess uptake of Na and also protected the ill effects of excess Na on the uptake and accumulation of K and Ca resulting in significant decline in Na/K ratio. In conclusion, Si mitigates the negative effects of NaCl in A. gerrardii by modifying nutrient uptake, osmolytes accumulation and up-regulating antioxidant system.     

Experimental investigation at CATANA facility of n-10B and p-11B reactions for the enhancement of proton therapy

The aim of the NEPTUNE (Nuclear process-driven Enhancement of Proton Therapy UNravEled) project is to investigate in detail both the physical and radiobiological phenomena that could justify an increase of the proton-induced cytogenetic effects in cells irradiated in presence of an agent containing natural boron.In this work, a double-stage silicon telescope coupled to different boron converters was irradiated at the CATANA proton therapy facility (INFN-LNS) for studying the proton boron fusion and the neutron boron capture reactions by discriminating secondary particles from primary protons.Different boron targets were developed by depositing boric acid, enriched with a higher than 99% content of ¹⁰B or ¹¹B, on a 50 µm thick PolyMethilMetacrylate (PMMA) substrate. The ¹⁰B target allows to evaluate the contribution of lithium and alpha particles produced by the boron neutron capture reaction triggered by secondary thermal neutrons, while the ¹¹B target is exploited for studying the effect of the p + ¹¹B → 3α nuclear reaction directly triggered by primary protons.Experimental results clearly show the presence of alpha particles from both the reactions. The silicon telescope is capable of discriminating, by means of the so-called “scatter plots”, the contribution of alpha particles originated by thermal neutrons on ¹⁰B with respect to the ones produced by protons impinging on ¹¹B. Although a reliable quantitative study of the alpha production rate has not been achieved yet, this work demonstrates that low energy and, therefore, high-LET particles from both the reactions can be measured.     

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. Received: 17 June 1998 / Accepted: 22 September 1998     

Impacts of silica-based defences in grasses on the feeding preferences of sheep

Grasses, which dominate many terrestrial ecosystems, sustain high densities of grazing mammals, so are of great economic and ecological importance. Traditionally, grasses are thought to be adapted to tolerate grazing rather than defend against it; however, silica deposited in the leaves of grasses has recently been shown to act as a feeding deterrent to invertebrate herbivores and small mammals. This study assesses whether silica is effective as a feeding deterrent to larger mammalian herbivores. We assess the impact of manipulated silica levels in five grass species on the feeding preferences of sheep both within and between grass species.Sheep feeding behaviour was driven by between-species differences in palatability. Hence, within a single species silica addition did not cause significant changes in feeding preference. However, there were significant differences in both the feeding preferences and bite rates between grass species, and these differences were much more marked when the grasses had been exposed to high levels of silica. The impacts that silica had on preference were least pronounced in palatable species (e.g. Poa annua) compared with less-palatable species (e.g. Brachypodium pinnatum and Festuca ovina). Sheep fed for longer, took more bites and had a higher bite rate on the grass species with the lowest leaf silica concentrations, namely P. annua.Sheep were less affected by silica defences than smaller, non-ruminant herbivores, but the changes in species preference rankings caused by silica suggest it may lead to changes in sward composition. Further, in species that are already relatively low in palatability, silica-induced reductions in bite rate could potentially reduce forage intake rates, with consequences for sheep performance.     

Silicification of auxospores in the araphid diatom Tabularia fasciculata (Bacillariophyta)

We report on auxospore wall structure and development in the araphid pennate diatom Tabularia fasciculata. Similar to most other pennates, these auxospores showed a typical bidirectional elongation, but unexpectedly bore no transverse perizonium, and with no detectable silicon during much of their expansion. Energy dispersive X-ray spectroscopy (EDS) analyses segregated auxospores into two types: (1) those containing no detectable silicon and (2) those with measureable amounts. Both types were of similar size. Silica precipitation began throughout the auxospore at or near maximal length, but initially was detectable in isolated regions throughout the structure. Following this initial condition, silicon was consistently detectable throughout auxospores of comparable size and corresponded to deposition of longitudinal perizonium (visible through the thin organic outer layer of the wall in some auxospores), followed by the deposition of the initial valves. Our results raise the question as to how the tubular shape of bidirectionally expanding auxospores up to ∼90 μm long is maintained in the absence of transverse siliceous elements restricting isodiametric expansion of the cell, which are present in all other known pennate auxospores and all but one other diatom. Our study is the first to systematically examine mineral elements of the auxospore wall analytically.     

Design and synthesis of silicon-containing tubulin polymerization inhibitors: Replacement of the ethylene moiety of combretastatin A-4 with a silicon linker

Silicon-containing combretastatin analogs were designed, synthesized and evaluated for stability and biological activities. Among them, compound 31 exhibited strong tubulin polymerization-inhibitory activity and very potent tumor cell growth-inhibitory activity (IC₅₀ = 0.007 μM) in MCF-7 cell proliferation assay. This compound also potently inhibited [³H]colchicine binding (90.7% inhibition at 3 μM). These activities were comparable to those of combretastatin A-4 (CA-4) (1). In addition, compound 31 was physico-chemically more stable than 1. These results suggest that a silicon linker can act as a bioisoster of a cis carbon–carbon double bond.