The absorption and transport of manganese by perennial ryegrass and white clover as affected by silicon

Summary The effects of added silicon on the absorption and transport of manganese in perennial ryegrass (an accumulator of Si) were determined and compared with those found in white clover (which has restricted Si uptake). The plants were grown in flowing solution culture in two experiments with Si in the nutrient solution maintained at 0, 10 or 20 mgl⁻¹ and Mn at 0.005 mgl⁻¹. By the final harvests, the plants contained concentrations of both Mn and Si that were comparable to those found in field-grown plants. In common with other findings, white clover had very much lower concentrations of Si in both shoots and roots than did ryegrass but there was no effect of Si treatment on the growth of either species. In both species, the concentrations of Mn were initially greater in roots than in shoots, but values in both plant parts decreased with time and by the final harvests, were similar. The rates of absorption of Mn by roots and its subsequent transport to shoots were also similar in both species. In contrast to findings for other species in other studies based on conventional solution culture, there was no effect of added Si on either absorption or transport of Mn in clover or ryegrass. It was therefore concluded that any effect of Si on the behaviour of Mn in plants must result from changes in distribution and partitioning within leaf tissues and cells.     

Influence of silicon and chitosan on growth and physiological attributes of maize in a saline field

Soil salinity is the main constraint for crop productivity in many parts of the world. Application of silicon (Si) and chitosan (Chi) can improve crop growth under saline soil conditions. The current study was aimed to examine the effects of Si and Chi on mitigation of salinity, morphological and physiological attributes as well as the antioxidant system of maize (Zea mays L.) under saline soil conditions. A field experiment was conducted that comprised of nine treatments as follows: (i) Control (no amendment), (ii) Silicon 40 kg ha⁻¹ (Si1), (iii) Chitosan 15 kg ha⁻¹ (Chi1), (iv) Si1 + Chi1, (v) Silicon 80 kg ha⁻¹ (Si2), (vi) Chitosan 30 kg ha⁻¹ (Chi2), (vii) Si2 + Chi2, (viii) Si1 + Chi2 and (ix) Si2 + Chi1. Application of Si and Chi substantially improved the morphological and physiological attributes as well as antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) of maize plants, and combined application of Si and Chi was more effective when compared with Si and Chi treatments separately. Membrane stability index was improved by 25%, relative water content by 26%, chlorophyll a by 69% and b by 56% with combined application of Si and chitosan (Si2 + Chi2) compared with control. The SOD, POD and CAT increased by 36%, 38% and 65% with Si2 + Chi2 compared with control. The results suggest that Si and Chi application is the possible option for alleviating salinity stress in maize plant. Further research is suggested to examine Si and Chi effects on various crop''s growth.     

The effect of silica exposure on the risk of lung cancer: A dose-response meta-analysis

BackgroundThe relationship between silica and the risk of developing lung cancer has been established in previous literature, but how much the level of exposure to silica can increase the risk of lung cancer is a question that has been addressed in this review.MethodsThree electronic databases, including MEDLINE, Scopus, and Web of Science were searched for relevant literature. For the dose-response relationship between exposure to silica and developing lung cancer, we performed a meta-analysis using the random-effects model. For each level of exposure, we calculated the overall risk ratio (RR) with 95% confidence intervals (CI).ResultsNineteen studies were included in the meta-analysis. There was a positive and significant increasing dose-response trend between silica exposure and the risk of developing lung cancer as follows: < 0.50 mg/m³ 1.14 (95% CI: 1.05, 1.23; I² = 79%), 0.50–0.99 mg/m³ 1.34 (95% CI: 1.05, 171; I² = 45%), 1.00–1.99 mg/m³ 1.14 (95% CI: 1.00, 1.30; I² = 70%), 2.00–2.99 mg/m³ 1.47 (95% CI: 1.05, 2.06; I² = 57%), 3.00–3.99 mg/m³ 1.44 (95% CI: 0.99, 2.11; I² = 58%), and ≥ 4.00 mg/m³ 1.64 (95% CI: 1.20, 2.24; I² = 88%). The heterogeneity across studies was mild to moderate.ConclusionsThe presence of a dose-response relationship favors the causal relationship between exposure to silica and developing lung cancer.     

The uptake and transport of silicon by perennial ryegrass and wheat

Summary 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.     

Synthesis and structural characterization of a pyridyl-substituted cyclodisilazane [(6-Me-Apy)2(μ-SiMe)2]; (6-Me-ApyH2=6-methyl-2-amino-pyridine)

Treatment of 6-Me-ApyH₂ (6-methyl-2-amino-pyridine) with one equivalent of nBuLi followed by addition of 0.5 equivalents of Cl₂SiMe₂ unexpectedly yields the cyclodisilazane [(6-Me-Apy)₂(μ-SiMe)₂]. [(6-Me-Apy)₂(μ-SiMe)₂] was characterised by ¹H, ¹³C and ²⁹Si NMR and IR spectroscopy, elemental analysis and X-ray crystallographic methods. The X-ray structure reveals a dinuclear compound having a four-membered Si₂N₂ core with coplanar aromatic rings.     

Imaging of chemiluminescent reactions in mesoscale silicon-glass microstructures

Chemiluminescent reactions in mesoscale analytical structures (chips) containing micrometer-sized interconnecting channels and chambers (pL-nL total volume) were imaged. The chips were fabricated by bonding Pyrex glass to etched pieces of silicon using a high-temperature diffusive bonding technique. In initial experiments light emission from an enhanced chemiluminescent horseradish peroxidase reaction and from a peroxyoxalate reaction contained in straight channels (300 μm wide × 20μ deep; volume 70.2 nL) and open chambers (812 μm wide, 400 μm deep, 5.2 mm long) linked by channels (100μm wide, 20 μm deep) to an exit and entry port were studied using a specially modified microplate holder and an Amerlite microplate luminometer. Light emission from more complex structures (two chambers interconnected by a branching channel 100 μm wide, 20 μm deep) filled with a solution containing alkaline phosphatase, Emerald, and CSPD^TM was imaged using a Photometrics Star 1 CCD camera. Detailed investigation of the detection and spatial resolution of the signal was performed on a Berthold Luminograph LB 980 using both the enhanced chemiluminescent horseradish peroxidase reaction and a peroxyoxalate reaction. We successfully resolved light emission from silicon structures with dimensions 100 μm wide and 20 μm deep. These simple silicon structures served as models for more complex designs that will be used for simultaneous multi-analyte assays in which an imaging system resolves and quantitates light emission from different locations on a silicon-glass analytical device.     

The pH dependence of siliconiron interaction in rats

A 2 x 2 x 3 factorial experiment was conducted to study the pH dependence of a silicon-iron interaction in vivo. The dietary treatments used in the factorial design were the following (mg/kg of diet): silicon, 0 and 500; iron, 35 and 187; acid-base, ammonium chloride as 0.5% of total diet (acidic), sodium bicarbonate as 1.0% of total diet (basic), or no supplementation of acid or base (control). The supplementation of 500 mg silicon/kg of diet increased plasma-iron concentration in rats fed the acidic or control diets, but not in rats fed the basic diet. A high dietary-iron level suppressed copper absorption and utilization and subsequently imposed a negative effect on its own utilization. An increase in the plasma total-cholesterol concentration caused by high dietary-iron level was likely a consequence of the antagonistic effect of iron on copper absorption and utilization. The use of cupric sulfate pentahydrate as the dietary-copper source in this study resulted in plasma copper concentrations that were approximately twice those obtained in a related study using cupric carbonate. Also, a 42% coefficient of variation (C.V.) for plasma-copper concentrations of rats fed cupric sulfate in this study was greatly reduced from the C.V. = 108% previously associated with the dietary cupric carbonate.     

Effect of silicon dioxide on expression of poly (ADP-Ribose) polymerase mRNA and protein

Silicon dioxide induces acute injury and chronic pulmonary fibrosis. International Agency for Research on Cancer (IARC) listed it as a human carcinogen in 1996. However, the molecular mechanisms to induce cancer are not understood yet. The content of poly (ADP-ribose) polymerases (PARP) mRNA and protein in Hela cells treated with concentrations of silicon dioxide up to 400 μg/ml was determined by real-time fluorogenetic quantitative PCR (RQ-PCR) and immunofluorescence assay, respectively. MTT assay was used to determine cell viability. The results showed that viability at 400 μg/ml silica was significantly decreased but not at lower concentrations. The protein content of γ-H2AX in silica-treated group was significantly higher than the controls. The PARP mRNA and protein levels were significantly reduced with a dose response manner from the lowest silicon dioxide level. Our findings suggested that silicon dioxide increased the expression of γ-H2AX and inhibited the expression of PARP mRNA and protein in Hela cells.     

Improving noise resistance of intrinsic rhythms in a square-wave burster model

The square-wave burster (Wang and Rinzel, 2003) is a class of autonomous bursting cells that share a bifurcation structure. It is known that this class of cells is involved in the generation of various life-supporting rhythms. In our research to realize an electronic circuit that mimics the rhythm generating mechanism in the square-wave burster, our circuit experimentally exhibited severe fluctuations in its rhythmic activity. We have found a noise-sensitive region in the phase portrait of the ideal model and have proposed modifications of the model that can reduce this fluctuation. A possible modification to ionic-conductance neuron models (Kohno and Aihara, 2011) was inspired by them. This modification, however, cannot be applied to a group of square-wave bursters, including the Butera–Rinzel–Smith model (0010 and 0050), which is a model of the pre-Bötzinger complex bursting neuron that plays a crucial role in the generation of respiration rhythms, because this modification premises that the slow dynamics originates from an activation gate variable of a hyperpolarizing ionic current. However, in some square-wave bursters, they are controlled by an inactivation gate variable of a depolarizing ionic current. In this study, we proposed a similar modification with a completely different mechanism that can be applied to this group of square-wave bursters. In the presence of noises, the modified Butera–Rinzel–Smith model can generate rhythmic activity that is more stable and similar to biological observations than the original model. The mechanisms underlying this modification are explained with noisy bifurcation diagrams.