Transport of Ferrocyanide by Two Eucalypt Species and Sorghum

The wastes from some industrial processes and the tailings from gold mining contain elevated concentrations of cyanide, which reacts with iron in the media to form iron cyanide complexes. This research examined the transport and possible metabolism of ferrocyanide by two native Australian trees, blue mallee and sugar gum, and by sorghum. Hydroponic studies using ¹⁵N-labeled ferrocyanide showed that both tree species transported ferrocyanide into roots and displayed significant increases in ¹⁵N enrichment and concentration with no evidence of phytotoxicity. A subsequent experiment with blue mallee and membrane-transport inhibitors showed that ¹⁵N enrichment was significantly inhibited in the presence of the protonophore carbonyl cyanide m-chlorophenylhydrazone, suggesting that ferrocyanide uptake is mediated partly by H⁺-symporters. A study of the time dependence of ¹⁵N translocation showed a rapid equilibration of ¹⁵N from ferrocyanide in the root of blue mallee, accompanied by a slow increase in shoot ¹⁵N, suggestive of the metabolism of ferrocyanide in plant roots. A similar experiment with sorghum showed a more rapid translocation of ¹⁵N, suggesting that the transport and/or metabolism of ferrocyanide by roots of this species may differ. The results offer additional incentive for the use of these species as vegetative cover over cyanidation wastes and for cyanide phytoremediation.     

Nitrogen supply and cyanide concentration influence the enrichment of nitrogen from cyanide in wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L.)

Cyanide assimilation by the β‐cyanoalanine pathway produces asparagine, aspartate and ammonium, allowing cyanide to serve as alternate or supplemental source of nitrogen. Experiments with wheat and sorghum examined the enrichment of ¹⁵N from cyanide as a function of external cyanide concentration in the presence or absence of nitrate and/or ammonium. Cyanogenic nitrogen became enriched in plant tissues following exposure to ¹⁵N‐cyanide concentrations from 5 to 200 µm , but when exposure occurred in the absence of nitrate and ammonium, ¹⁵N enrichment increased significantly in sorghum shoots at solution cyanide concentrations of ≥50 µm and in wheat roots at 200 µm cyanide. In an experiment with sorghum using ¹³C¹⁵N, there was also a significant difference in the tissue ¹³C:¹⁵N ratio, suggestive of differential metabolism and transport of carbon and nitrogen under nitrogen‐free conditions. A reciprocal ¹⁵N labelling study using KC¹⁵N and ¹⁵NH₄⁺ and wheat demonstrated an interaction between cyanide and ammonium in roots in which increasing solution ammonium concentrations decreased the enrichment from 100 µm cyanide. In contrast, with increasing solution cyanide concentrations there was an increase in the enrichment from ammonium. The results suggest increased transport and assimilation of cyanide in response to decreased nitrogen supply and perhaps to ammonium supply.     

Parameter estimation of a plant uptake model for cyanide: application to hydroponic data

A plant uptake model is applied to describe free cyanide and ferrocyanide transport and fate in willow (Salix eriocephala var. Michaux) grown in hydroponics. The model is applied to experimental data to determine best-fit parameter values, their associated uncertainty, and their relative importance to field-scale phytoremediation applications. The fitted model results, using least-squares optimization of the observed log concentrations, indicate that free cyanide volatilization from leaf tissue and free cyanide cell wall adsorption were negligible. The free cyanide maximum uptake rate and assimilate (noncyanide 15N) first-order leaf loss rate were the only coefficients that significantly affected the model goodness of fit and were concurrently sensitive to data uncertainty in the parameter optimization. Saturation kinetics may be applicable for free cyanide uptake into plants, but not for ferrocyanide uptake, which may occur via preferential protein-mediated or inefficient transpiration stream uptake. Within the free cyanide system, the relative magnitudes of the saturation uptake parameters and the demonstration of an active role for plants in uptake relative to transpiration suggest the potential importance of preferential diffusion through the cell membranes as reported in the literature, rather than protein-mediated uptake. The fitted 13-parameter model matched the observed data well except for the predicted stem and leaf tissue assimilate concentrations, which were significantly underestimated, particularly in the free cyanide system. These low predicted values, combined with the slightly underestimated solution free cyanide removal, suggest that noncyanide 15N redistribution in phloem should be considered.     

柳树对亚铁氰化物的吸收、代谢及其毒性研究

为探明亚铁氰化物在植物体内的迁移、转化及对植物的毒性作用,以长出新根须和嫩叶的垂柳(SalixbabylonicaL.)枝条为材料,在自行设计的250ml生物反应器中生长192h,培养温度为24.0±1℃,亚铁氰化物水溶液的浓度分别为52.99,105.98,211.95和317.93mgCNL-1。结果表明:(1)低浓度实验组(52.99mgCNL-1)水溶液中10.85%的亚铁氰化物被植物吸收,随着浓度的升高吸收到植物体内的亚铁氰化物的比例(%)依次递减,但是统计学分析显示各实验组单位体重(湿重)的植物吸收亚铁氰化物的量无显著性差异;(2)在植物的各个部位都能检测到微量的亚铁氰化物,表明亚铁氰化物通过植物的蒸腾作用在植物体内的迁移。由于没有检测到在气态下的总氰化物,表明植物的蒸腾作用没有将亚铁氰化物释放到大气中;(3)尽管植物吸收到体内的亚铁氰化物是有限的,但物质平衡实验证明其在植物体内迁移的过程中超过96%的都能被植物有效转化;(4)所用的4种亚铁氰化物浓度在192h内没有对柳树产生毒性作用。因此认为:依据亚铁氰化物在水溶液→植物→空气系统内的迁移和转化,亚铁氰化物的植物修复是可能的。     

Development of a plant uptake model for cyanide

A model for cyanide species uptake by willow (Salix eriocephala L. var. Michaux) was developed to interpret data from hydroponic experiments quantitatively. While the potential for cyanide phytoremediation has been demonstrated modeling will aid in determining plant processes that contribute to cyanide transport and metabolism in willow and will target specific physiological parameters for field-scale phytoremediation design and optimization. The objective of the model development was to gain insight into the relative role of different processes with respect to dissolved free and iron-complexed cyanide transport and assimilation in plants and to determine rates at which these processes occur within the willow plant under the experimental conditions. A physiologically-based model describing plant uptake, transport, and metabolism of cyanide species was developed to reflect the processes that influence the movement of cyanide into and throughout the plant. Plant compartmentalization (root, stem, and leaf) corresponded to the level of detail in the data collected via hydroponic experiments. Inclusion of more detailed intra- and intercellular processes would create a model inconsistent with the macroscale nature of the data. Mass balances around each compartment were developed via kinetic representations for the mass transfer processes and were combined to form a model describing the fate of cyanide species within plant-water systems.     

Effect of temperature on the uptake and metabolism of cyanide by weeping willows

Plants' uptake and metabolism of cyanide in response to changes in temperature was investigated. Pre-rooted weeping willows (Salix babylonica L.) were exposed to hydroponic solution spiked with potassium cyanide for 2-3 d. Ten different temperatures were used, ranging from 11 degrees C to 32 degrees C. Cyanide in water, plant tissue, and air was analyzed spectrophotometrically. The results revealed that significant amounts of the applied cyanide were removed from the aqueous solutions in the presence of plants. Small amounts of free cyanide were detected in plant materials in all treatments, but there was no clear trend that showed an increase or decrease in the accumulation in plant material with temperature. The highest cyanide metabolism rate for weeping willows was found at 32 degrees C with a value of 2.78 mg CN/(kg x d), whereas the lowest value was 1.20 mg CN/(kg x d) at ll degrees C. The temperature coefficient, Q10, which is the ratio of metabolism rates at a 10 degrees C difference, was determined for weeping willows to be 1.46. In conclusion, changes in temperature have a substantial influence on the uptake and metabolism of cyanide by plants, but cyanide accumulation does not increase with temperature.     

Physiologically based pharmacokinetic modeling of hydrogen cyanide in humans following the oral administration of potassium cyanide and cyanogenic glycosides from food

Abstract

Cyanogenic glycosides (CGs) are commonly found in some edible plants and seeds. After ingestion, CGs can release toxic hydrogen cyanide (HCN) in humans. At present, unfortunately, there is no tool capable of predicting the cyanide concentration in human blood and organs following oral administration of CG-containing food. The aim of this study was to develop a physiologically based pharmacokinetic (PBPK) model of cyanide following the ingestion of CG-containing food in humans. To develop this model, pharmacokinetic data concerning cyanide concentration levels in humans exposed to potassium cyanide (KCN) and CG-containing foods (persipan paste, linseed, cassava, and bitter apricot kernels) were obtained from published data. This study created a model structure consisting of four organ compartments including the lungs, kidneys, liver, and slowly perfused tissues by employing Berkeley Madonna software to extract three unknown parameters including the maximum velocity of rhodanese, the absorption rate constant, and the bioavailability for oral administration of KCN and the four CG-containing foods (equivalent a 6.8?mg dose of cyanide). The model was then validated by comparing the simulated results for the concentration-time courses of cyanide levels in venous blood with data from two clinical studies covering the oral administration of KCN and linseed at three other doses.     

Removal of Cyanide Contaminants from Rhizosphere Soil

Cyanide and cyanide-containing compounds from anthropogenic sources can be an environmental threat because of their potential toxicity. A remediation option for cyanide-contaminated soil may be through the use of plants and associated rhizosphere microorganimsms that have the ability to degrade cyanide compounds. Cyanogenic plant species are known to produce cyanide, but they also have the ability to degrade these compounds. In addition, the presence of these plants in soil may result in an increase in cyanide degrading microorganisms in the rhizosphere. Two cyanogenic species (Sorghum bicolor and Linum usitassium) and a noncyanogenic species (Panicum virgatum) were selected for a 200-day phytoremediation study to assess their potential use for removal of cyanide from soil. For both cyanogenic species, approximately 85% of the iron cyanide in soil was removed, whereas very little iron cyanide was removed in the unvegetated control or in the presence of Panicum virgatum. In addition, the activity of microbial communities in the rhizosphere of cyanogenic plants was higher than in cyanide-contaminated soil from unvegetated soil.     

The β‐cyanoalanine synthase pathway: beyond cyanide detoxification

Production of cyanide through biological and environmental processes requires the detoxification of this metabolic poison. In the 1960s, discovery of the β ‐cyanoalanine synthase ( β ‐CAS) pathway in cyanogenic plants provided the first insight on cyanide detoxification in nature. Fifty years of investigations firmly established the protective role of the β ‐CAS pathway in cyanogenic plants and its role in the removal of cyanide produced from ethylene synthesis in plants, but also revealed the importance of this pathway for plant growth and development and the integration of nitrogen and sulfur metabolism. This review describes the β ‐CAS pathway, its distribution across and within higher plants, and the diverse biological functions of the pathway in cyanide assimilation, plant growth and development, stress tolerance, regulation of cyanide and sulfide signalling, and nitrogen and sulfur metabolism. The collective roles of the β ‐CAS pathway highlight its potential evolutionary and ecological importance in plants.     

Molecular interaction of acrylonitrile and potassium cyanide with rat blood

The interaction of acrylonitrile (VCN) with rat blood has been investigated at the molecular level in an attempt to understand the possible mechanism of its toxicity. The results obtained were compared to those with potassium cyanide (KCN), a compound known to liberate cyanide (CN^?) in biologic conditions. The radioactivity derived from K¹⁴CN was eliminated faster than that from [1-¹⁴C]VCN. Up to a maximum of 94% of ¹⁴C from VCN in erythrocytes was detected covalently bound to cytoplasmic and membrane proteins, whereas 90% of the radioactivity from KCN in erythrocytes was found in the heme fraction of hemoglobin. Determination of specific activity showed that binding occurred more in vivo than in vitro which indicated that the VCN molecule was bioactivated inside erythrocytes. These results indicate that KCN interacts mainly through CN^? liberation and binding to heme, whereas VCN, which binds to cytoplasmic and membrane proteins, may cause damage to red cells by mechanisms other than release of CN^?.     

The interaction of defoliation and nutrient uptake in Sporobolus kentrophyllus,a short-grass species from the serengeti plains

Summary Sporobolus kentrophyllus, a grazing-tolerant C₄ grass from the southeastern Serengeti Plains, was grown in solution culture to examine the effects of clipping on the uptake, preference and subsequent transport of varying nitrogen forms. Clipping reduced offtake mass, crown mass ane root mass, resulting in a 58% decline in plant mass. Proportional biomass allocation to roots decreased with clipping, while tillering rates increased. Clipping also increased the nitrogen concentrations of all tissues, and plant nitrogen uptake (nitrogen accumulated throughout the experiment per gram root). The ¹⁵N concentrations (% atom excess) of all tissues were higher in clipped compared with unclipped plants, and the average ¹⁵N uptake rate of clipped plants was twice that of unclipped plants. The relative ¹⁵N allocation to aboveground mass, a measure of canopy sink strength, was higher in clipped plants. Plants fed ¹⁵N-ammonium or ¹⁵N-nitrate during the ¹⁵N pulse experiment had greater ¹⁵N tissue concentrations compared with urea-fed plants, and ¹⁵N uptake rates were higher in ammonium-fed and nitrate-fed plants, compared with urea-fed plants. The relative magnitudes of these differences were higher when plants were clipped. Clipped plants had higher uptake rates for potassium, phosphorus and sodium, while differences between clipping treatments for calcium, iron, and magnesium were indistinguishable. Rapid uptake rates for species on the southeastern Serengeti plains, particularly during grazing periods, have important implications for nutrient cycling in this system.     

Ethylene induced cyanide resistant respiration in orchid petal cells

Respiration of isolated Aranda orchid petal cells increased markedly after cut flowers were treated with ethylene. An increase in respiration was observed 15 to 20h after treatment which was further enhanced in the presence of oxygen and ethylene. Ethylene induces the development of a cyanide resistant pathway in fully opened orchid flower tissues where the cyanide resistant capacity is negligible. However, there appears a shift back to the cyanide sensitive pathway some time after induction.     

Degradation of ferrous(II) cyanide complex ions by Pseudomonas fluorescens

Degradation of ferrous(II) cyanide complex (ferrocyanide) ions by free cells of P. fluorescens in the presence of glucose and dissolved oxygen was investigated as a function of initial pH, initial ferrocyanide and glucose concentrations and aeration rate in a batch fermenter. The microorganism used the ferrocyanide ions as the sole source of nitrogen. The ferrocyanide biodegradation rate was 30.7 mg g⁻¹ h⁻¹ under the conditions of initial pH: 5, stirring rate: 150 rpm, aeration rate: 0.15 vvm, initial ferrous(II) cyanide complex ion and glucose concentrations: 100 mg l⁻¹ and 0.465 g l⁻¹, respectively. The culture utilized glucose as the main substrate following the non-competitive toxic component inhibition model in the presence of 100 mg l⁻¹ initial ferrous(II) cyanide complex ion concentration. The inhibition of ferrous(II) cyanide complex ions as a secondary substrate began at very low concentrations. A mathematical model, based on non-competitive substrate inhibition was used to describe the inhibitory effect of ferrous(II) cyanide complex ions on the growth of microorganism and the best fitted model parameters were determined by non-linear regression techniques.     

Biological degradation of cyanide compounds

Cyanide compounds are produced as waste products of a number of industrial processes and several routes for their removal from the environment are under investigation, including the use of biodegradation. The most recent developments in this area have come from studies of the hydrolytic and oxidative pathways for biodegradation and the conditions that affect their activity. The biodegradation of cyanide under anaerobic conditions has also recently demonstrated the feasibility for concomitant biogas generation, a possible economic benefit of the process. Significant advances have been reported in the use of plants for the phytoremediation of cyanide compounds and evidence for the biodegradation of thiocyanate and metal-cyanide complexes has become available. Despite these advances, however, physical and economic factors still limit the application of cyanide biodegradation, as do competing technologies.     

The iron component of sodium nitroprusside blocks NMDA-induced glutamate accumulation and intracellular Ca2+ elevation

These studies were designed to compare the effects of nitric oxide (NO) generating compounds with those of several iron containing, compounds which do not generate NO on glutamate receptor function. Stimulation of primary cultures of cerebellar granule cells with N-methyl-D-aspartate (NMDA) or kainate results in the elevation of intracellular calcium ([Ca²⁺]_i) and cGMP and the release of glutamate. The iron containing compounds, sodium nitroprusside (SNP), potassium ferrocyanide (K₄Fe(CN)₆) and potassium ferricyanide (K₃Fe(CN)₆) decrease the NMDA-induced release of glutamate. SNP is the only compound of the above 3 agents which generates NO. A non-iron, NO generating compound, S-nitroso-N-acetylpenicillamin (SNAP), has no effect on the NMDA-induced glutamate release. Potassium ferrocyanide (Fe II), but not potassium ferricyanide (Fe III), blocks NMDA-induced cGMP elevations after 3 min exposure times. This contrasts with the NO generating compounds (both SNP and SNAP) which elevate cGMP levels. Furthermore, both potassium ferrocyanide (Fe II) and SNP (Fe II) suppress the elevation of [Ca²⁺]_i induced by NMDA but neither potassium ferricyanide (Fe III) nor SNAP are effective in this regard. These effects are also independent of cyanide as another Fe II compound, ferrous sulfate (FeSO₄) is also able to suppress NMDA-induced elevations of [Ca²⁺]_i SNP was unable to suppress kainate receptor functions. Collectively, these results indicate that Fe II, independently of NO, has effects on NMDA receptor function.     

Mechanism of cyanide inhibition of Phloem translocation

Petiolar application of potassium cyanide inhibited ¹⁴C-assimilate translocation without affecting source leaf photosynthesis or phloem loading of sucrose in Phaseolus vulgaris. The inhibition of transport was correlated with disruption of the structural integrity of the sieve tubes (sieve pore blockage) rather than impairment of a metabolic process in the translocation path driving translocation.     

Organ-distribution of the metabolite 2-aminothiazoline-4-carboxylic acid in a rat model following cyanide exposure

The reaction of cyanide (CN^?) with cystine to produce 2-aminothiazoline-4-carboxylic acid (ATCA) is one of the independent detoxification pathways of cyanide in biological systems. In this report, in vivo production of ATCA and its distributions in plasma and organs were studied after a subcutaneous sublethal dose of 4?mg/kg body weight potassium cyanide (KCN) administration to rats. At this sublethal dose of KCN, ATCA concentration was not significantly increased in the plasma samples, however, it was found significantly increased in liver samples. These results suggested that ATCA might not be a good diagnostic biomarker in plasma for sublethal cyanide exposure; however, liver could serve as the right organ for the detection of ATCA in post-mortem examinations involving cyanide exposure in military, firefighting, industrial and forensic settings.     

15N NMR studies of the binding of 15N-labeled cyanide to various hemoglobins in intact erythrocyte.

¹⁵N-labeled cyanide binding to methemoglobins in intact erythrocytes has been studied by ¹⁵N NMR. The addition of C¹⁵N^? to human and dog hemoglobins in erythrocyte afforded hyperfine-shifted two ¹⁵N signals due to the C¹⁵N bound to ferric iron of the different heme-units. Single and three distinct signals were observed for rat and rabbit hemoglobins in erythrocyte. These C¹⁵N resonance positions are sensitive both to the structural difference in the hemoglobin subunits and to the variety of the animal sources. The C¹⁵N spectral difference between solution and intact hemoglobin cyanide is also discussed in relation to a possible change in the intra- and extracellular pH values.     

Archean geochemistry of formaldehyde and cyanide and the oligomerization of cyanohydrin

The sources and speciation of reduced carbon and nitrogen inferred for the early Archean are reviewed in terms of current observations and models, and known chemical reactions. Within this framework hydrogen cyanide and cyanide ion in significant concentration would have been eliminated by reaction with excess formaldehyde to form cyanohydrin (glycolonitrile), and with ferrous ion to form ferrocyanide. Natural reactions of these molecules would under such conditions deserve special consideration in modeling of primordial organochemical processes.As a step in this direction, transformation reactions have been investigated involving glycolonitrile in the presence of water. We find that glycolonitrile, formed from formaldehyde and hydrogen cyanide or cyanide ion, spontaneously cyclodimerizes to 4-amino-2-hydroxymethyloxazole. The crystalline dimer is the major product at low temperature (0 °C); the yield diminishes with increasing temperature at the expense of polymerization and hydrolysis products. Hydrolysis of glycolonitrile and of oxazole yields a number of simpler organic molecules, including ammonia and glycolamide. The spontaneous polymerization of glycolonitrile and its dimer gives rise to soluble, cationic oligomers of as yet unknown structure, and, unless arrested, to a viscous liquid, insoluble in water.A loss of cyanide by reaction with formaldehyde, inferred for the early terrestrial hydrosphere and cryosphere would present a dilemma for hypotheses invoking cyanide and related compounds as concentrated reactants capable of forming biomolecular precursor species. Attempts to escape from its horns may take advantage of the efficient concentration and separation of cyanide as solid ferriferrocyanide, and most directly of reactions of glycolonitrile and its derivatives.