Interaction between nickel and iron in the rat

The interaction between nickel and iron was confirmed in rat metabolism. In a fully-crossed, two-way, three by four, factorially designed experiment, female weanling rats were fed a basal diet supplemented with iron at 0, 25, 50, and 100 μg/g and with nickel at 0, 5, and 50 μg/g. The basal diet contained about 10 ng of nickel and 2.3 μg of iron/g. After nine weeks, dietary iron affected growth, hematocrit, hemoglobin, plasma cholesterol, and in liver affected total lipids, phospholipids, and the contents of copper, iron, manganese, and zinc. By manipulating the iron content of the diet, effects of dietary nickel were shown in rats that were not from dams fed a nickel-deprived diet. Nickel affected growth, hematocrit, hemoglobin, plasma alkaline phosphatase activity, plasma total lipids, and in liver affected total lipids, and the contents of copper, manganese, and nickel. The interaction between nickel and iron affected hematocrit, hemoglobin, plasma alkaline phosphatase activity, and plasma phospholipids, and in liver affected size, content of copper, and perhaps of manganese and nickel. In severely iron-deficient rats, the high level of dietary nickel partially alleviated the drastic depression of hematocrit and hemoglobin, and the elevation of copper in liver. Simultaneously, high dietary nickel did not increase the iron level in liver and was detrimental to growth and appearance of severely iron-deficient rats. In nickel-deprived rats fed the borderline iron-deficient diet (25 μg/g) hematocrit and hemoglobin also were depressed. However, 5 μg Ni/g of diet were just as effective as 50 μg Ni/g of diet in preventing those signs of nickel deprivation. The findings in the present study suggested that nickel and iron interact with each other at more than one locus.     

Effects of heavy metals and strontium on division of root cap cells and meristem structural organization

In order to define relations between the behavior of quiescent center cells and the condition of root cap cells, effects of various metal salts on the root meristem structure, root growth, and division of root cap cells were investigated. Two-day-old maize (Zea mays L., cv. Diamant) seedlings were incubated on solutions containing 35 μM Ni(NO₃)₂), 10 μM Pb(NO₃)₂, or 3 mM Sr(NO₃)₂ in the absence or in the presence of 3 mM Ca(NO₃)₂. Toxic effects of metals were assessed from inhibition of the primary root length increment following 24-h and 48-h incubations as compared to the roots grown on water or on 3 mM Ca(NO₃)₂ solution. Metal localization in the root apex tissues following 24-h and 48-h incubations was determined using histochemical techniques. Cell lengths in three upper layers of root cap columella were determined, and the mitotic index in these cells was calculated. In the absence of Ca(NO₃)₂, the metals were found both in the meristem and in the root cap. Pb and Sr were revealed primarily in the cell walls, and Ni, in the cell protoplasts. In the presence of Ca(NO₃)₂, metal content in all root tissues was decreased, and their toxic effect on root growth was ameliorated. Pb and Ni inhibited cell division in the root cap. Pb caused an increase in the root cap cell length as early as following 24-h incubation, and Ni, only following 48-h incubation. Pb activated division of quiescent center cells in the direction of root cap. These effects, as well as possible involvement of dermatogen and cortex cells, resulted in a regrowth of a new root cap already after a 24-h incubation period. In this case, the meristem was transformed from a closed structure into the open one. Following 48-h incubation, Ni brought about only few divisions of quiescent center cells in the direction of root cap. It was suggested that inhibition of divisions of the root cap upper layer cells and a decrease in the sloughing off its cells can stimulate the quiescent center cell divisions. A similarity of the quiescent center and animal stem cells is discussed.     

Preparation and Use of Samarium Diiodide (SmI2) in Organic Synthesis: The Mechanistic Role of HMPA and Ni(II) Salts in the Samarium Barbier Reaction

Although initially considered an esoteric reagent, SmI₂ has become a common tool for synthetic organic chemists. SmI₂ is generated through the addition of molecular iodine to samarium metal in THF.^1,2-3 It is a mild and selective single electron reductant and its versatility is a result of its ability to initiate a wide range of reductions including C-C bond-forming and cascade or sequential reactions. SmI₂ can reduce a variety of functional groups including sulfoxides and sulfones, phosphine oxides, epoxides, alkyl and aryl halides, carbonyls, and conjugated double bonds.^2-12 One of the fascinating features of SmI-₂-mediated reactions is the ability to manipulate the outcome of reactions through the selective use of cosolvents or additives. In most instances, additives are essential in controlling the rate of reduction and the chemo- or stereoselectivity of reactions.^13-14 Additives commonly utilized to fine tune the reactivity of SmI₂ can be classified into three major groups: (1) Lewis bases (HMPA, other electron-donor ligands, chelating ethers, etc.), (2) proton sources (alcohols, water etc.), and (3) inorganic additives (Ni(acac)₂, FeCl₃, etc).³Understanding the mechanism of SmI₂ reactions and the role of the additives enables utilization of the full potential of the reagent in organic synthesis. The Sm-Barbier reaction is chosen to illustrate the synthetic importance and mechanistic role of two common additives: HMPA and Ni(II) in this reaction. The Sm-Barbier reaction is similar to the traditional Grignard reaction with the only difference being that the alkyl halide, carbonyl, and Sm reductant are mixed simultaneously in one pot.^1,15 Examples of Sm-mediated Barbier reactions with a range of coupling partners have been reported,^1,3,7,10,12 and have been utilized in key steps of the synthesis of large natural products.^16,17 Previous studies on the effect of additives on SmI₂ reactions have shown that HMPA enhances the reduction potential of SmI₂ by coordinating to the samarium metal center, producing a more powerful,^13-14,18 sterically encumbered reductant^19-21 and in some cases playing an integral role in post electron-transfer steps facilitating subsequent bond-forming events.²² In the Sm-Barbier reaction, HMPA has been shown to additionally activate the alkyl halide by forming a complex in a pre-equilibrium step.²³Ni(II) salts are a catalytic additive used frequently in Sm-mediated transformations.^24-27 Though critical for success, the mechanistic role of Ni(II) was not known in these reactions. Recently it has been shown that SmI₂ reduces Ni(II) to Ni(0), and the reaction is then carried out through organometallic Ni(0) chemistry.²⁸These mechanistic studies highlight that although the same Barbier product is obtained, the use of different additives in the SmI₂ reaction drastically alters the mechanistic pathway of the reaction. The protocol for running these SmI₂-initiated reactions is described.     

Reduced cellular Ca availability enhances TDP-43 cleavage by apoptotic caspases

Accumulation of transactive response DNA binding protein (TDP-43) fragments in motor neurons is a post mortem hallmark of different neurodegenerative diseases. TDP-43 fragments are the products of the apoptotic caspases-3 and -7. Either excessive or insufficient cellular Ca²⁺ availability is associated with activation of apoptotic caspases. However, as far as we know, it is not described whether activation of caspases, due to restricted intracellular Ca²⁺, affects TDP-43 cleavage. Here we show that in various cell lineages with restricted Ca²⁺ availability, TDP-43 is initially cleaved by caspases-3 and -7 and then, also by caspases-6 and -8 once activated by caspase-3. Furthermore, we disclose the existence of a TDP-43 caspase-mediated fragment of 15 kDa, in addition to the well-known fragments of 35 and 25 kDa. Interestingly, with respect to the other two fragments this novel fragment is the major product of caspase activity on murine TDP-43 whereas in human cell lines the opposite occurs. This outcome should be considered when murine models are used to investigate TDP-43 proteinopathies.     

Physiological role of nickel and its toxic effects on higher plants

The focus of the review is on the specific aspects of nickel effect on plants as compared to other heavy metals; their specificity is derived from different physical and chemical properties. The various facets of the physiological role of nickel and its toxic activity in higher plants, its intracellular partition and transport in plant tissues and organ are discussed. The putative mechanisms of nickel hyperaccumulation are considered in several representatives of angiosperm plant families. The existing evidence was used to outline the metabolic changes in plants affected by nickel. The comparison with other heavy metals is used to disclose the general mechanisms that disturb plant mineral nutrition, water regime, photosynthesis, and morphogenesis as well as the common cell responses aimed at detoxification of heavy metals. The numerous nonspecific effects of heavy metals depend on their direct and indirect action; in addition, some effects of nickel are specific. To illustrate, high Ni content in endoderm and pericycle cells blocks cell divisions in the pericycle and results in the inhibition of root branching.     

Heterologous expression of cyan and yellow fluorescent proteins from the Kluyveromyces lactis KlMAL21–KlMAL22 bi-directional promoter

We have identified the Kluyveromyces lactis maltase (KlMAL22) and maltose permease (KlMAL21) intergenic region as a candidate bi-directional promoter for heterologous gene expression. The expressions of cyan and yellow fluorescent proteins from, respectively, the KlMAL22 and KlMAL21 orientations of the promoter, were compared between two promoter variants during growth in media containing glucose, galactose or glycerol. Expression from both orientations of the native promoter was repressed during growth in glucose and galactose and was induced during growth in glycerol. Disruption of a putative Mig1p binding site caused some de-repression of the maltase orientation of the promoter by 48 h of growth in glucose. The KlMAL21–-KlMAL22 bi-directional promoter can be used to carry out regulated expression of heterologous gene products.     

Bioremediation Potential of Chlorella: Spectroscopic,Kinetics, and Sem Studies

A dead dried alga, Chlorella sp., was used for the uptake of Cr⁺³, Cr₂O₇ ^?2, Cu⁺², and Ni⁺² from the aqueous solutions of these metal ions. The equilibrium data were fitted using the Langmuir and Freundlich isotherm model and the maximum uptakes for Cr⁺³, Cr₂O₇ ^?2, Ni⁺², and Cu⁺² were 98, 104, 108, and 183 mg/g, respectively. The Freundlich model, in comparison to the Langmuir model, better represented the sorption process. The kinetics of metal ions uptake by Chlorella sp. was best described by a pseudo-second order rate equation. Infrared spectroscopic data were employed to identify the site(s) of bonding in Chlorella sp. A scanning electron microscopic (SEM) study of pure dead Chlorella sp. and the species treated with different metal ions provided an idea of the extent of metal uptake by this species. The dead Chlorella sp took up maximum Cu(II). The size of the cell of the metal-treated Chlorella sp. obtained from SEM data is in agreement with the extent of metal uptake.     

NMR studies on Ni(II) induced cyclization of a histidine-tagged peptide.

A linear decapeptide, HGASYQDLGH, was synthesized and used as a model to evaluate the effect of nickel addition upon non-covalent backbone cyclization. The NMR data, obtained for the peptide in the presence of the metal ion, support the existence of predominant folded structures in solution, where the two His residues are maintained close to each other. These results suggest that insertion of even a single His residue at each peptide terminus can be used efficiently to reduce peptide flexibility without any backbone modification.     

Metal uptake by iron-efficient and inefficient oats

Metal uptake by oats depending on plant responses to Fe-deficiency stress was investigated. Coker 227 oats classified as Fe-efficient and TAM 0–312 oats as Fe-inefficient cultivars (Hopkins et al., 1992) were grown either alone or in combination in three sandy soils using a pot experiment. These soils were from a field trial with sludge-borne metals applications leading to an increased metal content. Plant shoots were harvested one month after growth. Because soil pH increased from 5.4 to 6.8, shoot Fe level decreased in the Fe-inefficient TAM 0–312 oats compared to Coker 227 oats when plants were grown alone. In combination, TAM 0–312 oats had a negative impact on the availability of Fe in the Fe-efficient Coker 227 oats. Especially, Coker 227 and TAM 0–312 shoots showed chlorosis in mixed culture with high Zn and Mn content in the soil (soil B). However, Fe content in TAM 0–312 shoots in mixed culture did not increase compared to monoculture in all soils. In metal-contaminated soils, TAM 0–312 oats grown alone obtained less Zn and Cd than Coker 227 oats. Additionally at soil pH 6.8, shoot Ni and Mn levels were also lower in TAM 0–312 oats than in Coker 227 oats. Shoot Zn, Cd, and Ni levels decreased in Coker 227 oats from mixed cultures, and were not different compared to those in TAM 0–312 oats. Cu uptake was similar in all treatments except for the mixed culture in soil B. Coker 227 oats have been found to release a phytosiderophore whereas TAM 0–312 did not (Brown et al., 1991). Results indicated that phytosiderophores may lead to a higher Zn, Cd and Ni supply in the rhizosphere of Coker 227 oats and to higher metal contents in their shoots than in TAM 0–312 oats which did not activate such mechanisms.