Evidence of Strong Orbital-Selective Spin-Orbital-Phonon Coupling in CrVO_{4}

Coupling of orbital degree of freedom with a spin exchange, i.e., Kugel-Khomskii-type interaction (KK), governs a host of material properties, including colossal magnetoresistance, enhanced magnetoelectric response, and photoinduced high-temperature magnetism. In general, KK-type interactions lead to deviation in experimental observables of coupled Hamiltonian near or below the magnetic transition. Using diffraction and spectroscopy experiments, here we report anomalous changes in lattice parameters, electronic states, spin dynamics, and phonons at four times the Néel transition temperature (T_{N}) in CrVO_{4}. The temperature is significantly higher than other d-orbital compounds such as manganites and vanadates, where effects are limited to near or below T_{N}. The experimental observations are rationalized using first-principles and Green's function-based phonon and spin simulations that show unprecedentedly strong KK-type interactions via a superexchange process and an orbital-selective spin-phonon coupling coefficient at least double the magnitude previously reported for strongly coupled spin-phonon systems. Our results present an opportunity to explore the effect of KK-type interactions and spin-phonon coupling well above T_{N} and possibly bring various properties closer to application, for example, strong room-temperature magnetoelectric coupling.

A strategically synthesized arseno-discriminatory tetra-phenoxido hetero-trinuclear complex envisioned for the recognition of iAs and oAs from Oryza sp. and aquatic crustaceans

A heterotrimetallic [Mn^II(Cu^II)₂(C₁₈H₁₈N₂O₂)₂] complex VBCMERI has been unveiled herein to monitor its synergistic propensity towards aqueous phase As3+ (iAs and oAs) detection. VBCMERI was structurally probed by numerous analytical tools like ESI-MS, FT-IR, and SCXRD. The aqueous phase selective chromogenic alteration of the sensory probe from greenish-yellow to colorless was observed owing to interaction with As³⁺ (cationic form, iAs). This phenomenon can be ascribed to the displacement of the Mn²⁺ center with As³⁺, which has further been experimentally validated through cyclic voltammetric titration studies, FT-IR, and ESI-MS, and theoretically corroborated with density functional theory calculations. Interestingly, aqueous phase selective turn-on fluorogenic enhancement of the sensory probe was observed upon interaction with AsO₂^- (anionic form, iAs) owing to the displacement of the arsenite anion with the pivalic acid group. The distinct chromogenic alteration from greenish-yellow to colorless and the fluorogenic enhancement of VBCMERI upon interaction with the respective As³⁺ (iAs) and AsO₂^- (iAs) were successfully implemented for monitoring arsenic contamination in groundwater samples and diverse types of Oryza sp. grains from the assorted arsenic-affected zones. The competitive accumulation of arsenobetaine (oAs) in the exoskeleton and muscles of aquatic crustaceans (herein, Penaeus sp.) can be distinctly differentiated based on the turn-on fluorogenic response. Based on the sensing response and competitive accumulation tendency of different forms of arsenic in different environments, arseno-adducts with VBCMERI have been theoretically modeled for corroboration with experimental findings. The VBCMERI-AsO2- adduct was also highly efficient in regenerating the VBCMERI sensor selectively in the presence of contaminants like Pb2+. This reversible behavior was further exploited to mimic a molecular-level 3-input-2-output logic gate ensemble.

Explicating the recognition phenomenon of hazardous nitro-aromatic compound from contaminated environmental and cellular matrices by rationally designed pyridine-functionalized molecular probes

In the quest of recognizing hazardous nitro-aromatic compounds in water, two pyridine-functionalized Schiff-base chemosensors, DMP ((E)-N-(3,4-dimethoxybenzylidene)(pyridin-2-yl)methanamine)) and MP (4-((E)-((pyridin-2-yl)methylimino)methyl)-2-ethoxyphenol) have been synthesized to detect mutagenic 2,4,6-Trinitrophenol (TNP) in soil, water as well as cellular matrices by producing turn-off emission responses as a combined consequence of PET and RET processes. Several experimental analyses including ESI-MS, FT-IR, photoluminescence, ¹H NMR titration, and the theoretical calculations ascertained the formation and sensing efficacies of the chemosensors. The analytical substantiations revealed that structural variation of the chemosensors played a significant role in improving the sensing efficiency, which would certainly be worthwhile in developing small molecular TNP sensors. The present work depicted that the electron density within the MP framework was more than that of DMP due to the intentional incorporation of -OEt and -OH groups. As a result, MP represented a strong interaction mode towards the electron-deficient TNP with a detection limit of 39 μM.

Magnetoelastic coupling and spin contributions to entropy and thermal transport in biferroic yttrium orthochromite. J Phys Condens Matter 2021;33:125702. [PMID: 33378273 DOI: 10.1088/1361-648x/abd781] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Direct engineering of material properties through exploitation of spin, phonon, and charge-coupled degrees of freedom is an active area of development in materials science. However, the relative contribution of the competing orders to controlling the desired behavior is challenging to decipher. In particular, the independent role of phonons, magnons, and electrons, quasiparticle coupling, and relative contributions to the phase transition free energy largely remain unexplored, especially for magnetic phase transitions. Here, we study the lattice and magnetic dynamics of biferroic yttrium orthochromite using Raman, infrared, and inelastic neutron spectroscopy techniques, supporting our experimental results with first-principles lattice dynamics and spin-wave simulations across the antiferromagnetic transition atT_N∼ 138 K. Spectroscopy data and simulations together with the heat capacity (C_p) measurements, allow us to quantify individual entropic contributions from phonons (0.01 ± 0.01k_Batom^-1), dilational (0.03 ± 0.01k_Batom^-1), and magnons (0.11 ± 0.01k_Batom^-1) acrossT_N. High-resolution phonon measurements conducted in a magnetic field show that anomalousT-dependence of phonon energies acrossT_Noriginates from magnetoelastic coupling. Phonon scattering is primarily governed by the phonon-phonon coupling, with little contribution from magnon-phonon coupling, short-range spin correlations, or magnetostriction effects; a conclusion further supported by our thermal conductivity measurements conducted up to 14 T, and phenomenological modeling.

Renormalization of electron-phonon coupling in the Mott-Ioffe-Regel limit due to point defects in the V1-x Ti x alloy superconductors

We report here the temperature dependence of electrical resistivity ([Formula: see text](T)), heat capacity (C(T)) and thermal conductivity ([Formula: see text](T)) of superconducting V_1-x Ti _x alloys in the absence and presence of external applied magnetic fields. The [Formula: see text](T) changes from positive temperature coefficient of resistivity (TCR) to negative TCR at about x  =  0.7 indicating that many of these alloys lie close to the Mott-Ioffe-Regel (MIR) limit. The jump in the C(T) across the superconducting transition temperature ([Formula: see text]) indicates that these alloys are in the intermediate coupling limit. The [Formula: see text](T) increases in certain V_1-x Ti _x alloys as the temperature decreases below the [Formula: see text] indicating that the phonons dominate the heat conduction in the superconducting state, whereas we found that the electrons are the major carriers of heat in the normal state. Our analysis suggests that the unusual features of thermal conductivity have origin in (i) the electron mean free path approaching the inter atomic distances (MIR limit) and (ii) the renormalization of the phonon mean free path due to the presence of point defects and the electron-phonon interaction.

Magnetotransport and magnetothermal properties of the ternary intermetallic compound TbFe2Al10

We have studied the temperature and field dependences of electrical resistivity and heat capacity of TbFe2Al10, and have also complimented the above studies with low field magnetization measurements. In zero magnetic field, TbFe2Al10 exhibits paramagnetic (PM) to ferrimagnetic (Ferri-I) and Ferri-I to antiferromagnetic (AFM) phase transitions below 17.6 and 10 K respectively. We have found that the electrical resistivity of TbFe2Al10 exhibits a sharp rise across the PM to Ferri-I phase transition in this compound. Our analysis indicates that this sharp rise of electrical resistivity is related to the formation of new zone boundaries (across the PM to Ferri-I phase transition) that reduce the area of the Fermi surface. We have found that TbFe2Al10 exhibits large magnetoresistance (MR) below 100 K. Overall, the MR behaviour of TbFe2Al10 below 17.6 K in different magnetic fields reveals strong competition between AFM and ferromagnetic (FM) correlations, which seems to be quite intrinsic to the magnetic structure of the compound. Our analysis indicates that the large MR and magnetocaloric effect persisting deep inside the PM regime of TbFe2Al10 is mainly related to the presence of FM spin fluctuations and the formation of a Griffiths like (GL) phase consisting of FM clusters within the PM regime. The formation of the GL phase may be mediated by the static crystal defects in the midst of the competing inter and intra layer magnetic interactions.

Electronic structure of Mo1-x Re x alloys studied through resonant photoemission spectroscopy

We studied the electronic structure of Mo-rich Mo1-x Re x alloys ([Formula: see text]) using valence band photoemission spectroscopy in the photon energy range 23-70 eV and density of states calculations. Comparison of the photoemission spectra with the density of states calculations suggests that, with respect to the Fermi level E F, the d states lie mostly in the binding energy range 0 to  -6 eV, whereas s states lie in the binding energy range  -4 to  -10 eV. We observed two resonances in the photoemission spectra of each sample, one at about 35 eV photon energy and the other at about 45 eV photon energy. Our analysis suggests that the resonance at 35 eV photon energy is related to the Mo 4p-5s transition and the resonance at 45 eV photon energy is related to the contribution from both the Mo 4p-4d transition (threshold: 42 eV) and the Re 5p-5d transition (threshold: 46 eV). In the constant initial state plot, the resonance at 35 eV incident photon energy for binding energy features in the range E F (BE  =  0) to  -5 eV becomes progressively less prominent with increasing Re concentration x and vanishes for x  >  0.2. The difference plots obtained by subtracting the valence band photoemission spectrum of Mo from that of Mo1-x Re x alloys, measured at 47 eV photon energy, reveal that the Re d-like states appear near E F when Re is alloyed with Mo. These results indicate that interband s-d interaction, which is weak in Mo, increases with increasing x and influences the nature of the superconductivity in alloys with higher x.

Evidence of multiband superconductivity in the β-phase Mo1-xRex alloys

We present a detailed study of the superconducting properties in the β-phase Mo(1-x)Re(x) (x = 0.25 and 0.4) solid solution alloys pursued through magnetization and heat capacity measurements. The temperature dependence of the upper critical field H(C2)(T) in these binary alloys shows a deviation from the prediction of the Werthamer-Helfand-Hohenberg (WHH) theory. The temperature dependence of superfluid density estimated from the variation of lower critical field H(C1) with temperature, cannot be explained within the framework of a single superconducting energy gap. The heat capacity also shows an anomalous feature in its temperature dependence. All these results can be reasonably explained by considering the existence of two superconducting energy gaps in these Mo(1-x)Re(x) alloys. Initial results of electronic structure calculations and resonant photoelectron spectroscopy measurements support this possibility and suggest that the Re-5d like states at the Fermi level may not intermix with the Mo-5p and 5s like states in the β-phase Mo(1-x)Re(x) alloys and contribute quite distinctly to the superconductivity of these alloys.

The magnetotransport properties of the intermetallic compound GdCu6

We have studied the temperature and magnetic field dependence of the electrical resistivity of GdCu(6) and have co-related the results with the temperature dependence of heat capacity and magnetization. The magnetoresistance of GdCu(6) is found to be positive both in the paramagnetic and antiferromagnetic regimes. Within the antiferromagnetic regime, the magnetoresistance is very high and increases to still higher values both with increasing field and decreasing temperature. In the paramagnetic regime the magnetoresistance continues to exhibit a finite positive value up to temperatures much higher than that corresponding to the antiferromagnetic to paramagnetic phase transition. We have shown through quantitative analysis that both the temperature dependences of resistivity and heat capacity indicate the presence of spin fluctuations within the paramagnetic regime of GdCu(6). The field dependence of electrical resistivity indicates that the positive magnetoresistance in the paramagnetic phase is not related to the orbital motion of the conduction electrons in a magnetic field (the Kohler rule). In contrast, our analysis indicates that these spin fluctuations are responsible for the positive magnetoresistance observed within this paramagnetic regime. The nature of the field dependence of electrical resistivity is found to be qualitatively similar both in the antiferromagnetic and paramagnetic regimes, which probably indicates that spin fluctuations in the paramagnetic regime are of the antiferromagnetic type.

The effect of external pressure on the magnetocaloric effect of Ni-Mn-In alloy

The martensitic transition in Ni(50)Mn(34)In(16) alloy has been studied by measuring the magnetization of the alloy as a function of temperature, magnetic field and pressure. Magnetic field and pressure have opposite effects on the martensitic transition in this alloy; the martensitic transition temperature decreases with increasing magnetic field but it increases with increasing pressure. The effect of pressure on the magnetocaloric properties of this large magnetocaloric effect alloy has been investigated in detail. The magnitude of the peak in the isothermal magnetic entropy change in Ni(50)Mn(34)In(16) increases with pressure. The temperature at which the magnetocaloric effect reaches the peak value in this alloy increases from near 240 K under ambient pressure to near 280 K under an external pressure of 9.5 kbar. The temperature corresponding to the peak in the isothermal magnetic entropy change increases with increasing pressure at a rate which matches the rate of increase of the martensite start temperature with increasing pressure. The temperature dependence of the isothermal magnetic entropy change under different pressures is found to follow a universal curve for a particular magnetic field change. These results show that pressure as a control parameter can be used to tune the temperature regime of the magnetocaloric effect in the alloy. The effect of pressure on the martensitic transition also gives a clue as regards the possibility of tuning this temperature regime with elemental substitution.

Glassy dynamics in magnetization across the first order ferromagnetic to antiferromagnetic transition in Fe0.955Ni0.045Rh

We present the results of magnetization relaxation measurements across the ferromagnetic to antiferromagnetic transition in Fe(0.955)Ni(0.045)Rh. The transition from the high temperature ferromagnetic phase to the low temperature antiferromagnetic phase seems to be arrested by increasing the applied magnetic field. The crossover from crystallization-like dynamics to glassy dynamics can be tracked by measuring isothermal time dependent magnetization at various constant temperatures while cooling across this ferromagnetic to antiferromagnetic transition. The initial conversion from the ferromagnetic to antiferromagnetic phase as a function of time at higher temperatures follows a distinct power law relaxation. The transition is incomplete at low temperatures with the stretched exponential relaxation behaviour dominating over the power law, which is indicative of glassy dynamics or the arrest of the kinetics of the phase transition. In the intermediate temperature regime, the magnetic relaxation can be explained as a combination of both the power law and stretched exponential. The temperature dependence of the time constant of the stretched exponential follows the Arrhenius law which is usually observed in the case of strong glass-forming liquids.

Temperature and magnetic field induced multiple magnetic transitions in DyAg(2)

The magnetic properties of the rare-earth intermetallic compound DyAg(2) are studied in detail with the help of magnetization and heat capacity measurements. It is shown that the multiple magnetic phase transitions can be induced in DyAg(2) both by temperature and magnetic field. The detailed magnetic phase diagram of DyAg(2) is determined experimentally. It was already known that DyAg(2) undergoes an incommensurate to commensurate antiferromagnetic phase transition close to 10 K. The present experimental results highlight the first order nature of this phase transition, and show that this transition can be induced by magnetic field as well. It is further shown that another isothermal magnetic field induced transition or metamagnetic transition exhibited by DyAg(2) at still lower temperatures is also of first order nature. The multiple magnetic phase transitions in DyAg(2) give rise to large peaks in the temperature dependence of the heat capacity below 17 K, which indicates its potential as a magnetic regenerator material for cryocooler related applications. In addition it is found that because of the presence of the temperature and field induced magnetic phase transitions, and because of short range magnetic correlations deep inside the paramagnetic regime, DyAg(2) exhibits a fairly large magnetocaloric effect over a wide temperature window, e.g., between 10 and 60 K.

The effect of substitution of Mn by Fe and Cr on the martensitic transition in the Ni50Mn34In16 alloy

The potential shape memory alloy Ni(50)Mn(34)In(16) is studied with partial substitution of Mn with Fe and Cr to investigate the effect of such substitution on the martensitic transition in the Ni-Mn-In alloy system. The results of ac susceptibility, magnetization and electrical resistivity measurements show that while the substitution with Cr increases the martensitic transition temperature, the substitution with Fe decreases it. Possible reasons for this shift in martensitic transition are discussed. Evidence of kinetic arrest of the austenite to martensite phase transition in the Fe substituted alloys is also presented. Unlike the kinetic arrest of the austenite to martensite phase transition in the parent Ni(50)Mn(34)In(16) alloy which takes place in the presence of high external magnetic field, the kinetic arrest of the austenite to martensite phase transition in the Fe doped alloy occurs even in zero magnetic field. The Cr substituted alloys, on the other hand, show no signature of kinetic arrest of this phase transition.

Increase in oxidative stress at low temperature in an antarctic bacterium

Association between cold stress and oxidative stress was demonstrated by measuring the activity of two antioxidant enzymes and the level of free radicals generated in two batches of cells of an Antarctic bacterium Pseudomonas fluorescens MTCC 667, grown at 22 and 4°C. Increase in oxidative stress in cells grown at low temperature was evidenced by increase in the activity of an enzyme and also in the amount of free radicals generated, in the cold-grown cells. The association between cold stress and oxidative stress demonstrated in this investigation bolsters the concept of interlinked stress response in bacteria.

Disorder influenced magnetic phase transition in the Ce(Fe 0.9 Ru 0.1)2 alloy

We have studied a 10% Ru-doped CeFe(2) alloy, Ce(Fe(0.9)Ru(0.1))(2), through magnetization, magnetotransport, and heat capacity measurements. This study shows that, while this alloy is antiferromagnetic at low temperatures and paramagnetic at high temperatures, there exists evidence of ferromagnetic ordering in the intermediate temperature regime. We show here that with 10% Ru doping the first order magnetic transition observed in the Ce(Fe(1 - x)Ru(x))(2) alloys with x < 0.08 is reduced to a quasi-continuous phase transition. The characteristic thermomagnetic history effects associated with the ferromagnetic-antiferromagnetic phase transition in the Ce(Fe(1 - x)Ru(x))(2) alloys with x < 0.08 are not observed in the Ce(Fe(0.9)Ru(0.1))(2) alloy. This alloy continues to exhibit the large magnetoresistance and large magnetocaloric effect associated with this first order magnetic transition in the alloys with smaller Ru concentration, but it does not show any energy loss due to thermomagnetic hysteresis. The present work thus shows how the introduction of quenched disorder due to alloying effects may be used to tune the first order magnetic transition in a material for more efficient functional use.

A scanning Hall probe imaging study of the field induced martensite-austenite phase transition in Ni50Mn34In16 alloy

The martensite to austenite phase transition in the off-stoichiometric Heusler alloy Ni(50)Mn(34)In(16) can be induced both by temperature change and by application of a magnetic field. We have used scanning Hall probe imaging to study the magnetic field induced martensite-austenite phase transition. The study provides clear visual evidence of the coexistence of the martensite and austenite phases across this field induced transition in both increasing and decreasing magnetic fields. Clear evidence of thermomagnetic history effects associated with the martensite-austenite phase transition is also obtained. Quantitative analysis of the magnetic field dependence of the volume fraction of the austenite phase in Ni(50)Mn(34)In(16) shows evidence of a nucleation and growth mechanism across the field induced martensite-austenite phase transition. The local M-H loops constructed from the Hall images indicate the presence of a landscape of the critical magnetic field (for the field induced transition) distributed over the sample volume and thus confirm the disorder influenced nature of this first-order magnetic phase transition.

Magnetic properties of the field-induced ferromagnetic state in MnSi

We present results of dc magnetization measurements focusing on the magnetic properties of the field-induced ferromagnetic state in MnSi. The temperature dependence of saturation magnetization in this ferromagnetic state exhibits the signatures of both spin wave excitations and itinerant electron ferromagnetism. The Arrott plots obtained from the isothermal field dependence of magnetization, however, are found to be distinctly nonlinear and hence cannot be explained within a simple framework of itinerant electron magnetism.

Mechanism of bacterial adaptation to low temperature

Survival of bacteria at low temperatures provokes scientific interest because of several reasons. Investigations in this area promise insight into one of the mysteries of life science - namely, how the machinery of life operates at extreme environments. Knowledge obtained from these studies is likely to be useful in controlling pathogenic bacteria, which survive and thrive in cold-stored food materials. The outcome of these studies may also help us to explore the possibilities of existence of life in distant frozen planets and their satellites.

First order magnetic transition in doped CeFe2 alloys: phase coexistence and metastability

First order ferromagnetic (FM) to antiferromagnetic (AFM) phase transition in doped CeFe2 alloys is studied with the micro-Hall probe technique. Clear visual evidence of magnetic phase coexistence on micrometer scales and the evolution of this phase coexistence as a function of temperature, magnetic field, and time across the first order FM-AFM transition is presented. Such phase coexistence and metastability arise as a natural consequence of an intrinsic disorder-influenced first order transition. The generality of these phenomena involving other classes of materials is discussed.

Chaperone-like properties of lysophospholipids

Lysophospholipids are metabolic intermediates in phospholipid turnover, detergent molecules with membrane-modulating effects, and multifunctional cellular growth factors in eukaryotic cells. In bacterial cells, lysophospholipids are mostly found in the form of lysophosphatidylethanolamine. We show that a heat shock from 30 to 42 degrees C increases four-fold the Escherichia coli pool of lysophosphoethanolamine and that lysophospholipids display chaperone-like properties. Lysophosphatidylethanolamine, like molecular chaperones such as DnaK, promotes the functional folding of citrate synthase and alpha-glucosidase after urea denaturation. Like chaperones, lysophophatidylethanolamine, lysophosphatidylcholine, lysophosphatidylinositol and lysophosphatidic acid prevent the aggregation of citrate synthase at 42 degrees C. The renaturation and solubilisation of proteins by lysophospholipids occur at micromolar concentrations of these compounds, close to their critical micellar concentration. Furthermore, lysophosphatidylethanolamine is much more efficient than other detergents tested for the renaturation and solubilisation of citrate synthase. In contrast with lysophospholipids, phosphatidylethanolamine and phosphatidylcholine are not able to promote citrate synthase folding nor to prevent its aggregation at 42 degrees C. The chaperone-like properties of lysophospholipids suggest that, in addition to their known functions, they might affect the structure and function of hydrophilic proteins.

Antizyme regulates the degradation of ornithine decarboxylase in fission yeast Schizosaccharomyces pombe. Study in the spe2 knockout strains

The mechanism of the regulatory degradation of ornithine decarboxylase (ODC) by polyamines was studied in fission yeast, Schizosaccharomyces pombe. To regulate cellular spermidine experimentally, we cloned and disrupted S-adenosylmethionine decarboxylase gene (spe2) in S. pombe. The null mutant of spe2 was devoid of spermidine and spermine, accumulated putrescine, and contained a high level of ODC. Addition of spermidine to the culture medium resulted in rapid decrease in the ODC activity caused by the acceleration of ODC degradation, which was dependent on de novo protein synthesis. A fraction of ODC forming an inactive complex concomitantly increased. The accelerated ODC degradation was prevented either by knockout of antizyme gene or by selective inhibitors of proteasome. Thus, unlike budding yeast, mammalian type antizyme-mediated ODC degradation by proteasome is operating in S. pombe.

Carotenoids of an Antarctic psychrotolerant bacterium, Sphingobacterium antarcticus, and a mesophilic bacterium, Sphingobacterium multivorum

The major carotenoid pigments of an Antarctic psychrotolerant bacterium, Sphingobacterium antarcticus, and a mesophilic bacterium, Sphingobacterium multivorum, were identified as zeaxanthin, beta-cryptoxanthin, and beta-carotene. Analysis was based on ultraviolet-visible spectroscopy, mass spectroscopy, and reversed-phase HPLC. Photoacoustic spectroscopy of intact bacterial cells revealed that the bulk of the pigments in S. antarcticus and S. multivorum was associated with the cell membrane. In vitro studies with synthetic membranes of phosphatidylcholine demonstrated that the major pigment was bound to the membranes and decreased their fluidity. The relative amounts of polar pigments were higher in cells grown at 5 degrees C than in cells grown at 25 degrees C. In the mesophilic strain, the synthesis of polar carotenoids was quantitatively less than that of the psychrotolerant strain.

Expression of abscisic acid-responsive element-binding protein in salt-tolerant indica rice (Oryza sativa L. cv. Pokkali)

As the products of abiotic stress and ABA inducible genes are predicted to play an important role in the mechanism of salt tolerance, the expression of transcription factor that recognizes abscisic acid-responsive element (ABRE) is likely to be regulated when plants are exposed to abiotic stress. Northern analysis of total RNA from control and salt-treated 10-day-old Pokkali (salt tolerant) rice plants was performed to find out the level of transcripts homologous to wheat cDNA (GC19) for EmBP-1 (bZIP class factor), a transcription factor that recognizes ABRE. Salinity stress (72 h)-induced accumulation of two transcripts, of 2.0 kb (r2.0) and 1.5 kb (r1.5), in roots was detected. Both transcripts were detectable even after 6 h of salt or abscisic acid treatment, whereas sheath and lamina showed constitutive levels of r1.5 transcript. When 32P-labeled DNA containing ABRE was used in a gel mobility shift assay, a low level of complex formation by binding factor was detected from the nuclear extract of lamina of control rice plants. Quantitative enhancement of complex formation was found with the nuclear extract prepared from the lamina of plants treated with 200 mM NaCl for 26 h over control nuclear extract, suggesting a step of regulation of expression of ABRE-binding protein in response to salinity stress. South-western blot analysis of equal amounts of nuclear proteins of lamina showed binding of 32P-labeled ABRE-DNA with two polypeptides (22-28 kDa) present at constitutive levels in control or NaCl-treated plants. Preincubation of the laminar nuclear extract of control plants, with spermidine or proline at 5 mM concentration showed quantitative enhancement of ABRE binding activity. Kinetics of spermidine stimulation showed gradual increase of complex formation from 5 mM concentration. Similarly, addition of GTP to the control nuclear extract also showed quantitative enhancement of complex formation and heparin was found to inhibit GTP activated complex formation by about 25%. Results may suggest the presence of ABRE binding protein in presynthesized and inactive form in control plants and GTP mediated activation is probably one of the way to regulate the expression of ABRE-binding factor.

Carotenoid pigments of an antarctic psychrotrophic bacterium Micrococcus roseus: temperature dependent biosynthesis, structure, and interaction with synthetic membranes

Pigmentation in a psychrotrophic M.roseus was found to be increased when the bacteria were grown at 5 degrees C as compared to its pigmentation at 25 degrees C. In addition more polar pigments were synthesised at low temperature. The pigments were identified as bacterioruberins and were demonstrated to bind to synthetic membranes of phosphatidylcholine with almost equal affinity, irrespective of the polarity of the pigments.

Expression of arginine decarboxylase in seedlings of indica rice (Oryza sativa L.) cultivars as affected by salinity stress

The effect of salinity stress on the activity of arginine decarboxylase (ADC, EC 4.1.1.19), the first enzyme in biosynthesis of polyamines (PA) from arginine, as well as its transcript level has been compared in salt-sensitive (M-1-48) and salt-tolerant (Pokkali) rice cultivars. Treatment of 72 h grown seedlings either with increasing concentrations of NaCl or with 150 mM NaCl for different time periods, showed a gradual increase of activity in Pokkali. In M-1-48 an immediate increase followed by sharp decrease was observed on prolonged treatment beyond 6 h or above 150 mM NaCl. To generate a DNA probe for ADC, the polymerase chain reaction was used with oat genomic DNA and sequence-specific primers. A region of oat genomic DNA containing a coding sequence for 166 amino acids of the C-terminal part of the ADC enzyme was amplified and called OAD1. Southern analysis of EcoRI- or BamHI-cut genomic DNAs from different cultivars of rice with OAD1 as the probe revealed strong hybridization with one DNA fragment of rice and restriction fragment length polymorphism (RFLP) was noticed. Northern analysis of total RNA of rice with OAD1 as the probe revealed hybridization with a transcript of similar size to the ADC transcript in oat. While in Pokkali, at least a 20-fold accumulation of OAD1 homologous transcript was detected after treatment with 200 mM NaCl, only a seven-fold increase in transcript level was found in M-1-48 after 150 mM NaCl treatment. Results suggest that in the salt-tolerant rice cultivar Pokkali, ADC enzyme activity increases and its transcript also accumulates during the prolonged salinity stress, this mechanism is absent in the salt-sensitive rice cultivar M-1-48 where a prolonged period of salinity stress down-regulates both ADC activity and its transcript level.

The major carotenoid pigment of a psychrotrophic Micrococcus roseus strain: fluorescence properties of the pigment and its binding to membranes

The fluorescence excitation and emission spectra are reported for P-3 (bis-dehydro-B-carotene-2-carboxylic acid), the major carotenoid pigment of psychrotrophic M. roseus. The excitation spectrum and the absorption spectrum showed good agreement with respect to the position of their peak maxima. The study also demonstrates that P-3 binds to liposomes prepared from synthetic lipids (PC, DOPG, or CL) or the total lipids of a mutant colourless M. roseus. Binding of P-3 to the membranes was accompanied by a decrease in the fluorescence emission intensity and a blue shift in lambda(em) maximum by 15 to 20 nm. The quantum yield of P-3 was observed to be low (1.7 x 10(-5)).

Control of methionine biosynthesis in Escherichia coli K12: a closer study with analogue-resistant mutants

Control of methionine biosynthesis in Escherichia coli K12 was reinvestigated by using methionine-analogue-resistant mutants. Norleucine (NL) and alpha-methylmethionine (MM) were found to inhibit methionine biosynthesis directly whereas ethionine (Et) competitively inhibited methionine utilization. Adenosylation of Et to generate S-adenosylethionine (AdoEt) by cell-free enzyme from E. coli K12 was demonstrated. Tolerance of increasing concentrations of NL by E. coli K12 mutants is expressed serially as phenotypes NLR, NLREtR, NLRMMR and finally NLREtRMMR. All spontaneous NLR mutants had a metK mutation, whereas NTG-induced mutants had mutations in both the metK and metJ genes. The kinetics of methionine adenosylation by the E. coli K12 cell-free enzyme were found to be similar to those reported for the yeast enzyme, showing the typical lag phase at low methionine concentration and disappearance of this phase when AdoMet was included in the incubation mixture. NL extended the lag phase, and lowered the rate of subsequent methionine adenosylation, but did not affect the shortening of the lag phase of adenosylation by AdoMet.

Rotation of the anatomic regions used for insulin injections and day-to-day variability of plasma glucose in type I diabetic subjects

Treatment of type I diabetes mellitus is hindered by the often large fluctuations in blood glucose concentration experienced by affected individuals. To determine to what extent day-to-day variation in blood glucose levels can be reduced if insulin is injected in the same anatomic region rather than in different regions using a rotational scheme, as is commonly recommended, 12 type I diabetic subjects were studied. Insulin injections were given in the abdomen for 3 days and rotated among arms, abdomen, and thighs for 3 days using a crossover design with random assignment of treatment order. Blood samples for measurement of plasma glucose levels were obtained at nine scheduled times on each day. Insulin dose, diet, and physical activity were held constant for each subject. During the abdominal injection period, the mean SD of plasma glucose levels and the mean variance of plasma glucose levels were both less at all nine time points than during the rotating injection period. Overall values for the SD of plasma glucose levels were 2.7 +/- 0.2 mmol/L for the abdominal injection period and 3.7 +/- 0.3 mmol/L for the rotating injection period. Overall values for the variance of plasma glucose levels were 9.2 +/- 1.4 mmol2/L2 for the abdominal injection period and 17.4 +/- 2.2 mmol2/L2 for the rotating injection period. We conclude that the common clinical practice of rotating the anatomic regions used for insulin injections increases day-to-day variation in blood glucose concentration. Use of a single anatomic region, eg, the abdomen, for all insulin injections may reduce this variation and allow greater precision in the adjustment of insulin doses.