Showing papers by "North Eastern Hill University published in 1997"

N2 Fixation by non-heterocystous cyanobacteria

Abstract: Many, though not all, non-heterocystous cyanobacteria can fix N2. However, very few strains can fix N2 aerobically. Nevertheless, these organisms may make a substantial contribution to the global nitrogen cycle. In this general review, N2 fixation by laboratory cultures and natural populations of non-heterocystous cyanobacteria is considered. The properties and subcellular location of nitrogenase in these organisms is described, as is the response of N2 fixation to environmental factors such as fixed nitrogen, O2 and the pattern of illumination. The integration of N2 fixation with other aspects of cell metabolism (in particular photosynthesis) is also discussed. Similarities and differences between different individual strains of non-heterocystous cyanobacteria are highlighted.

In vitro anthelmintic activity of root-tuber extract of Flemingia vestita, an indigenous plant in Shillong, India

Abstract: The in vitro activity of root-tuber-peel extract of Flemingia vestita, an indigenous plant consumed by the natives in Northeast India, was tested against helminth parasites. Live parasites (nematode: Ascaris suum from pigs, A. lumbricoides from humans, Ascaridia galli and Heterakis gallinarum from domestic fowl; cestode: Raillietina echinobothrida from domestic fowl; trematode: Paramphistomum sp. from cattle) were collected in 0.9 % physiological buffered saline (PBS) and maintained at 37 ± 1 °C. In vitro treatment of the parasites with the crude extract (50 mg/ml) in PBS revealed complete immobilization of the trematode and cestode in about 43 and 20 min, respectively. However, the cuticle-covered nematodes did not show any change in physical activity and remained viable even after a long period of exposure to the extract. Exposure of R. echinobothrida to genistein (0.5 mg/ml), an active principle isolated from the root-tuber peel, caused spontaneous loss of movement (paralysis) in 4.5 h, which was slower than the time required for praziquantel, the reference flukicide and cestodicide. The treated parasites showed structural alteration in their tegumental architecture. This study suggests the vermifugal activity of this plant extract against trematodes and cestodes.

Zero-temperature hysteresis in the random-field Ising model on a Bethe lattice

Abstract: We consider the single-spin-flip dynamics of the random-field Ising model on a Bethe lattice at zero temperature in the presence of a uniform external field. We determine the average magnetization as the external field is varied from to by setting up the self-consistent field equations, which we show are exact in this case. The qualitative behaviour of magnetization as a function of the external field unexpectedly depends on the coordination number z of the Bethe lattice. For z = 3, with a Gaussian distribution of the quenched random fields, we find no jump in magnetization for any non-zero strength of disorder. For , for weak disorder the magnetization shows a jump discontinuity as a function of the external uniform field, which disappears for a larger variance of the quenched field. We determine exactly the critical point separating smooth hysteresis curves from those with a jump. We have checked our results by Monte Carlo simulations of the model on three- and four-coordinated random graphs, which for large system sizes give the same results as on the Bethe lattice, but avoid surface effects altogether.

The Nonminimal Supersymmetric Standard Model at Large tan β

Abstract: We present a comprehensive analysis of the Nonminimal Supersymmetric Standard Model (NMSSM) for large values of tan β, the ratio of the vacuum expectation values of the two Higgs doublets, which arise when we impose the constraint of the unification of Yukawa couplings in the model. In this limit, we show that the vacuum expectation value of the singlet is forced to be large, of the order of 10 TeV. The singlet decouples from the lightest CP-even neutral Higgs boson and the neutralinos. We compare our results with the corresponding particle spectrum of the Minimal Supersymmetric Standard Model in the same limit. With the exception of the lightest Higgs boson, the particle spectrum in the model turns out to be heavy. The Higgs boson mass, after the inclusion of radiative corrections, is found to be in the neighborhood of ~ 130 GeV.

Tree seed germination and seedling establishment in treefall gaps and understorey in a subtropical forest of northeast India

Abstract: Seed germination, and survival and growth of seedlings of four dominant tree species, Quercus dealbata, Quercus griffithii, Quercus glauca and Schima khasiana were studied in the treefall gaps and forest understorey of an undisturbed mature-phase humid subtropical broadleaved forest in northeast India. Three important microenvironmental factors namely photosynthetically active radiation (PAR), soil moisture and litter depth, were also measured in the forest understorey and gaps and correlated with seedling mortality. Seed germination of S. khasiana was significantly higher in the treefall gaps than in the understorey; among the tree species studied, it had the highest germination. Quercus seedlings were abundant in the understorey and small gaps, while S. khasiana seedlings were more numerous in the large gaps. The survivorship curves for the seedling populations revealed that the three Quercus species survived better in the understorey, while S. khasiana did so in the gaps. PAR and soil moisture were positively correlated with tree seedling mortality, which occurred mainly during the winter months. The Quercus seedlings grew better in the forest understorey and small gaps and S. khasiana seedlings in the large gaps. The differential performance of the tree seedlings to the conditions prevailing in the understorey and gaps of two sizes indicates that different species were adapted to different light environments depending upon their optimum requirements. This could be an effective mechanism for promoting species coexistence in the forest community.

Carbamyl Phosphate Synthetases in an Air-Breathing Teleost, Heteropneustes fossilis

Abstract: The Indian air-breathing teleost fish Heteropneustes fossilis has been shown to have a functional urea cycle and to be able to switch from ammoniotelic to ureotelic nitrogen metabolism when exposed to high levels of ammonia or air. The objective of this study was to identify the type of carbamyl phosphate synthetase (CPS) catalyzing the first step of the urea cycle in H. fossilis . Mitochondrial CPS III [glutamine- and N-acetyl-L-glutamate (NAG)-dependent] and cytosolic CPS II (glutamine-dependent) activities were found to be present in liver, analogous to that described for two other teleosts that have CPS III activity. The same activities and subcellar localization were found in kidney. Unexpectedly, a CPS I-like activity (ammonia- and NAG-dependent) was found to be present at levels higher than the CPS III activity in the mitochondrial fraction of both liver and kidney. The urea cycle-related CPS III found in invertebrates and fish is considered to be the evolutionary precursor of the urea cycle-related CPS I in ureotelic mammalian and amphibian species. Whether or not this CPS I-like activity 1) is due to the presence of a separate CPS I gene in addition to a CPS III gene or 2) represents an adapted CPS III activity in H. fossilis , these results suggest that the presence of both CPS I-like and CPS III activities may play an important physiological adaptive role in the tolerance of these fish to high concentrations of external ammonia.

Dynamics of phase transitions in a liquid crystalline compound (TBDA) probed by Raman spectroscopy

Abstract: The precise value of linewidths obtained after correcting for the slitwidth effect for five Raman bands associated with the core of a liquid crystalline compound, terepthal-bis-decyl aniline (TBDA), have been studied in the temperature range of 12-472 K. The variation of the linewidth with temperature confirms two already reported phase transitions at 346 and 427 K. However, the phase transition at 427 K is not purely first order as reported earlier, but of mixed order in nature. From the measured linewidths of the N and CDN modes below room temperature, the estimated activation energy for rotation along the -N bond closely matches with the SI -SC phase transition temperature suggesting that the rotation about the -N bond is closely linked with this transition.

Effects of shifting cultivation on the environment

Abstract: Outlines the natural features of Mizoram ‐ climate, flora, fauna. Describes the cultivation systems employed and the problems generated ‐ erosion, burning, harm to indigenous plants and animals. Concludes by addressing the need to protect and conserve the natural forests and wild life.

Evaluating second year cropping on jhum fallows in Mizoram, north-eastern India: Soil fertility

Abstract: Changes in soil fertility were evaluated on young (6 year) and old (20 year) jhum fields in Mizoram, north-eastern India in response to various operations involved injhum such as slashing and burning of vegetation, cropping period, and intervening fallow period between first and second year cropping. The results demonstrate that the soil is richer in nutrients in old than young field prior to the start of jhum cultivation. Slash burning depletes soil acidity, carbon and nitrogen but elevates phosphorus and cations. Soil fertility declined during first cropping phase, and further declined during second cropping phase. After two cropping years, soil fertility of old field was almost at par with that of young field, signifying that the loss of soil fertility was more in old than young field. A short intervening fallow period between first and second year of cropping did not show any pronounced improvement in soil fertility, though it provided some biomass for second burning. Tilling caused maximum loss to soil fertility. The fertilizer treatments ended with comparable or better soil fertility in comparison to no-treatment plot. There seems to be none of the fertilizer treatments superior over others from the standpoint of ending soil fertility. The unifying conclusions of this series of investigations support the hypothesis that the second year cropping holds promise to reduce the demand for forested land for jhum, and lengthen the jhum cycle substantially.

Electrical Conductance and Viscosity of Concentrated H2SO4/H2O Binary Systems at Low Temperatures: Correlation with Phase Transitions

Abstract: Density, viscosity, and electrical conductance of concentrated H2SO4/H2O systems (above 66 wt % H2SO4) were measured in the subambient temperature region. The lowest temperature of measurement was 198 K. Density varied linearly with temperature. Viscosity and conductance data were fitted to the Vogel−Tammann−Fulcher (VTF) equation and also to the power-law equation, the latter being a better functional form to describe the temperature dependence of transport properties. Concentration dependences of viscosity, conductance, expansivity, and ideal glass transition temperature indicate the occurrence of structural changes in the H2SO4/H2O system in the regions 83−85 and 92−94 wt % H2SO4 which are attributed to the formations of H2SO4·H2O (at 84.48 wt% H2SO4) and the eutectic between H2SO4·H2O and H2O (at 93.8 wt % H2SO4), respectively. Above ∼75 wt % H2SO4 a direct correlation exists between the viscosity−concentration curve and the phase diagram of the H2SO4/H2O system.

Modulation of the clastogenic activity of bleomycin by reduced-glutathione, glutathione-ester and buthionine sulphoximine.

Abstract: In this study an attempt has been made to establish a relationship between bleomycin (BLM)-induced DNA damage and buthionine sulphoximine (BSO)-mediated modified endogenous glutathione (GSH) status in normal human lymphocytes. Present results demonstrate that depletion of endogenous GSH by BSO reduced the clastogenic action of BLM, whereas elevation of endogenous GSH by treating the cells with GSH and GSH-ester, potentiates the cytotoxicity of BLM. A significant reduction in the frequency of deletions and chromatid breaks was observed when BSO-treated cells were treated with BLM. Again the frequency of these two types of aberrations was increased significantly when GSH- and GSH-ester-treated cells were treated with BLM. The observed reduction in the effect of BLM in GSH-depleted cells could be explained on the basis of the failure of reactivation of the oxidized BLM by reducing agent GSH which is present endogenously. Similarly, it appears that radicals which are generated due to reduction of oxidized BLM by the increased level of cellular GSH, after treating the cells with GSH or GSH-ester, could be responsible for the increasing frequency of deletion and chromatid breaks.

Lecanid rotifers (Rotifera: Monogononta: Lecanidae) from North-Eastern India

Abstract: Thirty-five species of the family Lecanidae are examined from Tripura state in North-Eastern India. Of these, Lecane levistyla and L. scutata are interesting cold-water forms; L. batillifer is an Australasian element; L. acanthinula and L. sinuata are Oriental endemics and L. braumi, L. lateralis and L. simonneae are palaeotropical species. The lecanid fauna also includes the pantropical L. thienemanni and L. sola while the remainder are cosmopolitan and tropicopolitan elements.

Evaluating second year cropping on jhum fallows in Mizoram, north-eastern India: Energy and economic efficiencies

Abstract: Energy and economic efficiencies were evaluated on young (6 year) and old (20 year) jhum fields in Mizoram, north-eastern India during second year of cropping, and were compared with those in the first year. The effect of auxiliary measures such as tilling the soil or application of fertilizers (chemical or farm-yard manure or both in combination) was also examined on energy and economic efficiencies. The results indicated that traditional jhum cultivation is labour intensive and energy efficient, producing almost 15-20 times of energy invested. Energy and economic efficiencies decline with shortening of jhum cycle. These efficiencies decline further from first to second year of cropping. Tilling is not useful to improve either energy or economic efficiency. Fertilizer application, which is though profitable from the point of view of economic efficiency, is highly energy inefficient. Application of fertilizers during second year cropping can be encouraged. Organic manuring may be a better option than others to alleviate energy efficiency. However, a combination of organic and inorgamic manuring could be the best option to enhance economic efficiency.

Synthesis of functionalised cyclic nitrones via regioselective and unusual [3 + 2] cycloadditions of α-nitrosostyrenes with 1,3-diazabuta-1,3-dienes and imines

Abstract: The α-nitrosostyrenes 2, generated in situ from α-halogeno oximes, undergo regioselective [3 + 2] cycloaddition with 1,3-diazabuta-1,3-dienes 1 and 5 leading to the cyclic nitrones 3 and 6, respectively. Similarly, the cyclic nitrones 12 are also formed in reactions of 2 with the trisubstituted amidines 11. Thermolysis of the nitrones 3 and 12d–f gives imidazole derivatives 13. The nitrones 6, on the other hand, on thermolysis under similar conditions, give the amidine derivatives 17. Interestingly, the treatment of both 3 and 6 with NaBH4 in methanol and the reactions of 2 with N-arylbenzamidines also yield the imidazole derivatives 13.

Antifungal Activity of the Essential Oil of Hyptis suaveolens and Its Efficacy in Biocontrol Measures

Abstract: The essential oil from the leaves of Hyptis suaveolens (L.) Poit. (Family-Labiatae), a herbaceous annual weed, has been found to have significant antifungal activity against the soil-borne sclerof ial fungi, Rhizoctonia solani, Sclerof ium rolfsii and Sclerof inia sclerof iorum. Treatment with the oil drastically reduced the ascospore germination of S. sclerof iorum. More importantly, the oil in combination with antagonistic fungus Trichoderma harzianum controlled wilt and rof diseases of knol-khol (Brassica caulorapa Pasq.) caused by S. sclerof iorum. The oil appears to inhibit the fungal growth, but does nof destroy the viability of the three sclerof ial fungi.

Emergence of spinless and spin-1/2 particles from higher-dimensional gravity with D-dimensional torus as a compact manifold

Abstract: Using gravitational action for four-dimensional theory of R2-gravity, it has been shown earlier that, at high energy level, Ricci scalar R behaves like a physical field in addition to its usual nature as a geometrical field. The physical aspect of R is represented by spinless particles, called riccions. It is shown here that riccions can also be obtained from multi-dimensional R2-gravity. Further it is shown that these riccions disintegrate into fermion and anti-fermion pairs under certain conditions. Some physical properties of these fermions (here called riccinos) are discussed. On the basis of the results obtained here, one is tempted to speculate that our physical universe might have emerged through decay of riccions and riccinos.

Mutagenic significance of proton acidities in methylated guanine and thymine bases and deoxynucleosides: a theoretical study

Abstract: Proton changes have been advanced as being the key molecular basis for the mutagenecity of alkylated DNA bases and nucleosides, leading to questions as to which protons are involved and whether the protic changes are tautomeric shifts or abstractions. This semiempirical molecular orbital study seeks to clarify the issue by examining the various possibilities open for these protic changes in a number of methylated guanines and thymines and their deoxynucleosides. Proton shifts leading to tautomer formation are not predicted as being thermodynamically favourable in most cases. The most feasible proton abstractions are predicted to involve the Watson-Crick protons in all cases, which corroborates Watson-Crick proton loss as providing the key molecular basis for the induction of point mutations. The calculated proton acidities correlate well with experimental data. The gas-phase deprotonation enthalpies for a number of alkylated nucleosides are found to correlate linearly with the solvent-phase pK(a) values. The theoretically calculated enthalpies in a simulated aqueous solvent phase of the deprotonation reactions of various nucleic acid bases are also found to have good linear correlations with experimental pK(a) values. The consensus of these calculations is that O-6-alkyldeoxyguanosines, and O-2- and O-4-alkyldeoxythymidines would be mutagenic while N-7-alkyldeoxyguanosines would not be mutagenic (as experiment indicates). The untested N-3-methyldeoxyguanosine is predicted to be mutagenic. (C) 1997 Elsevier Science B.V.