Showing papers by "North Eastern Hill University published in 1990"

Community composition and tree population structure in a sub-tropical broad-leaved forest along a disturbance gradient

Abstract: Floristic composition, diversity, dominance and distribution pattern of species and tree population structure were studied in three stands of a sub-tropical wet hill broad-leaved forest of Meghalaya, India, along a disturbance gradient. Tree species diversity declined with increasing disturbance. Disturbed stands showed low equitability or high dominance and the undisturbed stand exhibited high equitability or low dominance. Contagious distribution among the tree species increased with increasing intensity of disturbance. Species showing regular distribution were restricted only to the undisturbed stand. Effect of disturbance on tree population structure was analysed using density-diameter curves. In the disturbed stands tree species showed reverse J-shaped and/or negative exponential curves, while those in the undisturbed stand exhibited sigmoid to bimodal mound shaped curves.

Kinetics of oxidation of amino acids by alkaline hexacyanoferrate(III)

Abstract: The kinetics of oxidation of amino acids (lysine, arginine, and histidine) by alkaline hexacyanoferrate(III) has been studied at constant ionic strength over the temperature range 318–338 K. The rate was dependent on the first powers of the concentrations of substrate and oxidant, but independent of the concentration of the alkali in the range studied. The reaction proceeds by way of the α-imino acid, formed in a rapid step, which then undergoes hydrolysis to give the corresponding α-keto acid.

Regulation of urease activity in the cyanobacterium Anabaena doliolum

Abstract: The effect of nitrogen sources on the activity of urease has been studied in the cyanobacterium Anabaena doliolum. De novo synthesis of urease occurred in the absence of an added nitrogen source, and the enzyme activity was almost equal when the medium contained either N2, NO3−, or urea. Ammonium grown cell showed repression in urease activity which was freed by l-methionine, dl-sulphoximine (MSX), an inhibitor of glutamine synthetase. NH4+, must therefore, be metabolised through glutamine synthetase before repressing the urease activity. NH4+ (up to 10 mM) did not inhibit the urease activity in vitro, suggesting that NH4+ does not inactivate the enzyme but represses its biosynthesis. When NH4+ grown cells were transferred to medium containing urea, the ability to hydrolyse urea required approximately 5 to 6 h for maximal expression. Chloramphenicol (50 μg ml−1) completely prevented the rise in urease activity. Ni2+ at concentrations of 0.01 and 0.05 μM enhanced the urease activity; however, the addition of 10mM citrate to the medium resulted in a drop in the increase in urease activity. The cells treated with chloramphenicol in combination with Ni2+ showed a higher level of urease activity as compared to chloramphenicol treated cells only, suggesting the antagonistic nature of Ni2+ against chloramphenicol mainly at the level of synthesis/activity of proteases.

Growth, photosynthesis and nitrogen fixation of Anabaena doliolum exposed to assam crude extract.

Abstract: Petroleum contaminants pose serious threat to the structure and functioning of aquatic ecosystems. Although their effects on various algal species have been studied before, heterocystous blue-green algae (cyanobacteria) have been little explored in this regard. Inadequate information concerning the effects of petroleum oils on them, especially on their nitrogen fixing system, prompted the authors to undertake this study. In this communication the authors report the influence of Assam crude on growth, photosynthesis ({sup 14}C incorporation), nitrogen fixation (nitrogenase activity) and heterocyst differentiation in Anabaena doliolum. This species and other heterocystous cyanobacteria occur widely in soil and aquatic ecosystems.

An ab initio calculation of the rotational-vibrational energies in the electronic ground state of NH2

Abstract: We have calculated ab initio the three-dimensional potential-energy surface of the NH2 molecule at 145 nuclear geometries spanning energy ranges of about 18 000 cm-1 for the NH stretch and 12 000 cm-1 for the bend. The ab initio configuration-interaction calculations were done using the multireference MRD-CI method. The calculated equilibrium configuration has NH bond length r e = 1·0207 A and bond angle α = 103·1°. The rotational-vibrational energies for 14NH2, 14NHD and 14ND2 were calculated variationally using the Morse-oscillator rigid-bender internal-dynamics Hamiltonian. For 14NH2 we calculate that υ1 = 3267 (3219) cm-1, υ2 = 1462 (1497) cm-1 and υ3 = 3283 (3301) cm-1, where experimental values are given in parentheses.

Correlation between nitrogenase and glutamine synthetase expression in the cyanobacterium Anabaena cylindrical

Abstract: Distribution pattern and levels of nitrogenase (EC 1.7.99.2) and glutamine synthetase (GS, EC 6.3.1.2) were studied in N2-, NO3− and NH4+ grown Anabaena cylindrica (CCAP 1403/2a) using immunogold electron microscopy. In N2- and NO3− grown cultures, heterocysts were formed and nitrogenase activity was present. The nitrogenase antigen appeared within the heterocysts only and showed an even distribution. The level of nitrogenase protein in the heterocysts was identical with both nitrogen sources. In NO3− grown cells the 30% reduction in the nitrogenase activity was due to a corresponding decrease in the heterocyst frequency and not to a repressed nitrogenase synthesis. In NH4− grown cells, the nitrogenase activity was almost zero and new heterocysts were formed to a very low extent. The heterocysts found showed practically no nitrogenase protein throughout the cytoplasm, although some label occurred at the periphery of the heterocyst. This demonstrates that heterocyst differentiation and nitrogenase expression are not necessarily correlated and that while NH4+ caused repression of both heterocyst and nitrogenase synthesis, NO3− caused inhibition of heterocyst differentiation only. The glutamine synthetase protein label was found throughout the vegetative cells and the heterocysts of all three cultures. The relative level of the GS antigen varied in the heterocysts depending on the nitrogen source, whereas the GS level was similar in all vegetative cells. In N2- and NO3+ grown cells, where nitrogenase was expressed, the GS level was ca 100% higher in the heterocysts compared to vegetative cells. In NH4+ grown cells, where nitrogenase was repressed, the GS level was similar in the two cell types. The enhanced level of GS expressed in heterocysts of N2 and NO3− grown cultures apparently is related to nitrogenase expression and has a role in assimilation of N2derived ammonia.

Microfungal species associated with the gut content and casts ofDrawida assamensis gates

Abstract: Microfungi were isolated from earthworm (Drawida assamensis) gut contents and freshly laid worm casts of a pineapple plantation field using Warcup’s soil plate method. A total of 17 species of microfungi were isolated, out of which 16 occurred in the anterior region, 12 in the middle region and 10 in the posterior region of the gut and 10 in the worm cast respectively. One species was restricted to posterior region of the gut and the worm cast. The digestion of microfungi in earthworm’s digestive tract occurred in a trend anterior>middle>posterior.

Solvent‐dependent vibrational relaxation studies in polar liquid

Abstract: Isotropic Raman line broadening studies were carried out for the CO stretching mode of vibration in N,N-dimethylformamide and cyclohexanone molecules in solution. The broadening for the Raman band is explained on the basis of hydrodynamic, multipole-multipole, induction and dispersion forces. The intercept on the linear graph [Γiso vs f(ρ, η, n)] is explained on the basis of induction forces and multipole interactions for dipolar and non-dipolar solvents.

Synthesis and Structural Information on Mercury(II) Chloride Complexes with Some Mono-Ortho Substituted Medially Metallized Type Azo Dyes

Abstract: The preparation of 1:2 and 1:1 mercury(II) chloride complexes with arylazo ligands is described. These compounds are freely soluble in methanol in they behave as non-electrolytes. Based on molar conductance, 1H n.m.r., electronic spectra and i.r. spectral features down to 200cm−1, complexes of arylazo-2-naphthol(L1H) and arylazopyridines (L3−L6) are considered as neutral, four-coordinated tetrahedral structures while complexes of arylazo-2-carboxylic acid (L2H) appear to be neutral, three-coordinated around mercury(II).

On the origin of anomalous ranges of 1.65 GeV 132Xe ions in Muscovite Mica

Abstract: Ranges of 1.65 GeV 132 Xe ions in muscovite mica, determined using solid state nuclear track detector (SSNTD) techniques, are shown to vary strongly with angle of incidence to the basal plane. This is explained within the framework of the Chadderton-Koul-Biersack (CKB) model for latent track formation in real crystals. Not only are there clear bursts of electronic energy loss at individual molecular layers, as seen in intermittent tracks in the electron microscope, but the range variation can also be ascribed to a basic refractive effect of individual molecular layers on the particle trajectories. This, in turn. provides a strong nonlinear electronic stopping. The strong uniaxial anisotropy of muscovite mica imposes a new orbital motion, referred to as “ridging” (or “bridging” in the upper angular limit) on the swift xenon ions. which are almost completely stripped of electrons. Neither “channelling” nor “quasichannelling“. which are determined by smaller critical angles, play any part in this specific aspect of anomalous range determination, which is entirely due to the smooth angular dependence of the “ridging” orbits on refracted pathways, and on the integrated stopping power sampled. The fact that incorporation of “ridging” and “bridging” into the broader picture now produces a complete angular set of classical positively charged particle orbits, encompassing all of real space in crystals. leads naturally to the construction of a new classical range ( R ) surface, quite analogous to the familiar Fermi surface of constant energy, described by conduction electron momentum vectors ( k ) in reciprocal space.

Effects of thyroidal, gonadal and adrenal hormones on tissue respiration of streaked frog, Rana limnocharis, at low temperature.

Abstract: In vivo and in vitro effects of thyroidal, gonadal and adrenal hormones were studied on the rate of liver and skeletal muscle respiration in both the sexes of R. limnocharis during active and inactive phases of the annual activity cycle. Triiodothyronine (L-T3) and thyroxine (L-T4) did not stimulate tissue (liver and muscle) respiration in any of the experiments irrespective of season, sex and temperature. Testosterone, estradiol and corticosterone stimulated O2 uptake significantly irrespective of season, sex and temperature. Adrenaline and nor-adrenaline also stimulated tissue respiration significantly during the winter month. Since the ambient temperature was low even during the active phase (max. temperature 21 degrees C), it seems that the frog might have developed tissue sensitivity for gonadal and adrenal hormones at low temperatures when thyroid hormones are calorigenically ineffective.

The genus Testudinella (Eurotatoria : Gnesiotrocha : Testudinellidae) in North-Eastern India

Abstract: Nine species and subspecies of the genus Testudinella are reported from North-Eastern India. Of these, six are new to India and eight to the North-Eastern region. Remarks are made on their distribution.

Temperature dependence of line width of SO42− modes in the Raman spectra of ammonium sulphate

Abstract: The electronic (900-250 nm), infrared and Raman (600-10 cm −1 ) spectra of polycrystalline samples of NbS 3 were investigated. A complete vibrational assignment is proposed and the band wavenumbers are compared for NbS 3 and the related ZrS 3 and NbS 2 Cl 2 . All the assignments have been checked by a complete valence force field calculation including intrachain, interchain and interlayer contributions. The potential energy distributions and mean square vibrational amplitudes so calculated and the values of force constants are in agreement with the two-dimensional character of the lattice dynamics in NbS 3