Strain-specific salt tolerance and chemotaxis ofAzospirillum brasilense and their associative N-fixation with finger millet in saline calcareous soil

Three salt-tolerantAzospirillum brasilense strains were isolated from the roots of finger millet grown in saline calcareous soil and characterized. The effect of various salts on growth and N₂ase activity of these strains was tested and strain STR1 was found more tolerant at higher concentrations of Cl^-, SO₄ ² and HCO₃ ^-. Bicarbonate was found to be the most toxic. The content and concentrations of root exudates of finger millet genotypes were different and chemotaxis to sugars, amino acids, organic acids and root exudates was strain specific. Under salt stress, significant interactions between strains and genotypes of finger millet resulted in different responses of N₂ase activity, endo- and exorhizospheric population, dry weight of root, shoot and grain yield.     

Evidence for a role of glutamine synthetase in assimilation of amino acids as nitrogen source in the cyanobacterium Nostoc muscorum.

Methylammonium/ammonium ion, glutamine, glutamate, arginine and proline uptake, and their assimilation as nitrogen sources, was studied in Nostoc muscorum and its glutamine synthetase-deficient mutant. Glutamine served as nitrogen source independent of glutamine synthetase activity. Glutamate was not metabolised as a nitrogen source but still inhibited nitrogenase activity and diazotrophic growth. Glutamine synthetase activity was essential for the assimilation of N2, ammonia, arginine and proline as nitrogen sources but not for the control of their transport, heterocyst formation, and production of ammonia or aminoacid dependent repressor signal for N2-fixing heterocysts. These results also suggest that glutamine synthetase serves as the sole route of ammonia assimilation and glutamine synthesis, and ammonia per se as the repressor signal for N2-fixing heterocysts and methylammonium (ammonium) transport.     

Retinopetal neuronal system in the brain of an air-breathing teleost fish,Channa punctata

Summary Retinopetal neurons were visualised in the telencephalon and diencephalon of an air-breathing teleost fish, Channa punctata, following administration of cobaltous lysine to the optic nerve. The labelled perikarya (n=45–50) were always located on the side contralateral to the optic nerve that had received the neuronal tracer. The rostral-most back-filled cell bodies were located in the nucleus olfactoretinalis at the junction between the olfactory bulb and the telencephalon. In the area ventralis telencephali, two groups of telencephaloretinopetal neurons were identified near the ventral margin of the telencephalon. The rostral hypothalamus exhibited retrogradely labelled cells in three discrete areas of the lateral preoptic area, which was bordered medially by the nucleus praeopticus periventricularis and nucleus praeopticus, and laterally by the lateral forebrain bundle. In addition to a dorsal and a ventral group, a third population of neurons was located ventral to the lateral forebrain bundle adjacent to the optic tract. The dorsal group of neurons exhibited extensive collaterals; a few extended laterally towards the lateral forebrain bundle, whereas others ran into the dorsocentral area of the area dorsalis telencephali. A few processes extended via the anterior commissure into the telencephalon ipsilateral to the optic nerve that had been exposed to cobaltous lysine. However, the ventral cell group did not possess collaterals. In the diencephalon, retinopetal cells were visualised in the nucleus opticus dorsolateralis located in the pretectal area; these were the largest retinopetal perikarya of the brain. The caudal-most nucleus that possessed labelled somata was the retinothalamic nucleus; it contained the largest number of retinopetal cells. The limited number of widely distributed neurons in the forebrain, some with extensive collaterals, might participate in functional integration of different brain areas involved in feeding, which in this species is influenced largely by taste, not solely by vision.     

Incidence of actinomycetes infection in women using intrauterine contraceptive devices

Pancervicovaginal smears taken from 350 women using an intrauterine contraceptive device (IUD) were screened for the presence of actinomycetes organisms. Of the 12 cases in which actinomycetes-like organisms were seen in Papanicolaou-stained smears, the presence of actinomycetes organisms was confirmed by immunofluorescence in 10 cases. The prevalence of actinomycetes infection was thus 2.8% (10 of 350 cases) in the IUD users. Eight (4.3%) of 173 symptomatic subjects had actinomycetes infections. Two of the positive cases were asymptomatic. Eight of the ten patients with confirmed actinomycetes infection were using the Cu T device while two were wearing the Lippes Loop IUD. Seven of the ten patients had been using an IUD for more than two years. The time of insertion of the IUD (postpuerperal, postmenstrual or after medical termination of pregnancy) did not show any correlation with the presence of actinomycetes infection. Actinomyces israelii was responsible for the infection in eight cases while Arachnia propionica was seen in two cases. The organisms could not be grown in culture.     

Nitrate metabolism in the cyanobacterium Anabaena cycadeae: Regulation of nitrate uptake and reductase by ammonia

Nitrogen regulation of nitrate uptake and nitrate reductase (EC 1.7.99.4) was studied in the cyanobacterium Anabaena cycadeae Reinke and its glutamine auxotroph. Development of the nitrate uptake system preceded, and was independent of, the development of the nitrate reductase system. The levels of both systems were several-fold higher in the glutamine auxotroph lacking glutamine synthetase (EC 6.3.1.2) than in the wild type strain having normal glutamine synthetase activity. The nitrate uptake system was found to be NH4-repressible and the nitrate reductase system NO₃⁻-inducible. NH₄⁺ was the initial repressor signal for the uptake process which was involved in the control of the NO₃⁻inducible reductase system.     

Increased osmotic tolerance of some Aspergilli isolated from ‘Usar’ (alkaline) soils — A possible indication of ecological specialization

Studies on the osmotic optima for growth of some Aspergilli isolated from Indian Usar (alkaline) soils have revealed the occurrence of four osmophilic and twenty-five other species which can be categorised as facultative tolerant on the basis of their osmotic concentration optima. In addition, the Usar soil strains possess a comparatively greater osmotic tolerance than their fertile soil counterparts which may be attributed to the relatively hypertonic conditions prevailing in Usar soils.     

Effect of environmental conditions on sclerotia and cleistothecia production in aspergillus

Summary Literature pertaining to sclerotial Aspergilli has been reviewed in brief. Observations on the effect of certain environmental conditions viz. pH, light, temperature of incubation, oxygen-deficient conditions and various relative humidity values on sclerotia production byAspergillus niger van Tieghem, (two strains),A. flavus Link (two strains),A. sclerotiorum Hüber (one strain) andA. paradoxus Fennell &Raper (one strain) and on cleistothecia production byA. nidulans (Eidam)Wint. (one strain) have been presented. Optimum pH for sclerotia or cleistothecia production was 7.5. In other respects sclerotia and cleistothecia behaved similarly. In general, condition showing maximum sclerotia or cleistothecia production was the one that showed maximum vegetative growth. Certain strains of the same species reponded differently to the same condition. Light completely inhibited sclerotia formation in one strain ofA. flavus. InA. paradoxus, in general, conditions favouring sclerotia production were those that inhibited (or retarded) the formation of conidial heads and the yellow pigment in the medium. Oxygen-deficient conditions inhibited or retarded sclerotia or cleistothecia formation. Production of sclerotia and cleistothecia increased with an increase in relative humidity values. No definite correlation could be observed between extent of sporulation and sclerotia or cleistothecia production except in case of relative humidity. Parallelism in the behaviour of sclerotia and cleistothecia production inAspergillus lends further support in favour of the hypothesis that in this genus sclerotia are sterile stromata.     

DNA binding site specificity of the Neurospora global nitrogen regulatory protein NIT2: Analysis with mutated binding sites

NIT2, a positive-acting regulatory protein in Neurospora crassa, activates the expression of a series of unlinked structural genes that encode nitrogen catabolic enzymes. NIT2 binding sites in the promoter regions of nit3, alc and lao have at least two GATA sequence elements. We have examined the binding affinity of the NIT2 protein for the yeast DAL5 wild-type upstream activation sequence UAS_NTR, which contains two GATA elements, and for a series of mutated binding sites, each differing from the wild-type site by a single base. Substitution for individual nucleotides within 5′ or 3′ sequences that flank the GATA elements had only modest effects upon NIT2 binding. In contrast, nearly all substitutions within the GATA elements almost completely eliminated NIT2 binding, demonstrating the importance of the GATA sequence for NIT2 binding. Four high-affinity binding sites for the NIT2 protein were found within a central region of the nit-2 gene itself.     

Inorganic nitrogen regulation of glutamate uptake in the cyanobacterium Nostoc muscorum

In Nostoc muscorum (Anabaena ATCC 27893) glutamate was not metabolised as a fixed nitrogen source, rather it functioned as an inhibitor of growth. The latter effect was nitrogen source specific and occurred in N₂-fixing cultures but not in cultures assimilating nitrate or ammonium. NO₃^--grown cultures lacked heterocysts and nitrogenase activity and showed a nearly 50% reduction in glutamate uptake rates, as well as in the final extent of glutamate taken up, compared to N₂-fixing or nitrogen-limited control cultures. NH₄⁺-grown cultures showed a similar response, except that the reduction in glutamate uptake rates and the final exten of glutamate taken up was over 80%. The present results suggest a relation between nitrate/ammounium nitrogen-dependent inhibition of glutamate uptake, probably via repression of the glutamate transport system, and glutamate toxicity.