Browsing by Author "Har Darshan Kumar"

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Effect of methionine-sulfoximine on nitrate uptake and photosynthesis in the cyanobacterium Anabaena doliolum Bharadwaja
(Springer-Verlag, 1988) Durg Vijai Singh; Har Darshan Kumar
l-Methionine-dl-sulfoximine (MSX) stimulated nitrate uptake but inhibited14CO2 fixation and O2 evolution in Anabaena doliolum. Nitrate uptake was inhibited by ammonium (NH4+) in the absence of MSX, but not in the presence of MSX. Glutamine or a derivative of it appears to be the actual negative effector of nitrate utilization. In presence of nitrate, MSX-treated cells of A. doliolum evolve more O2 than do untreated cells. Our results suggest a close relation between photoassimilation of carbon and utilization of nitrogen. © 1988 Springer-Verlag New York Inc.
Effects of Amino Acids, Carbohydrates and Phosphorus Sources on Growth and Alkaline Phosphatase Activity of the Marine Cyanobacterium Anabaena sp. Strain CA
(1997) Jeet Bahadur Singh; Deepak Vyas; Har Darshan Kumar
Alkaline phosphatase (APase) was found to be inducible in Anabaena sp. strain CA. Growth was less than control in presence of most amino acids except glycine and serine, but most amino acids enhanced APase activity. Highest APase activity was recorded in tyrosine supplemented culture followed by hydroxyproline, cystein, valine and glutamic acid. Threonine supplemented material showed lowest APase level (1.8 nmol/mg protein/min). Lactose, glucose, sodium pyruvate and succinate stimulated growth but not APase activity. APase activity was high in the presence of sucrose, mellibiose, mannitol, arabinose, maltose and sorbose, even though the growth in these supplements was less than in control. Organic phosphate sources supported good growth of the organism. Best growth occurred in presence of inorganic phosphate, adenosine diphosphate, fructose 1,6-diphosphate or ribulose 1,5-diphosphate, followed by other phosphorus sources tested. APase activity in presence of any of the organic phosphate sources was 3 to 5 fold low as compared to phosphate limited culture. Also, there was no APase activity in cultures grown on inorganic phosphate. These data indicate that most amino acids and a few carbohydrates (sucrose, mellibiose, arabinose and sorbose) are suitable for APase production. Lactose, glucose, pyruvate or succinate may be used as a carbon source during photoheterotrophic growth of the cyanobacterium. Glycine and serine are preferred nitrogen sources for its growth. Phosphate repressible APase activity has been found in Anabaena sp. strain CA.
EFFECTS OF QUENCHING AGENTS ON THE PHOTODYNAMICALLY‐INDUCED CHEMOTACTIC RESPONSE OF THE COLORLESS FLAGELLATE Polytomella magna
(1984) Wilhelm Nultsch; Har Darshan Kumar
Abstract In the presence of the photosensitizer riboflavin at high fluence rates a photoproduct, most probably H2O2, is formed which causes negative phototaxis in the colorless flagellate Polytomella magna. The aim of this study was to find out whether H2O2 is produced in a type I or II reaction. As has been shown, 1O2 quenchers either do not influence the photodynamic action of riboflavin (furfuryl ethanol, DPBF, l‐histidine, crocetin) or show slight quenching effects only at very high concentrations ≧ 10−2M (DABCO, DMF, imidazole). D2O is toxic to P. magna even in 1:1 and 1:2 mixtures with H2O. On the other hand, the quenching effect of 1,4‐benzoquinone, highly indicative for the type I pathway, is more than two orders of magnitude stronger than the one of the above mentioned 1O2 quenchers. The results suggest that H2O2 is produced in a type I reaction. Superoxide does not seem to be involved since superoxide dismutase does not diminish the photodynamic effect of riboflavin. Copyright © 1984, Wiley Blackwell. All rights reserved
Effects of some inhibitors and carbon sources on acetylene reduction and hydrogen production of isolated heterocysts of anabaena sp. (strain ca)
(1990) Dhruv Kumar; Har Darshan Kumar
Metabolically active heterocysts isolated from wild-type Anabaena sp. strain CA showed high rates of light dependent acetylene reduction and H2 evolution. Fructose and erythrose significantly stimulated nitrogenase activity but not H2 evolution. DCMU and cyanide were not effective. DBMIB significantly inhibited both nitrogenase and nitrogenase-catalysed H2 evolution. This inhibition was overcome by a catalytic amount of TMPD. These data suggest that in the isolated heterocysts all electrons, irrespective of source, must pass through the plastoquinone pool before reducing ferredoxin, which in turn can reduce dinitrogen to ammonia. © 1990 Taylor & Francis Group, LLC.
Hydrogen production by several cyanobacteria
(1992) Dhruv Kumar; Har Darshan Kumar
Twenty species belonging to eleven genera of nitrogen-fixing and non-nitrogen-fixing cyanobacteria were screened for production of hydrogen. Only one species each of Nostoc and Anabaena showed light- and nitrogenase-dependent aerobic hydrogen production. The highest rate of aerobic hydrogen production was recorded in Anabaena sp. strain CA. When incubated anaerobically under 99% Ar + 1% CO2, all the tested strains produced hydrogen. Nickel supplementation completely abolished hydrogen production both under aerobic and anaerobic conditions, except in Anabaena sp. strain CA, where only the rate of production was decreased. Species of Plectonema, Oscillatoria and Spirulina showed methyl viologen-dependent (hydrogenase-dependent) hydrogen production. Other physiological activities were also studied with a view to selecting a suitable organism for large-scale production of hydrogen. © 1992.
Observations on the Developmental Variability of Camptylonema lahorense Ghose
(Kluwer Academic Publishers, 1962) Har Darshan Kumar
The variability of Camptylonema lahorense G hose has been studied during its development both in nature and in unialgal cultures. In nature the alga is mostly unbranched whereas in cultures it shows profuse pseudo-branches, both single and geminate. Akinetes have not been found anywhere. Observations have also been recorded on the ecological factors determining the growth of the alga in nature. Slightly alkaline and base-deficient soils with variable nitrate content and moderate to high oxidation intensity determine its growth. In the light of present study, the systematic position and the affinities of the alga have been discussed. © 1962 Dr. W. Junk Publishers.
Protection of nitrogenase levels in dark-incubated cultures of anabaena sp. Strain ca by various carbon sources, and restoration of nitrogenase activity by oxygen
(1990) Dhruv Kumar; Har Darshan Kumar
Photoautotrophically grown, nitrogen-fixing cultures of Anabaena sp. strain CA lost nitrogenase activity completely after 4 h of incubation in the dark. The original level of nitrogenase activity was restored within 3 h of re-illumination and was apparently dependent on de novo protein synthesis. Several organic carbon sources protected nitrogenase activity. The heterocysts isolated from photoautotrophically grown cultures incubated in the dark (35 min) showed negligible nitrogenase activity. When these heterocysts were exposed to oxygen, glucose or fructose during isolation, normal activity was observed only with 02. Oxygen also enhanced the rate of initial H2 evolution from isolated heterocysts. © 1990 The British Phycological Society.
Regulatory effect of external pH on the intracellular pH in alkalophilic cyanobacteria Microcystis aeruginosa and Hapalosiphon welwltschii
(1994) Alka Dwivedi; Usha K. Srinivas; Hriday Narain Singh; Har Darshan Kumar
[No abstract available]
Response of the cyanobacterium nostoc muscorum to chromium and lead: The effect on phosphorus metabolism
(1993) Jeet Bahadur Singh; Smeo Mohan Prasad; Lal Chand Rai; Har Darshan Kumar
Significant amelioration of Cr and Pb toxicity was observed in Nostoc muscorum at high concentrations of phosphate. The effect of Cr and Pb on growth, photosynthetic oxygen evolution, carbon and nitrogen fixation of N. muscorum was less in cultures pre- and post-treated with high (80 μM) Phosphate concentration than in those treated with a lower (20 μM) Orthophosphate concentration. The uptake of Cr and Pb in the cyanobac-terial cells was not affected by phosphate concentration. Likewise phosphate uptake was not disturbed either by Cr or Pb. A rapid accumulation of polyphosphate bodies in the cells treated with Cr and Pb indicates that uptake and accumulation of phosphate was not inhibited. N. muscorum cells exposed to both the metals registered a notable decrease in the breakdown of polyphosphate bodies and acid and alkaline phosphatase activities. Cr and Pb competitively inhibited the activity of partially purified acid and alkaline phosphatases. It is concluded that Cr and Pb affect intracellular phosphate metabolism rather than the uptake and incorporation of phosphate in N. muscorum. © 1993, Applied Microbiology, Molecular and Cellular Biosciences Research Foundation. All rights reserved.
Services of algae to the environment
(2000) Lal Chand Rai; Har Darshan Kumar; Frieder Helmut Mohn; Carl Johannas Soeder
Being autotrophic, algae occupy a strategic place in the biosphere. They produce oxygen both directly and indirectly through the chloroplasts of all green plants. The chloroplasts are believed to have originated from archaic prokaryotic algae through endosymbiosis with primitive eukaryotic cells. Phytoplankton and other algae regulate the global environment not only by releasing oxygen but also by fixing carbon dioxide. They affect water quality, help in the treatment of sewage, and produce biomass. They can be used to produce hydrogen which is a clean fuel, and biodiesel, and fix N2 for use as a biofertilizer. Some other services of algae to the environment include restoration of metal damaged ecosystems, reducing the atmospheric CO2 load and mitigating global warming, reclamation of saline-alkaline unfertile lands, and production of dimethyl sulphide (DMS) and oxides of nitrogen (NOx) involved in the regulation of UV radiation, ozone concentration, and global warming. Algae can be valuable in understanding and resolving certain environmental issues.
Stimulation of in vivo nitrate reductase activity in the thermal cyanobacterium Oscillatoria princeps under microaerobic conditions
(Springer-Verlag, 1986) Mahendra Jha; Ashok Kumar; Har Darshan Kumar
Nitrate reductase activity in the thermal cyanobacterium Oscillatoria princeps was studied in vivo. Nitrite production by O. princeps grown microaerobically was four- to seven-fold higher than that in aerobic controls. Whereas microaerobic conditions caused instantaneous stimulation of nitrate reductase activity, addition of 40% O2 in air immediately inhibited it. Exposure of another cyanobacterium Anabaena doliolum to microaerobic conditions had no effect on NO2- production. © 1986 Springer-Verlag New York Inc.