Showing papers on "Nitrogen fixation published in 1968"

Formation of the nitrogen-fixing enzyme system in Azotobacter vinelandii.

Abstract: The formation and activity of nitrogenase2 in Azotobacter vinelandii OP was examined using a cell-free assay system. A lag period of about 30 min occurred between the exhaustion of the combined nitrogen source and growth on N2. Cells grown on ammonium acetate or potassium nitrate had no detectable nitrogenase activity. Nitrogenase activity appeared in cells, grown under a flowing gas phase of 20% O2 – 60% He, about 45 min after the exhaustion of ammonia. Nitrogenase formation was inhibited in a closed system with an atmosphere containing 40% O2 but not by one containing 20% O2. Hydrogen did not inhibit enzyme formation. The question of whether N2 is required for the formation of the enzyme could not be answered as this gas could not be completely eliminated from the growth system. Chloramphenicol prevented the formation of the enzyme and inhibited nitrogen fixation in whole cells, but had no effect on cell-free enzyme activity. A brief rise in turbidity which occurred during nitrogenase formation appeared...

Ecological Importance of Snowbrush Ceanothus Velutinus in the Oregon Cascades

Abstract: Twelve stands of snowbrush were selected for a biomass study to estimate nitrogen fixation under field conditions west of the summit of the Oregon Cascades Total nitrogen in the upper 2 ft of soil was higher under snowbrush than in the open, but the difference may have been caused by loss of nitrogen from open areas rather than by nitrogen fixation Total nitrogen in the upper 15 cm of soil under snowbrush did not differ from that found under nonfixing shrub species Various shrub species may increase the total soil nitrogen under their canopies, however, if only by accumulation from sites that lack vegetation More nitrogen may be tied up in the biomass of mature snowbrush stands than in stands of other shrubs The difference could be explained by nitrogen fixation, which may range from zero to about 20 kg/ha per year under conditions of this study Nodulated snowbrush seedlings produced 25 times the dry weight that non—nodulated seedlings produced in a nitrogen deficient soil Sixty—one per cent of the nitrogen in nodulated greenhouse seedlings was fixed Such fixation rates may be reached on infertile soils in the field, but they seem unlikely on soils of medium or better fertility This point seems to be substantiated by delay in nodulation of snowbrush in soils with increased levels of organic matter Bioassay tests using Douglas fir seeds and hemlock seedlings showed that snowbrush did not add to the soil any significant amount of nitrogen by nitrogen fixation The species contributes to the formation of a new organic layer, however, through large amounts of nitrogen—rich litter

An electron donor system for nitrogenase-dependent acetylene reduction by extracts of soybean nodules.

Abstract: The catalysis of nitrogen reduction by extracts of nitrogen-fixing organisms requires an ATPgenerating system and a source of electrons (1, 2, 5, 11, 13). The phosplhoroclastic reaction provides botlh ATP anid electrons for the reduction of nitrogen by cell-free extracts of Clostridium1t pasteurianumn (2, 5, 13) and ferredoxin functions as the natural electron carrier from the phlosphoroclastic reaction to nitrogenase ('12). Some evidence has been reported (2) that boro,hydride, hydrogen, NADH or NAiDPH, in presence of ferredoxin, will serve as a reductant for nitrogen fixation by the clostridial system. Cell-free extracts of Azotobacter vinelandiz (1) and bacteroids from soybean nodules (11) also catalvze the reduction of N. to NH, but an exogenous souirce of both reductant and ATP must be furnisihed. Probablv the phvsiological source of reductant and ATP for nitrogen fixation by leguime nodules and azotobacter is the respiratory electron transport chain with its associated oxidative phosphorvlation. All efforts however to coutple nitrogen fixation by cell-free extracts of these organisms to naturally occutrring oxidation-redutction reactions have failed. There are no reports of the identification in azotobacter or legume nodules of a low potential electron carrier analogous to ferredoxin. Using the reduction of acetylene to etlhy-lene as a measure of nitrogenase activity (3, 14), evidence has been obtaiined that NADH genierated by the fl-hydroxybutyrate dehvdrogenase reaction or high concentrations of NADH supplied directly function as a source of electrons for acetvlene redutction by extracts of nodule bacteroids or azotobacter. Activity also is dependent 1110pon an ATP-generating system and a suiitable dye. Cell-free extracts of soybean nodlules were prepared by the nmetho(d of Kochi, Evan,s, and Ruissell (10, 11) with minor changes to improve the nitrogenase activity. Ethyrlene production from acetylene was measuired by a method described by Kelly,

Comparative Studies of Nitrogen Fixation by Soybean Root Nodules, Bacteroid Suspensions and Cell-free Extracts

Abstract: SUMMARY: Rhizobium japonicum (CC711) was used to infect soybean seeds from which plants were grown. From the root nodules, bacteroid suspensions with initial rates of nitrogen fixation as high as those calculated for bacteroids in intact nodules were prepared. Oxygen, which was required for fixation by intact nodules and bacteroid suspensions, caused the eventual loss of bacteroid nitrogen-fixing ability, accompanied by an increase in O2-uptake. In intact nodules and in bacteroid suspensions, increasing O2 pressures resulted in higher values for K m of nitrogen fixation. V max also increased with increasing pO2 and this was shown to be consistent with the characteristics of nitrogen fixation by anaerobic cell-free extracts of bacteroids which required an energy source (ATP), and a reductant (sodium dithionite). Higher concentrations of carbon monoxide were required to inhibit nitrogen fixation by intact nodules than by bacteroid suspensions. Carbon monoxide was a competitive inhibitor of nitrogen fixation in bacteroid suspensions and Ki (CO) and Km (N2) values showed that the nitrogenase had about 30 times the apparent affinity for CO that it had for N2. In cell-free extracts of bacteroids, the nitrogen-fixing activity remained in the supernatant fluid after centrifugation at 100,000 g for 30 min. The extracts were inactivated at 0°. The Km for nitrogen fixation by cell-free extracts was variable, 62-118 (N2 concentration in mm. Hg. pressure), compared with 50-60 for intact nodules and 20 for intact bacteroids when Km for these was measured in the range of pO2 in which it was only slightly affected by O2. The Ki for inhibition of nitrogen fixation by CO in extracts was similar to values obtained with intact bacteroids.

Nitrogen fixation by cell-free extracts of Klebsiella penumoniae.

Abstract: A cell-free system which permits nitrogen fixation by extracts of Klebsiella pneumoniae M5al (formerly Aerobacter aerogenes) has been developed. It is, essentially, that system described by Bulen and associates for Azotobacter vinelandii, utilizing ATP as a source of energy and dithionite as a source of electrons. The Michaelis constant for fixation has been estimated to be 0.12 atm. The extracts possessed an ATP-dependent hydrogen evolving system. Hydrogen evolution from these extracts was less under nitrogen than under helium in the presence of ATP. Nitrogen gas appears to be the inducer of nitrogen fixation. In the absence of N2, no induction of nitrogenase occurs. Nitrogenase is absent in cells grown on NH4+-N. There is a lag of about 13 h after the introduction of N2 gas into a culture which has depleted its supply of NH4+-N before nitrogenase can be detected. For reasons discussed in the text, this conclusion must be regarded as tentative at this time. Ammonium ion appears to prevent the synthesis o...

Nitrogen Fixation and the Utilization of Other Inorganic Nitrogen Sources in a Subarctic Lake

Abstract: A year-round limnological study of the biological utilization of molecular nitrogen, ammonia, and nitrate in Smith Lake, a small subarctic lake in interior Alaska, showed that ammonia was consistently the most important nitrogen source. Of the two main algal production periods, the first took place under the ice in May, and depended on ammonia accumulated during the winter for a nitrogen source. The population at this time consisted largely of microflagellates. Chlamydomonas, Euglena, Chlorella, and Mellamonas were among the identified algae present. Immediately after the ice melted from the lake surface, a second population developed. These algae, consisting almost exclusively of Anabaena flos-aquae, used ammonia, nitrate, and molecular nitrogen simultaneously. During the remainder of the summer, uptake rates remained relatively low, with ammonia the most important nitrogen source; during the fall, nitrate uptake briefly approached the magnitude of ammonia uptake. 15N tracer methods were used to measure ...

Interrelations of micro-organisms and mulberryII. Phyllosphere microflora and nitrogen fixation in leaf and root surfaces

Abstract: The mulberry leaves were shown to harbour substantial populations of bacteria, streptomycetes, yeasts, and moulds. Azotobacter and Beijerinckia were observed to contribute to nearly 5 to 10 per cent of the bacterial population. When grown in water culture under sterile conditions, Azotobacter inoculation on the leaf or root surface was found to increase plant growth, dry wt, and nitrogen content of the mulberry. The beneficial effect of Azotobacter was largely influenced by the presence of a carbon source in the plant nutrient solution. The root inoculation in comparison to leaf application was found to confer greater benefits to the growing plant. The presence of carbohydrates and amino acids in the leaf leachates of mulberry was shown. The mutual beneficial nature of the association of the plant and Azotobacter has been brought to light.

Nodulation of Legumes in the Sudan: Cross-Inoculation Groups and the Associated Rhizobium Strains

Abstract: Cross-inoculation tests, based on nodule formation and nitrogen fixation, were made on 21 species of legumes commonly found in the Sudan. The results showed that they may be grouped according to the accepted system of classification, but there were some important inconsistencies in the cowpea group. For instance, Arachis hypogaea and Acacia spp. have their own strains of Rhizobium. The cultural and physiological characters of the rhizobia studied were generally similar to those known for other species of the organisms.

Regulation of Nitrogen Fixation in Azotobacter vinelandii OP and in an Apparently Partially Constitutive Mutant

Abstract: Methylamine and 2-methylalanine appeared to act as co-repressors of nitrogenase in Azotobacter vinelandii OP. They inhibited the growth of this organism on molecular nitrogen but not on nitrate, ammonia, or Casamino Acids; they prevented the formation of nitrogenase by cells transferred from repression to induction conditions; and they did not inhibit the activity of nitrogenase in vitro. A mutant of strain OP, selected on the basis of its relative resistance to methylalanine, appeared partially constitutive because nitrogenase in this strain was less sensitive to repressors than was the enzyme in the wild-type strain.

Taxonomy of Azotomonas Species

Abstract: The ability of two strains of Azotomonas insolita and one strain classified only as Azotomonas species to use molecular nitrogen was investigated by use of several techniques. Molecular 15N2 incorporation by growing cultures of Azotomonas was inconsistent and limited. In addition, attempts to demonstrate nitrogen fixation in growing cultures by the radioactive 13N2 technique were negative. Experiments were done in which the total nitrogen content of a culture was determined by a micro-Kjeldahl method. None of these experiments resulted in a significant increase in total nitrogen. Attempts to show a diauxie effect, that is, transition from growth on NH4+ to N2, were also unsuccessful. Nitrogen fixation by cell-free extracts of A. insolita was negative, as determined by reduction of N2 to NH3, and reduction of cyanide, of acetylene, and of azide. These negative results suggest that the taxonomic reclassification of the genus Azotomonas should be considered.

Interferência do cálcio e nitrogênio na fixação simbiótica do nitrogênio por duas variedades de Phaseolus vulgaris L.

Abstract: A greenhouse experiment was carried out to study the interference of calcium and nitrogen in symbiotic nitrogen fixation of beans. The experiment had a factorial design including four calcium levels, four nitrogen levels and two varieties, namely Venezuela and Rico 23. The variety Venezuela showed more abundant nodulation, which was less affected by environmental effects not controlled in this experiment. Both varieties increased nodule weight at the 10 ppm N-level but this increase varied with the variety at different calcium levels. N at 40 ppm reduced nodulation in all treatments except the variety Rico 23 at the two lowest calcium levels. Neither of the varieties fixed nitrogen equivalent to 40 ppm of N applied as fertilizer, the variety Venezuela with 200 ppm of gypsum reaching the highest amount of N fixed (95% of the maximal total N reached by this variety with 40 ppm N). The nitrogen fixation of the variety Rico 23 reached only 50% of the best treatment with 40 ppm of N. It was concluded that physiological differences between bean varieties related to calcium and nitrogen nutrition can be responsible for plant determined deficiencies in nodulation.

Nitrogen fixation by lucerne on several soils in pot culture

Abstract: Nitrogen fixation by lucerne (Medicago sativa) was measured on ten agricultural soils in pot culture. There was a three-fold variation in nitrogen fixation, smallest quantities being fixed on a red brown earth, a euchrozem, and a wiesenboden. Both lucerne yield and nitrogen fixation were significantly correlated with soil pH over a range of 6.2 to 8.6 when phosphorus and sulphur were applied. These two nutrients caused significant increases in lucerne yields and nitrogen fixation on all soils. Fixed nitrogen originating solely from the underground parts of the lucerne plants caused significant increases in the nitrogen yield of wheat grown subsequently on the same soils.

Inoculação, adubação nitrogenada e revestimento calcário em três variedades de soja ( Glycine max (L.) Merril)

Abstract: Three field experiments were conducted in consecutive years at different areas utilizing a 3 x 3 x 3 factorial design consisting of three varieties, three nitrogen treatments (0, inoculation and mineral nitrogen) and three lime treatments (0, lime pelleting and liming the soil) with the objectives of studying the interference of mineral nitrogen and liming on nitrogen fixation and yield of different varieties of soybeans. In the three experiments the variety Mamouth showed better nodulation than the other two varieties, the nodulation being less affected by the treatments, including inoculation. The variety Pelikan presented the poorest nodulation. The variety Abura, in one of the experiments, had as poor nodulation as the variety Pelikan while in another, in the inoculated plots it nodulated as well as the variety Mamouth. This shows varying dependence of nodulation upon environmental effects in the different varieties. Liming increased nodulation of soybeans only in one of the experiments although the pH of all three soils was acid (4,8; 5,8 and 5,4). In the same experiment lime pelleting of the seeds was more effective than liming. Lime pelleting in one other experiment had similar efficiency but only when the seeds were inoculated (interaction N x lime treatments.) In relation to soybean yield significant differences were only observed between varieties which follow the general pattern of nodulation, Mamouth and Abura being more productive than Pelikan. In two of the experiments the nitrogen treatments were also significant showing higher yields with inoculation than with mineral nitrogen in one, while in another, mineral nitrogen was more effective than inoculation. There was, in two of the experiments, a highly significant regression of soybean yield with nodule weight indicating that nitrogen fixation was the limiting factor of soybean production, when no nitrogen fertilizer was used.