Nitrogen fixation

About: Nitrogen fixation is a research topic. Over the lifetime, 7940 publications have been published within this topic receiving 232921 citations. The topic is also known as: GO:0009399.

Inhibition of Nitrogen Fixation in Soybean Plants Supplied with Nitrate I. Nitrite Accumulation and Formation of Nitrosylleghemoglobin in Nodules

Abstract: The present investigation was undertaken in order to examine the influence on nitrogen fixation of the accumulation of nitrite, as result of the supply of exogenous nitrate, in soybean nodules, and to clarify the relationship between the inhibition of nitrogen fixation, the formation of nitrite in the nodule cytosol, and the decrease in leghemoglobin function due to the formation of LbNO under such conditions

The Effects of Anaerobiosis on Nitrogenase Synthesis and Heterocyst Development by Nostocacean Cyanobacteria

Abstract: SUMMARY: Effective nitrogenase synthesis by nostocacean cyanobacteria (including one mutant strain unable to form heterocysts or fix nitrogen aerobically) was induced in the light in the absence of molecular oxygen. Anaerobiosis was maintained during induction by treating the organisms with dichloromethylurea which prevents photosynthetic oxygen production. Under these special conditions both synthesis and activity of nitrogenase were light-dependent, the required ATP being produced by cyclic photophosphorylation. Enzyme synthesis and activity were also dependent on the availability of an organic substrate that could serve both as a general source of carbon and as a source of reductant. The organic requirement could be fulfilled by the intracellular glycogen reserve or, in facultative hetero-trophs, by a utilizable sugar (e.g. glucose). Nitrogenase synthesized anaerobically was highly susceptible to inactivation by molecular oxygen in vivo: exposure of a suspension of anaerobically induced filaments to 20% (v/v) O2 for 1 h caused total and irreversible destruction of the enzyme. Anaerobic nitrogenase synthesis was not accompanied by the differentiation of mature heterocysts, the morphogenetic process being arrested at an early (proheterocyst) stage. After the gratuitous anaerobic synthesis of nitrogenase, introduction of either N2, nitrate or ammonia to the illuminated, anaerobic suspension resulted in a rapid accumulation of cyanophycin granules in both vegetative cells and proheterocysts. Cyanophycin was randomly deposited in vegetative cells, but localized at the cell poles of the proheterocysts. The bearing of these findings on the role played by the heterocyst in nitrogen fixation is discussed.

Root Growth and Dry Matter Distribution of Soybean as Affected by Phosphorus Stress, Nodulation, and Nitrogen Source1

Abstract: gy reducing nitrate when NO3-N is the source of available N. Thus, for legumes able to form symbiotic associations with Rh izobium, the pattern of dry matter distribution (DMD) within the plant will differ depending upon its mode of N nutrition. The partitioning of dry matter between root and shoot is a heritable characteristic determined by the genotype of the plant (Andrews, 1939; Shank, 1943). Root morphology likewise is considered to be genetically determined (Smith, 1934; Zobel, 1975; Street, 1969). The expression of these characteristics can be altered by environmental conditions. Deficiencies of essential mineral nutrients have been shown to affect both the DMD within the plant and lateral root development. Plants deficient in N or P tend to accumulate relatively more dry matter in their roots than do plants which are adequately supplied (Turner, 1922; Brouwer, 1962). Weisum (1958) demonstrated that root branching in pea (Ptsum sattvum L.) was stimulated by nutrients as follows: NO3-N>P>K> Mg>Ca. Nitrate applied to a discrete root segment increased both the rate of lateral root extension and number of lateral roots per unit length of root (Hackett, 1972; Mdntyre and Raju, 1967; Drew, 1975). The establishment of an active N-fixing nodule system on the roots of a legume complicates these relationships. During the vegetative stage of growth, active root nodules utilize significant quantities of photosynthate for nodule growth and for N fixation (Minchin and Pate, 1972; Herridge and Pate, 1977). Summerfield et al. (1977) found that the root:shoot dry weight ratio in cowpea (Yigna unguiculata L. Walp.) was larger in nonnodulated plants than in nodulated plants grown at equivalent levels of applied N. Experiments with red clover (Trifolium pratense L.) and barrel medic (Medicago tribuloides Desr.) indicate that there is an inverse relationship between nodule number and lateral root formation (Nutman, 1948; Dart and Pate, 1959). Also, there are qualitative observations concerning differences between the root morphology of grain legumes provided combined N and those which are effectively nodulated (Weber, 1966; Wych and Rains, 1978). The purpose of this study was to define the changes in DMD and root development in the soybean plant as influenced by the mode of N nutrition, the magnitude of root nodulation, and P deficiency. ABSTRACT

Biological nitrogen fixation: A key to world protein

Abstract: 1. Characteristics and methodology of the C2H2-C2H4 assay forin situ measurement of N2 fixation are outlined. 2. Electron micrographic analysis of the developmental morphology of the natural soybean symbiosis and C2H2-C2H4 analysis indicate that increasing N2-fixing activity from 12–35 days of age is accompanied by an increase in bacteroid number per cell, bacteroid number per vesicle and inclusions per bacteroid. The mole ratio of leghemoglobin to nitrogenase also increases from 50 to a relatively constant plateau of 500 to 1500 during this period. The quantitative validity of the C2H2-C2H4 assay as a measure of N2 fixation during a complete growth cycle of soybeans on nitrogen-free medium is demonstrated by Σ (C2H2→C2H4)×28/3 values which are 75–95% of the values determined for N2 fixed by Kjeldahl analyses. 3. A technique for the establishment of the first callus N2-fixing symbiosis in mixed cultures ofRhizobium legume provides a defined experimental system for exploration of legume symbiosis. N2-fixing activity is about 1% of the natural system and is influenced by exogenous auxins and cytokinins. Morphology, including infection threads and vesicle enclosed bacteroids, is similar to the nodule system. 4. N2-fixing activity of field-grown soybeans, including varieties which differed in flowering characteristics and maturity dates, and of peanuts was determined biweekly with the C2H2-C2H4 assay. Activity extended from nodule initiation to senescence and correlated with the nitrogen demands of the plant and in most cases >90% of the N2 fixed during the 60–70 day period of fruit formation and maturation. A logarithmic relationship between N2-fixing activity and age, and N2 fixed and age was demonstrated as a fundamental characteristic of these annual symbionts,i.e. log N2 fixed =k(t−t 0), wheret 0 is age at activity initiation. The resultant parameters: 1) age at activity initiation, 2) calculated rate of daily increase (7–9% for soybeans and 7–10% for peanuts), 3) age at end of logarithmic phase (about 80 days for soybeans), and 4) total N2 fixed (about 250 mg per soybean plant) are useful bases for evaluation of environmental, bacterial and host effects on N2 fixation. Various N fertilizers applied at planting and flowering inhibited N2 fixation of soybeans by decreasing the rate of daily increase. 5. Physical and chemical characteristics of nitrogenase, including those of crystalline Mo-Fe protein, reactions of nitrogenase, and model studies are consistent with a proposed mechanism. 6. Potential utilities of N2 fixation research include increased food protein production via initially enhanced N2 fixation of legumes such as soybeans and eventually extension of N2-fixing symbioses to non-legumes and new chemistry of N2, including the direct incorporation of aerial N2 into important organic compounds.

Review: Nitrogen Fixing Microorganisms

Abstract: Microorganisms employed to enhance the availability of nutrients, viz., nitrogen (by fixing atmosphere N ), to the crops are called biofertilizers. In recent years, biofertilizers have emerged as an important 2 component for biological nitrogen fixation. It offers an economically attractive and ecologically sound route for augmenting nutrient supply. Plant growth promoting species are commonly used to improve crop yield. In addition to their agricultural usefulness, there are potential benefits in environmental applications. Thus various species of Rhizobium for legumes, blue - green algae (BGA) or cynaobacteria and Azolla (a fern containing symbiotic N - fixing BGA, i.e., Azolla Anabaena Azollae) for wet land rice and Azotobacter / Azospirillum for 2 several crops can play significant role in agriculture.