Topic
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.
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TL;DR: One group of proteins secreted by rhizobia have homologues in bacterial pathogens and may have been co-opted by rhzobia for symbiotic purposes.
Abstract: Rhizobia - a diverse group of soil bacteria - induce the formation of nitrogen-fixing nodules on the roots of legumes. Nodulation begins when the roots initiate a molecular dialogue with compatible rhizobia in the soil. Most rhizobia reply by secreting lipochitooligosaccharidic nodulation factors that enable entry into the legume. A molecular exchange continues, which, in compatible interactions, permits rhizobia to invade root cortical cells, differentiate into bacteroids and fix nitrogen. Rhizobia also use additional molecular signals, such as secreted proteins or surface polysaccharides. One group of proteins secreted by rhizobia have homologues in bacterial pathogens and may have been co-opted by rhizobia for symbiotic purposes.
293 citations
TL;DR: Hypotheses concerning factors causing cyanobacterial dominance in freshwaters are reviewed against evidence from four different types of lakes and it is argued that either cyanobacteria should not be treated as a group or that more information is needed.
Abstract: Hypotheses concerning factors causing cyanobacterial dominance in freshwaters are reviewed against evidence from four different types of lakes. It is argued that either cyanobacteria should not be treated as a group or that more information is needed. It
293 citations
TL;DR: The formation and activity of nitrogenase2 in Azotobacter vinelandii OP was examined using a cell-free assay system and the question of whether N2 is required for the formation of the enzyme could be answered as this gas could not be completely eliminated from the growth system.
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...
291 citations
TL;DR: Whether chick-pea (Cicer arietinum L.) is an important crop in saline stress on nitrogen fixation is due to a limitation is ascertained.
Abstract: utes is more a consequence of damage produced by salt stress than of a protective strategy. Plants of chick-pea (Cicer arietinum L. cv. ILC1919) inoculated with Mesorhizobium ciceri strain ch‐191 Key words: Chick-pea, salt stress, nitrogen fixation, photowere grown in a controlled environmental chamber, synthesis, ammonium assimilation. and were administered salt (0, 50, 75, and 100 mM NaCl) during the vegetative period. Four harvests (4, 7, 11, and 14 d after treatment) were analysed. The Introduction aim was to ascertain whether the negative effect of Chick-pea (Cicer arietinum L.) is an important crop in saline stress on nitrogen fixation is due to a limitation
288 citations
TL;DR: It is suggested that molybdenum limitation may be common in highly weathered acidic soils, and may constrain the ability of some forests to acquire new nitrogen in response to CO2 fertilization.
Abstract: Biological nitrogen fixation limits plant growth and carbon exchange at local to global scales. Long-term nutrient manipulation experiments in forests and short-term manipulation experiments in microcosms suggest that the micronutrient molybdenum, a component of the nitrogen-fixing enzyme nitrogenase, limits nitrogen fixation by asymbiotic bacteria in tropical soils in Panama. Nitrogen fixation, the biological conversion of di-nitrogen to plant-available ammonium, is the primary natural input of nitrogen to ecosystems1, and influences plant growth and carbon exchange at local to global scales2,3,4,5,6. The role of this process in tropical forests is of particular concern, as these ecosystems harbour abundant nitrogen-fixing organisms1,4 and represent one third of terrestrial primary production4,7,8. Here we show that the micronutrient molybdenum, a cofactor in the nitrogen-fixing enzyme nitrogenase, limits nitrogen fixation by free-living heterotrophic bacteria in soils of lowland Panamanian forests. We measured the fixation response to long-term nutrient manipulations in intact forests, and to short-term manipulations in soil microcosms. Nitrogen fixation increased sharply in treatments of molybdenum alone, in micronutrient treatments that included molybdenum by design and in treatments with commercial phosphorus fertilizer, in which molybdenum was a ‘hidden’ contaminant. Fixation did not respond to additions of phosphorus that were not contaminated by molybdenum. Our findings show that molybdenum alone can limit asymbiotic nitrogen fixation in tropical forests and raise new questions about the role of molybdenum and phosphorus in the tropical nitrogen cycle. We suggest that molybdenum limitation may be common in highly weathered acidic soils, and may constrain the ability of some forests to acquire new nitrogen in response to CO2 fertilization9.
286 citations