Some aspects of the biology of nitrogen-fixing organisms

1987 ◽  
Vol 317 (1184) ◽  
pp. 111-129 ◽  
Keyword(s):  
Nitrogen Fixation ◽  
Root Hairs ◽  
Atp Synthesis ◽  
Host Cells ◽  
Diffusion Resistance ◽  
Nitrogen Fixing ◽  
Active Nitrogen ◽  
Rapid Responses ◽  
Infection Threads ◽  
Eukaryotic Organisms

Eukaryotic organisms do not fix nitrogen. Animals generally have no need to do so because of their complex food-acquisition and waste-disposal systems. Plants, by using carbon polymers for structural purposes, minimize their need for nitrogen. When very nitrogen-limited, to enter into symbiosis with nitrogen-fixing microorganisms may be the most controllable method for eukaryotes to obtain fixed nitrogen. Filamentous, heterocystous nitrogen-fixing cyanobacteria may be better adapted to a free-living than to a symbiotic existence, because of their complexity. In symbioses, their photosynthetic machinery becomes redundant and the need to differentiate heterocysts as well as derepress nif genes may be a disadvantage. This could in part account for the greater success of symbioses involving the structurally simpler genera Frankia , Rhizobium and Bradyrhizobium . Nitrogen fixation by legume nodules can be controlled by varying the oxygen supply. This control may be effected by a variable diffusion resistance, enabling oxygen required for ATP synthesis to be matched to available photosynthate. Such a resistance, which is probably located in the nodule cortex, may also be used to reduce nitrogen fixation in the presence of combined nitrogen and could also facilitate rapid responses to other forms of stress. Alternative resistances to gaseous diffusion may operate when water supplies are restricted. Rhizobium and Bradyrhizobium follow different patterns of differentiation into nitrogen-fixing bacteroids. These patterns are coupled with retention or loss of viability and with significant or no natural enrichment of the bacteroids with 15 N respectively. The basic patterns of each type are subject to host-modification. Recent studies on structures of primitive legume nodules show some parallels both with actinorhizas and with nodules on Parasponia induced by Bradyrhizobium . In particular, distribution of rhizobia in nodule tissues is intercellular and infection threads are formed only when bacteria ‘enter’ host cells; there is no intracellular ‘bacteroid’ stage. These threads are retained in the active nitrogen-fixing cells. Many legumes and some actinorhizas are not infected via root hairs. Therefore two of the stages often considered typical of the development of effective legume nodules, i.e. ‘release’ of bacteria into vesicles bounded by peribacteroid membrane and infection through root hairs, can be omitted; these omissions may be of use in attempts to transfer nodulating ability to new genera.

scholarly journals TECHNOLOGY PECULIARITIES OF NEW BIOLOGICAL PREPARATION MICROHUMIN

2008 ◽  
Vol 7 ◽  
pp. 57-68
Author(s):  
V.V. Volkogon ◽  
O.M. Berdnikov ◽  
E.I. Volkogon ◽  
N.P. Shtan’ko
Keyword(s):  
Nitrogen Fixation ◽  
Growth And Development ◽  
Spring Barley ◽  
Research Data ◽  
Biologically Active ◽  
Nitrogen Fixing ◽  
Active Nitrogen ◽  
Associative Nitrogen Fixation ◽  
Biological Preparation ◽  
Effect On Growth

The paper covers research data on technology elaboration of new biological preparation Microhumin. It was shown that combination of biologically active biohumus extract with the suspension of active nitrogen fixing strain of azospirills in certain ratio results in creation of preparation performing additive stimulatory effect on growth and development of spring barley plants and activity of associative nitrogen fixation.

scholarly journals NITROGEN FIXING BACTERIA OF SPRING WHEAT ROOT ZONE

2013 ◽  
Vol 17 ◽  
pp. 7-20
Author(s):  
O. V. Nadkernychna ◽  
E. P. Kopylov
Keyword(s):  
Nitrogen Fixation ◽  
Spring Wheat ◽  
Root Zone ◽  
Molecular Nitrogen ◽  
Wheat Root ◽  
Nitrogen Fixing ◽  
Nitrogen Fixing Bacteria ◽  
Active Nitrogen ◽  
Nitrogen Fixation Activity ◽  
Fixation Activity

The paper presents the study of active nitrogen fixation bacteria of genera Azotobacter, Azospirillum, Bacillus, Flavobacterium, Enterobacter and Pseudomonas isolated from root zone of spring wheat plants. The ability of selected diazotrophs to form associative systems with spring wheat was investigated. The most significant increase of molecular nitrogen fixation activity in root zone of plants was observed under the Azospirillum species background.

scholarly journals Active nitrogen fixation by Crocosphaera expands their niche despite the presence of ammonium – A case study

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Keisuke Inomura ◽  
Takako Masuda ◽  
Julia M. Gauglitz
Keyword(s):  
Nitrogen Fixation ◽  
Mechanistic Model ◽  
Energy Costs ◽  
High Electron ◽  
Nitrogen Fixing ◽  
Active Nitrogen ◽  
State Culture ◽  
Nitrogen Fixers ◽  
Efficient Alternative

Abstract Unicellular nitrogen fixer Crocosphaera contributes substantially to nitrogen fixation in oligotrophic subtropical gyres. They fix nitrogen even when significant amounts of ammonium are available. This has been puzzling since fixing nitrogen is energetically inefficient compared with using available ammonium. Here we show that by fixing nitrogen, Crocosphaera can increase their population and expand their niche despite the presence of ammonium. We have developed a simple but mechanistic model of Crocosphaera based on their growth in steady state culture. The model shows that the growth of Crocosphaera can become nitrogen limited despite their capability to fix nitrogen. When they fix nitrogen, the population increases by up to 78% relative to the case without nitrogen fixation. When we simulate a simple ecological situation where Crocosphaera exists with non-nitrogen-fixing phytoplankton, the relative abundance of Crocosphaera increases with nitrogen fixation, while the population of non-nitrogen-fixing phytoplankton decreases since a larger fraction of fixed nitrogen is consumed by Crocosphaera. Our study quantitatively supports the benefit of nitrogen fixation despite the high electron/energy costs, even when an energetically efficient alternative is available. It demonstrates a competitive aspect of Crocosphaera, permitting them to be regionally significant nitrogen fixers.

scholarly journals Morphology of root nodules and nodule-like structures formed by Rhizobium and Agrobacterium strains containing a Rhizobium meliloti megaplasmid.

1983 ◽  
Vol 97 (3) ◽  
pp. 787-794 ◽  
Author(s):  
C H Wong ◽  
C E Pankhurst ◽  
A Kondorosi ◽  
W J Broughton
Keyword(s):  
Normal Development ◽  
Rhizobium Meliloti ◽  
Root Nodules ◽  
Root Hairs ◽  
Host Cells ◽  
Donor Strain ◽  
Intercellular Spaces ◽  
Infection Threads ◽  
Infected Cells ◽  
Rhizobium Sp

We examined expression of the megaplasmid pRme41b of Rhizobium meliloti in two different Rhizobium sp. Strains and in Agrobacterium tumefaciens. Transfer of pRme41b into these bacteria was facilitated by insertion of a recombinant plasmid coding for mobilization functions of RP4 into the nif region (Kondorosi, A., E. Kondorosi, C.E. Pankhurst, W. J. Broughton, and Z. Banfalvi, 1982, Mol. Gen. Genet., 188:433-439). In all cases, transconjugants formed nodule-like structures on the roots of Medicago sativa. These structures were largely composed of meristematic cells but they were not invaded by bacteria. Bacteria were found only within infection threads in root hairs, and within intercellular spaces of the outermost cells of the structures. The donor strain of R. meliloti containing pAK11 or pAK12 in pRme41b initially produced nodules on M. sativa that did not fix nitrogen (Fix-). In these nodules, bacteria were released from infection threads into the host cells but they did not multiply appreciably. Any bacteroids formed degenerated prematurely. In some cases, however, reversion to a Fix+ phenotype occurred after 4 to 6 wk. Bacteria released into newly infected cells in these nodules showed normal development into bacteriods.

scholarly journals Infection and Invasion of Roots by Symbiotic, Nitrogen-Fixing Rhizobia during Nodulation of Temperate Legumes

2004 ◽  
Vol 68 (2) ◽  
pp. 280-300 ◽  
Author(s):  
Daniel J. Gage
Keyword(s):  
Root Hair ◽  
Composite Structures ◽  
Hair Growth ◽  
Root Hairs ◽  
Infection Thread ◽  
Nitrogen Fixing ◽  
Indeterminate Nodules ◽  
Infection Threads ◽  
Root Hair Growth ◽  
Temperate Legumes

SUMMARY Bacteria belonging to the genera Rhizobium, Mesorhizobium, Sinorhizobium, Bradyrhizobium, and Azorhizobium (collectively referred to as rhizobia) grow in the soil as free-living organisms but can also live as nitrogen-fixing symbionts inside root nodule cells of legume plants. The interactions between several rhizobial species and their host plants have become models for this type of nitrogen-fixing symbiosis. Temperate legumes such as alfalfa, pea, and vetch form indeterminate nodules that arise from root inner and middle cortical cells and grow out from the root via a persistent meristem. During the formation of functional indeterminate nodules, symbiotic bacteria must gain access to the interior of the host root. To get from the outside to the inside, rhizobia grow and divide in tubules called infection threads, which are composite structures derived from the two symbiotic partners. This review focuses on symbiotic infection and invasion during the formation of indeterminate nodules. It summarizes root hair growth, how root hair growth is influenced by rhizobial signaling molecules, infection of root hairs, infection thread extension down root hairs, infection thread growth into root tissue, and the plant and bacterial contributions necessary for infection thread formation and growth. The review also summarizes recent advances concerning the growth dynamics of rhizobial populations in infection threads.

scholarly journals INCREASING SOIL FERTILITY AS A RESULT OF THE ACCUMULATION OF NITROGEN BY LEGUMINOUS CROPS

2020 ◽  
pp. 48-60
Author(s):  
Ihor Didur ◽  
Victoriia Shevchuk
Keyword(s):  
Nitrogen Fixation ◽  
Plant Growth ◽  
Soil Fertility ◽  
Growth Regulator ◽  
Plant Growth Regulator ◽  
Humus Content ◽  
Organic Fertilizers ◽  
Natural Fertility ◽  
Nitrogen Fixing ◽  
Active Nitrogen

Analysis of literary sources shows that legume-rhizobial systems annually fix nitrogen from the atmosphere in the amount of from 40 to 300 kg of per 1 ha of crop. Crops of legumes by Nitrogen fixation capabilities play an important role in saving and improvement of the natural soil fertility. It is known that in the process of the crop rotation with legumes the species composition of soil microorganisms is restored, as a result stable soil fertility rate is supported. Legumes plants are valuable siderata. Green legume fertilizer has a positive effect on increasing the productivity of plants, causes to the conservancy and increase of soil fertility. The plowing of the siderates leads to an increase in the humus content in the soil and the availability of phosphate treatment, a reduction in nitrogen gas losses from the soil. After decomposition and mineralization of leguminous siderata, the soil is replenished with nutritious macro- and microelements. Siderata is able to loosen heavy soils, improve their structure, and inhibit the growth of weeds that create water deficiency and reduce the content of minerals in the soil. Growing of peas leads to increased of the absorption efficiency of organic fertilizers by the following crops. The article approves the results of increasing the nitrogen-fixing ability of sowing pea with applying of the microbial preparation Bioinoculant and plant growth regulator Mars EL, and their role in increasing of biological nitrogen content for repair of soil fertility. It was established that the symbiotic activity of pea plants depends on the growth phase of the crop. The highest indexes of active nitrogen-fixing nodules on the roots of pea plants were found in the budding phase after pre-sowing seed complex treatment with Bioinoculant and growth regulator Mars EL. It was researched that he combined use of Bioinoculant and plant growth regulator Mars EL provided the increase of the mass of active nodules at the roots of the plant by 33% (phase of formation of 5-6 leaves), 38,8% (budding phase) and 22,8% (flowering phase) compared to the control. It was found that the use of inoculant and plant growth regulator with N30P30K30 fertilizer background leads to the greatest concentration of nodules on the main roots of the plants. The nodules had a pink color. In the technological process, the pre-sowing treatment of pea seeds with Bioinoculant and plant growth regulator Mars EL is an important perspective for improving the symbiotic activity of culture. This induces the reproduction of the soil's natural fertility. It is advisable to investigate the effect of inoculation and growth regulators with the different mechanism of action on the symbiotic activity of winter peas. Key words: soil fertility, legumes, siderata, symbiotic nitrogen fixation, inoculant, plant growth regulator

scholarly journals Succinoglycan Is Required for Initiation and Elongation of Infection Threads during Nodulation of Alfalfa byRhizobium meliloti

1998 ◽  
Vol 180 (19) ◽  
pp. 5183-5191 ◽  
Author(s):  
Hai-Ping Cheng ◽  
Graham C. Walker
Keyword(s):  
Molecular Weight ◽  
Fluorescent Protein ◽  
Rhizobium Meliloti ◽  
Root Hairs ◽  
Invasion Process ◽  
Nitrogen Fixing ◽  
Excess Production ◽  
Infection Threads ◽  
Reduced Rate ◽  
Green Fluorescent

ABSTRACT Rhizobium meliloti Rm1021 must be able to synthesize succinoglycan in order to invade successfully the nodules which it elicits on alfalfa and to establish an effective nitrogen-fixing symbiosis. Using R. meliloti cells that express green fluorescent protein (GFP), we have examined the nature of the symbiotic deficiency of exo mutants that are defective or altered in succinoglycan production. Our observations indicate that anexoY mutant, which does not produce succinoglycan, is symbiotically defective because it cannot initiate the formation of infection threads. An exoZ mutant, which produces succinoglycan without the acetyl modification, forms nitrogen-fixing nodules on plants, but it exhibits a reduced efficiency in the initiation and elongation of infection threads. An exoHmutant, which produces symbiotically nonfunctional high-molecular-weight succinoglycan that lacks the succinyl modification, cannot form extended infection threads. Infection threads initiate at a reduced rate and then abort before they reach the base of the root hairs. Overproduction of succinoglycan by theexoS96::Tn5 mutant does not reduce the efficiency of infection thread initiation and elongation, but it does significantly reduce the ability of this mutant to colonize the curled root hairs, which is the first step of the invasion process. TheexoR95::Tn5 mutant, which overproduces succinoglycan to an even greater extent than theexoS96::Tn5 mutant, has completely lost its ability to colonize the curled root hairs. These new observations lead us to propose that succinoglycan is required for both the initiation and elongation of infection threads during nodule invasion and that excess production of succinoglycan interferes with the ability of the rhizobia to colonize curled root hairs.

scholarly journals Actin Depolymerizing Factor Modulates Rhizobial Infection and Nodule Organogenesis in Common Bean

2020 ◽  
Vol 21 (6) ◽  
pp. 1970
Author(s):  
Yolanda Ortega-Ortega ◽  
Janet Carrasco-Castilla ◽  
Marco A. Juárez-Verdayes ◽  
Roberto Toscano-Morales ◽  
Citlali Fonseca-García ◽  
...  
Keyword(s):  
Nitrogen Fixation ◽  
Root Hairs ◽  
Fine Tuning ◽  
Actin Binding ◽  
Vascular Bundles ◽  
Nodule Number ◽  
Nitrogen Fixation Activity ◽  
Fixation Activity ◽  
Infection Threads ◽  
Cytoskeletal Rearrangements

Actin plays a critical role in the rhizobium–legume symbiosis. Cytoskeletal rearrangements and changes in actin occur in response to Nod factors secreted by rhizobia during symbiotic interactions with legumes. These cytoskeletal rearrangements are mediated by diverse actin-binding proteins, such as actin depolymerization factors (ADFs). We examined the function of an ADF in the Phaseolus vulgaris–rhizobia symbiotic interaction (PvADFE). PvADFE was preferentially expressed in rhizobia-inoculated roots and nodules. PvADFE promoter activity was associated with root hairs harbouring growing infection threads, cortical cell divisions beneath root hairs, and vascular bundles in mature nodules. Silencing of PvADFE using RNA interference increased the number of infection threads in the transgenic roots, resulting in increased nodule number, nitrogen fixation activity, and average nodule diameter. Conversely, overexpression of PvADFE reduced the nodule number, nitrogen fixation activity, average nodule diameter, as well as NODULE INCEPTION (NIN) and EARLY NODULIN2 (ENOD2) transcript accumulation. Hence, changes in ADFE transcript levels affect rhizobial infection and nodulation, suggesting that ADFE is fine-tuning these processes.

scholarly journals Development of Functional Symbiotic White Clover Root Hairs and Nodules Requires Tightly Regulated Production of Rhizobial Cellulase CelC2

2011 ◽  
Vol 24 (7) ◽  
pp. 798-807 ◽  
Author(s):  
Marta Robledo ◽  
José I. Jiménez-Zurdo ◽  
M. José Soto ◽  
Encarnación Velázquez ◽  
Frank Dazzo ◽  
...  
Keyword(s):  
Cell Wall ◽  
White Clover ◽  
Rhizobium Leguminosarum ◽  
Plant Cell Wall ◽  
Root Nodules ◽  
Root Hairs ◽  
Nitrogen Fixing ◽  
Plant Host ◽  
Root Cortex ◽  
Infection Threads

The establishment of rhizobia as nitrogen-fixing endosymbionts within legume root nodules requires the disruption of the plant cell wall to breach the host barrier at strategic infection sites in the root hair tip and at points of bacterial release from infection threads (IT) within the root cortex. We previously found that Rhizobium leguminosarum bv. trifolii uses its chromosomally encoded CelC2 cellulase to erode the noncrystalline wall at the apex of root hairs, thereby creating the primary portal of its entry into white clover roots. Here, we show that a recombinant derivative of R. leguminosarum bv. trifolii ANU843 that constitutively overproduces the CelC2 enzyme has increased competitiveness in occupying aberrant nodule-like root structures on clover that are inefficient in nitrogen fixation. This aberrant symbiotic phenotype involves an extensive uncontrolled degradation of the host cell walls restricted to the expected infection sites at tips of deformed root hairs and significantly enlarged infection droplets at termini of wider IT within the nodule infection zone. Furthermore, signs of elevated plant host defense as indicated by reactive oxygen species production in root tissues were more evident during infection by the recombinant strain than its wild-type parent. Our data further support the role of the rhizobial CelC2 cell wall–degrading enzyme in primary infection, and show evidence of its importance in secondary symbiotic infection and tight regulation of its production to establish an effective nitrogen-fixing root nodule symbiosis.

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