Role In Biological Nitrogen Fixation Research Articles

Three separate pathways in Rhizobium leguminosarum maintain phosphatidylcholine biosynthesis, which is required for symbiotic nitrogen fixation with clover.

Understanding the molecular mechanisms of symbiotic nitrogen fixation has important implications for sustainable agriculture. The presence of the phospholipid phosphatidylcholine (PC) in the membrane of rhizobia is critical for the establishment of productive nitrogen-fixing root nodules on legume plants. The reasons for the PC requirement are unknown. Here, we employed Rhizobium leguminosarum and clover as model system for a beneficial plant-microbe interaction. We found that R. leguminosarum produces PC by three distinct pathways. The relative contribution of these pathways to PC formation was determined in an array of single, double, and triple mutant strains. Several of the PC biosynthesis enzymes were purified and biochemically characterized. Most importantly, we demonstrated the essential role of PC formation by R. leguminosarum in nitrogen fixation and pinpointed a specific enzyme indispensable for plant-microbe interaction. Our study offers profound insights into bacterial PC biosynthesis and its pivotal role in biological nitrogen fixation.

Temporal variations of biological nitrogen fixation and diazotrophic communities associated with artificial seaweed farms

Diazotrophic communities contribute inorganic nitrogen for the primary productivity of the marine environment by biological nitrogen fixation (BNF). They play a vital role in the biogeochemical cycle of nitrogen in the marine ecological environment. However, there is still an incomplete understanding of BNF and diazotrophs in artificial seaweed farms. Therefore, this study comprehensively investigated the temporal variations of BNF associated with Gracilariopsis lemaneiformis, as well as the diazotrophic communities associated with macroalgae and its surrounding seawater. Our results revealed that a total of 13 strains belonging to Proteobacteria and Bacteroidetes were identified as N2-fixing bacteria using azotobacter selective solid medium and nifH gene cloning. Subsequently, BNF and diazotrophic communities were characterized using the acetylene reduction method and high-throughput sequencing of the nifH gene, respectively. The results showed that nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis varied significantly among four different cultivation periods, i.e., Cultivation Jan. (CJ), Cultivation Feb. (CF), Cultivation Mar. (CM), Cultivation Apr. (CA). Among them, the nitrogenase activity and nifH gene abundance of epiphytic bacteria on G. lemaneiformis in CM were significantly higher than those in CJ, CF, and CA, indicating that the BNF of eiphytic bacteria on G. lemaneiformis was markedly enhanced. Combined with the data on environmental factors, it was found that the low concentration of nitrogen and phosphorus in CM might considerably boost the BNF of epiphytic bacteria in G. lemaneiformis. The sequencing results of the nifH gene showed that the α-diversity of diazotrophic communities associated with G. lemaneiformis and seawater in CM was higher than that in other cultivation periods. In addition, the diazotrophic communities on G. lemaneiformis were significantly different in CJ, CF, CM, and CA, and they were significantly diverse from diazotrophic communities in seawater. LEfSe analysis indicated that Rhodobacterales, Hyphomonadaceae, Robiginitomaculum, and Robiginitomaculum antarcticum within α-proteobacteria played a remarkable role in BNF in response to nitrogen nutrient deficiency. Taken together, these results provide a unique insight into the interaction between macroalgae and its epiphytic bacteria and lay a foundation for further research on the mechanism of action of nitrogen-cycling microorganisms associated with macroalgae.

Diazotrophic Bacterial Response to Herbicide Toxicity: In vitro Analysis

Diazotrophic bacteria play critical role in biological nitrogen fixation (BNF), and the application of herbiced significantly affect growth and activities of these bacteria. To investigate this, 1.0 ml of broth stock culture containing 2.9 x 105 cfu/ml and 2.6 x 106 cfu/ml of Azotobacter and Bradyrhizobium, respectively were inoculated into 10.0 ml of their respective growth medium [ TDC broth, and Yeast extract mannitol broth (YEMB)] containing 0, 0.5, 1.0, 1.5 and 2.0 % v/v of the respective herbicides, atrazine, glyphosate, paraquat and 2,4-D. Thereafter, plate counts of the diazotrophs for each concentration was made at 24, 48, 72 and 120 h intervals using spread plate method on TDC agar and YEMA after incubation at room temperature (30 ± 2 ℃) for 72 h. The LC50 of the respective herbicides for Azotobacter and Bradyrhizobium was determined at 120 h using Probit analysis. Results showed that all tested concentrations except control, retarded diazotrophic bacterial population growth. Growth reduction increased progressively with increased concentrations of herbicides (P < 0.05). In general, herbicides were found to suppress the growth of diazotrophs by 29.7 – 100 %. The LC50 indicated symbiotic Bradyrhizobium displayed greater sensitivity to tested herbicides than free-living Azotobacter (P < 0.05). Conclusively, herbicides suppressed diazotrophic bacterial growth.

Effects of Phosphorus Fertilizer on Agronomic, Grain Yield and Other Physiological Traits of Some Selected Legume Crops

Phosphorous is another nutrient that is critically important for legumes and the clover plants that are fixing nitrogen, but all plants need phosphorous as they do nitrogen. Legumes need a higher level of P fertility than the neighbouring grass plants. Phosphorus is vital for plant growth, and is a component of the nucleic acid structure of plants and bio-membranes. Therefore, it is important in cell division and tissue development. It is also involved in the energy metabolism of cells and is required for the biosynthesis of primary and secondary metabolites in plants. Legume crops requires less nitrogen but application of phosphorus and potassium plays a vital role in getting high yield per unit area. The application of phosphorus increases dry matter at harvest, number of pods plant -1 , seeds pod -1 , 1000 grain weight, seed yield and total biomass of mung bean. The experimental results of different authors stated that the highest number of pod plant -1 and grain yield of soyabean were obtained from maximum level of phosphorus as compared to other treatments. common bean crop dependent on nitrogen fixation needs more inorganic phosphorus than the same crop provided with mineral nitrogen. Common beans are therefore especially susceptible to low soil phosphorus when accompanied by low soil. Phosphorus also plays an important role in biological nitrogen fixation, for the symbiotic fixation of nitrogen to occur, the roots have to interact with compatible rhizobia in the soil and factors that affect root growth or the activity of the host plant would affect nodulation. however, the rate of phosphorus is varied from place to place, or it’s governed by the amount of P status in the soil. Since, legume crops demanding more P than other nutrient, we have to apply it obtained best grain yield. Keywords: Bacteria, Dry matter, Grain yield, Legume and Nodule DOI: 10.7176/JBAH/12-12-01 Publication date: June 30 th 2022

Late‐season N fertilization effects on soybean seed protein and biological N2 fixation

AbstractSoybean [Glycine max (L.) Merr.] seed protein concentration has been declining over the past decades with protein values falling below the ∼40% (dry weight base) required for optimal industrial processing. Further refinement of management practices is needed to help maintain concentrations above market standards. The objective of this work was to evaluate the impact of N fertilization during late reproductive stage on soybean seed protein on two cultivars differing in seed protein concentration in order to untangle the role of biological nitrogen fixation (BNF) to mediate seed protein responses. In experiments at two planting dates, late N fertilization was applied as either a foliar or soil‐applied fertilizer and consisted of applying 80 kg ha–1 of N from R3 to R6 with four 20 kg ha–1 N applications. Both cultivar and planting date affected seed yield and protein concentration, ranging from 3,242 to 3,949 kg ha–1 and 34.8 to 38.4 g 100 g–1, respectively. Soil and foliar N fertilizations had no effect on yield or N uptake but had positive effects on seed protein concentration (+2 g 100 g–1) only in the late‐planted experiments. Applying N in the soil inhibited BNF. The amount of N2 fixed during the seed‐filling period, expressed per unit seed, is a relatively good predictor of the response of seed protein to N fertilization suggesting a critical role of BNF during this stage for securing a high concentration of seed protein.

Role of Biological Nitrogen Fixation (BNF) in Sustainable Agriculture: A Review

Agriculture has an enormous environmental footprint. One of the best ways to mitigate climate change is to create balanced food systems based on sustainable agriculture. To reduce the chemical dependence scientists are engineering crop plants for N 2 fixation and they are focused on the biological process BNF (Biological Nitrogen Fixation) for the needs of N2 for crop plant soils. N2 fixed by the BNF process reduces the production cost, Green House gas (GHG) emissions, pollution of surface and ground water. Several management practices are there which influence BNF process in agricultural system. They are N- fertilization species genotype and cultivar and seeding ratios. Better management practices can help to improve N2 fixation. This review highlights the agro-economic importance of BNF and shows it as a cost effective, non- polluting way to improve the soil fertility and crop production.

Bacterial Indole-3-Acetic Acid Influences Soil Nitrogen Acquisition in Barley and Chickpea.

Farming of barley and chickpea is nitrogen (N) fertilizer dependent. Using strategies that increase the nitrogen use efficiency (NUE) and its components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE) would reduce the N fertilizer application in the soil and its adverse environmental effects. We evaluated the effects of three different strains of diazotroph Klebsiella (K.p. SSN1, K.q. SGM81, and K.o. M5a1) to understand the role of biological nitrogen fixation (BNF) and bacterial indole-3-acetic acid (IAA) on NUE of the plants. A field study revealed that K.p. SSN1 results in profound increment of root surface area by eightfold and threefold compared to uninoculated (control) in barley and chickpea, respectively. We measured significant increase in the plant tissue nitrogen, chlorophyll content, protein content, nitrate reductase activity, and nitrate concentration in the inoculated plants (p ≤ 0.05). Treated barley and chickpea exhibited higher NUE and the components compared to the control plants (K.p. SSN1 ≥ K.q. SGM81> K.o. M5a1). Specifically, K.q. SGM81 treatment in barley increased NUpE by 72%, while in chickpea, K.p. SSN1 increased it by 187%. The substantial improvement in the NUpE and NUE by the auxin producers K.p. SSN1 and K.q. SGM81 compared with non-auxin producer K.o. M5a1 was accompanied by an augmented root architecture suggesting larger contribution of IAA over marginal contribution of BNF in nitrogen acquisition from the soil.

Quantitative proteomic analysis reveals altered enzyme expression profile in Zea mays roots during the early stages of colonization by Herbaspirillum seropedicae.

The use of plant growth-promoting bacteria as agricultural inoculants of plants should be encouraged because of their prominent role in biological nitrogen fixation, the increase of nutrient uptake by roots, abiotic stress mitigation, and disease control. The complex mechanisms underlying the association between plant and beneficial bacteria have been increasingly studied, and proteomic tools can expand our perception regarding the fundamental molecular processes modulated by the interaction. In this study, we investigated the changes in protein expression in maize roots in response to treatment with the endophytic diazotrophic Herbaspirillum seropedicae and the activities of enzymes related to nitrogen metabolism. To identify maize proteins whose expression levels were altered in the presence of bacteria, a label-free quantitative proteomic approach was employed. Using this approach, we identified 123 differentially expressed proteins, of which 34 were upregulated enzymes, in maize roots cultivated with H. seropedicae. The maize root colonization of H. seropedicae modulated the differential expression of enzymes involved in the stress response, such as peroxidases, phenylalanine ammonia-lyase, and glutathione transferase. The differential protein profile obtained in the inoculated roots reflects the effect of colonization on plant growth and development compared with control plants.

Differential Response of Promiscuous Soybean to Local Diversity of Indigenous and Commercial Bradyrhizobium Inoculation Under Contrasting Agroclimatic Zones

Promiscuous soybeans are grain legumes that nodulate with diverse strains of indigenous Bradyrhizobium and play a significant role in biological nitrogen fixation through symbiosis. However, experiments on the potential use of promiscuous soybean varieties have recorded very low nodulation and poor nitrogen fixation probably due to ineffective native Bradyrhizobium isolates. Experiments were designed to investigate symbiotic nitrogen fixation of two promiscuous soybean varieties (SB8 and SB126) with indigenous Bradyrhizobium isolates in contrasting agroclimatic zones through greenhouse and field experiments. Inoculation of soybeans in the greenhouse had a significant (p < 0.001) effect on shoot and nodule dry weight. The best performing indigenous isolates RI9 and RI4 from the greenhouse study outperformed the commercial inoculant (Biofix) in symbiotic effectiveness with 119.17%, 142.35% and 101.01%, respectively. Inoculation in the field experiments showed a significant (p < 0.0001) increase in shoot dry weight and grain yield of promiscuous soybean. Agroclimatic zones showed significant (p < 0.0001) variability in above ground biomass of soybean due to inoculation. Despite the apparent promiscuity of the soybean varieties used, the response in nodulation suggests the cultivars grown under contrasting agroclimatic zones have a preference to specific Bradyrhizobium isolates.

Natural atmospheric deposition of molybdenum: a global model and implications for tropical forests

Molybdenum (Mo) is an essential trace metal that plays a central role in biological nitrogen fixation (BNF) as the cofactor in the conventional form of the nitrogenase enzyme. The low availability of Mo in soils often constrains BNF in many terrestrial ecosystems. Atmospheric sources may supply a critical source of exogenous Mo to regions with highly weathered soils likely low in Mo, particularly in tropical forests where BNF is thought to be high. Here, we present results of a global model of Mo deposition that considers the principal natural sources of atmospheric Mo—windborne mineral dust, sea-salt aerosols, and volcanic sources—which operate over geologic time. The largest source of mineral dust globally is from North Africa. We quantified Mo concentrations in dust and sediments from the Bodele Depression, a large source within North Africa, to constrain our model. Because the Mo concentration of seawater is relatively high for a trace element, we also hypothesized that sea-salt aerosols would contribute atmospheric Mo. Our model predicts higher Mo deposition to terrestrial ecosystems along coasts downstream in trade winds, near active volcanoes, and in areas that receive dust deposition from North Africa, such as the northern Amazon Basin, the Caribbean, and Central America. Regions with higher Mo deposition tend to be areas where BNF has previously been measured. The lowest Mo deposition occurs in the high latitudes, northern parts of North America, Western Australia, Southern Africa, and much of central South America. Atmospheric transport of Mo likely plays an important role in supplying Mo to ecosystems across geologic time, particularly in regions with highly weathered soils.

NifPred: Proteome-Wide Identification and Categorization of Nitrogen-Fixation Proteins of Diaztrophs Based on Composition-Transition-Distribution Features Using Support Vector Machine

As inorganic nitrogen compounds are essential for basic building blocks of life (e.g., nucleotides and amino acids), the role of biological nitrogen-fixation (BNF) is indispensible. All nitrogen fixing microbes rely on the same nitrogenase enzyme for nitrogen reduction, which is in fact an enzyme complex consists of as many as 20 genes. However, the occurrence of six genes viz., nifB, nifD, nifE, nifH, nifK, and nifN has been proposed to be essential for a functional nitrogenase enzyme. Therefore, identification of these genes is important to understand the mechanism of BNF as well as to explore the possibilities for improving BNF from agricultural sustainability point of view. Further, though the computational tools are available for the annotation and phylogenetic analysis of nifH gene sequences alone, to the best of our knowledge no tool is available for the computational prediction of the above mentioned six categories of nitrogen-fixation (nif) genes or proteins. Thus, we proposed an approach, which is first of its kind for the computational identification of nif proteins encoded by the six categories of nif genes. Sequence-derived features were employed to map the input sequences into vectors of numeric observations that were subsequently fed to the support vector machine as input. Two types of classifier were constructed: (i) a binary classifier for classification of nif and non-nitrogen-fixation (non-nif) proteins, and (ii) a multi-class classifier for classification of six categories of nif proteins. Higher accuracies were observed for the combination of composition-transition-distribution (CTD) feature set and radial kernel, as compared to the other feature-kernel combinations. The overall accuracies were observed >90% in both binary and multi-class classifications. The developed approach further achieved >92% accuracy, while evaluated with blind (independent) test datasets. The developed approach also produced higher accuracy in identifying nif proteins, while evaluated using proteome-wide datasets of several species. Furthermore, we established a prediction server nifPred (http://webapp.cabgrid.res.in/nifPred) to assist the scientific community for proteome-wide identification of six categories of nif proteins. Besides, the source code of nifPred is also available at https://github.com/PrabinaMeher/nifPred. The developed web server is expected to supplement the transcriptional profiling and comparative genomics studies for the identification and functional annotation of genes related to BNF.

Nitrogen Fixation Inputs in Pasture and Early Successional Forest in the Brazilian Amazon Region: Evidence From a Claybox Mesocosm Study

AbstractThe role of biological nitrogen fixation (BNF) during secondary forest succession and in tropical pastures has been investigated and debated for several decades. Here we present results of a replicated experimental study in a degraded cattle pasture of eastern Amazonia using mass balance and a 15N tracer in lined soil pit mesocosms with three treatments: (1) plant‐free control plots, (2) pasture grass Brachiaria brizantha, and (3) regrowth of early successional secondary forest species. Accumulation of N in grass biomass slightly exceeded estimates of net N mineralization from the plant‐free control plots but was within the margin of error, so inputs of BNF may not have been needed. In contrast, the secondary forest vegetation accumulated about 3 times as much biomass N annually as the net N mineralization estimate, suggesting at least some role for BNF. Based on isotopic and mass measurements of N‐fixing species, BNF was estimated to contribute at least 27 ± 3% of mean annual plant uptake in the secondary forest regrowth vegetation plots. Although BNF is probably important for recuperation of tropical secondary forests following land use change, the majority of the N taken up by both grasses and secondary forest regrowth arose from mineralization of the stocks of soil N.

Chemical soil attributes after wheat cropping under nitrogen fertilization and inoculation with Azospirillum brasilense

Azospirillum brasilense plays an important role in biological nitrogen fixation (BNF) in grasses. However, further studies are needed to define how much mineral N can be applied while simultaneously maintaining BNF contribution and maximizing crop yield and to determine the impact of these practices on soil fertility. Thus, we aimed to investigate the effect of inoculation with A. brasilense, in conjunction with varying N doses and sources in a Cerrado soil, on soil chemical attributes after two years of irrigated wheat production. The experiment was initiated in Selvíria - MS under no-tillage production in an Oxisol in 2014 and 2015. The experimental design was a randomized block design with four replications, and treatments were arranged in a 2 x 5 x 2 factorial arrangement as follows: two N sources (urea and Super N - urea with inhibitor of the enzyme urease NBPT (N - (n-butyl thiophosphoric triamide))), five N rates (0, 50, 100, 150 and 200 kg ha-1), and with or without seed inoculation with A. brasilense. The increase in N rates did not influence the chemical soil attributes. Super N acidified the soil more compared to urea. A. brasilense inoculation reduced the effect of soil acidification in intensive irrigated wheat cultivation; however, the base extraction was higher, resulting in a lower soil CEC after cultivation with inoculation. Therefore, the cultivation of wheat inoculated with A. brasilense was not harmful to soil fertility because it did not reduce the base saturation and organic matter content (P, K, Ca, Mg, and S).

Rhizobia: a potential biocontrol agent for soilborne fungal pathogens.

Rhizobia are a group of organisms that are well known for their ability to colonize root surfaces and form symbiotic associations with legume plants. They not only play a major role in biological nitrogen fixation but also improve plant growth and reduce disease incidence in various crops. Rhizobia are known to control the growth of many soilborne plant pathogenic fungi belonging to different genera like Fusarium, Rhizoctonia, Sclerotium, and Macrophomina. Antagonistic activity of rhizobia is mainly attributed to production of antibiotics, hydrocyanic acid (HCN), mycolytic enzymes, and siderophore under iron limiting conditions. Rhizobia are also reported to induce systemic resistance and enhance expression of plant defense-related genes, which effectively immunize the plants against pathogens. Seed bacterization with appropriate rhizobial strain leads to elicitation and accumulation of phenolic compounds, isoflavonoid phytoalexins, and activation of enzymes like L-phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), peroxidase (POX), polyphenol oxidase (PPO), and others involved in phenylpropanoid and isoflavonoid pathways. Development of Rhizobium inoculants with dual attributes of nitrogen fixation and antagonism against phytopathogens can contribute to increased plant growth and productivity. This compilation aims to bring together the available information on the biocontrol facet of rhizobia and identify research gaps and effective strategies for future research in this area.

Nitrogenase Assembly: Strategies and Procedures.

Nitrogenase is a metalloenzyme system that plays a critical role in biological nitrogen fixation, and the study of how its metallocenters are assembled into functional entities to facilitate the catalytic reduction of dinitrogen to ammonia is an active area of interest. The diazotroph Azotobacter vinelandii is especially amenable to culturing and genetic manipulation, and this organism has provided the basis for many insights into the assembly of nitrogenase proteins and their respective metallocofactors. This chapter will cover the basic procedures necessary for growing A. vinelandii cultures and subsequent recombinant transformation and protein expression techniques. Furthermore, protocols for nitrogenase protein purification and substrate reduction activity assays are described. These methods provide a solid framework for the assessment of nitrogenase assembly and catalysis.

A Comparative Nitrogen Balance and Productivity Analysis of Legume and Non-legume Supported Cropping Systems: The Potential Role of Biological Nitrogen Fixation.

The potential of biological nitrogen fixation (BNF) to provide sufficient N for production has encouraged re-appraisal of cropping systems that deploy legumes. It has been argued that legume-derived N can maintain productivity as an alternative to the application of mineral fertilizer, although few studies have systematically evaluated the effect of optimizing the balance between legumes and non N-fixing crops to optimize production. In addition, the shortage, or even absence in some regions, of measurements of BNF in crops and forages severely limits the ability to design and evaluate new legume–based agroecosystems. To provide an indication of the magnitude of BNF in European agriculture, a soil-surface N-balance approach was applied to historical data from 8 experimental cropping systems that compared legume and non-legume crop types (e.g., grains, forages and intercrops) across pedoclimatic regions of Europe. Mean BNF for different legume types ranged from 32 to 115 kg ha−1 annually. Output in terms of total biomass (grain, forage, etc.) was 30% greater in non-legumes, which used N to produce dry matter more efficiently than legumes, whereas output of N was greater from legumes. When examined over the crop sequence, the contribution of BNF to the N-balance increased to reach a maximum when the legume fraction was around 0.5 (legume crops were present in half the years). BNF was lower when the legume fraction increased to 0.6–0.8, not because of any feature of the legume, but because the cropping systems in this range were dominated by mixtures of legume and non-legume forages to which inorganic N as fertilizer was normally applied. Forage (e.g., grass and clover), as opposed to grain crops in this range maintained high outputs of biomass and N. In conclusion, BNF through grain and forage legumes has the potential to generate major benefit in terms of reducing or dispensing with the need for mineral N without loss of total output.

A Synthetic Single-Site Fe Nitrogenase: High Turnover, Freeze-Quench (57)Fe Mössbauer Data, and a Hydride Resting State.

The mechanisms of the few known molecular nitrogen-fixing systems, including nitrogenase enzymes, are of much interest but are not fully understood. We recently reported that Fe-N2 complexes of tetradentate P3(E) ligands (E = B, C) generate catalytic yields of NH3 under an atmosphere of N2 with acid and reductant at low temperatures. Here we show that these Fe catalysts are unexpectedly robust and retain activity after multiple reloadings. Nearly an order of magnitude improvement in yield of NH3 for each Fe catalyst has been realized (up to 64 equiv of NH3 produced per Fe for P3(B) and up to 47 equiv for P3(C)) by increasing acid/reductant loading with highly purified acid. Cyclic voltammetry shows the apparent onset of catalysis at the P3(B)Fe-N2/P3(B)Fe-N2(-) couple and controlled-potential electrolysis of P3(B)Fe(+) at -45 °C demonstrates that electrolytic N2 reduction to NH3 is feasible. Kinetic studies reveal first-order rate dependence on Fe catalyst concentration (P3(B)), consistent with a single-site catalyst model. An isostructural system (P3(Si)) is shown to be appreciably more selective for hydrogen evolution. In situ freeze-quench Mössbauer spectroscopy during turnover reveals an iron-borohydrido-hydride complex as a likely resting state of the P3(B)Fe catalyst system. We postulate that hydrogen-evolving reaction activity may prevent iron hydride formation from poisoning the P3(B)Fe system. This idea may be important to consider in the design of synthetic nitrogenases and may also have broader significance given that intermediate metal hydrides and hydrogen evolution may play a key role in biological nitrogen fixation.

Role of Diazotrophic Bacteria in Biological Nitrogen Fixation and Plant Growth Improvement

Though there is an abundant supply of nitrogen in the atmosphere, it cannot be used directly by the biological systems since it has to be combined with the element hydrogen before their incorporation. This process of nitrogen fixation (N₂-fixation) may be accomplished either chemically or biologically. Between the two elements, biological nitrogen fixation (BNF) is a microbiological process that converts atmospheric di-nitrogen (N₂) into plant-usable form. In this review, the genetics and mechanism of nitrogen fixation including genes responsible for it, their types and role in BNF are discussed in detail. Nitrogen fixation in the different agricultural systems using different methods is discussed to understand the actual rather than the potential N₂-fixation procedure. The mechanism by which the diazotrophic bacteria improve plant growth apart from nitrogen fixation such as inhibition of plant ethylene synthesis, improvement of nutrient uptake, stress tolerance enhancement, solubilization of inorganic phosphate and mineralization of organic phosphate is also discussed. Role of diazotrophic bacteria in the enhancement of nitrogen fixation is also dealt with suitable examples. This mini review attempts to address the importance of diazotrophic bacteria in nitrogen fixation and plant growth improvement.

INFLUENCE OF BORON DOSES ON THE YIELD OF MUNGBEAN CULTIVARS GROWN UNDER SEMI-ARID ENVIRONMENT

Ponte Academic JournalAug 2016, Volume 72, Issue 8 INFLUENCE OF BORON DOSES ON THE YIELD OF MUNGBEAN CULTIVARS GROWN UNDER SEMI-ARID ENVIRONMENTAuthor(s): Jamshaid Qamar , Abdul Rehman, Rafi Qamar,Muhammad Asghar Ali, Kaleem Ahmad and Shahwar Ibne AslamJ. Ponte - Aug 2016 - Volume 72 - Issue 8 doi: 10.21506/j.ponte.2016.8.12 Abstract:Significance of micronutrients are similarly essential as macronutrients for plant growth and development. Boron has a vital role in biological nitrogen fixation in pulses, which resulted in significant production. Mungbean (Vigna radiata L.) is a primeval and familiar crop among Asian countries due to its dietary and nutritional value. A field experiment was conducted during 2013 at Agronomic Research Area, University College of Agriculture, University of Sargodha, Pakistan to evaluate the efficacy of B in three Mungbean cultivars namely NM-92, NM-11 and AZRI-06 through the application of B in the form of Borax (11%). The B treatments comprised; 0 ppm (Bo), 5 ppm (B1), 10 ppm (B2) and 15 ppm (B3) on growth and yield of mungbean cultivars. Born was applied as foliar on vegetative and reproductive stage. Results revealed that different doses of boron affected the growth and yield of mungbean cultivars. Number of pods per plant, number of seeds per pod, 1000-seed weight (g) and seed yield (t ha-1) was significantly affected by different boron doses. Optimum dose of boron improved the yield whereas dispersion from optimum range yield was reduced. The interaction between boron doses and Mungbean cultivars was also recorded significantly. Download full text:Check if you have access through your login credentials or your institution Username Password

Symbiosomes: temporary moonlighting organelles.

Symbiosomes are a unique structural entity that performs the role of biological nitrogen fixation, an energy-demanding process that is the primary entryway of fixed nitrogen into the biosphere. Symbiosomes result from the infection of specific rhizobial strains into the roots of an appropriate leguminous host plant forming an organ referred to as a nodule. Within the infected plant cells of the nodule, the rhizobia are encased within membrane-bounded structures that develop into symbiosomes. Mature symbiosomes create an environment that allows the rhizobia to differentiate into a nitrogen-fixing form called bacteroids. The bacteroids are surrounded by the symbiosome space, which is populated by proteins from both eukaryotic and prokaryotic symbionts, suggesting this space is the quintessential component of symbiosis: an inter-kingdom environment with the single purpose of symbiotic nitrogen fixation. Proteins associated with the symbiosome membrane are largely plant-derived proteins and are non-metabolic in nature. The proteins of the symbiosome space are mostly derived from the bacteroid with annotated functions of carbon metabolism, whereas relatively few are involved in nitrogen metabolism. An appreciable portion of both the eukaryotic and prokaryotic proteins in the symbiosome are also 'moonlighting' proteins, which are defined as proteins that perform roles unrelated to their annotated activities when found in an unexpected physiological environment. The essential functions of symbiotic nitrogen fixation of the symbiosome are performed by co-operative interactions of proteins from both symbionts some of which may be performing unexpected roles.