Academic literature on the topic 'Rhizobia root colonization'
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Journal articles on the topic "Rhizobia root colonization"
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Chi, Feng, Shi-Hua Shen, Hai-Ping Cheng, Yu-Xiang Jing, Youssef G. Yanni, and Frank B. Dazzo. "Ascending Migration of Endophytic Rhizobia, from Roots to Leaves, inside Rice Plants and Assessment of Benefits to Rice Growth Physiology." Applied and Environmental Microbiology 71, no. 11 (2005): 7271–78. http://dx.doi.org/10.1128/aem.71.11.7271-7278.2005.
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ABSTRACT Rhizobia, the root-nodule endosymbionts of leguminous plants, also form natural endophytic associations with roots of important cereal plants. Despite its widespread occurrence, much remains unknown about colonization of cereals by rhizobia. We examined the infection, dissemination, and colonization of healthy rice plant tissues by four species of gfp-tagged rhizobia and their influence on the growth physiology of rice. The results indicated a dynamic infection process beginning with surface colonization of the rhizoplane (especially at lateral root emergence), followed by endophytic colonization within roots, and then ascending endophytic migration into the stem base, leaf sheath, and leaves where they developed high populations. In situ CMEIAS image analysis indicated local endophytic population densities reaching as high as 9 × 1010 rhizobia per cm3 of infected host tissues, whereas plating experiments indicated rapid, transient or persistent growth depending on the rhizobial strain and rice tissue examined. Rice plants inoculated with certain test strains of gfp-tagged rhizobia produced significantly higher root and shoot biomass; increased their photosynthetic rate, stomatal conductance, transpiration velocity, water utilization efficiency, and flag leaf area (considered to possess the highest photosynthetic activity); and accumulated higher levels of indoleacetic acid and gibberellin growth-regulating phytohormones. Considered collectively, the results indicate that this endophytic plant-bacterium association is far more inclusive, invasive, and dynamic than previously thought, including dissemination in both below-ground and above-ground tissues and enhancement of growth physiology by several rhizobial species, therefore heightening its interest and potential value as a biofertilizer strategy for sustainable agriculture to produce the world's most important cereal crops.
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Lancelle, Susan A., and John G. Torrey. "Early development of Rhizobium-induced root nodules of Parasponia rigida. II. Nodule morphogenesis and symbiotic development." Canadian Journal of Botany 63, no. 1 (1985): 25–35. http://dx.doi.org/10.1139/b85-005.
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The Rhizobium-induced root nodules of Parasponia rigida (Ulmaceae) outwardly resemble those formed on actinorhizal plants, being coralloid in shape and consisting of multiple, branched lobes. The details of nodule morphogenesis also resemble more closely those which occur in an actinorhizal association than a typical Rhizobium–legume association and include prenodule formation, initiation of modified lateral roots which are termed nodule lobe primordia, and rhizobial colonization of tissues derived from the nodule lobe primordia to form the primary nodule lobes. Mature nodule lobe structure is actinorhizallike. Each lobe has an apical meristem and a central vascular cylinder which is surrounded by an uninfected inner cortex and then a zone of infected tissue. Peripheral to the infected tissue is an uninfected outer cortex. Infection threads and intercellular rhizobia progress continuously toward the apical meristem but do not infect the meristem itself. The establishment of the symbiosis in the host cells involves continuous thread formation after the initial infection until the host cells are nearly filled with rhizobia enclosed in threads. The rhizobia remain in threads throughout the symbiotic relationship and are not released from the threads as occurs in bacteroid formation in legumes.
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Nguyen, Tran Hong Nha, Laurent Brechenmacher, Joshua T. Aldrich, et al. "Quantitative Phosphoproteomic Analysis of Soybean Root Hairs Inoculated with Bradyrhizobium japonicum." Molecular & Cellular Proteomics 11, no. 11 (2012): 1140–55. http://dx.doi.org/10.1074/mcp.m112.018028.
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Root hairs are single hair-forming cells on roots that function to increase root surface area, enhancing water and nutrient uptake. In leguminous plants, root hairs also play a critical role as the site of infection by symbiotic nitrogen fixing rhizobia, leading to the formation of a novel organ, the nodule. The initial steps in the rhizobia-root hair infection process are known to involve specific receptor kinases and subsequent kinase cascades. Here, we characterize the phosphoproteome of the root hairs and the corresponding stripped roots (i.e. roots from which root hairs were removed) during rhizobial colonization and infection to gain insight into the molecular mechanism of root hair cell biology. We chose soybean (Glycine max L.), one of the most important crop plants in the legume family, for this study because of its larger root size, which permits isolation of sufficient root hair material for phosphoproteomic analysis. Phosphopeptides derived from root hairs and stripped roots, mock inoculated or inoculated with the soybean-specific rhizobium Bradyrhizobium japonicum, were labeled with the isobaric tag eight-plex iTRAQ, enriched using Ni-NTA magnetic beads and subjected to nanoRPLC-MS/MS1 analysis using HCD and decision tree guided CID/ETD strategy. A total of 1625 unique phosphopeptides, spanning 1659 nonredundant phosphorylation sites, were detected from 1126 soybean phosphoproteins. Among them, 273 phosphopeptides corresponding to 240 phosphoproteins were found to be significantly regulated (>1.5-fold abundance change) in response to inoculation with B. japonicum. The data reveal unique features of the soybean root hair phosphoproteome, including root hair and stripped root-specific phosphorylation suggesting a complex network of kinase-substrate and phosphatase-substrate interactions in response to rhizobial inoculation.
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Sahur, Asmiaty. "The Interaction between Endophytic Actinomycetes and Rhizobium in Leguminous Plants." Journal of Tropical Crop Science 2, no. 3 (2015): 29–34. http://dx.doi.org/10.29244/jtcs.2.3.29-34.
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Biological N2 fixation represents the major source of N input in many agricultural soils including those in arid regions where little artificial fertilizer is applied. The major N2-fixing systems in agriculture are the symbiotic systems, where bacteria such as rhizobia interact with legumes to fix atmospheric nitrogen which plays a significant role in improving the fertility and productivity of low-N soils. The symbiotic association of legume-rhizobium is initiated by the colonization of the rhizosphere by the rhizobia and subsequent attachment to the root hairs of the host plant. Furthermore, the host will produce flavonoids, such as luteolin in alfalfa and diazedin in soybean, which interact with nod protein in the rhizobia. Moreover, this process then elicits the expression of a cluster of nodulation genes such as nod, nol, and noe in the rhizobia. The interaction is potentially of great importance to the health and growth in nature of this nodulating legume.The interaction between endophytic Actinomycetes and rhizobia in leguminous plants is one way to improve the capability of leguminous plants to fix atmospheric nitrogen in plant roots and contribute to the plants nutrition. From other studies, we know that certain types of Actinomycetes, for example Streptomyces, interact with peas to form healthy roots as an effective site to form nodules and improve biological nitrogen fixation. Knowledge about this activity against fungal pathogens might lead to finding biocontrol agents for use in sustainable agricultural practices.Root-colonizing soil borne Actinomycetes might influence root nodulation in leguminous plants by increasing root nodulation frequency, possibly at the sites of infection by Rhizobium spp. Actinomycetes also colonize and sporulate within the surface cell layers of the nodules. This colonization leads to an increase in the average size of the nodules that form and improves the vigor of the bacteroids which generate the red color within the nodules by enhancing nodular assimilation of iron and possibly other soil nutrients. Keywords: symbiotic, biological, nitrogen, molecular interaction
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Laus, Marc C., Trudy J. Logman, Anton A. N. van Brussel, et al. "Involvement of exo5 in Production of Surface Polysaccharides in Rhizobium leguminosarum and Its Role in Nodulation of Vicia sativa subsp. nigra." Journal of Bacteriology 186, no. 19 (2004): 6617–25. http://dx.doi.org/10.1128/jb.186.19.6617-6625.2004.
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ABSTRACT Analysis of two exopolysaccharide-deficient mutants of Rhizobium leguminosarum, RBL5808 and RBL5812, revealed independent Tn5 transposon integrations in a single gene, designated exo5. As judged from structural and functional homology, this gene encodes a UDP-glucose dehydrogenase responsible for the oxidation of UDP-glucose to UDP-glucuronic acid. A mutation in exo5 affects all glucuronic acid-containing polysaccharides and, consequently, all galacturonic acid-containing polysaccharides. Exo5-deficient rhizobia do not produce extracellular polysaccharide (EPS) or capsular polysaccharide (CPS), both of which contain glucuronic acid. Carbohydrate composition analysis and nuclear magnetic resonance studies demonstrated that EPS and CPS from the parent strain have very similar structures. Lipopolysaccharide (LPS) molecules produced by the mutant strains are deficient in galacturonic acid, which is normally present in the core and lipid A portions of the LPS. The sensitivity of exo5 mutant rhizobia to hydrophobic compounds shows the involvement of the galacturonic acid residues in the outer membrane structure. Nodulation studies with Vicia sativa subsp. nigra showed that exo5 mutant rhizobia are impaired in successful infection thread colonization. This is caused by strong agglutination of EPS-deficient bacteria in the root hair curl. Root infection could be restored by simultaneous inoculation with a Nod factor-defective strain which retained the ability to produce EPS and CPS. However, in this case colonization of the nodule tissue was impaired.
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Tirichine, Leïla, Euan K. James, Niels Sandal, and Jens Stougaard. "Spontaneous Root-Nodule Formation in the Model Legume Lotus japonicus: A Novel Class of Mutants Nodulates in the Absence of Rhizobia." Molecular Plant-Microbe Interactions® 19, no. 4 (2006): 373–82. http://dx.doi.org/10.1094/mpmi-19-0373.
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Root-nodule development in legumes is an inducible developmental process initially triggered by perception of lipochitin-oligosaccharide signals secreted by the bacterial microsymbiont. In nature, rhizobial colonization and invasion of the legume root is therefore a prerequisite for formation of nitrogen-fixing root nodules. Here, we report isolation and characterization of chemically induced spontaneously nodulating mutants in a model legume amenable to molecular genetics. Six mutant lines of Lotus japonicus were identified in a screen for spontaneous nodule development under axenic conditions, i.e., in the absence of rhizobia. Spontaneous nodules do not contain rhizobia, bacteroids, or infection threads. Phenotypically, they resemble ineffective white nodules formed by some bacterial mutants on wild-type plants or certain plant mutants inoculated with wild-type Mesorhizobium loti. Spontaneous nodules formed on mutant lines show the ontogeny and characteristic histological features described for rhizobia-induced nodules on wild-type plants. Physiological responses to nitrate and ethylene are also maintained, as elevated levels inhibit spontaneous nodulation. Activation of the nodule developmental program in spontaneous nodules was shown for the early nodulin genes Enod2 and Nin, which are both upregulated in spontaneous nodules as well as in rhizobial nodules. Both monogenic recessive and dominant spontaneous nodule formation (snf) mutations were isolated in this mutant screen, and map positions were determined for three loci. We suggest that future molecular characterization of these mutants will identify key plant determinants involved in regulating nodulation and provide new insight into plant organ development.
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Perrine, Francine M., Joko Prayitno, Jeremy J. Weinman, Frank B. Dazzo, and Barry G. Rolfe. "Rhizobium plasmids are involved in the inhibition or stimulation of rice growth and development." Functional Plant Biology 28, no. 9 (2001): 923. http://dx.doi.org/10.1071/pp01046.
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This paper originates from an address at the 8th International Symposium on Nitrogen Fixation with Non-Legumes, Sydney, NSW, December 2000 We examined growth responses of rice seedlings (Oryza sativaL. cv. Pelde) to specific Rhizobium strains and their mutants, to investigate the molecular basis of colonization and the stimulation or inhibition of rice growth and development by rhizobia. Inoculation experiments with rice seedlings showed that specific Rhizobium isolates of these rice-associated and legume-associated rhizobia could either promote, inhibit, or have no influence on rice plant growth. There are genes on certain plasmids of Rhizobium leguminosarum bv. trifolii and R. leguminosarum bv. viciae that affect the growth and development of rice root morphology. Additionally, we found that bacteria can intimately associate with, and enter into, rice seedling roots by alternative mechanisms to those encoded by the symbiotic (pSym) and the tumour-inducing (Ti) plasmids. Investigations suggest an involvement of the phytohormone auxin, and possibly nitrate, in this complex rice–Rhizobium interaction.
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Banuelos, Jacob, Esperanza Martínez-Romero, Noé Manuel Montaño, and Sara Lucía Camargo-Ricalde. "Rhizobium tropici and Riboflavin Amendment Conditions Arbuscular Mycorrhiza Colonization in Phaseolus vulgaris L." Agronomy 13, no. 3 (2023): 876. http://dx.doi.org/10.3390/agronomy13030876.
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Phaseolus vulgaris L. (Leguminosae) forms symbioses with arbuscular mycorrhizal fungi (AMF) and nitrogen-fixing rhizobia (NFB). The tripartite relationship uses molecular singals to establish intracellular symbioses in roots. The goal of this study was to determine if Rhizobium tropici CIAT 899 and exogenous riboflavin (vitamin B2) have an effect on AMF species selection and root colonization of P. vulgaris. Using SSU rRNA fragment amplification of DNA extracted from P. vulgaris roots, we found that the presence of R. tropici altered the relative distribution of AMF species. Dominikia bernensis (Ohel) was the most abundant AMF species in P. vulgaris roots but when R. tropici was co-inoculated, Glomus species dominated. Rhizobacteria such as R. tropici, secrete riboflavin and could affect AMF symbiosis. Addition of 50 μM riboflavin to P. vulgaris, increased plant growth (28%), dry nodule weight (18%), AMF colonization (248%) and mycorrhizal vesicle frequency (56%) in bean roots. 3.12 and 12.5 µM riboflavin favored the presence of Glomus macrocarpum in P. vulgaris roots. This work provides de basis for further investigation of rhizobial and mycorrhizal co-inoculation of Phaseolus vulgaris bean.
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Vald�s-L�pez, Oswaldo, Dhileepkumar Jayaraman, Junko Maeda, et al. "A Novel Positive Regulator of the Early Stages of Root Nodule Symbiosis Identified by Phosphoproteomics." Plant and Cell Physiology 60, no. 3 (2018): 575–86. http://dx.doi.org/10.1093/pcp/pcy228.
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Abstract Signals and signaling pathways underlying the symbiosis between legumes and rhizobia have been studied extensively over the past decades. In a previous phosphoproteomic study on the Medicago truncatula–Sinorhizobium meliloti symbiosis, we identified plant proteins that are differentially phosphorylated upon the perception of rhizobial signals, called Nod factors. In this study, we provide experimental evidence that one of these proteins, Early Phosphorylated Protein 1 (EPP1), is required for the initiation of this symbiosis. Upon inoculation with rhizobia, MtEPP1 expression was induced in curled root hairs. Down-regulation of MtEPP1 in M. truncatula roots almost abolished calcium spiking, reduced the expression of essential symbiosis-related genes (MtNIN, MtNF-YB1, MtERN1 and MtENOD40) and strongly decreased nodule development. Phylogenetic analyses revealed that orthologs of MtEPP1 are present in legumes and specifically in plant species able to host arbuscular mycorrhizal fungi, suggesting a possible role in this association too. Short chitin oligomers induced the phosphorylation of MtEPP1 like Nod factors. However, the down-regulation of MtEPP1 affected the colonization of M. truncatula roots by arbuscular mycorrhizal fungi only moderately. Altogether, these findings indicate that MtEPP1 is essential for the establishment of the legume–rhizobia symbiosis but might plays a limited role in the arbuscular mycorrhizal symbiosis.
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Unay, Jovelyn, and Xavier Perret. "A Minimal Genetic Passkey to Unlock Many Legume Doors to Root Nodulation by Rhizobia." Genes 11, no. 5 (2020): 521. http://dx.doi.org/10.3390/genes11050521.
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In legume crops, formation of developmentally mature nodules is a prerequisite for efficient nitrogen fixation by populations of rhizobial bacteroids established inside nodule cells. Development of root nodules, and concomitant microbial colonization of plant cells, are constrained by sets of recognition signals exchanged by infecting rhizobia and their legume hosts, with much of the specificity of symbiotic interactions being determined by the flavonoid cocktails released by legume roots and the strain-specific nodulation factors (NFs) secreted by rhizobia. Hence, much of Sinorhizobium fredii strain NGR234 symbiotic promiscuity was thought to stem from a family of >80 structurally diverse NFs and associated nodulation keys in the form of secreted effector proteins and rhamnose-rich surface polysaccharides. Here, we show instead that a mini-symbiotic plasmid (pMiniSym2) carrying only the nodABCIJ, nodS and nodD1 genes of NGR234 conferred promiscuous nodulation to ANU265, a derivative strain cured of the large symbiotic plasmid pNGR234a. The ANU265::pMiniSym2 transconjugant triggered nodulation responses on 12 of the 22 legumes we tested. On roots of Macroptilium atropurpureum, Leucaena leucocephala and Vigna unguiculata, ANU265::pMiniSym2 formed mature-like nodule and successfully infected nodule cells. While cowpea and siratro responded to nodule colonization with defense responses that eventually eliminated bacteria, L. leucocephala formed leghemoglobin-containing mature-like nodules inside which the pMiniSym2 transconjugant established persistent intracellular colonies. These data show seven nodulation genes of NGR234 suffice to trigger nodule formation on roots of many hosts and to establish chronic infections in Leucaena cells.
Dissertations / Theses on the topic "Rhizobia root colonization"
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Parco, Socorro Z. "The influence of motility of rhizobium leguminosarum biovar trifolii TA1 on the colonization and nodulation of roots of trifolium subterraneum cv. Mt. Barker." Thesis, Parco, Socorro Z. (1993) The influence of motility of rhizobium leguminosarum biovar trifolii TA1 on the colonization and nodulation of roots of trifolium subterraneum cv. Mt. Barker. Masters by Research thesis, Murdoch University, 1993. https://researchrepository.murdoch.edu.au/id/eprint/51939/.
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The significance of motility for root colonisation and nodulation was investigated by comparing the behaviour of well-characterised motile (MNF 1000) and non-motile (MNF 1005) strains of Rhizobium leguminosarum bv. trifolii. A very small volume (5 pi) was used to inoculate clover (Trifolium subtcrrancum cv. Mt. Barker) roots to avoid mass flow of organisms. The nodulation pattern was used as an index of the colonisation of the roots; it was assessed by a grid-sectioning technique which divided the soil column into 1 cm cubes, or by gamma-ray computer assisted tomography (CAT) scanning. Direct rhizosphere counts were used as an alternative way of determining root colonisation.
From equal inocula, the motile strain produced more nodules than the nonmotile. Grid-sectioning showed that the motile strain produced nodules at distances further from the inoculation point than the non-motile mutant. However, the technique suffered from the distortion of root aiH nodule distribution caused by the introduction of the sectioning plate.
Attempts were made to use CAT scanning as a non-destructive, nondistorting technique to generate a three-dimensional picture of nodule distribution in the soil columns. Although some 70% of the known nodules corresponded to areas of low density in the scans, the technique currently lacks sufficient resolution.
When the root nodule bacteria were located on the roots by direct counting, the motile strain was found along the whole of the tap root, while the non-motile mutant was essentially confined to a small zone at the inoculation point, rhizosphere counts indicated a much greater spread of the motile strain than did The measurement of the nodule distribution.
In steam-treated soil, both nodulation and rhizosphere counts indicate that the motile strain colonised the clover root system much more extensively than did the non-motile strain.
Book chapters on the topic "Rhizobia root colonization"
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Jiménez-Gómez, Alejandro, Esther Menéndez, José D. Flores-Félix, Paula García-Fraile, Pedro F. Mateos, and Raúl Rivas. "Effective Colonization of Spinach Root Surface by Rhizobium." In Biological Nitrogen Fixation and Beneficial Plant-Microbe Interaction. Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-32528-6_10.
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Phillips, Donald A., Wolfgang R. Streit, Hanne Volpin, and Cecillia M. Joseph. "Plant Regulation of Root Colonization by Rhizobium Meliloti." In Biological Fixation of Nitrogen for Ecology and Sustainable Agriculture. Springer Berlin Heidelberg, 1997. http://dx.doi.org/10.1007/978-3-642-59112-9_27.
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Reddy, P. M., J. K. Ladha, R. B. So, et al. "Rhizobial communication with rice roots: Induction of phenotypic changes, mode of invasion and extent of colonization." In Opportunities for Biological Nitrogen Fixation in Rice and Other Non-Legumes. Springer Netherlands, 1997. http://dx.doi.org/10.1007/978-94-011-5744-5_9.
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Tchebotar, V. K., U. G. Kang, and S. Akao. "Effect of Combined Inoculation of White Clover with Gus-Marked and Wild Strains of Rhizobium and Azospirillum on Nodulation and Root Colonization." In Biological Nitrogen Fixation for the 21st Century. Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5159-7_244.
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Sharma, Gayatri. "Microbes as Artists of Life." In Symbiosis in Nature [Working Title]. IntechOpen, 2023. http://dx.doi.org/10.5772/intechopen.109532.
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Scientists have been knocking the wood to ascertain the symbiotic relationships of tiny living creatures, that is, microorganisms with other beings such as plants, animals, insects, and humans. The concept of “symbiosis” got its existence in 1879, which means “living together.” Microorganisms show a great deal of diverse interactions such as commensalism (moochers), mutualism (both benefitted), and parasitism (one benefitted and other unharmed) with other living beings and mutualism being the most common of all, thus forming a range of antagonistic to cooperative symbiotic relationships. These tiny creatures interact with plants by forming lichens (fungi and algae), mycorrhizae (plants and roots of higher plants), root noodles (Rhizobium) and acting as keyworkers in plant’s rhizosphere promoting growth and development. Microbial community also extends itself to kingdom Animalia establishing relationships with phylum Mammalia including humans, animals, and the most abundant species of phylum Arthropoda, that is, insects such as termites, which have colonization of bacteria in gut to digest wood cellulose. Scientists have discovered that most studied organisms—mussels found in deep-sea hydrothermal vents too live in a mutualistic association whereby bacteria get protection and mussels get nutrition as bacteria use chemicals from hydrothermal fluid producing organic compounds.
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Teixeira, Fernando. "Legumes Cropping and Nitrogen Fixation under Mediterranean Climate: The Case of Montado/Dehesa System." In Sustainable Development. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.104473.
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Climate change contributes to the environmental pressures that the Montado/Dehesa systems are experiencing, leading to an impoverishment of the floristic composition of the understorey. The strongly acidic soils of these systems are associated with nutrient deficiencies, nutritional disorders and the toxicity of metals, especially Mn and Al; these problems are discussed with emphasis on the antagonism between Fe and Mn and the relationship between K concentration and Mg uptake and concentration. The potential for the use of the legume-rhizobia symbiosis to increase biological nitrogen fixation and avenues for research are discussed. The co-colonization of the roots of legumes with arbuscular mycorrhizal (AM) fungi and the effects on P and Mn uptake are discussed. A better understanding of the relationships between soil pH, organic matter content (SOM), microbial community, soil P content and the plant strategies to mobilize it, as well as plant effects on the soil solution concentrations of Mn, is important for the management of these systems. The increase of biological nitrogen fixation in these systems, through the breeding of tolerant cultivars to acidic soils and a stepwise legumes enrichment, alongside soil fertility management, may contribute to increasing biomass production, SOM content and overall ecological plasticity.
Reports on the topic "Rhizobia root colonization"
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Kapulnik, Yoram, and Donald A. Phillips. Isoflavonoid Regulation of Root Bacteria. United States Department of Agriculture, 1996. http://dx.doi.org/10.32747/1996.7570561.bard.
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The overall objective of this project was to develop a conceptual framework for enhancing root colonization by beneficial bacteria. To accomplish this aim we tested the hypothesis that production and excretion of the plant phytoalexin medicarpin can be used for creation of a special niche along the legume roots, where beneficial microorganism, such as rhizobium, will have a selective advantage. On the Israeli side it was shown that higher medicarpin levels are exuded following the application of Rhizobium meliloti to the rhizosphere but the specific biochemical pathway governing medicarpin production was not induced significantly enough to support a constant production and excretion of this molecule to the rhizosphere. Furthermore, pathogenic bacteria and chemical elicitors were found to induce higher levels of this phytoalexin and it became important to test its natural abundance in field grown plants. On the US side, the occurrence of flavonoids and nucleosides in agricultural soils has been evaluated and biologically significant quantities of these molecules were identified. A more virulent Agrobacterium tumefaciens strain was isolated from alfalfa (Medicago sativa L.) which forms tumors on a wide range of plant species. This isolate contains genes that increase competitive colonization abilities on roots by reducing the accumulation of alfalfa isoflavonoids in the bacterial cells. Following gene tagging efforts the US lab found that mutation in the bacterial efflux pump operons of this isolate reduced its competitive abilities. This results support our original hypothesis that detoxification activity of isoflavenoids molecules, based on bacterial gene(s), is an important selection mechanism in the rhizosphere. In addition, we focused on biotin as a regulatory element in the rhizosphere to support growth of some rhizosphere microorganisms and designed a bacterial gene construct carrying the biotin-binding protein, streptavidin. Expressing this gene in tobacco roots did not affect the biotin level but its expression in alfalfa was lethal. In conclusion, the collaborative combination of basic and applied approaches toward the understanding of rhizosphere activity yielded new knowledge related to the colonization of roots by beneficial microorganisms in the presence of biological active molecules exuded from the plant roots.