Root Nodules Of Plants Research Articles

Biocontrol of Fusarium Root Rot in the Common Bean (Phaseolus vulgaris L.) by using Symbiotic Glomus mosseae and Rhizobium leguminosarum

The interaction between VA mycorrhiza Glomus mosseae (Gm), root rodulating symbiont Rhizobium leguminosarum (Rl), and root rot pathogen Fusarium solani (Fs) on the common bean (Phaseolus vulgaris) in relation to plant growth, nutrient uptake, disease severity, rhizosphere microbial biomass, and nutrient availability was investigated. Mycorrhizal plants yielded significantly greater plant biomass and mobilized more N and P uptake as compared to nonmycorrhizal plants or those infected with Fs. However, the mycorrhizal root colonizing ability, in presence of Fs, was reduced by 27%, whereas Rl enhanced it by 37%. The inoculation of Gm, besides decreasing propagule number of Fs in the rhizosphere, decreased pathogenic root rot by 34 to 77%. However, in the presence of Rl, Gm-inoculated plants were more tolerant of the fungal root pathogen. The Gm + Rl inoculated plants not only had maximum plant biomass and root nodulation, but also exhibited higher microbial biomass, alkaline phosphatase activity, and available phosphorus in their rhizosphere. Rl, alone or in association with Gm, caused the maximum increase in mineral nitrogen (NH4 + and NO3 −) content in soil. These results indicate that Gm has a vital role in inhibiting the root pathogen from invasion, more so in the presence of R. leguminosarum.

The peribacteroid membrane

The objective of this review is to summarise current knowledge about the structure and function of the peribacteroid membrane from the root nodules of leguminous plants. The information is presented in terms of development of this symbiotic membrane from its origin, through proliferation and in the mature state. There are clear indications that the peribacteroid membrane has a distinct structure and function at each developmental stage. The mature peribacteroid membrane has been the most intensively studied. The lipid and protein content of the mature peribacteroid membrane is discussed with particular emphasis on genetic and functional studies of the proteins. The mechanism and control of peribacteroid membrane biogenesis is also discussed. There is evidence for a specific biogenetic pathway for this membrane which requires both symbiotic partners for its correct functioning.

Leghemoglobin-derived Radicals: EVIDENCE FOR MULTIPLE PROTEIN-DERIVED RADICALS AND THE INITIATION OF PERIBACTEROID MEMBRANE DAMAGE

Reaction of H2O2 with ferric leghemoglobin (metLb, the monomeric, oxygen-carrying, heme protein from root nodules of nitrogen-fixing plants) has been previously shown to generate an iron(IV)-oxo (ferryl) species and at least one protein radical. The latter has been suggested to be a tyrosine-derived phenoxyl radical present at Tyr-133 in the soybean protein and Tyr-138 in the lupin protein. To obtain further information on these protein radicals and their potential interaction with the physiologically important peribacteroid membrane (which surrounds the microsymbiont in vivo), EPR spin trapping studies have been carried out with soybean metLb. Evidence has been obtained for at least two additional protein-derived radicals in addition to the phenoxyl radical; these radicals are transient and reactive in nature. These species are carbon-centered, and at least one is a tertiary species (.CR1R2R3); these radicals may be side chain- or alpha-carbon-derived, their exact sites have not been determined. Some of these radicals are on the protein surface and may be key intermediates in the formation of protein dimers. These radicals have been shown to be capable of reacting with peribacteroid membrane fractions, with the consequent generation of lipid-derived radicals. The formation of such radicals may result in the depletion of membrane antioxidants and the initiation of lipid peroxidation. This transfer of damage from the heme center via the protein surface to neighboring membranes may be of considerable biological significance; the destruction of this membrane is one of the earliest observable events in root nodule senescence and is associated with the loss of nitrogen-fixing activity.

The role of lipochitooligosaccharides in root nodule organogenesis and plant cell growth

Lipochitooligosaccharides (Nod signals) excreted by rhizobia induce the formation of symbiotic root nodules in leguminous plants. This process is host plant specific, depending on the structural modifications of Nod signals. Rapid responses of plant roots in single cell assays have provided powerful tools in dissecting Nod signal transduction pathways and in elucidating the molecular basis of host specificity. Recent findings indicate that lipochitooligosaccharides, as well as symbiosis-related genes, also function in non legumes, pointing to a general role for these elements in plant morphogenesis.

Cycling of amino compounds in symbiotic lupin

The composition of amino acids was determined in the xylem and phloem sap of symbiotic lupins grown under a variety of treatments designed to alter the rate of nitrogen fixation. Asparagine was the major amino acid in both xylem and phloem with glutamine, glutamate and aspartate also major components. GABA had a high concentration in the xylem while valine was a major component in the phloem. Exposure to combined nitrogen in the form of either ammonium or nitrate caused a reduction in specific nitrogenase activity and was associated with subsequent changes in both of the translocated saps. Inhibiting nitrogen fixation by exposing nodules to oxygen produced a lower amide to amine ratio in the xylem sap (1.3:1) compared with control and nitrate ratios (2.6:1) and ammonium ratios (7.1:1). Similar ratios for amide amine were also observed in the phloem sap. Labelling studies using 15N2 to follow nitrogen fixation, ammonium assimilation and amino acid transport have shown rapid accumulation of label into glutamine with subsequent enrichment in glutamate, aspartate, alanine, and GABA. Asparagine was found in high concentrations in nodules and became slowly enriched. Labelled nitrogen fixed and assimilated in nodules was detected 40 min later in stem xylem extracts, largely as the amides glutamine and asparagine. These experiments provide evidence that large amounts of nitrogenous compounds are cycled through the root nodules of symbiotic plants (contributing approximately 50% of xylem N) and that differences in the composition of the phloem sap may influence nodule growth and activity.

Regulation of plant morphogenesis by Lipo‐Chitin oligosaccharides

Abstract Lipo‐chitin oligosaccharides (LCOs), produced by rhizobia, are causative agents of the formation of root nodules in leguminous plants. As outlined in this review, the root nodulation process presents a valuable model system to study plant morphogenesis. The knowledge that resulted from the studies of the biological function and biosynthesis of the rhizobial LCOs is summarized. It has been postulated that LCOs are representatives of a general class of signal molecules involved in plant and animal morphogenesis. Discussed is how the present knowledge can be used for future studies on the function of LCOs in morphogenesis and in the search for analogue signal molecules produced by plants and animals.

Studies on the root nodules of leguminous plants: The production of indole acetic acid in culture by a Rhizobium sp. from a leguminous climbing shrub Derris scandens benth

AbstractThe Rhizobium sp. When isolated form the root nodules of a leguminous climbing shrub Derris scandens produced a high amount of indole acetic acid (IAA) (135.2 μg/ml) from the tryptophan‐supple‐mented basal medium. Growth and IAA production started simultaneously, and the maximum amount of IAA was produced as a secondary metabolite in the stationary phase of growth. The IAA production by the Rhizobium sp. was increased by 503% when the medium was supplemented with mannitol (2%), KNO3 (0.2%), nicotinic acid (0.1 μg/ml) and MnSO4 (1 μg/ml) in addition to tryptophan (4 mg/ml)/The possible role of the rhizobial production of IAA on the rhizobia‐legume symbiosis is also discussed.

Sequences of nifX, nifW, nifZ, nifB and two ORF in the frankia nitrogen fixation gene cluster

The actinomycete Frankia alni fixes N 2 in root nodules of several non-leguminous plants. It is one of the few known N 2-fixing members of the high-GC Gram + lineage of prokaryotes. Thus, we have undertaken a study of its nitrogen fixation gene ( n/f) organization to compare with that of the more extensively characterized proteobacteria. A cosmid (pFN1) containing the n/f region of Fa CpI1 was isolated from a cosmid library using the nifHDK genes of Fa CpI1 as a probe. A 4.5-kb BamHI fragment that mapped downstream from the previously characterized n/fHDK genes was cloned and sequenced. Based on nt and aa sequence similarities to n/f from other N2-fixing bacteria, eight ORF were identified and designated nifX, orf3, orfl, nifW, n/fZ, nifB, orf2 and n/fU. A region that hybridized to Rhizobium meliloti and Klebsiella pneumoniae n/fA did not appear to contain a n/fA-like gene. We have revised the map of the Fa n/f region to reflect current information.

Evolution of cytochrome oxidase, an enzyme older than atmospheric oxygen.

Cytochrome oxidase is a key enzyme in aerobic metabolism. All the recorded eubacterial (domain Bacteria) and archaebacterial (Archaea) sequences of subunits 1 and 2 of this protein complex have been used for a comprehensive evolutionary analysis. The phylogenetic trees reveal several processes of gene duplication. Some of these are ancient, having occurred in the common ancestor of Bacteria and Archaea, whereas others have occurred in specific lines of Bacteria. We show that eubacterial quinol oxidase was derived from cytochrome c oxidase in Gram-positive bacteria and that archaebacterial quinol oxidase has an independent origin. A considerable amount of evidence suggests that Proteobacteria (Purple bacteria) acquired quinol oxidase through a lateral gene transfer from Gram-positive bacteria. The prevalent hypothesis that aerobic metabolism arose several times in evolution after oxygenic photosynthesis, is not sustained by two aspects of the molecular data. First, cytochrome oxidase was present in the common ancestor of Archaea and Bacteria whereas oxygenic photosynthesis appeared in Bacteria. Second, an extant cytochrome oxidase in nitrogen-fixing bacteria shows that aerobic metabolism is possible in an environment with a very low level of oxygen, such as the root nodules of leguminous plants. Therefore, we propose that aerobic metabolism in organisms with cytochrome oxidase has a monophyletic and ancient origin, prior to the appearance of eubacterial oxygenic photosynthetic organisms.

Effects of cobalt on plants

Effects of cobalt on plants

Field response of the Glycine-bradyrhizobium symbiosis to modified early-nodule occupancy

A 2 yr field study was conducted to monitor the response of the Glycine-Bradyrhizobium symbiosis to high initial levels of nodulation by selected strains of B. japonicum when grown in soil containing indigenous soybean bradyrhizobia. Nodulated soybean seedlings were prepared under greenhouse conditions and transplanted to 15N-amended field microplots when ca 23 days old. The population of indigenous bradyrhizobia at the study site was ca 7 × 10 5g −1 soil. Inoculation treatments included strains USDA 122 (a superior N 2 fixer), USDA 94 (a strong rhizobitoxine producer), and a soil suspension containing a mixture of strains indigenous to the study site. Occupancy of root nodules was monitored serologically with an ELISA and morphologically by colony type on yeast extract-mannitol agar. The frequencies of serogroups 122 and 94 in early-formed (tap root) nodules of plants receiving USDA 122 and 94 as inocula dropped from 99.5 and 94.5% during vegetative growth to 55.0 and 28.5% during seedfill, respectively. The incidence of B. japonicum DNA homology Group II increased during host development for those plants initially treated with the soil suspension. Relative to the soil control treatment, inoculation with USDA 122 significantly increased soybean seed yield by 32%, N 2 fixation by 29% and total shoot N content by 30%. Conversely, USDA 94 decreased the magnitude of these variables by 39, 44 and 42%, respectively. These results demonstrate that the successful introduction of contrasting strains of B. japonicum into early-formed nodules can modify soybean productivity despite subsequent nodulation by indigenous soybean bradyrhizobia.

Influence of Pseudomonas syringae R25 and P. putida R105 on the growth and N2 fixation (acetylene reduction activity) of pea (Pisum sativum L.) and field bean (Phaseolus vulgaris L.)

The effects of inoculating field peas (Pisum sativum L.) with Rhizobium leguminosarum and field beans (Phaseolus vulgaris L.) with R. phaseoli, alone or in combination with Pseudomonas syringae R25 and/or P. putida R105, were assessed under gnotobiotic conditions in growth pouches and in potted soil in a growth chamber. Inoculation of peas with P. syringae R25 or P. putida R105 alone had no effect on plant growth in pouches. In soil, however, the isolate R25 inhibited nitrogenase activity (as assessed by acetylene reduction assay) of nodules formed by indigenous rhizobia; strain R105 stimulated pea seedling emergence and nodulation. P. syringae R25 inhibited the growth of beans in either plant-growth system. P. putida R105, however, had no effects on beans in pouches, but reduced plant root biomass and nodulation by indigenous rhizobia in soil. Coinoculation of pea seeds with R. leguminosarum and either of the pseudomonads significantly (P<0.01) increased shoot, root, and total plant weight in growth pouches, but had no effect in soil. Co-inoculation of field beans with R. phaseoli and P. putida R105 had no effects on plant biomass in growth pouches or in soil, but the number of nodules and the acetylene reduction activity was significantly (P<0.01) increased in the soil. In contrast, co-inoculation of beans with rhizobia and P. syringae R25 had severe, deleterious effects on seedling mergence, plant biomass, and nodulation in soil and growth pouches. Isolate R25 was responsible for the deleterious effects observed. Although plant growth-promoting rhizobacteria may interact synergistically with root-nodulating rhizobia, the PGPR selected for one crop should be assessed for potential hazardous effects on other crops before being used as inoculants.

High-pressure freezing improves quantitative and qualitative structural data in the actinomycete microsymbiont frankia

Symbiotic plant root nodules containing the nitrogen-fixing bacterium Frankia occur on a variety of woody shrubs and trees. Ever since the first micrographs of freeze substituted cells of Frankia in culture were published there has been impetus to see if freeze substitued nodule tissue will improve imaging of Frankia in vivo. High pressure freezing/freeze substitution (HPFS) accomplishes this.Frankia is an actinomycete that fixes N2 in a specialized multicellular, spherical structure termed the “symbiotic vesicle” that is surrounded by a multilamellate envelope (MLE) comprised of lipids. Early work based on MLE birefringence suggested the MLE was a O2 diffusion barrier, thereby protecting nitrogenase from O2- inactivation. Recently this has been challenged by freeze fracture data. Traditionally it has been assumed that the MLE is electrontranslucent because the lamina of the MLE are extracted by dehydration solvents, producing the “void space”--an extraction artifact hindering TEM analysis of MLE structure.En bloc staining with chromic acid stains the MLE, showing that the MLE is present after exposure to dehydration solvents and that the void space results from tissue shrinkage in the symbiotic vesicle (Figure 1).

Specific detection of rhizobia in root nodules and soil using the polymerase chain reaction

The polymerase chain reaction (PCR) amplification of specific DNA sequences, allows specific and sensitive detection of bacteria at the genus, species or strain level depending on the design of the oligonucleotide primers. In this study we utilized 20 mer primers that flanked a 300 bp region of the npt II gene of the transposon Tn5 thus allowing for the amplification of this region. Insertion of the Tn 5 element into rhizobia allowed for detection of these cells using PCR amplification. Using the npt II-specific primers and Tn5 insertion mutants of Rhizobium leguminosarum bv. phaseoli we were able to detect these specific rhizobia strains in root nodules of bean plants and in inoculated soils. Utilization of genus-specific gene sequences would allow for estimates of cells of that genus in environmental samples. Conversely, use of gene sequences common to rhizobia, e.g. nif and nod sequences, would give estimates of the population of rhizobia. This paper serves to illustrate the use of PCR, for detecting gene sequences in an environmental sample such as a root nodule.

Induction of Pre-Infection Thread Structures in the Leguminous Host Plant by Mitogenic Lipo-Oligosaccharides of Rhizobium

Root nodules of leguminous plants are symbiotic organs in which Rhizobium bacteria fix nitrogen. Their formation requires the induction of a nodule meristem and the formation of a tubular structure, the infection thread, through which the rhizobia reach the nodule primordium. In the Rhizobium host plants pea and vetch, pre-infection thread structures always preceded the formation of infection threads. These structures consisted of cytoplasmic bridges traversing the central vacuole of outer cortical root cells, aligned in radial rows. In vetch, the site of the infection thread was determined by the plant rather than by the invading rhizobia. Like nodule primordia, pre-infection thread structures could be induced in the absence of rhizobia provided that mitogenic lipo-oligosaccharides produced by Rhizobium leguminosarum biovar viciae were added to the plant. In this case, cells in the two outer cortical cell layers containing cytoplasmic bridges may have formed root hairs. A common morphogenetic pathway may be shared in the formation of root hairs and infection threads.

Positive effects of cement kiln exhausts on legume crops under simulation study

Soil application of cement kiln exhausts (electrostatic precipitator dust) at both lower and higher concentrations did not inhibit growth, nodule formation, and productivity inCajanus cajan, vigna radiata, andVigna mungo. In fact, growth was promoted, possibly because of the dust containing most of the elements, such as N, Ca, Fe, Mg, Mn, K, Zn, P, S, and Cu, which are needed for plant growth and root nodulation. Foliar application of the dust did not affect chlorophylls and carotenoids. The rate of photosynthesis as measured by CO2 uptake and stomatal diffusive resistance of all legumes were not affected. There was a biomagnification of Mg and K in leaves and seeds. Addition of the ESP dust did not affect either the soil or nodule rhizobial population. It is evident that the dust did not act as a phytotoxicant but as an elixir of plant life.

Interaction between root and stem nodulation in hydroponically grown plants ofSesbania rostrata

Abstract Plant growth parameters, nitrogen content, root and stem nodulation, and acetylene reduction activity of nodules after root and shoot inoculation of hydroponically grown plants of Sesbania rostrata were studied. Stem nodulation reduced the number of root nodules whether stem inoculation was done simultaneously before or after root inoculation. Stem inoculation seven days after root inoculation gave best plant growth. Acetylene reduction was greatest in the root nodules. No significant difference in nitrogen % was observed with the different types of inoculation.

Metal tolerance of isolates of Rhizobium leguminosarum biovar Trifolii from soil contaminated by past applications of sewage sludge

We tested the tolerance to Cu, Ni, Cd and Zn of two isolates of Rhizobium leguminosarum biovar trifolii isolated from root nodules of clover plants grown in metal-contaminated sewage sludge treated plots (S-isolates) at Woburn Experimental Farm, and two isolates from root nodules of clover plants grown in uncontaminated control plots treated with farmyard manure (F-isolates). Survival of the isolates was compared in solutions containing different concentrations of Cu, Ni, Cd or Zn. The S-isolates from metal-contaminated soil were tolerant to larger concentrations of Cu, Ni, Cd and Zn compared to the F-isolates from uncontaminated control soil. The F-isolates were killed at concentrations of 0.002 μg ml −1 Cu, 0.2 μg ml −1 Cd 0.8 μg ml −1 Ni and 0.8 μg, ml −1 Zn within 72h, whilst the S-isolates survived, albeit in reduced numbers, at concentrations of 0.01 μg ml −1 Cu and 1.0 μg ml −1 Zn, but were killed by 1.0 μg ml −1 Ni and 0.8 μg ml −1 Cd within 72 h. A particularly strong increase in tolerance to Zn was shown by the S-isolates compared to other metals at the same concentrations. Thus, the order of decreasing toxicity in solution to the two F-isolates was Cu > Cd > Zn = Ni, but for the two S-isolates it was Cu > Cd > Ni > Zn. The S-isolates have multiple metal tolerance that enables them to survive in metal-contaminated soil, but they have lost their ability to fix nitrogen with Trifolium repens L. The F-isolates can fix nitrogen, but these do not survive in metal-contaminated soil because they lack tolerance to these metals.

Formation of Novel Polysaccharides by Bradyrhizobium japonicum Bacteroids in Soybean Nodules

Certain strains of Bradyrhizobium japonicum form a previously unknown polysaccharide in the root nodules of soybean plants (Glycine max (L.) Merr.). The polysaccharide accumulates inside of the symbiosome membrane-the plant-derived membrane enclosing the bacteroids. In older nodules (60 days after planting), the polysaccharide occupies most of the symbiosome volume and symbiosomes become enlarged so that there is little host cytoplasm in infected cells. The two different groups of B. japonicum which produce different types of polysaccharide in culture produce polysaccharides of similar composition in nodules. Polysaccharide formed by group I strains (e.g., USDA 5 and USDA 123) is composed of rhamnose, galactose, and 2-O-methylglucuronic acid, while polysaccharide formed by group II strains (e.g., USDA 31 and USDA 39) is composed of rhamnose and 4-O-methylglucuronic acid. That the polysaccharide is a bacterial product is indicated by its composition plus the fact that polysaccharide formation is independent of host genotype but is dependent on the bacterial genotype. Polysaccharide formation in nodules is common among strains in serogroups 123, 127, 129, and 31, with 27 of 39 strains (69%) testing positive. Polysaccharide formation in nodules is uncommon among other B. japonicum serogroups, with only 1 strain in 18 (6%) testing positive.

Direct detection of a globin-derived radical in leghaemoglobin treated with peroxides.

The root nodules of leguminous plants contain an oxygen-carrying protein which is somewhat similar to myoglobin. Reaction of the Fe3+ form of this protein (metleghaemoglobin; MetLb) with H2O2 is known to generate a ferryl [iron(IV)-oxo] species. This intermediate, which is analogous to Compound II of peroxidases and ferryl myoglobin, is one oxidizing equivalent above the initial level. In the present study it is shown that the second oxidizing equivalent from the peroxide is rapidly transferred into the surrounding protein, generating a protein radical which has been detected by e.p.r. spectroscopy; this reaction is analogous to that observed with metmyoglobin. An identical protein-derived species is observed with all three forms of MetLb tested (a, c1, c3) and with a number of other hydroperoxides and two-electron oxidants. This latter result, the observation that the concentration of this species is not affected by certain hydroxyl-radical scavengers, and the loss of the radical when the oxy or deoxy forms are used, demonstrate that this species is formed by electron transfer within the protein rather than by the generation and subsequent reaction of hydroxyl radicals (and related species from the other hydroperoxides). The e.p.r. signal of this species, which decays rapidly with a half-life of approx. 40 s, is consistent with the formation of a sterically constrained tyrosine-derived phenoxyl radical; protein-iodination experiments lend support to this assignment. Reaction between the radical and a number of other compounds has been observed, demonstrating that it is at least partially exposed on the surface of the protein. Analysis of the protein structure suggest that the radical may be centred on a tyrosine residue present at position 132 in the protein; this residue is close to the haem prosthetic group, which would facilitate rapid electron transfer.