SEARCH · PubMed Health

Results for “nodulation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 505 records · Page 28Linked to original sources

PubMed1968

Calcium and Nodulation in Subterranean Clover (Trifolium subterraneum L.).

From a study of the effects of Ca ions on the nodulation of subterranean clover in flowing culture solutions it is concluded that root infection or nodule initiation has a higher Ca requirement than either nodule development or host plant growth in the presence of fixed nitrogen.Increasing Ca concentration from 246 to 720 mum had no effect on growth of the host plant but increased the number of nodules from 7 to 24 per plant. Decreasing Ca concentration from 246 to 4 mum progressively decreased both plant growth and nodule numbers.It is suggested that nodule infection or initiation required higher solution concentration of Ca than nodule development since transferring plants after 10 days in lower Ca treatments to 720 mum Ca for 7 days did not increase nodule numbers above those on plants treated continuously at low Ca. Similarly transferring plants from 720 mum Ca to lower Ca treatments did not decrease nodule numbers much below those on plants grown continuously at 720 mum Ca even though growth was depressed. Once initiated, nodule development proceeded at concentrations of Ca too low for plant growth.The high Ca requirement for root infection or nodule initiation was not thought to be due to effects on survival or growth of Rhizobium and could not be related to effects of Ca on a number of relevant processes:-tap root length, root hair development, or lateral root initiation.

Journal Article↗

PubMed1982

Effect of Atmospheric CO(2) Enrichment on Growth, Nonstructural Carbohydrate Content, and Root Nodule Activity in Soybean.

The objective of this study was to determine whether the supply of current photosynthate was limiting root nodule activity. Both short-term (36 hours) and long-term (16 days) periods of CO(2) enrichment were imposed on vegetative, growth chamber-grown soybean plants (Glycine max. [L.] Merr. cv. ;Clay') to increase the supply of current photosynthate and to observe the effects on photosynthate partitioning in the plants, plant growth, and root nodule activity.Neither total nor specific nodule activities were increased during exposure to short-term (36 hours) CO(2) enrichment. Dry weight of the leaves increased after 12, 24, and 36 hours of CO(2) enrichment and dry weight of the stems plus petioles increased after 36 hours of CO(2) enrichment. Dry weights of the roots and nodules were not altered by short-term CO(2) enrichment. Short-term CO(2) enrichment increased the total nonstructural carbohydrates in the leaves and stems plus petioles, but not in the roots and nodules. Analyses of the separate pools of carbohydrate reserves indicated that the majority of the additional carbohydrate provided by short-term CO(2) enrichment was stored as leaf starch with relatively little being partitioned to the roots and nodules.Long-term CO(2) enrichment (16 days) did not enhance specific nodule activity. Shoot, root, and nodule dry weights were increased 109, 34%, and 56% respectively. Total nodule activity per plant was significantly enhanced only after 16 days of treatment and was related to increased nodule mass. These results indicate that the increased total nodule activity in response to CO(2) enrichment is a consequence of a general growth response of the plant.Results of both studies indicate that nodule activity was not directly limited by current photosynthesis but rather by the partitioning and utilization of photosynthate in the plant.

Journal Article↗

PubMed1982

Root and Nodule Enzymes of Ammonia Assimilation in Two Plant-Conditioned Symbiotically Ineffective Genotypes of Alfalfa (Medicago sativa L.).

Biochemical and physiological parameters associated with nitrogen metabolism were measured in nodules and roots of glasshouse-grown clones of two symbiotically ineffective alfalfa (Medicago sativa L.) genotypes supplied with either NO(3) (-) or NH(4) (+). Significant differences were observed between genotypes for nodule soluble protein concentrations and glutamine synthetase (GS) and glutamate synthase (GOGAT) specific activities, both in untreated controls and in response to applied N. Nodule soluble protein of both genotypes declined in response to applied N, while nodule GS, GOGAT, and glutamate dehydrogenase (GDH) specific activities either decreased or remained relatively constant. In contrast, no genotype differences were observed in roots for soluble protein concentrations and GS, GOGAT, and GDH specific activities, either in untreated controls or in response to applied N. Root soluble protein levels and GS and GOGAT specific activities of N-treated plants increased 2- to 4-fold within 4 days and then decreased between days 13 and 24. Root GDH specific activity of NH(4) (+)-treated plants increased steadily throughout the experiment and was 50 times greater than root GS or GOGAT specific activities by day 24.Enzymological data indicate that nodules of these ineffective alfalfa genotypes are uniquely differentiated plant organs. Decreasing or constant plant GS and GOGAT specific activities in ineffective nodules in response to applied N suggest that factors in addition to N supply are involved in the induction of high levels of plant ammonia-assimilating enzymes in nodules. Genotype differences observed for nodule enzyme specific activities support the concept that ineffectiveness may be expressed in different ways within the nodule. Senescence was evident in ineffective nodules of N-treated plants of both genotypes, indicating that nodule senescence induced by applied N may not be closely linked to symbiotic effectiveness in alfalfa. Data for ammonia-assimilating enzymes in roots suggest the GS/GOGAT pathway operates only at low levels of soil N and that GDH functions to detoxify high levels of soil NH(4) (+).

Journal Article↗

PubMed1983

Alfalfa root nodule carbon dioxide fixation : I. Association with nitrogen fixation and incorporation into amino acids.

In vivo CO(2) fixation activity and in vitro phosphoenolpyruvate carboxylase activity were demonstrated in effective and ineffective nodules of alfalfa (Medicago sativa L.) and in the nodules of four other legume species. Phosphoenolpyruvate carboxylase activity was greatly reduced in nodules from both host and bacterially conditioned ineffective alfalfa nodules as compared to effective alfalfa nodules.Forage harvest and nitrate application reduced both in vivo and in vitro CO(2) fixation activity. By day 11, forage harvest resulted in a 42% decline in in vitro nodule phosphoenolpyruvate carboxylase activity while treatment with either 40 or 80 kilograms nitrogen per hectare reduced activity by 65%. In vitro specific activity of phosphoenolpyruvate carboxylase and glutamate synthase were positively correlated with each other and both were positively correlated with acetylene reduction activity.The distribution of radioactivity in the nodules of control plants (unharvested, 0 kilograms nitrogen per hectare) averaged 73% into the organic acid and 27% into the amino acid fraction. In nodules from harvested plants treated with nitrate, near equal distribution of radioactivity was observed in the organic acid (52%) and amino acid (48%) fractions by day 8. Recovery to control distribution occurred only in those nodules whose in vitro phosphoenolpyruvate carboxylase activity recovered.The results demonstrate that CO(2) fixation is correlated with nitrogen fixation in alfalfa nodules. The maximum rate of CO(2) fixation for attached and detached alfalfa nodules at low CO(2) concentrations (0.13-0.38% CO(2)) were 18.3 and 4.9 nanomoles per hour per milligram dry weight, respectively. Nodule CO(2) fixation was estimated to provide 25% of the carbon required for assimilation of symbiotically fixed nitrogen in alfalfa.

Journal Article↗

PubMed1986

Is There a Relationship between Infection by Rhizobia and Occurrence of Disomatic Nuclei in Nodules of Alfalfa (Medicago sativa L.)?

Cytological examination of nodules from diploid, tetraploid, and octoploid alfalfa (Medicago sativa L.) plants revealed that the proportion of nodule cells infected by rhizobia was not significantly affected by nuclear ploidy of the host plant. Flow cytometry was used to determine the influence of host plant nuclear ploidy on the nuclear ploidy of infected cells. In nodules from diploid plants, most of the nuclei were tetraploid, whereas in nodules from tetraploid plants, about half of the nodule nuclei were tetraploid and half were octoploid; in octoploid plants, most of the nodule nuclei were octoploid. The occurrence of disomatic nuclei was independent of infection of nodule cells by rhizobia, because diploid plants had mostly disomatic nodule nuclei, and octoploid plants had mostly monosomatic nodule nuclei, whereas all nodules maintained a constant proportion of infected to uninfected cells. These results do not support the earlier hypothesis that infected nodule cells contain disomatic nuclei.

Journal Article↗

PubMed1987

Steady and nonsteady state gas exchange characteristics of soybean nodules in relation to the oxygen diffusion barrier.

An open gas exchange system was used to monitor the nonsteady state and steady state changes in nitrogenase activity (H(2) evolution in N(2):O(2) and Ar:O(2)) and respiration (CO(2) evolution) in attached, excised, and sliced nodules of soybean (Glycine max L. Merr.) exposed to external pO(2) of 5 to 100%. In attached nodules, increases in external pO(2) in steps of 10 or 20% resulted in sharp declines in the rates of H(2) and CO(2) evolution. Recovery of these rates to values equal to or greater than their initial rates occurred within 10 to 60 minutes of exposure to the higher pO(2). Recovery was more rapid at higher initial pO(2) and in Ar:O(2) compared to N(2):O(2). Sequential 10% increments in pO(2) to 100% O(2) resulted in rates of H(2) evolution which were 1.4 to 1.7 times the steady state rate at 20% O(2) in Ar. This was attributed to a relief at high pO(2) from the 40% decline in nitrogenase activity that was induced by Ar at a pO(2) of 20%. Changes in nodule respiration rate could not account for the nodules' ability to adjust to high external pO(2), supporting the hypothesis that soybean nodules have a variable barrier to O(2) diffusion which responds slowly (within minutes) to changes in pO(2). Nodule excision and slicing resulted in 45 and 78% declines, respectively, in total specific nitrogenase activity at 20% O(2). In contrast with the result obtained with intact nodules, subsequent 10% increases in pO(2) in Ar:O(2) did not result in transient declines in H(2) evolution rates, but in the rapid attainment of new steady state rates. Also, distinct optima in nitrogenase activity were observed at about 60% O(2). These results were consistent with an increase in the diffusive resistance of the nodule cortex following nodule excision or nodule slicing. This work also shows the importance of using intact plants and continuous measurements of gas exchange in studies of O(2) diffusion and nitrogenase activity in legume nodules.

Journal Article↗

PubMed1988

Role of Motility and Chemotaxis in Efficiency of Nodulation by Rhizobium meliloti.

Spontaneous mutants of Rhizobium meliloti L5-30 defective in motility or chemotaxis were isolated and compared against the parent with respect to symbiotic competence. Each of the mutants was able to generate normal nodules on the host plant alfalfa (Medicago sativa), but had slightly delayed nodule formation, diminished nodulation in the initially susceptible region of the host root, and relatively low representation in nodules following co-inoculation with equal numbers of the parent. When inoculated in growth pouches with increasing dosages of the parental strain, the number of nodules formed in the initially susceptible region of the root increased sigmoidally, with an optimum concentration of about 10(5) to 10(6) bacteria/plant. The dose-response behavior of the nonmotile and nonchemotactic mutants was similar, but they required 10- to 30-fold higher concentrations of bacteria to generate the same number of nodules. The distribution frequencies of nodules at different positions along the primary root were very similar for the mutants and parent, indicating that reduced nodulation by the mutants in dose-response experiments probably reflects reduced efficiency of nodule initiation rather than developmentally delayed nodule initiation. The number of bacteria that firmly adsorbed to the host root surface during several hours of incubation was 5- to 20-fold greater for the parent than the mutants. The mutants were also somewhat less effective than their parent as competitors in root adsorption assays. It appears that motility and chemotaxis are quantitatively important traits that facilitate the initial contact and adsorption of symbiotic rhizobia to the host root surface, increase the efficiency of nodule initiation, and increase the rate of infection development.

Journal Article↗

PubMed2004

Expression of nir, nor and nos denitrification genes from Bradyrhizobium japonicum in soybean root nodules.

Expression of Bradyrhizobium japonicum wild-type strain USDA110 nirK, norC and nosZ denitrification genes in soybean root nodules was studied by in situ histochemical detection of beta-galactosidase activity. Similarly, P(nirK)-lacZ, P(norC)-lacZ, and P(nosZ)-lacZ fusions were also expressed in bacteroids isolated from root nodules. Levels of beta-galactosidase activity were similar in both bacteroids and nodule sections from plants that were solely N(2)-dependent or grown in the presence of 4 mM KNO(3). These findings suggest that oxygen, and not nitrate, is the main factor controlling expression of denitrification genes in soybean nodules. In plants not amended with nitrate, B. japonicum mutant strains GRK308, GRC131, and GRZ25, that were altered in the structural nirK, norC and nosZ genes, respectively, showed a wild-type phenotype with regard to nodule number and nodule dry weight as well as plant dry weight and nitrogen content. In the presence of 4 mM KNO(3), plants inoculated with either GRK308 or GRC131 showed less nodules, and lower plant dry weight and nitrogen content, relative to those of strains USDA110 and GRZ25. Taken together, the present results revealed that although not essential for nitrogen fixation, mutation of either the structural nirK or norC genes encoding respiratory nitrite reductase and nitric oxide reductase, respectively, confers B. japonicum reduced ability for nodulation in soybean plants grown with nitrate. Furthermore, because nodules formed by each the parental and mutant strains exhibited nitrogenase activity, it is possible that denitrification enzymes play a role in nodule formation rather than in nodule function.

Journal Article↗

PubMed2006

Clinicopathological features of focal nodular hyperplasia-like nodules in 130 cirrhotic explant livers.

OBJECTIVES: Focal nodular hyperplasia-like nodules (FNH-like nodules) are focal lesions occurring in liver cirrhosis and are morphologically very similar to classical FNH in an otherwise normal liver. They are sometimes misdiagnosed as hepatocellular carcinoma (HCC) on imaging because both types of lesions show arterial-phase enhancement. Although the morphological, immunohistochemical, and imaging features of FNH-like nodules are well-known, their pathogenesis and role in hepatocarcinogenesis have not been studied in detail. Therefore, we performed a detailed pathological evaluation of 130 cirrhotic explant livers and correlated these data with the clinical features of the patients. METHODS: All cirrhotic explant livers were uniformly sliced at 5-mm intervals and all detected focal lesions were microscopically classified according to internationally accepted criteria. The obtained data regarding FNH-like nodules were then correlated with other pathological findings and with clinical data obtained during pretransplant evaluation and recorded in a database. RESULTS: FNH-like nodules were present in 15% of patients and their small size (75% of cases < 1 cm) appears to preclude detection by imaging in almost all cases. The presence of esophageal varices and pretransplant treatment with chemoembolization were independently and significantly associated with the presence of FNH-like nodules. There were no associations between FNH-like nodules on the one hand and low-grade dysplastic nodules, high-grade dysplastic nodules, and HCCs on the other hand. CONCLUSIONS: The clinicopathological features of FNH-like nodules support the hypothesis that vascular alterations in liver cirrhosis play an important role in their pathogenesis and that FNH-like nodules do not have an increased risk of malignant transformation.

Aged↗

PubMedDate not supplied

Contrast harmonic ultrasound of spontaneous liver nodules in 32 dogs.

Thirty-two dogs with spontaneous hepatic nodules were given intravenous ultrasound contrast medium (Definity or Sonovue) and imaged with contrast harmonic software on a conventional ultrasound machine system. Digital video images were initially reviewed to describe the perfusion pattern of malignant nodules. The images were reviewed again to test this pattern against all individual nodules. Subjectively, there was improved conspicuity of malignant nodules after contrast enhancement compared with conventional imaging and increased numbers of malignant nodules were often noted. There was decreased conspicuity of benign nodules and no additional nodules were seen after contrast enhancement. There was a highly significant (P < 0.0001) association of malignancy with a hypoechoic nodule at surrounding normal liver peak contrast enhancement. Benign nodules were isoechoic to the surrounding normal liver at peak contrast enhancement. Only one benign nodule (hepatoma) had regions of hypoechogenicity compared with the surrounding normal liver at peak liver contrast enhancement. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were highly significant (P < 0.0001) (100%, 94.1%, 93.8%, 100%, and 96.9%, respectively). No complications or morbidity was noted throughout the course of the study. Contrast harmonic ultrasound appears to be accurate at discriminating between naturally occurring benign and malignant nodules in the liver of dogs.

Adenocarcinoma↗

PubMed1990

DNA Hybridization Probe for Use in Determining Restricted Nodulation among Bradyrhizobium japonicum Serocluster 123 Field Isolates.

Several soybean plant introduction (PI) genotypes have recently been described which restrict nodulation of Bradyrhizobium japonicum serocluster 123 in an apparently serogroup-specific manner. While PI 371607 restricts nodulation of strains in serogroup 123 and some in serogroup 127, those in serogroup 129 are not restricted. When DNA regions within and around the B. japonicum I-110 common nodulation genes were used as probes to genomic DNA from the serogroup strains USDA 123, USDA 127, and USDA 129, several of the probes differentially hybridized to the nodulation-restricted and -unrestricted strains. One of the gene regions, cloned in plasmid pMJS12, was subsequently shown to hybridize to 4.6-kilobase EcoRI fragments from DNAs from nodulation-restricted strains and to larger fragments in nodulation-unrestricted strains. To determine if the different hybridization patterns could be used to predict nodulation restriction, we hybridized pMJS12 to EcoRI-digested genomic DNAs from uncharacterized serocluster 123 field isolates. Of the 36 strains examined, 15 were found to have single, major, 4.6-kilobase hybridizing EcoRI fragments. When tested for nodulation, 80% (12 of 15) of the strains were correctly predicted to be restricted for nodulation of the PI genotypes. In addition, hybridization patterns obtained with pMJS12 and nodulation phenotypes on PI 371607 indicated that there are at least three types of serogroup 127 strains. Our results suggest that the pMJS12 gene probe may be useful in selecting compatible host-strain combinations and in determining the suitability of field sites for the placement of soybean genotypes containing restrictive nodulation alleles.

Journal Article↗

PubMed2003

Compatibility of rhizobial genotypes within natural populations of Rhizobium leguminosarum biovar viciae for nodulation of host legumes.

Populations of Rhizobium leguminosarum biovar viciae were sampled from two bulk soils, rhizosphere, and nodules of host legumes, fava bean (Vicia faba) and pea (Pisum sativum) grown in the same soils. Additional populations nodulating peas, fava beans, and vetches (Vicia sativa) grown in other soils and fava bean-nodulating strains from various geographic sites were also analyzed. The rhizobia were characterized by repetitive extragenomic palindromic-PCR fingerprinting and/or PCR-restriction fragment length polymorphism (RFLP) of 16S-23S ribosomal DNA intergenic spacers as markers of the genomic background and PCR-RFLP of a nodulation gene region, nodD, as a marker of the symbiotic component of the genome. Pairwise comparisons showed differences among the genetic structures of the bulk soil, rhizosphere, and nodule populations and in the degree of host specificity within the Vicieae cross-inoculation group. With fava bean, the symbiotic genotype appeared to be the preponderant determinant of the success in nodule occupancy of rhizobial genotypes independently of the associated genomic background, the plant genotype, and the soil sampled. The interaction between one particular rhizobial symbiotic genotype and fava bean seems to be highly specific for nodulation and linked to the efficiency of nitrogen fixation. By contrast with bulk soil and fava bean-nodulating populations, the analysis of pea-nodulating populations showed preferential associations between genomic backgrounds and symbiotic genotypes. Both components of the rhizobial genome may influence competitiveness for nodulation of pea, and rhizosphere colonization may be a decisive step in competition for nodule occupancy.

Bacterial Proteins↗

PubMed1983

Ultrastructural analysis of ineffective alfalfa nodules formed by nif::Tn5 mutants of Rhizobium meliloti.

Ineffective alfalfa nodules formed by Rhizobium meliloti nif::Tn5 mutants were examined by light and electron microscopy. R. meliloti nifH::Tn5 mutants formed nodules that were similar in structure to wild-type nodules except that nifH- bacteroids accumulated a compact, electron-dense body. In contrast to nodules induced by wild type and nifH mutants, nifDK- R. meliloti mutants induced nodules which contained numerous starch grains and prematurely senescent bacteroids. In addition, meristematic activity in nifDK- nodules ceased significantly earlier than in nifH- nodules. All mutant nodules exhibited elevated levels of rough endoplasmic reticulum and Golgi membranes compared to wild-type nodule cells. These elevated levels may reflect either a response to nitrogen starvation in the ineffective nodules or an abnormal synthesis and export of nodule-specific proteins during later developmental stages.

Histocytochemistry↗

PubMed1986

Nodulation inhibition by Rhizobium leguminosarum multicopy nodABC genes and analysis of early stages of plant infection.

During analysis of early events in the infection and nodulation of Vicia hirsuta roots inoculated with normal and mutant strains of Rhizobium leguminosarum and strains containing cloned nodulation (nod) genes, a number of novel observations were made. (i) Alternating zones of curled and straight root hairs were seen on roots of V. hirsuta inoculated with the wild-type strain of R. leguminosarum. This phasing of root hair curling was not seen if plants were grown under continuous light or continuous dark conditions. (ii) Reduced nodulation and delayed nodule initiation was observed with a strain carrying a Tn5 mutation in the nodE gene. In addition the phased root hair curling was absent, and root hair curling was observed along the length of the root. (iii) The nodABC genes cloned on a multicopy plasmid in a wild-type strain inhibited nodulation but induced a continuous root hair curling response. Those few nodules that eventually formed were found to contain bacteria which had lost the plasmid carrying the nodABC genes. (iv) With a strain of Rhizobium cured of its indigenous symbiotic plasmid, but containing the cloned nodABCDEF genes, continuous root hair curling on V. hirsuta was observed. However, no infection threads were observed, and surprisingly, it did appear that initial stages of nodule development occurred. Observations of thin sections of these early developing nodules indicated that early nodule meristematic divisions may have occurred but that no bacteria were found within the nodules and no infection threads were observed either within the nodule bumps or within any of the root hairs. It was concluded that for normal infections to occur, precise regulation of the nod genes is required and that overexpression of the root hair curling genes inhibits the normal infection process.

Bacterial Proteins↗

PubMed1994

Root nodulation of Sesbania rostrata.

The tropical legume Sesbania rostrata can be nodulated by Azorhizobium caulinodans on both its stem and its root system. Here we investigate in detail the process of root nodulation and show that nodules develop exclusively at the base of secondary roots. Intercellular infection leads to the formation of infection pockets, which then give rise to infection threads. Concomitantly with infection, cortical cells of the secondary roots dedifferentiate, forming a meristem which has an "open-basket" configuration and which surrounds the initial infection site. Bacteria are released from the tips of infection threads into plant cells via "infection droplets," each containing several bacteria. Initially, nodule differentiation is comparable to that of indeterminate nodules, with the youngest meristematic cells being located at the periphery and the nitrogen-fixing cells being located at the nodule center. Because of the peculiar form of the meristem, Sesbania root nodules develop uniformly around a central axis. Nitrogen fixation is detected as early as 3 days following inoculation, while the nodule meristem is still active. Two weeks after inoculation, meristematic activity ceases, and nodules then show the typical histology of determinate nodules. Thus, root nodule organogenesis in S. rostrata appears to be intermediate between indeterminate and determinate types.

Cell Differentiation↗

PubMed1994

Lipopolysaccharide epitope expression of Rhizobium bacteroids as revealed by in situ immunolabelling of pea root nodule sections.

To investigate the in situ expression of lipopolysaccharide (LPS) epitopes on nodule bacteria of Rhizobium leguminosarum, monoclonal antibodies recognizing LPS macromolecules were used for immunocytochemical staining of pea nodule tissue. Many LPS epitopes were constitutively expressed, and the corresponding antibodies reacted in nodule sections with bacteria at all stages of tissue infection and cell invasion. Some antibodies, however, recognized epitopes that were only expressed in particular regions of the nodule. Two general patterns of regulated LPS epitope expression could be distinguished on longitudinal sections of nodules. A radial pattern probably reflected the local physiological conditions experienced by endosymbiotic bacteria as a result of oxygen diffusion into the nodule tissue. The other pattern of expression, which followed a linear axis of symmetry along a longitudinal section of the pea nodule, was apparently associated with the differentiation of nodule bacteria and the development of the nitrogen-fixing capacity in bacteroids. Basically similar patterns of LPS epitope expression were observed for pea nodules harboring either of two immunologically distinct strains of R. leguminosarum bv. viciae, although these epitopes were recognized by different sets of strain-specific monoclonal antibodies. Furthermore, LPS epitope expression of rhizobia in pea nodules was compared with that of equivalent strains in nodules of French bean (Phaseolus vulgaris). From these observations, it is suggested that structural modifications of Rhizobium LPS may play an important role in the adaptation of endosymbiotic rhizobia to the surrounding microenvironment.

Antibodies, Bacterial↗

PubMed2002

Identification and cloning of the bacterial nodulation specificity gene in the Sinorhizobium meliloti--Medicago laciniata symbiosis.

Medicago laciniata (cut-leaf medic) is an annual medic that is highly nodulation specific, nodulating only with a restricted range of Sinorhizobium meliloti. e.g., strain 102L4, but not with most strains that nodulate Medicago sativa (alfalfa), e.g., strains RCR2011 and Rm41. Our aim was to identify and clone the S. meliloti 102L4 gene implicated in the specific nodulation of M. laciniata and to characterize the adjacent nodulation (nod) region. An 11-kb EcoRI DNA fragment from S. meliloti 102L4 was shown to complement strain RCR2011 for nodulation of M. laciniata. Nucleotide sequencing revealed that this fragment contained nodABCIJ genes whose overall arrangement was similar to those found in strains RCR2011 and Rm41, which do not nodulate M. laciniata. Data for Tn5 mutagenesis of the nodABCIJ region of strain 102L4 suggested that the nodC gene was involved in the specific nodulation of M. laciniata. Tn5 insertions in the nodIJ genes gave mutants with nodulation delay phenotypes on both M. laciniata and M. sativa. Only subclones of the 11-kb DNA fragment containing a functional nodC gene from strain 102L4 were able to complement strain RCR2011 for nodulation of M. laciniata. The practical implications of these findings are discussed in the context of the development of a specific M. sativa - S. meliloti combination that excludes competition for nodulation by bacterial competitors resident in soil.

Amino Acid Sequence↗

PubMedDate not supplied

Benign versus malignant hepatic nodules: MR imaging findings with pathologic correlation.

According to the currently used nomenclature, there are only two types of hepatocellular nodular lesions: regenerative lesions and dysplastic or neoplastic lesions. Regenerative nodules include monoacinar regenerative nodules, multiacinar regenerative nodules, cirrhotic nodules, segmental or lobar hyperplasia, and focal nodular hyperplasia. Dysplastic or neoplastic nodules include hepatocellular adenoma, dysplastic foci, dysplastic nodules, and hepatocellular carcinoma (HCC). Many of these types of hepatic nodules play a role in the de novo and stepwise carcinogenesis of HCC, which comprises the following steps: regenerative nodule, low-grade dysplastic nodule, high-grade dysplastic nodule, small HCC, and large HCC. State-of-the-art magnetic resonance (MR) imaging facilitates detection and characterization in most cases of hepatic nodules. State-of-the-art MR imaging includes single-shot fast spin-echo imaging, in-phase and opposed-phase T1-weighted gradient-echo imaging, T2-weighted fast spin-echo imaging with fat saturation, and two-dimensional or three-dimensional dynamic multiphase contrast material-enhanced imaging.

Carcinoma, Hepatocellular↗