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PubMed1985

Expression of plant genes during the development of pea root nodules.

The expression of plant genes involved in the pea-Rhizobium symbiosis was studied by analysing mRNA from root nodules. The RNA was translated in vitro and the translation products were separated by two-dimensional gel electrophoresis. The results show differential expression of nodulin genes during root nodule development. One gene encoding N-40' is expressed at a significant level 5 days before the leghemoglobin genes. Most other nodulin genes are expressed more of less concomitantly with the leghemoglobin genes whereas the N-21 mRNA is only present late during the development. In the development of ineffective root nodules induced by infection with different nod+fix- mutants of R. leguminosarum all nodulin genes are expressed except for the N-21 gene. The results suggest that neither bacteroid development, heme excretion nor nitrogen fixation are essential for the induction of nodulin gene expression in the host plant. Further, it appears that the amount of leghemoglobin in ineffective nodules is regulated at a post-transcriptional level.

Electrophoresis, Gel, Two-Dimensional↗
PubMed2005

Architecture of infection thread networks in developing root nodules induced by the symbiotic bacterium Sinorhizobium meliloti on Medicago truncatula.

During the course of the development of nitrogen-fixing root nodules induced by Sinorhizobium meliloti on the model plant Medicago truncatula, tubules called infection threads are cooperatively constructed to deliver the bacterial symbiont from the root surface to cells in the interior of the root and developing nodule. Three-dimensional reconstructions of infection threads inside M. truncatula nodules showed that the threads formed relatively simple, tree-like networks. Some characteristics of thread networks, such as branch length, branch density, and branch surface-to-volume ratios, were remarkably constant across nodules in different stages of development. The overall direction of growth of the networks changed as nodules developed. In 5-d-old nodules, the overall growth of the network was directed inward toward the root. However, well-defined regions of these young networks displayed an outward growth bias, indicating that they were likely in the process of repolarizing their direction of development in response to the formation of the outward-growing nodule meristem. In 10- and 30-d-old nodules, the branches of the network grew outward toward the meristem and away from the roots on which the nodules developed.

Computer Simulation↗
PubMed2002

Genetic dissection of the initiation of the infection process and nodule tissue development in the Rhizobium-pea (Pisum sativum L.) symbiosis.

Twelve non-nodulating pea (Pisum sativum L.) mutants were studied to identify the blocks in nodule tissue development. In nine, the reason for the lack of infection thread (IT) development was studied; this had been characterized previously in the other three mutants. With respect to IT development, mutants in gene sym7 are interrupted at the stage of colonization of the pocket in the curled root hair (Crh- phenotype), mutants in genes sym37 and sym38 are blocked at the stage of IT growth in the root hair cell (Ith- phenotype) and mutants in gene sym34 at the stage of IT growth inside root cortex cells (Itr- phenotype). With respect to nodule tissue development, mutants in genes sym7, sym14 and sym35 were shown to be blocked at the stage of cortical cell divisions (Ccd- phenotype), mutants in gene sym34 are halted at the stage of nodule primordium (NP) development (Npd- phenotype) and mutants in genes sym37 and sym38 are arrested at the stage of nodule meristem development (Nmd- phenotype). Thus, the sequential functioning of the genes Sym37, Sym38 and the gene Sym34 apparently differs in the infection process and during nodule tissue development. Based on these data, a scheme is suggested for the sequential functioning of early pea symbiotic genes in the two developmental processes: infection and nodule tissue formation.

Meristem↗
PubMed1978

Membranes in lupin root nodules. II. Preparation and properties of peribacteroid membranes and bacteroid envelope inner membranes from developing lupin nodules.

Peribacteroid membranes and bacteroid envelope inner membranes have been isolated from developing lupin nodules. Isolation of the peribacteroid membranes was achieved by first preparing membrane-enclosed bacteroids free from other plant organelles or membranes. The peribacteroid membranes were then released by osmotic shock and purified by centrifugation to equilibrium on sucrose gradients. The bacteroids were broken in a pressure cell and the bacteroid envelope inner membranes were isolated using sucrose gradient fractionation of the bacteroid total envelope preparation. The density of the peribacteroid membranes decreased during the period of development of N2-fixation in lupin nodules from 1.148 g/ml for nodules from 12-day plants to 1.137 g/ml for nodules from 18-day plants. The density of the bacteroid envelope inner membranes from nodules from 18-day plants was 1-153 g/ml. The identity and homogeneity of the isolated membranes was established, by comparison with membranes in intact nodules, using phosphotungstic acid and silver staining of thin sections and particle densitites on faces of freeze-fracture replicas of the membranes. Analyses for NADH oxidase and succinate dehydrogenase, spectral analyses and gel-electrophoretic analysis of proteins were also used to characterize the membrane and soluble protein fractions from the nodules. The ratio of lipid to protein was 6.1 for the peribacteroid membranes and 2.5 for the bacteroid envelope inner membranes. Leghaemoglobin was localized in the plant cytoplasm in lupin nodules and not in the peribacteroid space.

Cell Fractionation↗
PubMed1979

Sequence complexities of the poly(A)-containing mRNA in uninfected soybean root and the nodule tissue developed due to the infection by Rhizobium.

In order to determine the number of structural genes expressed specifically in root nodules, the total complexities of poly(A) + polysomal RNA populations from uninfected roots and mature nodules were compared. Hybridization kinetics of nodule poly(A) + RNA (NRNA) to its cDNA (NcDNA) revealed a very abundant component comprising 18--20% of the NRNA. This component was shown to be leghaemoglobin (Lb) by the similarity of its kinetics of hybridization to that of purified Lb-cDNA. The hybridization kinetics of uninfected root cDNA (RcDNA) to root poly(A) + RNA (RRNA) indicate that this abundant RNA fraction is absent in RRNA. The extent of sequence homologies between root and nodule tissue was determined by heterologous hybridizations of RcDNA to NRNA and vice versa. The data suggest that the mRNA populations of the two tissues are substantially homologous, though shifts in abundance of certain sequences are quite marked. The hybridization of purified Lb-cDNA to total polysomal RNA from developing nodules shows that the increase in concentration of Lb-mRNA sequences parallels the leghaemoglobin synthesis in this tissue. Lb sequences appear to increase between 8 and 13 days after infection with Rhizobium.

Kinetics↗
PubMed2006

Spatial and temporal organization of sucrose metabolism in Lotus japonicus nitrogen-fixing nodules suggests a role for the elusive alkaline/neutral invertase.

Symbiotic nitrogen fixation (SNF) in legume nodules is a highly energy demanding process, fuelled by plant-supplied carbohydrates mainly in the form of sucrose. In this study, we have combined molecular and biochemical approaches in order to study the spatial and temporal organisation of sucrose metabolism in nitrogen-fixing nodules of the model legume Lotus japonicus, with an emphasis on the neglected role of alkaline/neutral invertase. For this purpose, a full-length cDNA clone coding for an alkaline/neutral invertase isoform, termed LjInv1, was identified in a L. japonicus mature nodule cDNA libraries. Alkaline/neutral invertase activity was also found to be the predominant invertase activity in mature nodules. Real-time reverse-transcription polymerase chain reaction analysis was used in order to study the temporal expression patterns of LjInv1 in parallel with genes encoding acid invertase and sucrose synthase (SuSy) isoforms, and enzymes involved in the subsequent hexose partitioning including hexokinase, phosphoglucomutase (PGM) and phosphoglucose isomerase (PGI). The spatial organisation of sucrose metabolism was studied by in situ localisation of LjInv1 transcripts and alkaline/neutral invertase activity, and SuSy protein during nodule development. Furthermore, the spatial organisation of hexose metabolism was investigated by histochemical localisation of hexokinase, PGM and PGI activities in mature nodules. The results considered together indicate that alkaline/neutral invertase could contribute to both the Glc-1-P and Glc-6-P pools in nodules, fuelling both biosynthetic processes and SNF. Furthermore, transcript profiling analysis revealed that genes coding for hexokinase and putative plastidic PGM and PGI isoforms are upregulated during the early stages of nodule development, while the levels of transcripts corresponding to cytosolic PGM and PGI isoforms remained similar to uninfected roots, indicating a possible role of LjInv1 in producing hexoses for starch production and other biosynthetic processes in developing nodules.

Amino Acid Sequence↗
PubMed2006

Dysplastic nodules frequently develop into hepatocellular carcinoma in patients with chronic viral hepatitis and cirrhosis.

BACKGROUND: Advances in imaging technology have enhanced the detection of small nodular lesions during the course of chronic liver disease. METHODS: Between 1995 and 2002, the authors examined 154 consecutive patients with small hepatic nodules without hepatocellular carcinoma (HCC) over a median duration of 2.8 years. The median size of these nodules was 14 mm (range, 7-40 mm). The initial histopathologic diagnosis included high-grade dysplastic nodule (HGDN) (n=13), low-grade dysplastic nodule (LGDN) (n=42), and regenerative nodule (RN) (n=99). RESULTS: A total of 29 (18.8%) nodules developed into HCC during the observation period. Cumulative HCC development rates at the first, third, and fifth year were 46.2%, 61.5%, and 80.8% for HGDN; 2.6%, 30.2%, and 36.6% for LGDN; and 3.3%, 9.7%, and 12.4% for RN, respectively. The rate of HCC development was significantly higher in the HGDN group than for other types (P<0.001). Multivariate analysis disclosed that histopathologic diagnosis (P<0.001) and findings on computed tomographic arterial portography (CT-AP) (P=0.004) were significantly associated with future HCC development. The hazard ratios of HGDN and LGDN were 16.8 (95% confidence interval [CI], 6.19-45.6) and 2.96 (95% CI, 1.20-7.31), respectively. A decrease in portal blood flow also showed a significantly high hazard ratio of 3.04 (95% CI, 1.42-6.50). Approximate annual development rate to HCC was 20% in patients with HGDN and 10% in LGDN. CONCLUSION: HGDN should be considered a precancerous lesion when it appears during follow-up of chronic viral hepatitis or cirrhosis. Reduced portal blood flow in the nodule on computed tomography-AP is also an important predictor for development of hepatocellular carcinoma.

Adult↗
PubMed1996

Development of hepatomas in hyperplastic nodules induced in the rat liver: detection with superparamagnetic iron oxide-enhanced magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Hyperplastic nodules developed in cirrhotic livers reportedly show accumulations of superparamagnetic iron oxide (SPIO) on magnetic resonance (MR) images, whereas hepatocellular carcinomas do not. We examined whether SPIO-enhanced MR imaging would detect cancerous liver lesions within hyperplastic nodules. METHODS: The study included 40 rats with N-2-fluorenyldiacetamide (FAA)-induced liver tumors. Spin-echo T1-, T2-, and proton density-weighted images were obtained at 1.5 T before and after the administration of SPIO. We evaluated 47 tumors accumulating iron particles on SPIO-enhanced MR images. Among the 47 tumors, 33 were observed on MR images obtained 10-26 weeks after the initiation of the carcinogenic diet. The signal intensity changes within the tumors were observed at 2 weeks and were compared with histologic findings. As a control study, 30 hyperintense (non-SPIO-enhanced) tumors also received pathologic examination. RESULTS: Hyperintense (non-SPIO-enhanced) foci within hypointense (SPIO-enhanced) tumors were observed in seven of the 33 tumors on all pulse sequences, and hyperintense (non-SPIO-enhanced), enlarged foci were observed in three of the seven lesions. In the remaining 26 lesions, the signal intensity of the tumor was totally hypointense on all pulse sequences at initial and follow-up MR imaging. During the 2-week follow-up period, 15 hypointense (SPIO-enhanced) tumors were replaced by hyperintense (non-SPIO-enhanced) tumors. Histologically, SPIO-accumulating tumors were hyperplastic nodules; the lesions that did not accumulate SPIO were hepatocellular carcinomas or hyperplastic nodules with atypical cells. CONCLUSION: MR imaging using SPIO detects the development of hepatocellular carcinoma at an early stage in our animal model.

2-Acetylaminofluorene↗
PubMed1985

Prospective serum thyroglobulin measurements in assessing the risk of developing thyroid nodules in patients exposed to childhood neck irradiation.

We examined 327 patients with a history of cervical radiation treatment for benign conditions and followed them for an average of 5.6 yr. These patients were selected because they initially had normal examinations and normal serum thyroglobulin levels. Of the 327 patients, 48 developed thyroid nodules, and an additional 30 had other clinical changes in their thyroids. Serum thyroglobulin increased by 4.0 +/- 0.6 (+/- SEM) ng/ml in those who remained normal, by 13.4 +/- 5.2 ng/ml in those who were no longer normal, and by 17.1 +/- 8.2 ng/ml in those who developed nodules. We conclude that increasing levels of serum thyroglobulin identify patients who should be examined and followed more carefully for thyroid nodules and thyroid cancer.

Age Factors↗
PubMed1994

ENOD12, an early nodulin gene, is not required for nodule formation and efficient nitrogen fixation in alfalfa.

To demonstrate the importance of an extensively studied early nodulin gene ENOD12 in symbiotic nodule development, plants of different Medicago sativa subspecies were tested for the presence or absence of ENOD12 alleles. In M. s. ssp coerulea w2 (Mcw2), two ENOD12 genes were detected, whereas in M. s. ssp quasifalcata k93 (Mqk93) only one gene was present. In both plants, the ENOD12 genes were expressed in nodules induced by Rhizobium meliloti. The nucleotide sequence of the ENOD12 genes showed that the two Mcw2-specific genes were similar to the ENOD12A and ENOD12B genes of the tetraploid M. s. ssp sativa. ENOD12 from Mqk93 was similar to the corresponding gene found in M. truncatula. From the aligned ENOD12 sequences, an evolutionary tree was constructed. Genetic analysis of the progenies of a cross between Mqk93 and Mcw2 showed that several offspring in F1 carried a null allele originating from Mcw2, and among the F2 progenies, plants with the null allele only lacking the ENOD12 gene appeared. Surprisingly, the ENOD12-deficient plants were similar to their wild-type parents in viability, nodule development, nodule structure, and nitrogen fixation efficiency. Therefore, we concluded that in Medicago the ENOD12 gene is not required for symbiotic nitrogen fixation. Furthermore, we proposed that the heterozygous nature of these legumes can be exploited for the identification of mutated alleles of other known nodulin genes; this will permit the construction of plant mutants deficient in these genes.

Alleles↗
PubMed1992

The PsENOD12 Gene Is Expressed at Two Different Sites in Afghanistan Pea Pseudonodules Induced by Auxin Transport Inhibitors.

A number of early nodulin genes are expressed in specific cell types as pea (Pisum sativum) root nodules develop. The Pisum sativum early nodulin PsENOD2 is detected only in the uninfected cells of the nodule parenchyma, whereas PsENOD12 is expressed at two spatially removed sites: in root hairs and adjacent cortical cells, both of which can be invaded by Rhizobium entering through infection threads, and in derivatives of newly divided root inner cortical cells that establish the nodule primordium. We tested whether Rhizobium infection is required for triggering PsENOD12 gene expression by inducing nodule-like structures on Afghanistan pea roots with the auxin transport inhibitor N-(1-naphthyl)phthalamic acid (NPA). These nodule-like structures lack infection threads but resemble Rhizobium-induced nodules in other aspects. For one, both PsENOD2 and PsENOD12 transcripts were detected in these structures. PsENOD2 mRNA was localized by in situ hybridization to a zone equivalent to the nodule parenchyma of Rhizobium-induced nodules, whereas PsENOD12 transcripts were detected in a group of cells comparable to the nodule primordium of developing nodules. In addition, PsENOD12 mRNA was detected in uninfected root hairs 48 h after NPA treatment. These results indicate that infection is not a trigger for PsENOD12 gene expression in Afghanistan pea and rather suggest that the expression of the PsENOD2 and PsENOD12 genes is correlated with the differentiation of specific cell types in the developing nodule.

Journal Article↗
PubMed2005

Tumorigenesis of K-ras mutation in human endometrial carcinoma via upregulation of estrogen receptor.

OBJECTIVE: To investigate the tumorigenesis of mutant [12Asp]-K-ras in endometrial carcinoma and its relationship with ER. METHODS: We constructed pcDI-[12Asp]K-ras4B by inserting full-length [12Asp]K-ras4B from human endometrial carcinoma Hec-1A cells, into pcDI vector. Cell proliferation of NIH3T3 after transfection with pcDI-[12Asp]K-ras4B was measured by MTT assay. The cell transformation was determined by colony formation and tumor nodule development. [12Asp]-K-ras4B-NIH3T3 cells were transfected with constitutively active pCMV-RafCAAX and dominant-negative pCMV-RafS621A. Cell growth was measured by MTT assay and [3H]thymidine incorporation. After transfected with pcDI-[12Asp]K-ras4B or pCMV-RafS621A, the cells were harvested for Western blot and reporter assay to determine the expression and transcriptional activity of ERalpha and ERbeta, respectively. RESULTS: [12Asp]-K-ras4B enhanced NIH3T3 cells proliferation after 48 h post-transfection (P < 0.05). More colonies were grown 10 days after incubating pcDI-[12Asp]-K-ras4B-NIH3T3 cells (13.48%) than pcDI-NIH3T3 (4.26%) or untreated NIH3T3 (2.33%). The pcDI-[12Asp]-K-ras4B-NIH3T3 cells injected to the nude mice Balb/C developed tumor nodules with poor-differentiated cells after 12 days. An increase of ERalpha and ERbeta was observed in pcDI-[12Asp]-K-ras4B-NIH3T3 cells. RafS621A downregulated ERalpha and ERbeta expression. Estrogen induced the ER transcriptional activity by 5-fold in pcDI-NIH3T3 cells, 13-fold in pcDI-[12Asp]K-ras4B-NIH3T3 and 19-fold in HEC-1A. RafS621A suppressed the ER transcriptional activity. CONCLUSIONS: K-ras mutation induces tumorigenesis in endometrium, and this malignant transformation involves Raf signaling pathway and ER.

Animals↗
PubMed2005

SrSymRK, a plant receptor essential for symbiosome formation.

The symbiosis between legumes and rhizobia is essential for the nitrogen input into the life cycle on our planet. New root organs, the nodules, are established, which house N2-fixing bacteria internalized into the host cell cytoplasm as horizontally acquired organelles, the symbiosomes. The interaction is initiated by bacterial invasion via epidermal root hair curling and cell division in the cortex, both triggered by bacterial nodulation factors. Of the several genes involved in nodule initiation that have been identified, one encodes the leucine-rich repeat-type receptor kinase SymRK. In SymRK mutants of Lotus japonicus or its orthologs in Medicago sp. and Pisum sativum, nodule initiation is arrested at the level of the root hair interaction. Because of the epidermal block, the role of SymRK at later stages of nodule development remained enigmatic. To analyze the role of SymRK downstream of the epidermis, the water-tolerant legume Sesbania rostrata was used that has developed a nodulation strategy to circumvent root hair responses for bacterial invasion. Evidence is provided that SymRK plays an essential role during endosymbiotic uptake in plant cells.

Amino Acid Sequence↗
PubMed2006

A novel fix- symbiotic mutant of Lotus japonicus, Ljsym105, shows impaired development and premature deterioration of nodule infected cells and symbiosomes.

Nitrogen-fixing symbiosis between legume plants and rhizobia is established through complex interactions between two symbiotic partners. To identify the host legume genes that play crucial roles in such interactions, we isolated a novel Fix- mutant, Ljsym105, from a model legume Lotus japonicus MG-20. The Ljsym105 plants displayed nitrogen-deficiency symptoms after inoculation with Mesorhizobium loti under nitrogen-free conditions, but their growth recovered when supplied with nitrogen-rich nutrients. Ljsym105 was recessive and monogenic and mapped on the upper portion of chromosome 4. The mutant Ljsym105 formed an increased number of small and pale-pink nodules. Nitrogenase (acetylene reduction) activity per nodule fresh weight was low but retained more than 50% of that of the wild-type nodules. Light and electron microscopic observations revealed that the Ljsym105 nodule infected cells were significantly smaller than those of wild-type plants, contained enlarged symbiosomes with multiple bacteroids, and underwent deterioration of the symbiosomes prematurely as well as disintegration of the whole infected cell cytoplasm. These results indicate that the ineffectiveness of the Ljsym105 nodules is primarily due to impaired growth of infected cells accompanied with the premature senescence induced at relatively early stages of nodule development. These symbiotic phenotypes are discussed in respect to possible functions of the LjSym105 locus in the symbiotic interactions required for establishment of the nitrogen-fixing symbiosis.

Chromosome Mapping↗
PubMed2004

2-O-methylation of fucosyl residues of a rhizobial lipopolysaccharide is increased in response to host exudate and is eliminated in a symbiotically defective mutant.

When Rhizobium etli CE3 was grown in the presence of Phaseolus vulgaris seed extracts containing anthocyanins, its lipopolysaccharide (LPS) sugar composition was changed in two ways: greatly decreased content of what is normally the terminal residue of the LPS, di-O-methylfucose, and a doubling of the 2-O-methylation of other fucose residues in the LPS O antigen. R. etli strain CE395 was isolated after Tn5 mutagenesis of strain CE3 by screening for mutant colonies that did not change antigenically in the presence of seed extract. The LPS of this strain completely lacked 2-O-methylfucose, regardless of whether anthocyanins were present during growth. The mutant gave only pseudonodules in association with P. vulgaris. Interpretation of this phenotype was complicated by a second LPS defect exhibited by the mutant: its LPS population had only about 50% of the normal amount of O-antigen-containing LPS (LPS I). The latter defect could be suppressed genetically such that the resulting strain (CE395 alpha 395) synthesized the normal amount of an LPS I that still lacked 2-O-methylfucose residues. Strain CE395 alpha 395 did not elicit pseudonodules but resulted in significantly slower nodule development, fewer nodules, and less nitrogenase activity than lps(+) strains. The relative symbiotic deficiency was more severe when seeds were planted and inoculated with bacteria before they germinated. These results support previous conclusions that the relative amount of LPS I on the bacterial surface is crucial in symbiosis, but LPS structural features, such as 2-O-methylation of fucose, also may facilitate symbiotic interactions.

Carbohydrate Sequence↗
PubMed1997

Simulation of subtle lung nodules in projection chest radiography.

PURPOSE: To measure the radiologic characteristics of subtle lung nodules and develop nodule phantoms that simulate these characteristics. MATERIALS AND METHODS: From a database of chest radiographs, 16 radiographs that showed confirmed subtle lung nodules were selected. The optical density values surrounding each nodule were obtained, and the radiologic characteristic of the nodules were evaluated. A set of Teflon nodule phantoms with similar x-ray transmission and variability was designed and fabricated. The contrast characteristics of the images of the nodule phantoms were measured. RESULTS: Most of the subtle nodules appeared to have diffuse edges with Gaussian-like contrast profiles. The contrast and size characteristics of the nodule phantom images fulfilled the design criteria within a 4% deviation. CONCLUSION: The radiologic pattern of subtle lung nodules is poorly simulated by nodule phantoms with simple spherical or disk shapes. The nodule phantoms in this study produce realistic radiographic patterns with an energy-dependent attenuation equivalent to that of tissue. The nodule phantoms are intended for use in experiments involving human subjects.

Humans↗
PubMed2001

[Rheumatoid arthritis among mapuche aborigines. A 16 years experience in the IX Region of the Chile].

BACKGROUND: Mapuche, Chilean natives, represent approximately 9.8% of Chilean population and in the IX region of the country, they account for 18.4% of population over 15 years old. They preserve some socio-cultural characteristics that make them different to the rest of the population. AIM: To describe the epidemiological characteristics rheumatoid arthritis among Mapuche natives. SUBJECTS AND METHODS: Retrospective review of patients of Mapuche origin with rheumatoid arthritis, seen at Temuco Hospital between 1980 and 1996. RESULTS: Among 308 cases gathered, only 106 (93 women, aged 55 +/- 10 years old) complied with 1987 American College of Rheumatology (ACR) criteria for rheumatoid arthritis. The disease began between 29 and 52 years old in 73% of patients and the mean delay in diagnosis was 4.4 years. At diagnosis, 99% had symmetric poliarthritis, 28.3% had either fatigue, fever or weight loss, and 46.9% were in class III or in class IV of ACR-1991. Fifty three percent of patients developed Sicca syndrome, 36% developed nodules, 23% developed Raynaud phenomenon, 11% developed pulmonary involvement, 7% developed vasculitis, 5% developed neurological manifestations and 19% developed ophthalmologic involvement. Rheumatoid factor was positive in 78% and 73% had erosions. HLA DR4 was (+) in 60% of 30 patients. Thirty percent required 3 or more disease modifying drugs and prednisone over 10 mg/day. There was no correlation between functional capacity and several other features of the disease. CONCLUSIONS: Mapuche rheumatoid arthritis patients are detected late and have a poor functional capacity at the time of diagnosis. They also have a higher proportion of extraarticular manifestations, more erosions and require more aggressive treatments.

Adult↗
PubMed1991

Effect of localized nitrate application on isoflavonoid concentration and nodulation in split-root systems of wild-type and nodulation-mutant soybean plants.

Although isoflavonoids are known to be inducers of nod genes in Bradyrhizobium japonicum, it was recently proposed that internal root levels of isoflavonoids may be important in nodule development on soybean (Glycine max [L.] Merr.). The hypernodulating soybean mutants were shown to accumulate higher root concentrations of isoflavonoid compounds (daidzein, genistein, and coumestrol) and to be more extensively nodulated than was the Williams parent when inoculated with B. japonicum. The hypernodulating mutants and the parent line, Williams, also showed decreased isoflavonoid concentrations and decreased nodule development if N was applied. The current study evaluated the effect of localized NO(3) (-) application on root isoflavonoid concentration and on nodulation in split-root systems of the Williams wild type and a hypernodulating mutant (NOD1-3). Nitrate application markedly decreased isoflavonoid concentrations in non-inoculated soybean roots. When roots were inoculated, nodule number, weight, and nitrogenase activity were markedly suppressed on the root-half receiving 5 millimolar NO(3) (-) compared with the other root-half receiving 0 millimolar NO(3) (-). High performance liquid chromatographic analyses of root extracts showed that the root-half receiving 5 millimolar NO(3) (-) was markedly lower in isoflavonoid concentrations in both soybean lines. This was partially due to the localized stimulatory effect of NO(3) (-) on root growth. The inoculated NOD1-3 mutant had higher isoflavonoid concentrations than did the Williams control in both the presence and absence of NO(3) (-). These results provide evidence that the site of N application primarily controls the site of nodulation inhibition, possibly through decreasing isoflavonoid levels. Although the effect of NO(3) (-) on nodule development and root isoflavonoid concentration was strongly localized, there was evidence that NO(3) (-) also resulted in a systemic effect on root isoflavonoids. The results are consistent with previous speculation that internal levels of root isoflavonoids may affect nodule development.

Journal Article↗