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PubMed1992

Stimulation of nodulation in field peas (Pisum sativum) by low concentrations of ammonium in hydroponic culture.

Although the inhibitory effects of high concentrations of mineral N (> 1.0 mM) on nodule development and function have often been studied, the effects of low, static concentrations of NH4+ (< 1.0 mM) on nodulation are unknown. In the present experiments we examine the effects of static concentrations of NH4+ at 0, 0.1 and 0.5 mM in flowing, hydroponic culture on nodule establishment and nitrogenase activity in field peas [Pisum sativum L. cv. Express (Svalöf AB)] for the initial 28 days after planting (DAP). Peas grown in the presence of low concentrations of NH4+ had significantly greater nodule numbers (up to 4-fold) than plants grown without NH4+. Nodule dry weight per plant was significantly higher at 14, 21 and 28 DAP in plants grown in the presence of NH4+, but individual nodule mass was lower than in plants grown without NH4+. The nodulation pattern of the plants supplied with NH4+ was similar to that often reported for supernodulating mutants, however the plants did not express other growth habits associated with supernodulation. Estimates of N2 fixation indicate that the plus-NH4+ peas fixed as much or more N2 than the plants supplied with minus-NH4+ nutrient solution. There were no significant differences in nodule numbers, nodule mass or NH4+ uptake between the plants grown at the two concentrations of NH4+. Nodulation appeared to autoregulate by 14 DAP in the minus-NH4+ treatment. Plant growth and N accumulation in the minus-NH4+ plants lagged behind those of the plus-NH4+ treatments prior to N2 fixation becoming well established in the final week of the experiment. The plus-NH4+ treatments appeared not to elicit autoregulation and plants continued to initiate nodules throughout the experiment.

Culture Media↗

PubMed2001

Clinicopathological study of a hilar nodule in the livers of long-term survivors with biliary atresia.

With the application of liver transplantation for patients with biliary atresia (BA), we have had the opportunity to review the clinicopathologic features of the native livers from 10 transplanted BA patients. A single large nodule at porta hepatis (hilar nodule) was noted in three of 10 patients, and an ill-defined nodule-like lesion at porta hepatis was present in two other patients. The three BA patients with hilar nodules were long-term survivors, compared to the patients with nodule-like and those without nodules. The hilar nodules measured between 5.0 cm and 8.0 cm and histologically, they were partly surrounded by fibrous septa with relatively well-preserved liver architectures and fewer inflammatory cells at the portal triads when compared to the surrounding cirrhotic lesions. No nuclear or cellular atypia was observed. Proliferating cell nuclear antigen labeling index was higher in the surrounding cirrhotic lesions than the hilar nodules. The nodule-like lesions at porta hepatis also showed similar light microscopic and immunohistochemical features as the hilar nodules. These hilar nodules did not seem to contain any malignant potential. The benign histology with relatively well-preserved liver architecture and the preferential site of occurrence at porta hepatis where bile seemed to flow more smoothly, suggested possible residues of less-affected hepatic tissues.

Biliary Atresia↗

PubMed1997

RecA-like proteins are components of early meiotic nodules in lily.

Early meiotic nodules (also called recombination nodules) are proteinaceous structures about 100 nm in diameter that are associated with forming synaptonemal complexes (SCs) during early prophase I of meiosis. Although their function is unknown, early nodules may be involved in searching for DNA homology before synaptic initiation. Two potential components of early nodules are Rad51 and Dmc1 proteins. These proteins are important for meiotic recombination in eukaryotes and are homologous to RecA, the major protein that catalyzes homologous pairing and DNA strand exchange in prokaryotes. In addition, Rad51 has been localized by immunofluorescence in abundant foci that may correspond to early nodules in yeast, lily, and mouse. In yeast and lily, Dmc1 and Lim15, the lily homolog of Dmc1, colocalize with Rad51. Here, using electron microscopic immunogold localization to spreads of zygotene and early pachytene SCs from lily, we confirm that RecA-like proteins are components of early nodules. The antibody used was generated to full-length tomato Rad51 protein and binds to both Rad51 and Lim15 in immunoblots of lily primary microsporocyte proteins. The labeled early nodules are heterogeneous in size and are associated with both axial elements and SCs. There are two classes of early nodules, those that are densely labeled with gold and those that are not labeled at all. This result may be due to technical limitations associated with using spread preparations or to differences in the nodules themselves. The presence of Rad51 and/or Lim15 proteins in early nodules supports the hypothesis that early nodules are involved in recombination-related events during meiosis.

Journal Article↗

PubMed1995

Hormonal regulation of sex differentiated parameters in liver nodules from rats treated in the resistant hepatocyte model.

Sex differentiation of liver functions has been shown to be attenuated in preneoplastic rat liver nodules. The present study was performed to investigate whether nodules from male rats are to some extent withdrawn from the normal growth hormone (GH) regulation of these functions. Male and female Wistar rats were treated according to a modified resistant hepatocyte model (RH-model), with diethylnitrosamine initiation and promotion with intragastric administration of 2-acetylaminofluorene (2-AAF) combined with partial hepatectomy (PH). Eleven months post-initiation male rats were treated with either human (hGH) or bovine growth hormone (bGH) or ovine prolactin (oPRL) by continuous infusion for 1 week. The mRNA expression of a number of genes known to be sex differentiated in liver from adult control rats was compared in nodular and surrounding tissue from nodule-bearing male, female and hormone-treated male rats. The basal mRNA expression of the female-predominant cytochrome P4502C12 (CYP2C12) was increased and the male-predominant CYP2C11 was decreased in liver nodules from male rats compared with the surrounding liver. Expression of the prolactin receptor (PRL-r; female > male) and the steroid 5 alpha-reductase (female > male) genes was decreased in male nodules, whereas no difference was observed with respect to GH-receptor (GH-r; female > male) expression in nodules versus surrounding tissue. Early nodules obtained from males treated according to the original RH-model (dietary 2-AAF, 0.02%) and isolated 2 weeks after completion of the 2-AAF/PH treatment showed significantly lower GH-r mRNA levels than the total liver tissue. In hepatocellular carcinomas from hormonally unmanipulated males 11 months post-initiation the decrease in PRL-r expression was even more pronounced than in the nodules and a significant decrease in GH-r expression was seen. In female nodules the only significant difference with respect to the sex differentiated parameters was a lower 5 alpha-reductase expression than in the surrounding tissue. Continuous infusion of both hGH and bGH feminized the expression of all the sex differentiated genes in male tissues and eliminated the previously detected differences between nodules and surrounding tissue. oPRL also eliminated the differences between nodules and surrounding tissue in males and partly feminized the expression of both the 5 alpha-reductase and the PRL-r genes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed2000

Weather and nodule mediated variations in delta 13C and delta 15N values in field-grown soybean (Glycine max L.) with special interest in the analyses of xylem fluids.

The nodulating soybean (Enrei) and its non-nodulating mutant (EN 1282) were grown in outdoor plots for 2 years (1994: extraordinary dry, high temperature, 1995: ordinary year). Carbon and nitrogen accumulation, delta 13C and delta 15N values in plant parts and xylem fluids and delta 15N values in the water-extractable soil N were analysed throughout the growing period. Plant growth in 1994 was rapid during the early growth stages, but no pods were produced. In 1995, plant growth was normal and pods were formed. The delta 13C values of the leaves were less negative in 1994 than in 1995 and the nodulated plants showed less negative delta 13C values than non-nodulated plants in both years. The delta 13C values of the leaves during the vegetative phase were positively correlated to the leaf N concentrations. Leaf N concentrations in their turn were influenced by nodulation and weather conditions and/or soil available N. The delta 15N values in the plants and xylem fluids were lower in the nodulated soybean than in non-nodulated soybean in both years, and estimates of the contribution of N2 fixation in nodulated plants based on plant top delta 15N values were 7-14% in 1994 and 37-63% in 1995. The delta 13C values of xylem fluids did not differ between nodulated and non-nodulated plants. Thus, the expected contribution by phosphopenolpyruvate carboxylase-mediated CO2 fixation in the root nodules to plant C-incorporation could not have been significant.

Carbon↗

PubMed1978

Mammary nodules in beagle dogs administered investigational oral contraceptive steroids.

Of 172 beagle dogs administered oral contraceptive steroids for 5-7 years, 114 developed 1,156 nodules in the mammary gland region. Most of these nodules arose 2.5-3.5 years after initiation of treatment. Approximately 16% of the nodules were transient and disappeared spontaneously from the mammary gland during the study. A total of 925 nodules were present in 99 dogs at the time of death or necropsy. These nodules were classified as benign mammary dysplasias (7.0%), lobular or intraductal hyperplasias (31.4%), simple adenomas (20.8%), complex adenomas (25.4%), benign mixed tumors (5.3%), malignant tumors (3.6%), or nonmammary lesions (6.5%). Histologically, the mammary nodules were representative primarily of the hyperplasias and tumors that occur spontaneously in the mammary glands of the dog. The only major exception was the presence of 82 simple adenomas that had basaloid features. Most of the contraceptive-related mammary nodules developed in dogs receiving the combination of progestion and mestranol at 10 or 25 times the proposed human dosage. Control dogs and dogs receiving mestrenol alone had few mammary nodules. Combinations of anagestone acetate and mestranol and chloroethynyl norgestrel (WY-4355) and mestranol produced large numbers of nodules at 10 and 25 times the proposed human dosage, whereas ethynerone plus mestranol produced large numbers of nodules only at 25 times the proposed human dosage. Ethynerone, when given alone at 25 times the proposed human dosage, was associated with fewer mammary nodules. Malignant neoplasms were seen in dogs given 10 and 25 times the proposed human dosage of anagestone acetate plus mestranol and 25 times the proposed human dosage of WY-4355 plus mestranol and ethynerone plus mestranol. This study strongly associates certain combinations of progestin and mestranol with mammary neoplasia in dogs.

Adenoma↗

PubMed2005

Aldehyde oxidase (AO) in the root nodules of Lupinus albus and Medicago truncatula: identification of AO in meristematic and infection zones.

Phytohormones are involved in the organogenesis of legume root nodules. The source of the auxin indole-3-acetic acid (IAA) in nodules has not been clearly determined. We studied the enzyme aldehyde oxidase (AO; EC 1.2.3.1), that catalyzes the last step of IAA biosynthesis in plants, in the nodules of Lupinus albus and Medicago truncatula. Primordia and young lupin nodules and mature M. truncatula nodules showed AO activity bands after native polyacrylamide gel electrophoresis. Gel activity analyses using indole-3-aldehyde as substrate indicated that the nodules of white lupin and M. truncatula have the capability to synthesize IAA via the indole-3-pyruvic acid pathway. Immunolocalization and in situ hybridization experiments revealed that AO is preferentially expressed in the meristematic and the invasion zones in Medicago nodules and in the lateral meristematic zone of Lupinus nodules. High IAA immunolabeling was also detected in the meristematic and invasion zones. Low expression levels and no AO activity were detected in lupin Fix- nodules that displayed restricted growth and early senescence. We propose that local synthesis of IAA in the root nodule meristem and modulation of AO expression and activity are involved in regulation of nodule development.

Abscisic Acid↗

PubMed2000

Carbon metabolism in developing soybean root nodules: the role of carbonic anhydrase.

A full-length cDNA clone encoding carbonic anhydrase (CA) was isolated from a soybean nodule cDNA library. In situ hybridization and immunolocalization were performed in order to assess the location of CA transcripts and protein in developing soybean nodules. CA transcripts and protein were present at high levels in all cell types of young nodules, whereas in mature nodules they were absent from the central tissue and were concentrated in cortical cells. The results suggested that, in the earlier stages of nodule development, CA might facilitate the recycling of CO2 while at later stages it may facilitate the diffusion of CO2 out of the nodule system. In parallel, sucrose metabolism was investigated by examination of the temporal and spatial transcript accumulation of sucrose synthase (SS) and phosphoenolpyruvate carboxylase (PEPC) genes, with in situ hybridization. In young nodules, high levels of SS gene transcripts were found in the central tissue as well as in the parenchymateous cells and the vascular bundles, while in mature nodules the levels of SS gene transcripts were much lower, with the majority of the transcripts located in the parenchyma and the pericycle cells of the vascular bundles. High levels of expression of PEPC gene transcripts were found in mature nodules, in almost all cell types, while in young nodules lower levels of transcripts were detected, with the majority of them located in parenchymateous cells as well as in the vascular bundles. These data suggest that breakdown of sucrose may take place in different sites during nodule development.

Amino Acid Sequence↗

PubMed2001

Effect of mutations in Pisum sativum L. genes blocking different stages of nodule development on the expression of late symbiotic genes in Rhizobium leguminosarum bv. viciae.

In this report, the expression of late symbiotic genes (fnrN, fixN, and nifA) of Rhizobium leguminosarum bv. viciae was studied in nodules of mutant pea lines blocked at four successive stages of nodule development. Bacterial gene expression was analyzed in situ with transcriptional gusA reporter gene fusions. As a control, a constitutively expressed gusA gene was included. In the nodules of Nop(nodule persistence) mutants (mutant in gene sym13), which had not yet exhibited signs of premature senescence, the expression patterns observed were identical to those in wild-type nodules. Normal expression of fusions also occurred in nodules defective at the infection droplet differentiation stage (mutant in gene sym40) in which bacteria are endocytosed, but infection threads and infection droplets are hypertrophied. In contrast, in Itn- (infection thread formation inside the nodule tissue) mutants (mutant gene sym33), in which there is no endocytosis of bacteria, expression of the constitutive fusion was only in infection threads and no activity was shown for the other fusions. From this it can be concluded that functionality of the plant gene Sym33, i.e., bacterial endocytosis, is a prerequisite for the expression of late symbiotic genes in the microsymbiont. No morphologically distinct interzone II-III could be detected in nodules blocked at the bacteroid differentiation stage (mutants in gene sym31). The constitutive fusion was expressed equally throughout the nodule tissue (except for the meristem), and the activity of fusions to late symbiotic genes increased gradually with a maximal expression level at the base of the nodule. This is consistent with an altered oxygen barrier previously reported for these nodules. By including double mutants, earlier results on sequential functioning of gene pairs sym33-sym40 and sym31-sym13 could be confirmed and it could be demonstrated that the developmental epistasis found at the morphological level also is reflected in the expression pattern of late symbiotic genes in the microsymbiont.

Genes, Bacterial↗

PubMed2004

Induction and spatial organization of polyamine biosynthesis during nodule development in Lotus japonicus.

Putrescine and other polyamines are produced by two alternative pathways in plants. One pathway starts with the enzyme arginine decarboxylase (ADC; EC 4.1.1.19), the other with ornithine decarboxylase (ODC; EC 4.1.1.17). Metabolite profiling of nitrogen-fixing Lotus japonicus nodules, using gas chromatography coupled to mass spectrometry, revealed a two- to sixfold increase in putrescine levels in mature nodules compared with other organs. Genes involved in polyamine biosynthesis in L japonicus nodules were identified by isolating cDNA clones encoding ADC (LjADC1) and ODC (LjODC) from a nodule library. Searches of the public expressed sequence tag databases revealed the presence of a second gene encoding ADC (LjADC2). Real-time reverse-transcription-polymerase chain reaction analysis showed that LjADC1 and LjADC2 were expressed throughout the plant, while LjODC transcripts were detected only in nodules and roots. Induction of LjODC and LjADC gene expression during nodule development preceded symbiotic nitrogen fixation. Transcripts accumulation was maximal at 10 days postinfection, when a 6.5-fold increase in the transcript levels of LjODC was observed in comparison with the uninfected roots, while a twofold increase in the transcript levels of LjADC1 and LjADC2 was detected. At later stages of nodule development, transcripts for ADC drastically declined, while in the case of ODC, transcript accumulation was higher than that in roots until after 21 days postinfection. The expression profile of genes involved in putrescine biosynthesis correlated well with the expression patterns of genes involved in cell division and expansion, including a L. japonicus Cyclin D3 and an alpha-expansin gene. Spatial localization of LjODC and LjADC1 gene transcripts in developing nodules revealed that both transcripts were expressed in nodule inner cortical cells and in the central tissue. High levels of LjADC1 transcripts were also observed in both nodule and connecting root vascular tissue, suggesting that putrescine and other polyamines may be subject to long-distance transport. Our results indicate that polyamines are primarily involved in physiological and cellular processes involved in nodule development, rather than in processes that support directly symbiotic nitrogen fixation and assimilation.

Amino Acid Sequence↗

PubMed2003

Dual genetic pathways controlling nodule number in Medicago truncatula.

We report the isolation and characterization of a new Medicago truncatula hyper-nodulation mutant, designated sunn (super numeric nodules). Similar to the previously described ethylene-insensitive mutant sickle, sunn exhibits a 10-fold increase in the number of nodules within the primary nodulation zone. Despite this general similarity, these two mutants are readily distinguished based on anatomical, genetic, physiological, and molecular criteria. In contrast to sickle, where insensitivity to ethylene is thought to be causal to the hyper-nodulation phenotype (R.V. Penmetsa, D.R. Cook [1997] Science 275: 527-530), nodulation in sunn is normally sensitive to ethylene. Nevertheless, sunn exhibits seedling root growth that is insensitive to ethylene, although other aspects of the ethylene triple response are normal; these observations suggest that hormonal responses might condition the sunn phenotype in a manner distinct from sickle. The two mutants also differ in the anatomy of the nodulation zone: Successful infection and nodule development in sunn occur predominantly opposite xylem poles, similar to wild type. In sickle, however, both infection and nodulation occur randomly throughout the circumference of the developing root. Genetic analysis indicates that sunn and sickle correspond to separate and unlinked loci, whereas the sunn/skl double mutant exhibits a novel and additive super-nodulation phenotype. Taken together, these results suggest a working hypothesis wherein sunn and sickle define distinct genetic pathways, with skl regulating the number and distribution of successful infection events, and sunn regulating nodule organogenesis.

Ethylenes↗

PubMed1992

Gibberellins and the Legume-Rhizobium Symbiosis : III. Quantification of Gibberellins from Stems and Nodules of Lima Bean and Cowpea.

Lima bean (Phaseolus lunatus L.) plants inoculated with Bradyrhizobium sp. strain 127E14 displayed a period of marked internode elongation that was not observed in plants inoculated with other compatible bradyrhizobia, including strain 127E15. When strain 127E14 nodulated an alternate host, cowpea (Vigna unguiculata L. Walp), a similar, although less dramatic growth response induced by the bacteria was observed. It has been speculated that the elongative growth promotion brought about by inoculation with strain 127E14 is mediated by gibberellins (GAs). Using deuterated internal standards and gas chromatography-mass spectroscopy analysis, we have quantified the levels of GA(1), GA(20), GA(19), and GA(44) in nodules and stems of two varieties of lima bean (bush and pole) and one variety of cowpea that were inoculated with either strain 127E14 or 127E15. In nodules formed by strain 127E14 on lima bean, endogenous levels of GA(20) and GA(19) were 10 to 40 times higher (35-88 ng/g dry weight) than amounts found in nodules formed by strain 127E15 (2.2-3.9 ng/g dry weight). Relative amounts of GA(44) were also higher (4- to 11-fold) in 127E14 nodules, but this increase was less pronounced. The rhizobial-induced increase of these GAs in the nodule occurred in both pole and bush varieties and seemed to be independent of host morphology. Regardless of rhizobial inoculum, levels of the "bioactive" GA(1) in the nodule (0.3-1.1 ng/g dry weight) were similar. In cowpea nodules, a similar, although smaller, difference in GA content due to rhizobial strain was observed. The concentration of GA(1) in lima bean stems was generally higher than that observed in the nodule, whereas concentrations of the other GAs measured were lower. In contrast with the nodule, GA concentrations in lima bean stems were not greater in plants inoculated with strain 127E14, and in some cases the slower growing plants inoculated with strain 127E15 actually had higher levels of GA(20), GA(19), and GA(44). Thus, there were major differences in concentrations of the precursors to GA(1) in nodules formed by the two bacterial strains, which were positively correlated with the observed elongation growth. These results support the hypothesis that the rhizobial strain modifies the endogenous GA status of the symbiotic system. This alteration in GA balance within the plant, presumably, underlies the observed growth response.

Journal Article↗

PubMed2004

PvUPS1, an allantoin transporter in nodulated roots of French bean.

Nodulated legumes receive their nitrogen via nitrogen-fixing rhizobia, which exist in a symbiotic relationship with the root system. In tropical legumes like French bean (Phaseolus vulgaris) or soybean (Glycine max), most of the fixed nitrogen is used for synthesis of the ureides allantoin and allantoic acid, the major long-distance transport forms of organic nitrogen in these species. The purpose of this investigation was to identify a ureide transporter that would allow us to further characterize the mechanisms regulating ureide partitioning in legume roots. A putative allantoin transporter (PvUPS1) was isolated from nodulated roots of French bean and was functionally characterized in an allantoin transport-deficient yeast mutant showing that PvUPS1 transports allantoin but also binds its precursors xanthine and uric acid. In beans, PvUPS1 was expressed throughout the plant body, with strongest expression in nodulated roots, source leaves, pods, and seed coats. In roots, PvUPS1 expression was dependent on the status of nodulation, with highest expression in nodules and roots of nodulated plants compared with non-nodulated roots supplied with ammonium nitrate or allantoin. In situ RNA hybridization localized PvUPS1 to the nodule endodermis and the endodermis and phloem of the nodule vasculature. These results strengthen our prediction that in bean nodules, PvUPS1 is involved in delivery of allantoin to the vascular bundle and loading into the nodule phloem.

Allantoin↗

PubMed2006

Biosynthesis of ascorbic acid in legume root nodules.

Ascorbic acid (vitamin C) is a major antioxidant and redox buffer, but is also involved in other critical processes of plants. Recently, the hypothesis has been proposed that legume nodules are unable to synthesize ascorbate and have to import it from the shoot or root, thus providing a means by which the plant regulates nodule senescence. The last step of ascorbate biosynthesis in plants is catalyzed by L-galactono-1,4-lactone dehydrogenase (GalLDH). The mRNAs encoding GalLDH and three other enzymes involved in ascorbate biosynthesis are clearly detectable in nodules. Furthermore, an active membrane-bound GalLDH enzyme is present in nodule mitochondria. Biochemical assays on dissected nodules reveal that GalLDH activity and ascorbate are correlated in nodule tissues and predominantly localized in the infected zone, with lower levels of both parameters (relative to the infected tissues) in the apex (87%) and senescent region (43%) of indeterminate nodules and in the peripheral tissues (65%) of determinate nodules. In situ RNA hybridization showed that the GalLDH mRNA is particularly abundant in the infected zone of indeterminate and determinate nodules. Thus, our results refute the hypothesis that ascorbate is not synthesized in nodules and lend support to a previous conclusion that ascorbate in the infected zone is primarily involved in the protection of host cells against peroxide damage. Likewise, the high ascorbate and GalLDH activity levels found in the apex of indeterminate nodules strongly suggest a participation of ascorbate in additional functions during symbiosis, possibly related to cell growth and division and to molecular signaling.

Ascorbate Peroxidases↗

PubMed1994

Acclimation of Soybean Nodules to Changes in Temperature.

This study examines how O2 status, respiration rate, and nitrogenase activity of soybean (Glycine max) nodules acclimate to short-term (<30 min) temperature change from 20 to 15[deg]C or from 20 to 25[deg]C. Acclimation responses were compared between nodules on uninhibited plants and nodules that were severely O2 limited by exposure to Ar:O2. In uninhibited nodules the decrease in temperature caused a rapid inhibition of nitrogenase activity followed by partial recovery, whereas in Ar:O2-inhibited nodules the temperature decrease caused a minor stimulation followed by a gradual decline in nitrogenase activity. In contrast, the temperature increase caused a gradual increase in nitrogenase activity in uninhibited nodules, and an initial inhibition followed by a rapid rise in Ar:O2-inhibited nodules. In both uninhibited and Ar:O2-inhibited nodules, temperature had only minor effects on the degree to which nitrogenase activity was limited by O2 supply, but nodule permeability to O2 diffusion was greater at 25[deg]C, and less at 15[deg]C, than that measured at 20[deg]C. On the basis of these data, we propose that temperature change alters the nodule's respiratory demand and that the observed changes in nodule permeability occur to maintain control over the infected cell O2 concentration as the O2 demand increases at high temperature or decreases at low temperature.

Journal Article↗

PubMed1994

The Role of Oxygen in the Regulation of Nitrogenase Activity in Drought-Stressed Soybean Nodules.

The aim of this study was to investigate the mechanism of nitrogenase inhibition in drought-stressed soybean (Glycine max L.) nodules to determine whether this stress was similar to other inhibitory treatments (e.g. detopping) known to cause an O2 limitation of nodule metabolism. Nodulated soybean plants were either detopped or subjected to mild, moderate, or severe drought stress by growth in different media and by withholding water for different periods. All treatments caused a decline in nitrogenase activity, and in the drought-stressed nodules, the decline was correlated with more negative nodule water potentials. Increases in rhizosphere O2 concentration stimulated nitrogenase activity much more in detopped plants than in drought-stressed plants, reflecting a greater degree of O2 limitation with the detopped treatment than with the drought-stressed treatment. These results indicated that drought stress differs from many other inhibitory treatments, such as detopping, in that its primary cause is not a decrease in nodule permeability and a greater O2 limitation of nodule metabolism. Rather, drought stress seems to cause a decrease in the maximum O2-sufficient rate of nodule respiration or nitrogenase activity, and the changes in nodule permeability reported to occur in drought-stressed nodules may be a response to elevated O2 concentrations in the infected cell that may occur as nodule respiration declines.

Journal Article↗

PubMed1995

Morphological and Molecular Characteristics of Host-Conditioned Ineffective Root Nodules in Cowpea.

In cowpea (Vigna unguiculata [L.] Walp.) a recessive allele, designated cpi, elicits the formation of non-N2-fixing nodules with all bacterial isolates tested. Comparisons of mutant and wild-type nodules demonstrated that the ineffective nodules were anatomically similar to the wild type and contained both infection threads and bacteroids. Ineffective nodules were smaller, however, largely because of the reduced size of the infected cells. Additionally, the number of bacteroids was reduced and senescence occurred prematurely in the infected cells. Grafting studies demonstrated that the defect in nodule development was controlled by the root rather than the shoot. Northern analysis of four nodulin genes indicated that in the ineffective nodules transcript levels of the early nodulin VuENOD2 were initially reduced but were equivalent to wild-type nodules by 21 d. In contrast, transcript levels of the early nodulin VuB were initially similar in both genotypes but as the nodules matured the mRNA levels declined more slowly in the ineffective nodules. The late nodulins leghemoglobin and uricase were expressed in the ineffective nodules but at greatly reduced levels. Thus, the cpi-conditioned defect in nodulation is associated with impaired bacteroid maturation and maintenance, altered nodulin expression, and accelerated senescence.

Journal Article↗

PubMed1997

The aberrant cell walls of boron-deficient bean root nodules have no covalently bound hydroxyproline-/proline-rich proteins.

B-deficient bean (Phaseolus vulgaris L.) nodules examined by light microscopy showed dramatic anatomical changes, mainly in the parenchyma region. Western analysis of total nodule extracts examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that one 116-kD polypeptide was recognized by antibodies raised against hydroxyproline-rich glycoproteins (HRGPs) from the soybean (Glycine max) seed coat. A protein with a comparable molecular mass of 116 kD was purified from the cell walls of soybean root nodules. The amino acid composition of this protein is similar to the early nodulin (ENOD2) gene. Immunoprecipitation of the soybean ENOD2 in vitro translation product showed that the soybean seed coat anti-HRGP antibodies recognized this early nodulin. Furthermore, we used these antibodies to localize the ENOD2 homolog in bean nodules. Immunocytochemistry revealed that in B-deficient nodules ENOD2 was absent in the walls of the nodule parenchyma. The absence of ENOD2 in B-deficient nodules was corroborated by performing hydroxyproline assays. Northern analysis showed that ENOD2 mRNA is present in B-deficient nodules; therefore, the accumulation of ENOD2 is not affected by B deficiency, but its assembly into the cell wall is. B-deficient nodules fix much less N2 than control nodules, probably because the nodule parenchyma is no longer an effective O2 barrier.

Boron↗