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PubMed2005

Glutathione and homoglutathione play a critical role in the nodulation process of Medicago truncatula.

Legumes form a symbiotic interaction with bacteria of the Rhizobiaceae family to produce nitrogen-fixing root nodules under nitrogen-limiting conditions. This process involves the recognition of the bacterial Nod factors by the plant which mediates the entry of the bacteria into the root and nodule organogenesis. We have examined the importance of the low molecular weight thiols, glutathione (GSH) and homoglutathione (hGSH), during the nodulation process in the model legume Medicago truncatula. Using both buthionine sulfoximine, a specific inhibitor of GSH and hGSH synthesis, and transgenic roots expressing GSH synthetase and hGSH synthetase in an antisense orientation, we showed that deficiency in GSH and hGSH synthesis inhibited the formation of the root nodules. This inhibition was not correlated to a modification in the number of infection events or to a change in the expression of the Rhizobium sp.-induced peroxidase rip1, indicating that the low level of GSH or hGSH did not alter the first steps of the infection process. In contrast, a strong diminution in the number of nascent nodules and in the expression of the early nodulin genes, Mtenod12 and Mtenod40, were observed in GSH and hGSH-depleted plants. In conclusion, GSH and hGSH appear to be essential for proper development of the root nodules during the symbiotic interaction.

Buthionine Sulfoximine↗
PubMed1977

Root and nodule respiration in relation to acetylene reduction in intact nodulated peas.

Inoculated pea plants (Pisum sativum L.) were grown with N-free nutrients in a controlled environment room and rates of respiratory CO(2) evolution and C(2)H(2) reduction by the intact nodulated roots were determined. Experiments followed changes related to diurnal cycles, light and dark treatments, partial defoliation, aging of plants and NH(4)NO(3) addition. In all experiments, changes in C(2)H(2) reduction were associated with parallel changes in the respiration rate, although in all but the defoliation experiment there was a basal level of respiration which was independent of the rate of C(2)H(2) reduction. In conditions which affected growth or plant size as well as C(2)H(2) reduction, respiration changed by an average of 0.42 mg CO(2) (mumol C(2)H(2) reduced)(-1). However, some treatments decreased C(2)H(2) reduction without greatly changing the growth and in these conditions respiration was decreased by an average of 0.27 mg CO(2) (mumol C(2)H(2) reduced)(-1). While this value may also include some respiration associated with other processes, it is proposed that it more closely estimates respiration directly associated with energy utilization for acetylene reduction; whereas the higher value includes respiration related to maintenance and growth processes as well.

Journal Article↗
PubMed2004

The promoter of the Vicia faba L. leghemoglobin gene VfLb29 is specifically activated in the infected cells of root nodules and in the arbuscule-containing cells of mycorrhizal roots from different legume and nonlegume plants.

The VfLb29 leghemoglobin gene promoter was polymerase chain reaction-amplified from a Vicia faba genomic library and was fused to the gusAint coding region. Expression of the chimeric gene was analyzed in transgenic hairy roots of the legumes V. faba, V. hirsuta, and Medicago truncatula as well as in transgenic Nicotiana tabacum plants. The VfLb29 promoter was found to be specifically active not only in the infected cells of the nitrogen-fixing zone of root nodules but also in arbuscule-containing cells of transgenic V. faba and M. truncatula roots colonized by the endomycorrhizal fungus Glomus intraradices. In addition to these two legumes, specific expression in arbuscule-containing cells was also observed in the nonlegume N. tabacum. All studies were done in comparison to the V. faba leghemoglobin gene promoter VfLb3 that as VfLb29 was expressed in the infected cells of root nodules but showed no activity in endomycorrhiza. An activation of the VfLb29 promoter due to hypoxia in metabolically active tissues was excluded. The conserved activation in arbuscule-containing cells of legumes and the nonlegume N. tabacum suggests a conserved trigger for this promoter in legume and nonlegume endomycorrhiza symbioses.

Anaerobiosis↗
PubMed1991

Alfalfa Controls Nodulation during the Onset of Rhizobium-induced Cortical Cell Division.

The formation of first nodules inhibits subsequent nodulation in younger regions of alfalfa (Medicago sativa L.) roots by a feedback regulatory mechanism that controls nodule number systemically (G Caetano-Anollés, WD Bauer [1988] Planta 175: 546-557). Following inoculation with wild-type Rhizobium meliloti, almost all infections associated with cortical cell division developed into mature nodules. While the distribution of Rhizobium- induced cell divisions closely paralleled the distribution of first emergent nodules, only 9 to 15% of total cell division foci failed to become functional nodules. Nodule formation was restricted to the primary root when plants were inoculated before lateral root emergence. Excision of these primary root nodules allowed nodules to reappear in lateral roots clustered around the location of the root tip at the time of nodule removal. Apparently, this region regained susceptibility to infection within the first hours after excision of primary nodules and suppression of nodulation was restored a day later probably due to the development of new infection foci. Our results suggest that alfalfa controls nodulation during the onset of cell division in the root cortex and not during infection development as in soybean.

Journal Article↗
PubMed2002

Short-term metabolic responses of soybean root nodules to nitrate.

Soybean (Glycine max L. Merr.) plants exposed to 10 mM KNO(3) for a 4 d period were used to test the correlation between nitrogenase activity, gene expression and sucrose metabolism. Nitrate caused the down-regulation of sucrose synthase (SS) transcripts within 1 d, although a decline in nodule SS activity and an increase in nodule sucrose content only occurred after 3-4 d. In a second experiment, plants were exposed to (15)N-labelled nitrate for 48 h to determine the time period during which nitrate was taken up, and to relate this to the decline in apparent nitrogenase activity (H(2) production in air) and the reduction in SS gene transcript levels. The peak of nitrate uptake appeared to be between 8 h and 14 h whilst apparent nitrogenase activity began to decline at about 17.5 h. The SS mRNA signal declined markedly between 14 h and 24 h. The correlative association of these factors is clear. However, SS activity per se does not appear to be related to the initial decline in apparent nitrogenase activity as a result of nitrate uptake. These findings, therefore, do not support the hypothesis that the regulation of nodule function is mediated by the regulation of SS activity.

Blotting, Northern↗
PubMed2006

Multiple groESL operons are not key targets of RpoH1 and RpoH2 in Sinorhizobium meliloti.

Among the rhizobia that establish nitrogen-fixing nodules on the roots of host plants, many contain multiple copies of genes encoding the sigma factor RpoH and the chaperone GroEL/GroES. In Sinorhizobium meliloti there are two rpoH genes, four groESL operons, and one groEL gene. rpoH1 mutants are defective for growth at high temperature and form ineffective nodules, rpoH1 rpoH2 double mutants are unable to form nodules, and groESL1 mutants form ineffective nodules. To explore the roles of RpoH1 and RpoH2, we identified mutants that suppress both the growth and nodulation defects. These mutants do not suppress the nitrogen fixation defect. This implies that the functions of RpoH1 during growth and RpoH1/RpoH2 during the initiation of symbiosis are similar but that there is a different function of RpoH1 needed later during symbiosis. We showed that, unlike in Escherichia coli, overexpression of groESL is not sufficient to bypass any of the RpoH defects. Under free-living conditions, we determined that RpoH2 does not control expression of the groE genes, and RpoH1 only controls expression of groESL5. Finally, we completed the series of groE mutants by constructing groESL3 and groEL4 mutants and demonstrated that they do not display symbiotic defects. Therefore, the only groESL operon required by itself for symbiosis is groESL1. Taken together, these results suggest that GroEL/GroES production alone cannot explain the requirements for RpoH1 and RpoH2 in S. meliloti and that there must be other crucial targets.

Bacterial Proteins↗
PubMed1988

Gamma-rays and EMS induced pentaphyllous mutant in black gram (Vigna mungo).

Pentaphyllous mutants in black gram were isolated in M2 generation of a segregating family, irradiated at 20 kR. The genetic nature of mutants was tested by hybridizing with controls, and chi-square tests applied to the F2 population, proved it to be a monogenic recessive. The pentaphyllous mutant had a greater number of pods and leaves per plant and larger and more root nodules. It also showed improved nutritional value with increased seed protein percentage and no increase in TIA (trypsin inhibitor activity).

Amino Acids↗
PubMed2003

Root and nodule growth in Pisum sativum L. in relation to photosynthesis: analysis using 13C-labelling.

The effect of the nitrogen source (gaseous nitrogen, N2, or nitrate ions, NO3-) on the use of carbon (C) for root and nodule growth of pea (Pisum sativum L.) was investigated using 13C-labelling of assimilated CO2 at various stages of growth. Nitrate supply and growing conditions (sowing dates, air CO2 concentration) were varied to alter photosynthetic rates. Nodules are the sink with the highest demand for C in both the vegetative and flowering stages, growing at the expense of shoot and root in the vegetative stage, but only at the expense of roots at flowering. Until flowering, the addition of C into root and nodule biomass was linearly related to pre-existing biomass, thus determining net sink strengths which decreased with root and nodule age. Nodule growth patterns did not depend on the N source, whereas root growth was increased by nitrate when nodule biomass was low. At seed filling, the increase in C of biomass of the root system was no longer related to pre-existing biomass and C was preferentially diverted to roots of plants assimilating nitrate, or to nodules for plants fixing N2.

Algorithms↗
PubMed2003

Comparison of four Sesbania species to remediate Pb/Zn and Cu mine tailings.

A 6-month greenhouse pot trial was performed, aimed at screening appropriate Sesbania species for remediation of Pb/Zn and Cu mine tailings. Performances of young seedlings of four Sesbania species (S. cannabina, S. grandiflora, S. rostrata, and S. sesban) were compared with and without inoculation of rhizobia. Seedlings were planted in two types of tailings amended with garden soil or garden soil mixed with river sediment. The results indicated that inoculated plants generally produced a higher biomass than samples without inoculation. Pb/Zn mine tailings containing rather high concentrations of total and water-soluble Cu, Pb, and Zn were toxic to plant growth compared with Cu mine tailings, according to the growth performance of the four species. Sesbania sesban and S. rostrata showed superior growth performance, compared to the other two species. Thus, they can serve as pioneer species to modify the barren environment, by providing organic matter and essential nutrients such as nitrogen, upon decomposition, in a relatively short period of time. This is especially true for S. rostrata, which is an annual plant that forms both stem and root nodules. However, a longer-term field trial should be conducted to investigate if superior species can beneficially modify the habitat for the growth of subsequent plant communities.

Biomass↗
PubMed1990

Effectiveness of Different Frankia Cell Types as Inocula for the Actinorhizal Plant Casuarina.

The soil bacterium Frankia of the Actinomycetales, capable of forming N(2)-fixing symbiotic root nodules on a diverse array of actinorhizal plants, has several morphological forms when grown in pure culture. Fresh hydrated preparations of whole cells, hyphae, and spores were all infective on seedlings of Casuarina at different dilutions. Desiccated hyphae showed no infection capacity, while desiccated spores remained infective, although at a reduced level. On the basis of most-probable-number statistics, spore suspensions were 3 orders of magnitude more infective than hyphae.

Journal Article↗
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↗
PubMed1992

Photosynthate metabolism in the source leaves of n(2)-fixing soybean plants.

Soybean plants (Glycine max [L.] Merr. cv Williams), which were symbiotic with Bradyrhizobium japonicum, and which grew well upon reduced nitrogen supplied solely through N(2) fixation processes, often exhibited excess accumulation of starch and sucrose and diminished soluble protein in their source leaves. Nitrate and ammonia, when supplied to the nodulated roots of N(2)-fixing plants, mediated a reduction of foliar starch accumulation and a corresponding increase in soluble protein in the source leaves. This provided an opportunity to examine the potential metabolic adjustments by which NO(3) (-) and NH(4) (+) (N) sufficiency or deficiency exerted an influence upon soybean leaf starch synthesis. When compared with soybean plants supplied with N, elevated starch accumulation was focused in leaf palisade parenchyma tissue of N(2)-fixing plants. Foliar activities of starch synthesis pathway enzymes including fructose-1,6-bisphosphate phosphatase, phosphohexoisomerase, phosphoglucomutase (PGM), as well as adenosine diphosphate glucose pyrophosphorylase (in some leaves) exhibited highest activities in leaf extracts of N(2)-fixing plants when expressed on a leaf protein basis. This was interpreted to mean that there was an adaptation of these enzyme activities in the leaves of N(2)-fixing plants, and this contributed to an increase in starch accumulation. Another major causal factor associated with increased starch accumulation was the elevation in foliar levels of fructose-6-phosphate, glucose-6-phosphate, and glucose-1-phosphate (G1P), which had risen to chloroplast concentrations considerably in excess of the K(m) values for their respective target enzymes associated with starch synthesis, e.g. elevated G1P with respect to adenosine diphosphate glucose pyrophosphorylase (ADPG-PPiase) binding sites. The cofactor glucose-1,6-bisphosphate (G1,6BP) was found to be obligate for maximal PGM activity in soybean leaf extracts of N(2)-fixing as well as N-supplemented plants, and G1,6BP levels in N(2)-fixing plant leaves was twice that of levels in N-supplied treatments. However the concentration of chloroplastic G1,6BP in illuminated leaves was computed to be saturating with respect to PGM in both N(2)-fixing and N-supplemented plants. This suggested that the higher level of this cofactor in N(2)-fixing plant leaves did not confer any higher PGM activation and was not a factor in higher starch synthesis rates. Relative to plants supplied with NO(3) (-) and NH(4) (+), the source leaf glycerate-3-phosphate (3-PGA) and orthophosphate (Pi) concentrations in leaves of N(2)-fixing plants were two to four times higher. Although Pi is a physiological competitive inhibitor of leaf chloroplast ADPG-PPiase, and hence, starch synthesis, elevated chloroplast 3-PGA levels in N(2)-fixing plant leaves apparently prevented interference of Pi with ADPG-PPiase catalysis and starch synthesis.

Journal Article↗
PubMed2001

GmZIP1 encodes a symbiosis-specific zinc transporter in soybean.

The importance of zinc in organisms is clearly established, and mechanisms involved in zinc acquisition by plants have recently received increased interest. In this report, the identification, characterization and location of GmZIP1, the first soybean member of the ZIP family of metal transporters, are described. GmZIP1 was found to possess eight putative transmembrane domains together with a histidine-rich extra-membrane loop. By functional complementation of zrt1zrt2 yeast cells no longer able to take up zinc, GmZIP1 was found to be highly selective for zinc, with an estimated K(m) value of 13.8 microm. Cadmium was the only other metal tested able to inhibit zinc uptake in yeast. An antibody raised against GmZIP1 specifically localized the protein to the peribacteroid membrane, an endosymbiotic membrane in nodules resulting from the interaction of the plant with its microsymbiont. The specific expression of GmZIP1 in nodules was confirmed by Northern blot, with no expression in roots, stems, or leaves of nodulated soybean plants. Antibodies to GmZIP1 inhibited zinc uptake by symbiosomes, indicating that at least some of the zinc uptake observed in isolated symbiosomes could be attributed to GmZIP1. The orientation of the protein in the membrane and its possible role in the symbiosis are discussed.

Amino Acid Sequence↗
PubMed2003

Proteome analysis. Novel proteins identified at the peribacteroid membrane from Lotus japonicus root nodules.

The peribacteroid membrane (PBM) forms the structural and functional interface between the legume plant and the rhizobia. The model legume Lotus japonicus was chosen to study the proteins present at the PBM by proteome analysis. PBM was purified from root nodules by an aqueous polymer two-phase system. Extracted proteins were subjected to a global trypsin digest. The peptides were separated by nanoscale liquid chromatography and analyzed by tandem mass spectrometry. Searching the nonredundant protein database and the green plant expressed sequence tag database using the tandem mass spectrometry data identified approximately 94 proteins, a number far exceeding the number of proteins reported for the PBM hitherto. In particular, a number of membrane proteins like transporters for sugars and sulfate; endomembrane-associated proteins such as GTP-binding proteins and vesicle receptors; and proteins involved in signaling, for example, receptor kinases, calmodulin, 14-3-3 proteins, and pathogen response-related proteins, including a so-called HIR protein, were detected. Several ATPases and aquaporins were present, indicating a more complex situation than previously thought. In addition, the unexpected presence of a number of proteins known to be located in other compartments was observed. Two characteristic protein complexes obtained from native gel electrophoresis of total PBM proteins were also analyzed. Together, the results identified specific proteins at the PBM involved in important physiological processes and localized proteins known from nodule-specific expressed sequence tag databases to the PBM.

Cell Membrane↗
PubMed1992

Aspartate aminotransferase in effective and ineffective alfalfa nodules : cloning of a cDNA and determination of enzyme activity, protein, and mRNA levels.

Aspartate aminotransferase (AAT) is a key plant enzyme affecting nitrogen and carbon metabolism, particularly in legume root nodules and leaves of C(4) species. To ascertain the molecular genetic characteristics and biochemical regulation of AAT, we have isolated a cDNA encoding the nodule-enhanced AAT (AAT-2) of alfalfa (Medicago sativa L.) by screening a root nodule cDNA expression library with antibodies. Complementation of an Escherichia coli AAT mutant with the alfalfa nodule AAT-2 cDNA verified the identity of the clone. The deduced amino acid sequence of alfalfa AAT-2 is 53 and 47% identical to animal mitochondrial and cytosolic AATs, respectively. The deduced molecular mass of AAT-2 is 50,959 daltons, whereas the mass of purified AAT-2 is about 40 kilodaltons as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the protein's N-terminal domain (amino acids 1-59) contains many of the characteristics of plastid-targeting peptides. We postulate that AAT-2 is localized to the plastid. Southern blot analysis suggests that AAT-2 is encoded by a small, multigene family. The expression of AAT-2 mRNA in nodules is severalfold greater than that in either leaves or roots. Northern and western blots showed that expression of AAT activity during effective nodule development is accompanied by a sevenfold increase in AAT-2 mRNA and a comparable increase in enzyme protein. By contrast, plant-controlled ineffective nodules express AAT-2 mRNA at much lower levels and have little to no AAT-2 enzyme protein. Expression of root nodule AAT-2 appears to be regulated by at least two events: the first is independent of nitrogenase activity; the second is associated with nodule effectiveness.

Journal Article↗
PubMed2002

Role of rhizobial biosynthetic pathways of amino acids, nucleotide bases and vitamins in symbiosis.

Rhizobia require the availability of 20 amino acids for the establishment of effective symbiosis with legumes. Some of these amino acids are synthesized by rhizobium, whereas the remaining are supplied by the host plant. The supply from plant appears to be plant-type specific. Alfalfa provides arginine, cysteine, isoleucine, valine and tryptophan, and cowpea and soybean provide histidine. The production of ornithine and anthranilic acid, the intermediates in the biosynthetic pathways of arginine and tryptophan, respectively, seems to be essential for effective symbiosis of Sinorhizobium meliloti with alfalfa. The expression of ilvC gene of S. meliloti is required for induction of nodules on the roots of alfalfa plants. An undiminished metabolic flow through the rhizobial pathways for the synthesis of purines and pyrimidines and the synthesis of biotin, nicotinic acid, riboflavin and thiamine by rhizobium appear to be requirements for normal symbiosis. To the best of our knowledge, this is the first review article on the role of rhizobial biosynthetic pathways of amino acids, nucleotide bases and vitamins in rhizobium-legume symbiosis. The scientific developments of about 35 years in this field have been reviewed.

Amino Acids↗
PubMedDate not supplied

Vegetative tissue lectins of peanut (A. hypogaea).

Lectin activities in roots, nodules, stems and leaves of 1-6 week old peanut plant (A. hypogaea) were checked by erythrocyte (human and rabbit) agglutination and sugar inhibition assays. Human and rabbit erythrocyte agglutinating activities were specifically inhibited by lactose/cellobiose (SLII) and methyl alpha-mannoside (SLI) respectively. Seeds, embryos and cotyledons agglutinated neuraminidase treated human erythrocytes and that activity was inhibited by T-disaccharide. In the roots of field grown plants SLI was the major activity, while nodules showed both activities (SLI and SLII). Specific activities of SLI and SLII were maximal in stem tissue and hypocotyl exhibited minimal levels. Actively growing tissues like newly emerging young leaves and elongating stem contained more SLII activity in comparison to the mature tissues. Immunological test indicated that all the vegetative tissue lectins are serologically related.

Animals↗