51
|
Tyerman SD, Niemietz CM, Bramley H. Plant aquaporins: multifunctional water and solute channels with expanding roles. PLANT, CELL & ENVIRONMENT 2002; 25:173-194. [PMID: 11841662 DOI: 10.1046/j.0016-8025.2001.00791.x] [Citation(s) in RCA: 293] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
There is strong evidence that aquaporins are central components in plant water relations. Plant species possess more aquaporin genes than species from other kingdoms. According to sequence similarities, four major groups have been identified, which can be further divided into subgroups that may correspond to localization and transport selectivity. They may be involved in compatible solute distribution, gas-transfer (CO2, NH3) as well as in micronutrient uptake (boric acid). Recent advances in determining the structure of some aquaporins gives further details on the mechanism of selectivity. Gating behaviour of aquaporins is poorly understood but evidence is mounting that phosphorylation, pH, pCa and osmotic gradients can affect water channel activity. Aquaporins are enriched in zones of fast cell division and expansion, or in areas where water flow or solute flux density would be expected to be high. This includes biotrophic interfaces between plants and parasites, between plants and symbiotic bacteria or fungi, and between germinating pollen and stigma. On a cellular level aquaporin clusters have been identified in some membranes. There is also a possibility that aquaporins in the endoplasmic reticulum may function in symplasmic transport if water can flow from cell to cell via the desmotubules in plasmodesmata. Functional characterization of aquaporins in the native membrane has raised doubt about the conclusiveness of expression patterns alone and need to be conducted in parallel. The challenge will be to elucidate gating on a molecular level and cellular level and to tie those findings into plant water relations on a macroscopic scale where various flow pathways need to be considered.
Collapse
Affiliation(s)
- S. D. Tyerman
- School of Biological Sciences, Flinders University Adelaide, GPO Box 2100, Adelaide SA 5001, Australia
| | | | | |
Collapse
|
52
|
Abstract
Nonselective cation channels are a diverse group of ion channels characterized by their low discrimination between many essential and toxic cations. They are ubiquitous in plant tissues and are active in the plasma membrane, tonoplast, and other endomembranes. Members of this group are likely to function in low-affinity nutrient uptake, in distribution of cations within and between cells, and as plant Ca2+ channels. They are gated by diverse mechanisms, which can include voltage, cyclic nucleotides, glutamate, reactive oxygen species, and stretch. These channels dominate tonoplast cation transport, and the selectivity and gating mechanisms of tonoplast nonselective cation channels are comprehensively reviewed here. This review presents the first classification of plant nonselective cation channels and the first full description of nonselective cation channel candidate sequences in the Arabidopsis genome.
Collapse
Affiliation(s)
- Vadim Demidchik
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EA, United Kingdom.
| | | | | |
Collapse
|
53
|
Williams LE, Miller AJ. TRANSPORTERS RESPONSIBLE FOR THE UPTAKE AND PARTITIONING OF NITROGENOUS SOLUTES. ANNUAL REVIEW OF PLANT PHYSIOLOGY AND PLANT MOLECULAR BIOLOGY 2001; 52:659-688. [PMID: 11337412 DOI: 10.1146/annurev.arplant.52.1.659] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The acquisition and allocation of nitrogenous compounds are essential processes in plant growth and development. The huge economic and environmental costs resulting from the application of nitrogen fertilizers make this topic very important. A diverse array of transporters varying in their expression pattern and also in their affinity, specificity, and capacity for nitrogenous compounds has been identified. Now the future challenge is to define their individual contribution to nitrogen nutrition and signalling processes. Here we have reviewed recent advances in the identification and molecular characterization of these transporters, concentrating on mechanisms existing at the plasma membrane. The review focuses on nitrate, ammonium, and amino acid transporter familes, but we also briefly describe what is known at the molecular level about peptide transporters and a recently identified family implicated in the transport of purines and their derivatives.
Collapse
Affiliation(s)
- LE Williams
- School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton, SO16, 7PX, United Kingdom; e-mail: , Biochemistry and Physiology Department, IARC-Rothamsted, Harpenden, Herts AL5 2JQ, United Kingdom; e-mail:
| | | |
Collapse
|
54
|
Marcaggi P, Coles JA. Ammonium in nervous tissue: transport across cell membranes, fluxes from neurons to glial cells, and role in signalling. Prog Neurobiol 2001; 64:157-83. [PMID: 11240211 DOI: 10.1016/s0301-0082(00)00043-5] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Most, but not all, animal cell membranes are permeable to NH3, the neutral, minority form of ammonium which is in equilibrium with the charged majority form NH4+. NH4+ crosses many cell membranes via ion channels or on membrane transporters, and cultured mammalian astrocytes and glial cells of bee retina take up NH4+ avidly, in the latter case on a Cl(-)-cotransporter selective for NH4+ over K+. In bee retina, a flux of ammonium from neurons to glial cells is an essential component of energy metabolism, which involves a flux of alanine from glial cells to neurons. In mammalian brain, both glutamate and ammonium are taken up preferentially by astrocytes and form glutamine. Glutamine is transferred to neurons where it is deamidated to re-form glutamate; the maintenance of this cycle appears to require a substantial flux of ammonium from neurons to astrocytes. In addition to maintaining the glial cell content of fixed N (a "bookkeeping" function), ammonium is expected to participate in the regulation of glial cell metabolism (a signalling function): it will increase conversion of glutamate to glutamine, and, by activating phosphofructokinase and inhibiting the alpha-ketoglutarate dehydrogenase complex, it will tend to increase the formation of lactate.
Collapse
Affiliation(s)
- P Marcaggi
- INSERM U394, Institut François Magendie, rue Camille Saint-Saëns, F-33077 Bordeaux Cedex, France
| | | |
Collapse
|
55
|
Salvemini F, Marini A, Riccio A, Patriarca EJ, Chiurazzi M. Functional characterization of an ammonium transporter gene from Lotus japonicus. Gene 2001; 270:237-43. [PMID: 11404021 DOI: 10.1016/s0378-1119(01)00470-x] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
NH(4)(+) is the main product of symbiotic nitrogen fixation and the external concentration of combined nitrogen plays a key regulatory role in all the different step of plant-rhizobia interaction. We report the cloning and characterization of the first member of the ammonium transporter family, LjAMT1;1 from a leguminous plant, Lotus japonicus. Sequence analysis reveals a close relationship to plant transporters of the AMT1 family. The wild type and two mutated versions of LjAMT1;1 were expressed and functionally characterized in yeast. LjAMT1;1 is transcribed in roots, leaves and nodules of L. japonicus plants grown under low nitrogen conditions, consistent with a role in uptake of NH(4)(+) by the plant cells.
Collapse
Affiliation(s)
- F Salvemini
- International Institute of Genetics and Biophysics. Via Marconi 12, 80125, Napoli, Italy
| | | | | | | | | |
Collapse
|
56
|
Britto DT, Siddiqi MY, Glass AD, Kronzucker HJ. Futile transmembrane NH4(+) cycling: a cellular hypothesis to explain ammonium toxicity in plants. Proc Natl Acad Sci U S A 2001; 98:4255-8. [PMID: 11274450 PMCID: PMC31212 DOI: 10.1073/pnas.061034698] [Citation(s) in RCA: 265] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2000] [Accepted: 01/22/2001] [Indexed: 11/18/2022] Open
Abstract
Most higher plants develop severe toxicity symptoms when grown on ammonium (NH(4)(+)) as the sole nitrogen source. Recently, NH(4)(+) toxicity has been implicated as a cause of forest decline and even species extinction. Although mechanisms underlying NH(4)(+) toxicity have been extensively sought, the primary events conferring it at the cellular level are not understood. Using a high-precision positron tracing technique, we here present a cell-physiological characterization of NH(4)(+) acquisition in two major cereals, barley (Hordeum vulgare), known to be susceptible to toxicity, and rice (Oryza sativa), known for its exceptional tolerance to even high levels of NH(4)(+). We show that, at high external NH(4)(+) concentration ([NH(4)(+)](o)), barley root cells experience a breakdown in the regulation of NH(4)(+) influx, leading to the accumulation of excessive amounts of NH(4)(+) in the cytosol. Measurements of NH(4)(+) efflux, combined with a thermodynamic analysis of the transmembrane electrochemical potential for NH(4)(+), reveal that, at elevated [NH(4)(+)](o), barley cells engage a high-capacity NH(4)(+)-efflux system that supports outward NH(4)(+) fluxes against a sizable gradient. Ammonium efflux is shown to constitute as much as 80% of primary influx, resulting in a never-before-documented futile cycling of nitrogen across the plasma membrane of root cells. This futile cycling carries a high energetic cost (we record a 40% increase in root respiration) that is independent of N metabolism and is accompanied by a decline in growth. In rice, by contrast, a cellular defense strategy has evolved that is characterized by an energetically neutral, near-Nernstian, equilibration of NH(4)(+) at high [NH(4)(+)](o). Thus our study has characterized the primary events in NH(4)(+) nutrition at the cellular level that may constitute the fundamental cause of NH(4)(+) toxicity in plants.
Collapse
Affiliation(s)
- D T Britto
- Department of Botany, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
| | | | | | | |
Collapse
|
57
|
Abstract
One of the paradigms of symbiotic nitrogen fixation has been that bacteroids reduce N2 to ammonium and secrete it without assimilation into amino acids. This has recently been challenged by work with soybeans showing that only alanine is excreted in 15N2 labelling experiments. Work with peas shows that the bacteroid nitrogen secretion products during in vitro experiments depend on the experimental conditions. There is a mixed secretion of both ammonium and alanine depending critically on the concentration of bacteroids and ammonium concentration. The pathway of alanine synthesis has been shown to be via alanine dehydrogenase, and mutation of this enzyme indicates that in planta there is likely to be mixed secretion of ammonium and alanine. Alanine synthesis directly links carbon catabolism and nitrogen assimilation in the bacteroid. There is now overwhelming evidence that the principal carbon sources of bacteroids are the C4-dicarboxylic acids. This is based on labelling and bacteroid respiration data, and mutation of both the dicarboxylic acid transport system (dct) and malic enzyme. L-malate is at a key bifurcation point in bacteroid metabolism, being oxidized to oxaloacetate and oxidatively decarboxylated to pyruvate. Pyruvate can be aminated to alanine or converted to acetyl-CoA where it either enters the TCA cycle by condensation with oxaloacetate or forms polyhydroxybutyrate (PHB). Thus regulation of carbon and nitrogen metabolism are strongly connected. Efficient catabolism of C4-dicarboxylates requires the balanced input and removal of intermediates from the TCA cycle. The TCA cycle in bacteroids may be limited by the redox state of NADH/NAD+ at the 2-ketoglutarate dehydrogenase complex, and a number of pathways may be involved in bypassing this block. These pathways include PHB synthesis, glutamate synthesis, glycogen synthesis, GABA shunt and glutamine cycling. Their operation may be critical in maintaining the optimum redox poise and carbon balance of the TCA cycle. They can also be considered to be overflow pathways since they act to remove or add electrons and carbon into the TCA cycle. Optimum operation of the TCA cycle has a major impact on nitrogen fixation.
Collapse
Affiliation(s)
- P Poole
- Division of Microbiology, School of Animal and Microbial Sciences, University of Reading, UK
| | | |
Collapse
|
58
|
Göttfert M, Röthlisberger S, Kündig C, Beck C, Marty R, Hennecke H. Potential symbiosis-specific genes uncovered by sequencing a 410-kilobase DNA region of the Bradyrhizobium japonicum chromosome. J Bacteriol 2001; 183:1405-12. [PMID: 11157954 PMCID: PMC95015 DOI: 10.1128/jb.183.4.1405-1412.2001] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The physical and genetic map of the Bradyrhizobium japonicum chromosome revealed that nitrogen fixation and nodulation genes are clustered. Because of the complex interactions between the bacterium and the plant, we expected this chromosomal sector to contain additional genes that are involved in the maintenance of an efficient symbiosis. Therefore, we determined the nucleotide sequence of a 410-kb region. The overall G+C nucleotide content was 59.1%. Using a minimum gene length of 150 nucleotides, 388 open reading frames (ORFs) were selected as coding regions. Thirty-five percent of the predicted proteins showed similarity to proteins of rhizobia. Sixteen percent were similar only to proteins of other bacteria. No database match was found for 29%. Repetitive DNA sequence-derived ORFs accounted for the rest. The sequenced region contained all nitrogen fixation genes and, apart from nodM, all nodulation genes that were known to exist in B. japonicum. We found several genes that seem to encode transport systems for ferric citrate, molybdate, or carbon sources. Some of them are preceded by -24/-12 promoter elements. A number of putative outer membrane proteins and cell wall-modifying enzymes as well as a type III secretion system might be involved in the interaction with the host.
Collapse
Affiliation(s)
- M Göttfert
- Institut für Genetik, Technische Universität Dresden, D-01062 Dresden, Germany.
| | | | | | | | | | | |
Collapse
|
59
|
Bago B, Pfeffer P, Shachar-Hill Y. Could the urea cycle be translocating nitrogen in the arbuscular mycorrhizal symbiosis? THE NEW PHYTOLOGIST 2001; 149:4-8. [PMID: 33853236 DOI: 10.1046/j.1469-8137.2001.00016.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Affiliation(s)
- Berta Bago
- Dpto. Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín (CSIC), calle Profesor Albareda 1, 18008-Granada, Spain
| | - Philip Pfeffer
- Microbial Biophysics and Biochemistry, USDA/ARS, 600 E. Mermaid Ln., Wyndmoor, 19038 PA, USA
| | - Yair Shachar-Hill
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces NM 88001, USA
| |
Collapse
|
60
|
Xi C, Schoeters E, Vanderleyden J, Michiels J. Symbiosis-specific expression of Rhizobium etli casA encoding a secreted calmodulin-related protein. Proc Natl Acad Sci U S A 2000; 97:11114-9. [PMID: 10995485 PMCID: PMC27157 DOI: 10.1073/pnas.210181097] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2000] [Indexed: 11/18/2022] Open
Abstract
Symbiosis between Rhizobium and its leguminous host requires elaborate communication between the partners throughout the interaction process. A calmodulin-like protein, termed calsymin, was identified in Rhizobium etli; a calmodulin-related protein in a Gram-negative bacterium had not been described previously. Calsymin possesses three repeated homologous domains. Each domain contains two predicted EF-hand Ca(2+)-binding motifs. Ca(2+)-binding activity of calsymin was demonstrated on purified protein. R. etli efficiently secretes calsymin without N-terminal cleavage of the protein. The gene encoding calsymin, casA, is exclusively expressed during colonization and infection of R. etli with the host. Expression of casA is controlled by a repressor protein, termed CasR, belonging to the TetR family of regulatory proteins. Mutation of the casA gene affects the development of bacteroids during symbiosis and symbiotic nitrogen fixation.
Collapse
Affiliation(s)
- C Xi
- F. A. Janssens Laboratory of Genetics, Katholieke Universiteit Leuven, Kardinaal Mercierlaan 92, B-3001, Heverlee, Belgium
| | | | | | | |
Collapse
|
61
|
Howitt SM, Udvardi MK. Structure, function and regulation of ammonium transporters in plants. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1465:152-70. [PMID: 10748252 DOI: 10.1016/s0005-2736(00)00136-x] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ammonium is an important source of nitrogen for plants. It is taken up by plant cells via ammonium transporters in the plasma membrane and distributed to intracellular compartments such as chloroplasts, mitochondria and vacuoles probably via different transporters in each case. Ammonium is generally not used for long-distance transport of nitrogen within the plant. Instead, most of the ammonium transported into plant cells is assimilated locally via glutamine synthetases in the cytoplasm and plastids. Ammonium is also produced by plant cells during normal metabolism, and ammonium transporters enable it to be moved from intracellular sites of production to sites of consumption. Ammonium can be generated de novo from molecular nitrogen (N(2)) by nitrogen-fixing bacteria in some plant cells, such as rhizobia in legume root nodule cells, and at least one ammonium transporter is implicated in the transfer of ammonium from the bacteria to the plant cytoplasm. Plant physiologists have described many of these ammonium transport processes over the last few decades. However, the genes and proteins that underlie these processes have been isolated and studied only recently. In this review, we consider in detail the molecular structure, function and regulation of plant ammonium transporters. We also attempt to reconcile recent discoveries at the molecular level with our knowledge of ammonium transport at the whole plant level.
Collapse
Affiliation(s)
- S M Howitt
- Division of Biochemistry and Molecular Biology, The Australian National University, Canberra, Australia
| | | |
Collapse
|
62
|
Allaway D, Lodwig EM, Crompton LA, Wood M, Parsons R, Wheeler TR, Poole PS. Identification of alanine dehydrogenase and its role in mixed secretion of ammonium and alanine by pea bacteroids. Mol Microbiol 2000; 36:508-15. [PMID: 10792736 DOI: 10.1046/j.1365-2958.2000.01884.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
N2-fixation by Rhizobium-legume symbionts is of major ecological and agricultural importance, responsible for producing a substantial fraction of the biosphere's nitrogen. On the basis of 15N-labelling studies, it had been generally accepted that ammonium is the sole secretion product of N2-fixation by the bacteroid and that the plant is responsible for assimilating it into amino acids. However, this paradigm has been challenged in a recent 15N-labelling study showing that soybean bacteroids only secrete alanine. Hitherto, nitrogen secretion has only been assessed from in vitro 15N-labelling studies of isolated bacteroids. We show that both ammonium and alanine are secreted by pea bacteroids. The in vitro partitioning between them will depend on whether the system is open or closed, as well as the ammonium concentration and bacteroid density. To overcome these limitations we identified and mutated the gene for alanine dehydrogenase (aldA) and demonstrate that AldA is the primary route for alanine synthesis in isolated bacteroids. Bacteroids of the aldA mutant fix nitrogen but only secrete ammonium at a significant rate, resulting in lower total nitrogen secretion. Peas inoculated with the aldA mutant are green and healthy, demonstrating that ammonium secretion by bacteroids can provide sufficient nitrogen for plant growth. However, plants inoculated with the mutant are reduced in biomass compared with those inoculated with the wild type. The labelling and plant growth studies suggest that alanine synthesis and secretion contributes to the efficiency of N2-fixation and therefore biomass accumulation.
Collapse
Affiliation(s)
- D Allaway
- School of Animal and Microbial Sciences, and Department of Soil Science, University of Reading, Reading, UK RG6 6AJ
| | | | | | | | | | | | | |
Collapse
|
63
|
Panter S, Thomson R, de Bruxelles G, Laver D, Trevaskis B, Udvardi M. Identification with proteomics of novel proteins associated with the peribacteroid membrane of soybean root nodules. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 2000; 13:325-33. [PMID: 10707358 DOI: 10.1094/mpmi.2000.13.3.325] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Soybean peribacteroid membrane (PBM) proteins were isolated from nitrogen-fixing root nodules and subjected to N-terminal sequencing. Sequence data from 17 putative PBM proteins were obtained. Six of these proteins are homologous to proteins of known function. These include three chaperones (HSP60, BiP [HSP70], and PDI) and two proteases (a serine and a thiol protease), all of which are involved in some aspect of protein processing in plants. The PBM homologs of these proteins may play roles in protein translocation, folding, maturation, or degradation in symbiosomes. Two proteins are homologous to known, nodule-specific proteins from soybean, nodulin 53b and nodulin 26B. Although the function of these nodulins is unknown, nodulin 53b has independently been shown to be associated with the PBM. All of the eight proteins with identifiable homologs are likely to be peripheral rather than integral membrane proteins. Possible reasons for this apparent bias are discussed. The identification of homologs of HSP70 and HSP60 associated with the PBM is the first evidence that the molecular machinery for co- or post-translational import of cytoplasmic proteins is present in symbiosomes. This has important implications for the biogenesis of this unique, nitrogen-fixing organelle.
Collapse
Affiliation(s)
- S Panter
- Department of Biochemistry and Molecular Biology, Australian National University, Canberra ACT, Australia
| | | | | | | | | | | |
Collapse
|
64
|
Davenport RJ, Tester M. A weakly voltage-dependent, nonselective cation channel mediates toxic sodium influx in wheat. PLANT PHYSIOLOGY 2000; 122:823-34. [PMID: 10712546 PMCID: PMC58918 DOI: 10.1104/pp.122.3.823] [Citation(s) in RCA: 120] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/17/1999] [Accepted: 11/19/1999] [Indexed: 05/18/2023]
Abstract
To determine the transporters responsible for toxic Na(+) influx in wheat (Triticum aestivum), root plasma membrane preparations were screened using the planar lipid bilayer technique as an assay for Na(+)-permeable ion channel activity. The predominant channel in the bilayer was a 44-pS channel that we called the nonselective cation (NSC) channel, which was nonselective for monovalent cations and weakly voltage dependent. Single channel characteristics of the NSC channel were compared with (22)Na(+) influx into excised root segments. Na(+) influx through the NSC channel resembled (22)Na(+) influx in its partial sensitivity to inhibition by Ca(2+), Mg(2+), and Gd(3+), and its insensitivity to all other inhibitors tested (tetraethylammonium, quinine, Cs(+), tetrodotoxin, verapamil, amiloride, and flufenamate). Na(+) influx through the NSC channel also closely resembled an instantaneous current in wheat root protoplasts (S.D. Tyerman, M. Skerrett, A. Garill, G.P. Findlay, R. Leigh [1997] J Exp Bot 48: 459-480) in its permeability sequence, selectivity for K(+) over Na(+) (approximately 1.25), insensitivity to tetraethylammonium, voltage independence, and partial sensitivity to Ca(2+). Comparison of tissue, protoplast (S.D. Tyerman, M. Skerrett, A. Garill, G.P. Findlay, R. Leigh [1997] J Exp Bot 48: 459-480), and single- channel data indicate that toxic Na(+) influx is catalyzed by a single transporter, and this is likely to be the NSC channel identified in planar lipid bilayers.
Collapse
Affiliation(s)
- R J Davenport
- Department of Plant Sciences, Downing Street, Cambridge CB2 3EA, United Kingdom.
| | | |
Collapse
|
65
|
Niemietz CM, Tyerman SD. Channel-mediated permeation of ammonia gas through the peribacteroid membrane of soybean nodules. FEBS Lett 2000; 465:110-4. [PMID: 10631315 DOI: 10.1016/s0014-5793(99)01729-9] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ammonia permeability of the peribacteroid membrane (PBM) from N(2)-fixing soybean nodules was measured (8x10(-5) m/s) using isolated PBM in a stopped-flow spectrofluorimeter. Ammonia (NH(3)) uptake into PBM vesicles was inhibited by up to 42% by HgCl(2) (EC(50)=2.9 microM, mercaptoethanol-reversible) and reduced by ATP pre-incubation. The activation energy of NH(3) uptake (52 kJ/mol) increased (118 kJ/mol) with HgCl(2). Water transport was also HgCl(2)-sensitive (EC(50)=52.6 microM), but increased by ATP pre-incubation. NH(3) and H(2)O may permeate via different pathways through Nodulin 26 or there is another protein on the PBM that is permeable to NH(3).
Collapse
Affiliation(s)
- C M Niemietz
- School of Biological Sciences, The Flinders University of South Australia, G.P.O. Box 2100, Adelaide, S.A., Australia
| | | |
Collapse
|
66
|
Javelle A, Chalot M, Söderström B, Botton B. Ammonium and methylamine transport by the ectomycorrhizal fungus Paxillus involutus and ectomycorrhizas. FEMS Microbiol Ecol 1999; 30:355-366. [PMID: 10568844 DOI: 10.1111/j.1574-6941.1999.tb00663.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Using [(14)C]methylamine as an analogue of ammonium, the kinetics and the energetics of NH(4)(+) transport were studied in the ectomycorrhizal fungus, Paxillus involutus (Batsch) Fr. The apparent half-saturation constant (K(m)) and the maximum uptake rate (V(max)) for the carrier-mediated transport derived from the Eadie-Hofstee transformation were 180 µM and 380 nmol (mg dry wt)(-1) min(-1,) respectively. Both pH dependence and inhibition by protonophores indicate that methylamine transport in P. involutus was dependent on the electrochemical H(+) gradient. Both long-term and short-term uptake experiments were consistent with regulation of ammonium/methylamine transport processes by the presence of an organic nitrogen source. Analysis of methylamine uptake by different P. involutus isolates revealed no obvious trend in the uptake capacities in relation to N deposition at the collection site. Kinetic parameters were determined in P. involutus/Betula pendula (Roth.) axenic association and in detached mycorrhizal roots isolated from forest sites. Enhanced methylamine uptake in the presence of the fungal symbiont was demonstrated. Homogeneous V(max) values were found for axenic and detached mycorrhizas, whereas K(m) values showed greater variations.
Collapse
Affiliation(s)
- A Javelle
- Laboratory of Forest Biology, U.A. INRA 977, University Henri Poincaré, Nancy I, Faculty of Sciences, F-54506, Vandoeuvre-Les-Nancy, France
| | | | | | | |
Collapse
|
67
|
Andreev IM, Dubrovo PN, Krylova VV, Izmailov SF. Functional identification of ATP-driven Ca2+ pump in the peribacteroid membrane of broad bean root nodules. FEBS Lett 1999; 447:49-52. [PMID: 10218580 DOI: 10.1016/s0014-5793(99)00262-8] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
A Ca2+ indicator arsenazo III was used to demonstrate calcium uptake activity of symbiosomes and the peribacteroid membrane (PBM) vesicles isolated from broad bean root nodules and placed in the medium containing ATP and Mg2+ ions. This process was shown to be rapidly stopped by vanadate, completely reversed in the presence of the calcium ionophore A23187 but insensitive to agents abolishing electrical potential or pH difference across the PBM. The presence of an endogenous calcium pool within isolated symbiosomes and bacteroids was detected using a Ca2+ indicator chlortetracycline. These results prove a primary active transport of Ca2+ through the PBM of legume root nodules and provide the first functional identification of an ATP-driven Ca2+-pump, most likely Mg2+-dependent Ca2+-translocating ATPase, in this membrane.
Collapse
Affiliation(s)
- I M Andreev
- Timiryazev Institute of Plant Physiology, Russian Academy of Sciences, Moscow
| | | | | | | |
Collapse
|
68
|
Nielsen KH, Schjoerring JK. Regulation of apoplastic NH4+ concentration in leaves of oilseed rape. PLANT PHYSIOLOGY 1998; 118:1361-8. [PMID: 9847110 PMCID: PMC34752 DOI: 10.1104/pp.118.4.1361] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/28/1998] [Accepted: 09/05/1998] [Indexed: 05/17/2023]
Abstract
Regulation of apoplastic NH4+ concentration in leaves of oilseed rape (Brassica napus L.) was studied using a vacuum-infiltration technique that allowed controlled manipulations of the apoplastic solution. In leaves infiltrated with NH4+-free solution, the apoplastic NH4+ concentration returned in less than 1.5 min to the preinfiltration level of 0.8 mM. Infiltrated 15NH4+ was rapidly diluted by 14NH4+/14NH3 effluxed from the cell. The exchange rate of 15N/14N over the apoplast due to combined 14N efflux from the symplast and 15N influx from the apoplastic solution was 29.4 &mgr;mol g-1 fresh weight h-1 between 0 and 5 min after infiltration. The net uptake of NH4+ into the leaf cells increased linearly with apoplastic NH4+ concentrations between 2 and 10 mM and could be partially inhibited by the channel inhibitors La3+ and tetraethylammonium and by Na+ and K+. When apoplastic pH increased from 5.0 to 8.0, the steady-state apoplastic NH4+ concentration decreased from 1.0 to 0.3 mM. Increasing temperature increased the rate of NH4+ net uptake and reduced the apoplastic steady-state NH4+ concentration. We conclude that the apoplastic solution in leaves of oilseed rape constitutes a highly dynamic NH4+ pool.
Collapse
Affiliation(s)
- KH Nielsen
- Plant Nutrition Laboratory, Department of Agricultural Sciences, Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Copenhagen, Denmark
| | | |
Collapse
|
69
|
Waters JK, Hughes BL, Purcell LC, Gerhardt KO, Mawhinney TP, Emerich DW. Alanine, not ammonia, is excreted from N2-fixing soybean nodule bacteroids. Proc Natl Acad Sci U S A 1998; 95:12038-42. [PMID: 9751786 PMCID: PMC21761 DOI: 10.1073/pnas.95.20.12038] [Citation(s) in RCA: 92] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Symbiotic nitrogen fixation, the process whereby nitrogen-fixing bacteria enter into associations with plants, provides the major source of nitrogen for the biosphere. Nitrogenase, a bacterial enzyme, catalyzes the reduction of atmospheric dinitrogen to ammonium. In rhizobia-leguminous plant symbioses, the current model of nitrogen transfer from the symbiotic form of the bacteria, called a bacteroid, to the plant is that nitrogenase-generated ammonia diffuses across the bacteroid membrane and is assimilated into amino acids outside of the bacteroid. We purified soybean nodule bacteroids by a procedure that removed contaminating plant proteins and found that alanine was the major nitrogen-containing compound excreted. Bacteroids incubated in the presence of 15N2 excreted alanine highly enriched in 15N. The ammonium in these assays neither accumulated significantly nor was enriched in 15N. The results demonstrate that a transport mechanism rather than diffusion functions at this critical step of nitrogen transfer from the bacteroids to the plant host. Alanine may serve only as a transport species, but this would permit physiological separation of the transport of fixed nitrogen from other nitrogen metabolic functions commonly mediated through glutamate.
Collapse
Affiliation(s)
- J K Waters
- Department of Biochemistry, University of Missouri, Columbia, MO 65211, USA
| | | | | | | | | | | |
Collapse
|
70
|
Kaiser BN, Finnegan PM, Tyerman SD, Whitehead LF, Bergersen FJ, Day DA, Udvardi MK. Characterization of an ammonium transport protein from the peribacteroid membrane of soybean nodules. Science 1998; 281:1202-6. [PMID: 9712587 DOI: 10.1126/science.281.5380.1202] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Nitrogen-fixing bacteroids in legume root nodules are surrounded by the plant-derived peribacteroid membrane, which controls nutrient transfer between the symbionts. A nodule complementary DNA (GmSAT1) encoding an ammonium transporter has been isolated from soybean. GmSAT1 is preferentially transcribed in nodules and immunoblotting indicates that GmSAT1 is located on the peribacteroid membrane. [14C]methylammonium uptake and patch-clamp analysis of yeast expressing GmSAT1 demonstrated that it shares properties with a soybean peribacteroid membrane NH4+ channel described elsewhere. GmSAT1 is likely to be involved in the transfer of fixed nitrogen from the bacteroid to the host.
Collapse
Affiliation(s)
- B N Kaiser
- Division of Biochemistry and Molecular Biology, The Australian National University, Canberra ACT 0200, Australia
| | | | | | | | | | | | | |
Collapse
|
71
|
Rojas-Ojeda P, Hernández LE, Brewin NJ, Carpena-Ruiz R. Comparison of Mg2+-dependent ATP hydrolase activities of pea nodule symbiosomes and of pea root plasmalemma, obtained by an aqueous polymer two-phase system. JOURNAL OF CHROMATOGRAPHY. B, BIOMEDICAL SCIENCES AND APPLICATIONS 1998; 711:139-49. [PMID: 9699983 DOI: 10.1016/s0378-4347(98)00110-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The characteristics of the Mg2+-dependent ATPase activity from the peribacteroid membrane of pea symbiosomes was compared with that from pea root plasma membranes. Enzyme inhibitors, optimum reaction pH, substrate specificity and antibody recognition were the main parameters examined. Both the symbiosomes and the root plasma membrane were purified with an aqueous polymer two-phase system (APS). The final concentration of the APS for the purification of symbiosomes were: 6.3% w/w dextran T500, 6.3% w/w poly(ethylene glycol) 3350, 5 mM KH2PO4-K2HPO4, 5 mM KCl, 0.33 M sucrose, (pH 7.85); for the root plasma membrane was: 6.2% (w/w) dextran T500, 6.2% poly(ethylene glycol) 3350, 330 mM sucrose, 5 mM K2HPO4 and 4 mM KCl (pH 7.8). The lack of contamination of pea symbiosomes with endoplasmic reticulum, mitochondria, broken bacteroids and/or tonoplast vesicles was established. Similarly, the aqueous two-phase system used here provided a fairly enriched root plasma membrane with low cross-contamination from other sources. Both symbiosomal and root plasma membrane ATPase activities were highly specific to ATP. The symbiosome ATPase apparently corresponds to an E1E2-ATPase mechanism, similar to that found at the plasma membrane. The similarity between these two ATPases was further supported by immuno-analysis. Mg2+-ATPase of pea symbiosome and root plasma membranes were very similar, by all parameters tested.
Collapse
Affiliation(s)
- P Rojas-Ojeda
- Departamento de Química Agrícola, Geología y Geoquímica, Universidad Autónoma de Madrid, Spain
| | | | | | | |
Collapse
|
72
|
Taté R, Riccio A, Merrick M, Patriarca EJ. The Rhizobium etli amtB gene coding for an NH4+ transporter is down-regulated early during bacteroid differentiation. MOLECULAR PLANT-MICROBE INTERACTIONS : MPMI 1998; 11:188-198. [PMID: 9487694 DOI: 10.1094/mpmi.1998.11.3.188] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
During development of root nodules, Rhizobium bacteria differentiate inside the invaded plant cells into N2-fixing bacteroids. Terminally differentiated bacteroids are unable to grow using the ammonia (NH3) produced therein by the nitrogenase complex. Therefore, the nitrogen assimilation activities of bacteroids, including the ammonium (NH4+) uptake activity, are expected to be repressed during symbiosis. By sequence homology the R. etli amtB (ammonium transport) gene was cloned and sequenced. As previously shown for its counterpart in other organisms, the R. etli amtB gene product mediates the transport of NH4+. The amtB gene is cotranscribed with the glnK gene (coding for a PII-like protein) from a nitrogen-regulated sigma 54-dependent promoter, which requires the transcriptional activator NtrC. Expression of the glnKamtB operon was found to be activated under nitrogen-limiting, free-living conditions, but down-regulated just when bacteria are released from the infection threads and before transcription of the nitrogenase genes. Our data suggest that the uncoupling between N2-fixation and NH3 assimilation observed in symbiosomes is generated by a transcriptional regulatory mechanism(s) beginning with the inactivation of NtrC in younger bacteroids.
Collapse
Affiliation(s)
- R Taté
- International Institute of Genetics and Biophysics, CNR, Naples, Italy
| | | | | | | |
Collapse
|
73
|
|
74
|
Abstract
Infection of legume roots or stems with soil bacteria of the Rhizobiaceae results in the formation of nodules that become symbiotic nitrogen-fixing organs. Within the infected cells of these nodules, bacteria are enveloped in a membrane of plant origin, called the peribacteroid membrane (PBM), and divide and differentiate to form nitrogen-fixing bacteroids. The organelle-like structure comprised of PBM and bacteroids is termed the symbiosome, and is the basic nitrogen-fixing unit of the nodule. The major exchange of nutrients between the symbiotic partners is reduced carbon from the plant, to fuel nitrogenase activity in the bacteroid, and fixed nitrogen from the bacteroid, which is assimilated in the plant cytoplasm. However, many other metabolites are also exchanged. The metabolic interaction between the plant and the bacteroids is regulated by a series of transporters and channels on the PBM and the bacteroid membrane, and these form the focus of this review.
Collapse
Affiliation(s)
- Michael K. Udvardi
- Division of Biochemistry and Molecular Biology, Faculty of Science, Australian National University, Canberra ACT, 0200, Australia
| | | |
Collapse
|
75
|
Michel-Reydellet N, Desnoues N, Elmerich C, Kaminski PA. Characterization of Azorhizobium caulinodans glnB and glnA genes: involvement of the P(II) protein in symbiotic nitrogen fixation. J Bacteriol 1997; 179:3580-7. [PMID: 9171403 PMCID: PMC179151 DOI: 10.1128/jb.179.11.3580-3587.1997] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
The nucleotide sequence and transcriptional organization of Azorhizobium caulinodans ORS571 glnA, the structural gene for glutamine synthetase (GS), and glnB, the structural gene for the P(II) protein, have been determined. glnB and glnA are organized as a single operon transcribed from the same start site, under conditions of both nitrogen limitation and nitrogen excess. This start site may be used by two different promoters since the expression of a glnB-lacZ fusion was high in the presence of ammonia and enhanced under conditions of nitrogen limitation in the wild-type strain. The increase was not observed in rpoN or ntrC mutants. In addition, this fusion was overexpressed under both growth conditions, in the glnB mutant strain, suggesting that P(II) negatively regulates its own expression. A DNA motif, similar to a sigma54-dependent promoter consensus, was found in the 5' nontranscribed region. Thus, the glnBA operon seems to be transcribed from a sigma54-dependent promoter that operates under conditions of nitrogen limitation and from another uncharacterized promoter in the presence of ammonia. Both glnB and glnBA mutant strains derepress their nitrogenase in the free-living state, but only the glnBA mutant, auxotrophic for glutamine, does not utilize molecular nitrogen for growth. The level of GS adenylylation is not affected in the glnB mutant as compared to that in the wild type. Under symbiotic conditions, the glnB and glnBA mutant strains induced Fix- nodules on Sesbania rostrata roots. P(II) is the first example in A. caulinodans of a protein required for symbiotic nitrogen fixation but dispensable in bacteria growing in the free-living state.
Collapse
Affiliation(s)
- N Michel-Reydellet
- Unité de Physiologie Cellulaire, Centre National de la Recherche Scientifique, Unité Recherche Associée 1300, Département des Biotechnologies, Institut Pasteur, Paris, France
| | | | | | | |
Collapse
|
76
|
Arcondéguy T, Huez I, Tillard P, Gangneux C, de Billy F, Gojon A, Truchet G, Kahn D. The Rhizobium meliloti PII protein, which controls bacterial nitrogen metabolism, affects alfalfa nodule development. Genes Dev 1997; 11:1194-206. [PMID: 9159400 DOI: 10.1101/gad.11.9.1194] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Symbiotic nitrogen fixation involves the development of specialized organs called nodules within which plant photosynthates are exchanged for combined nitrogen of bacterial origin. To determine the importance of bacterial nitrogen metabolism in symbiosis, we have characterized a key regulator of this metabolism in Rhizobium meliloti, the uridylylatable P(II) protein encoded by glnB. We have constructed both a glnB null mutant and a point mutant making nonuridylylatable P(II). In free-living conditions, P(II) is required for expression of the ntrC-dependent gene glnII and for adenylylation of glutamine synthetase I. P(II) is also required for efficient infection of alfalfa but not for expression of nitrogenase. However alfalfa plants inoculated with either glnB mutant are nitrogen-starved in the absence of added combined nitrogen. We hypothesize that P(II) controls expression or activity of a bacteroid ammonium transporter required for a functional nitrogen-fixing symbiosis. Therefore, the P(II) protein affects both Rhizobium nitrogen metabolism and alfalfa nodule development.
Collapse
Affiliation(s)
- T Arcondéguy
- Unité Mixte de Recherches (UMR) 215 Institut National de la Recherche Agronomique (INRA)/Centre National de la Recherche Scientifique (CNRS), Castanet-Tolosan, France
| | | | | | | | | | | | | | | |
Collapse
|
77
|
Schultze M, Kondorosi A. The role of lipochitooligosaccharides in root nodule organogenesis and plant cell growth. Curr Opin Genet Dev 1996; 6:631-8. [PMID: 8939723 DOI: 10.1016/s0959-437x(96)80094-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Lipochitooligosaccharides (Nod signals) excreted by rhizobia induce the formation of symbiotic root nodules in leguminous plants. This process is host plant specific, depending on the structural modifications of Nod signals. Rapid responses of plant roots in single cell assays have provided powerful tools in dissecting Nod signal transduction pathways and in elucidating the molecular basis of host specificity. Recent findings indicate that lipochitooligosaccharides, as well as symbiosis-related genes, also function in non legumes, pointing to a general role for these elements in plant morphogenesis.
Collapse
Affiliation(s)
- M Schultze
- Institut des Sciences Végétales, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
| | | |
Collapse
|
78
|
Abstract
Recently developed molecular and genetic approaches have enabled the identification and functional characterization of novel genes encoding ion channels, ion carriers, and water channels of the plant plasma membrane.
Collapse
Affiliation(s)
- S M Assmann
- Biology Department, Pennsylvania State University, 208 Mueller Laboratory, University Park, PA 16802, USA.
| | | |
Collapse
|
79
|
|