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Strieth D, Di Nonno S, Stiefelmaier J, Kollmen J, Geib D, Ulber R. Co-cultivation of diazotrophic terrestrial cyanobacteria and Arabidopsis thaliana. Eng Life Sci 2021; 21:126-136. [PMID: 33716612 PMCID: PMC7923583 DOI: 10.1002/elsc.202000068] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Revised: 09/29/2020] [Accepted: 09/30/2020] [Indexed: 11/08/2022] Open
Abstract
Diazotrophic cyanobacteria are able to fix N2 from the atmosphere and release it as bioavailable nitrogen what other organisms can utilize. Thus, they could be used as living nitrogen supplier whereby the use of fertilizer could be reduced in agricultural industry what results in a decrease of laughing gas released during fertilizer production. The diazotroph cyanobacterium Desmonostoc muscorum (D. muscorum) was characterized in shake flasks cultivated in nitrogen-free and nitrogen-containing medium. Similar growth rates were reached in both cultivations and the release of ammonium by D. muscorum was detected under nitrogen depletion. Subsequently, D. muscorum was co-cultivated with Arabidopsis thaliana (A. thaliana) in nitrogen-free medium. Additionally, the plant was cultivated in nitrogen containing and nitrogen-free medium without D. muscorum as reference. A co-cultivation led to higher growth rates of the cyanobacterium and similar growth of A. thaliana with similar maximum photochemical efficiency of photosystem II compared to the growth of nitrogen containing medium. Further, accumulation of cyanobacterial cells around the roots of A. thaliana was detected, indicating a successfully induced artificial symbiosis. Based on these results, D. muscorum could be a promising cyanobacterium as living nitrogen supplier for plants.
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Affiliation(s)
- Dorina Strieth
- Bioprocess EngineeringTechnical University KaiserslauternKaiserslauternGermany
| | - Sarah Di Nonno
- Bioprocess EngineeringTechnical University KaiserslauternKaiserslauternGermany
| | - Judith Stiefelmaier
- Bioprocess EngineeringTechnical University KaiserslauternKaiserslauternGermany
| | - Jonas Kollmen
- Bioprocess EngineeringTechnical University KaiserslauternKaiserslauternGermany
| | - Doris Geib
- Bioprocess EngineeringTechnical University KaiserslauternKaiserslauternGermany
| | - Roland Ulber
- Bioprocess EngineeringTechnical University KaiserslauternKaiserslauternGermany
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Kipp MA, Stüeken EE, Gehringer MM, Sterelny K, Scott JK, Forster PI, Strömberg CAE, Buick R. Exploring cycad foliage as an archive of the isotopic composition of atmospheric nitrogen. GEOBIOLOGY 2020; 18:152-166. [PMID: 31769156 DOI: 10.1111/gbi.12374] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/20/2019] [Revised: 10/16/2019] [Accepted: 11/05/2019] [Indexed: 06/10/2023]
Abstract
Molecular nitrogen (N2 ) constitutes the majority of Earth's modern atmosphere, contributing ~0.79 bar of partial pressure (pN2 ). However, fluctuations in pN2 may have occurred on 107 -109 year timescales in Earth's past, perhaps altering the isotopic composition of atmospheric nitrogen. Here, we explore an archive that may record the isotopic composition of atmospheric N2 in deep time: the foliage of cycads. Cycads are ancient gymnosperms that host symbiotic N2 -fixing cyanobacteria in modified root structures known as coralloid roots. All extant species of cycads are known to host symbionts, suggesting that this N2 -fixing capacity is perhaps ancestral, reaching back to the early history of cycads in the late Paleozoic. Therefore, if the process of microbial N2 fixation records the δ15 N value of atmospheric N2 in cycad foliage, the fossil record of cycads may provide an archive of atmospheric δ15 N values. To explore this potential proxy, we conducted a survey of wild cycads growing in a range of modern environments to determine whether cycad foliage reliably records the isotopic composition of atmospheric N2 . We find that neither biological nor environmental factors significantly influence the δ15 N values of cycad foliage, suggesting that they provide a reasonably robust record of the δ15 N of atmospheric N2 . Application of this proxy to the record of carbonaceous cycad fossils may not only help to constrain changes in atmospheric nitrogen isotope ratios since the late Paleozoic, but also could shed light on the antiquity of the N2 -fixing symbiosis between cycads and cyanobacteria.
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Affiliation(s)
- Michael A Kipp
- Department of Earth & Space Sciences, University of Washington, Seattle, WA, USA
- Virtual Planetary Laboratory - NASA Nexus for Exoplanet System Science, Seattle, WA, USA
| | - Eva E Stüeken
- Virtual Planetary Laboratory - NASA Nexus for Exoplanet System Science, Seattle, WA, USA
- School of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, UK
| | - Michelle M Gehringer
- Department of Microbiology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Kim Sterelny
- School of Philosophy, Australian National University, Canberra, ACT, Australia
- School of History, Philosophy, Political Science & International Relations, Victoria University of Wellington, Wellington, New Zealand
| | - John K Scott
- CSIRO Land and Water, Wembley, WA, Australia
- School of Biological Sciences, The University of Western Australia, Crawley, WA, Australia
| | - Paul I Forster
- Department of Environment & Science, Queensland Herbarium, Toowong, Qld, Australia
| | - Caroline A E Strömberg
- Department of Biology and Burke Museum of Natural History and Culture, University of Washington, Seattle, WA, USA
| | - Roger Buick
- Department of Earth & Space Sciences, University of Washington, Seattle, WA, USA
- Virtual Planetary Laboratory - NASA Nexus for Exoplanet System Science, Seattle, WA, USA
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Physiological Adaptations in Nitrogen-fixing Nostoc–Plant Symbiotic Associations. MICROBIOLOGY MONOGRAPHS 2007. [DOI: 10.1007/7171_2007_101] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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Root-based N2-fixing symbioses: Legumes, actinorhizal plants, Parasponia sp. and cycads. PLANT ECOPHYSIOLOGY 2005. [DOI: 10.1007/1-4020-4099-7_3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Meeks JC, Elhai J. Regulation of cellular differentiation in filamentous cyanobacteria in free-living and plant-associated symbiotic growth states. Microbiol Mol Biol Rev 2002; 66:94-121; table of contents. [PMID: 11875129 PMCID: PMC120779 DOI: 10.1128/mmbr.66.1.94-121.2002] [Citation(s) in RCA: 313] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Certain filamentous nitrogen-fixing cyanobacteria generate signals that direct their own multicellular development. They also respond to signals from plants that initiate or modulate differentiation, leading to the establishment of a symbiotic association. An objective of this review is to describe the mechanisms by which free-living cyanobacteria regulate their development and then to consider how plants may exploit cyanobacterial physiology to achieve stable symbioses. Cyanobacteria that are capable of forming plant symbioses can differentiate into motile filaments called hormogonia and into specialized nitrogen-fixing cells called heterocysts. Plant signals exert both positive and negative regulatory control on hormogonium differentiation. Heterocyst differentiation is a highly regulated process, resulting in a regularly spaced pattern of heterocysts in the filament. The evidence is most consistent with the pattern arising in two stages. First, nitrogen limitation triggers a nonrandomly spaced cluster of cells (perhaps at a critical stage of their cell cycle) to initiate differentiation. Interactions between an inhibitory peptide exported by the differentiating cells and an activator protein within them causes one cell within each cluster to fully differentiate, yielding a single mature heterocyst. In symbiosis with plants, heterocyst frequencies are increased 3- to 10-fold because, we propose, either differentiation is initiated at an increased number of sites or resolution of differentiating clusters is incomplete. The physiology of symbiotically associated cyanobacteria raises the prospect that heterocyst differentiation proceeds independently of the nitrogen status of a cell and depends instead on signals produced by the plant partner.
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Affiliation(s)
- John C Meeks
- Section of Microbiology, University of California, Davis, California 95616, USA.
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Silvester WB, Parsons R, Watt PW. Direct measurement of release and assimilation of ammonia in the Gunnera-Nostoc symbiosis. THE NEW PHYTOLOGIST 1996; 132:617-625. [PMID: 33863136 DOI: 10.1111/j.1469-8137.1996.tb01880.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
In Gunnera, Nostoc cells invade secretory tissue forming well defined symbiotic areas within the stems and are termed internal nodules (Silvester, 1976). Excised, but intact, internal stem Nostoc nodules taken from Gunnera magellanica show light-stimulated nitrogenase activity and release a small, but measurable, proportion of their current N2 fixation as NH3 into the external solution. When nodules are disrupted and Nostoc extracted anaerobically, 90% or more of the estimated N2 fixation is released from the Nostoc cells as NH3 into the surrounding medium. Use of 15 N2 confirmed that only 12% of N2 fixed is retained within the cells of Nostoc. The remaining 88% was identified as NH3 released outside the cells. Within the intact nodule system, 15 N2 uptake showed that 2-5% of recently fixed N2 remains within the Nostoc cells and up to 30% of extracellular N is in asparagine after 1 h. Evidence is presented that stimulation of nitrogenase by light in the intact Gunnera/Nostoc system produces more NH3 than can be assimilated by the host cells, resulting in significant NH3 accumulation.
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Affiliation(s)
- Warwick B Silvester
- Department of Biological Sciences, University of Dundee, Dundee DD1 4HN, Scotland, UK
| | - Richard Parsons
- Department of Biological Sciences, University of Dundee, Dundee DD1 4HN, Scotland, UK
| | - Peter W Watt
- Department of Anatomy and Physiology, University of Dundee, Dundee DD1 4HN, Scotland, UK
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Sallal AKJ. The presence of glutamine synthetase in the thylakoids of nitrogen-fixing cyanobacteriumNostoc muscorum. J Basic Microbiol 1996. [DOI: 10.1002/jobm.3620360210] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Ornithine cycle in Nostoc PCC 73102. Arginase, OCT and arginine deiminase, and the effects of addition of external arginine, ornithine, or citrulline. Arch Microbiol 1993. [DOI: 10.1007/bf00249027] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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Abstract
Gunnera L. develops a complex and intimate symbiosis with N2 -fixing cyanobacteria of the genus Nostoc, which renders the plant independent of combined nitrogen. The Nostoc-Gunnera symbiosis exhibits unique features compared to other cyanobacterial-plant symbioses: it is for example the only one that involves a flowering plant (angiosperm), the cyanobacterium infects specialized gland organs located on the stems of the host and once it has passed into the interior of the gland the cyanobacterium also enters the Gunnera cells where it starts to differentiate the highest frequency of heterocysts (the N2 -fixing cells) recorded in any cyanobacterial population. Gunnera has attracted scientific attention also for the following reasons: the genus has a peculiar geographic distribution of its subgenera and species in the Southern Hemisphere. It differs morphologically and anatomically from related plants and also shows an anomalous polystelic vascular system (polystely). This review gives an updated account of present knowledge concerning the Nostoc-Gunnera symbiosis. Emphasis will be on the development of the symbiotic tissue (the gland), the structure and function of the prokaryotic N2 -fixing cyanobacterium, the infection process and on the relationship between the pro- and eukaryotic partners prior to and following the establishment of symbiosis. CONTENTS Summary 379 I. Introduction 379 II. The Gunner a plant 380 III. The microsymbiont(s) 383 IV. The symbiosis 384 V. The gland 385 VI. The infection process 388 VII. Specificity 391 VIII. Impacts on the cyanobiont 392 IX. N2 fixation and release 393 X. Photosynthesis 396 XI. Concluding remarks 397 Acknowledgements 398 References 398.
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Affiliation(s)
- B Bergman
- Department of Botany, Stockholm University, S-106 91 Stockholm, Sweden
| | - C Johansson
- Department of Botany, Stockholm University, S-106 91 Stockholm, Sweden
| | - E Söderbäck
- Department of Botany, Stockholm University, S-106 91 Stockholm, Sweden
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Carpenter EJ, Bergman B, Dawson R, Siddiqui PJ, Söderbäck E, Capone DG. Glutamine synthetase and nitrogen cycling in colonies of the marine diazotrophic cyanobacteria Trichodesmium spp. Appl Environ Microbiol 1992; 58:3122-9. [PMID: 1359837 PMCID: PMC183058 DOI: 10.1128/aem.58.9.3122-3129.1992] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We examined freshly collected samples of the colonial planktonic cyanobacterium Trichodesmium thiebautii to determine the pathways of recently fixed N within and among trichomes. High concentrations of glutamate and glutamine were found in colonies. Glutamate and glutamine uptake rates and concentrations in cells were low in the early morning and increased in the late morning to reach maxima near midday; then uptake and concentration again fell to low values. This pattern followed that previously observed for T. thiebautii nitrogenase activity. Our results suggest that recently fixed nitrogen is incorporated into glutamine in the N2-fixing trichomes and may be passed as glutamate to non-N2-fixing trichomes. The high transport rates and concentrations of glutamate may explain the previously observed absence of appreciable uptake of NH4+, NO3-, or urea by Trichodesmium spp. Immunolocalization, Western blots (immunoblots), and enzymatic assays indicated that glutamine synthetase (GS) was present in all cells during both day and night. GS appeared to be primarily contained in cells of T. thiebautii rather than in associated bacteria or cyanobacteria. Double immunolabeling showed that cells with nitrogenase (Fe protein) contained levels of the GS protein that were twofold higher than those in cells with little or no nitrogenase. GS activity and the uptake of glutamine and glutamate dramatically decreased in the presence of the GS inhibitor methionine sulfoximine. Since no glutamate dehydrogenase activity was detected in this species, GS appears to be the primary enzyme responsible for NH3 incorporation.
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Affiliation(s)
- E J Carpenter
- Marine Sciences Research Center, State University of New York, Stony Brook 11794
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Lundquist PO, Huss-Danell K. Immunological studies of glutamine synthetase inFrankia-Alnus incanasymbioses. FEMS Microbiol Lett 1992. [DOI: 10.1111/j.1574-6968.1992.tb05199.x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
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Smith SE, Smith FA. Structure and function of the interfaces in biotrophic symbioses as they relate to nutrient transport. THE NEW PHYTOLOGIST 1990; 114:1-38. [PMID: 33874304 DOI: 10.1111/j.1469-8137.1990.tb00370.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
In this review we compare the structure and function of the interfaces between symbionts in biotrophic associations. The emphasis is on biotrophic fungal parasites and on mycorrhizas, although necrotrophic parasitic associations and the Rhizobium/legume symbiosis are mentioned briefly. We take as a starting point the observations that in the parasitic associations nutrient transport is polarized towards the parasite, whereas in mutualistic associations it is bidirectional. The structure and function of the interfaces are then compared. An important common feature is that in nearly all cases the heterotrophic symbiont (whether mutualistic or parasitic) is located topologically outside the cytoplasm of the host cells, in an apoplastic compartment. This means that nutrient movements across the interface must involve transport into and out of this apoplastic region through membranes of both organisms. Basic principles of membrane transport in uninfected cells are briefly reviewed to set the scene for a discussion of transport mechanisms which may operate in parasitic and mycorrhizal symbioses. The presence and possible roles of ATPases associated with membranes at the interfaces are discussed. We conclude that cytochemical techniques (used to demonstrate the activity of these enzymes) need to he extended and complemented by biochemical and biophysical studies in order to confirm that the activity is due to transport ATPases. Nevertheless, the distribution of activity appears to he in accord with polarized transport mechanisms in some pathogens and with bidirectional transport in mycorrhizas. The absence of ATPases on many fungal membranes needs re-examination. We emphasize that transport mechanisms between mycorrhizal symbionts cannot be viewed simply as the exchange of carbon for phosphate. Additional features include provision for transport of carbon and nitrogen as amino acids or amides and for ions such as K+ and H+ involved in the maintenance of charge balance and pH regulation, processes which also occur in parasitic associations. Interplant transport of nutrients via mycorrhizal hyphae is discussed in the context of these complexities. Some suggestions for the directions of future work are made. CONTENTS Summary 1 I. Introduction 2 II. The availability of nutrients to the symbionts 3 III. Structure of interfaces between symbionts 4 IV. Identity of nutrients transferred: an overview 12 V. Membrane transport: basic principles 14 VI. Transport at the interface of biotrophic symbioses 15 VII. Regulation of pH in biotrophic symbioses 25 VIII. Conclusions: 26.
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Affiliation(s)
- S E Smith
- Departments of Agricultural Biochemistry (Waite Agricultural Research Institute), The University of Adelaide, Adelaide, South Australia, Australia, 5001
| | - F A Smith
- Departments of Botany, The University of Adelaide, Adelaide, South Australia, Australia, 5001
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Lindblad P, Haselkorn R, Bergman B, Nierzwicki-Bauer SA. Comparison of DNA restriction fragment length polymorphisms of Nostoc strains in and from cycads. Arch Microbiol 1989; 152:20-4. [PMID: 2569858 DOI: 10.1007/bf00447006] [Citation(s) in RCA: 31] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
DNA was prepared from cyanobacteria freshly isolated from coralloid roots of natural populations of five cycad species: Ceratozamia mexicana mexicana (Mexico), C. mexicana robusta (Mexico), Dioon spinulosum (Mexico), Zamia furfuraceae (Mexico) and Z. skinneri (Costa Rica). Using the Southern blot technique and cloned Anabaena PCC 7120 nifK and glnA genes as probes, restriction fragment length polymorphisms of these cyanobacterial symbionts were compared. The five cyanobacterial preparations showed differences in the sizes of their DNA fragments hybridizing with both probes, indicating that different cyanobacterial species and/or strains were in the symbiotic associations. On the other hand, a similar comparison of cyanobacteria freshly collected from a single Encephalartos altensteinii coralloid root and from three independently subcultured isolates from the same coralloid root revealed that these were likely to be one and the same organism. Moreover, the complexity of restriction patterns shows that a mixture of Nostoc strains can associate with a single cycad species although a single cyanobacterial strain can predominate in the root of a single cycad plant. Thus, a wide range of Nostoc strains appear to associate with the coralloid roots of cycads.
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Affiliation(s)
- P Lindblad
- Department of Physiological Botany, University of Uppsala, Sweden
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Pate JS, Lindblad P, Atkins CA. Pathways of assimilation and transfer of fixed nitrogen in coralloid roots of cycad-Nostoc symbioses. PLANTA 1988; 176:461-471. [PMID: 24220942 DOI: 10.1007/bf00397652] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/1988] [Accepted: 07/25/1988] [Indexed: 06/02/2023]
Abstract
Freshly detached coralloid roots of several cycad species were found to bleed spontaneously from xylem, permitting identification of products of nitrogen transfer from symbiotic organ to host. Structural features relevant to the export of fixed N were described for Macrozamia riedlei (Fisch. ex Gaud.) Gardn. the principal species studied. Citrulline (Cit), glutamine (Gln) and glutamic acid (Glu), the latter usually in a lesser amount, were the principal translocated solutes in Macrozamia (5 spp.), Encephalartos (4 spp.) and Lepidozamia (1 sp.), while Gln and a smaller amount of Glu, but no Cit were present in xylem sap of Bowenia (1 sp.),and Cycas (2 spp.). Time-course studies of (15)N enrichment of the different tissue zones and the xylem sap of (15)N2-pulse-fed coralloid roots of M. riedlei showed earlier (15)N incorporation into Gln than into Cit, and a subsequent net decline in the (15)N of Gln of the coralloid-root tissues, whereas Cit labeling continued to increase in inner cortex and stele and in the xylem sap. Hydrolysis of the (15)N-labeled Cit and Gln consistently demonstrated much more intense labeling of the respective carbamyl and amide groups than of the other N-atoms. Coralloid roots of M. riedlei pulse-fed (14)CO2 in darkness showed (14)C labeling of aspartic acid (Asp) and Cit in all tissue zones and of Cit of xylem bleeding sap. Lateral roots and uninfected apogeotropic roots of M. riedlei and M. moorei also incorporated (14)CO2 into Cit. The (14)C of Cit was restricted to the carbamyl-C. Comparable (15)N2 and CO2-feeding studies on corallid roots of Cycas revoluta showed Gln to be the dominant product of N2 fixation, with Asp and alanine as other major (14)C-labeled amino compounds, but a total absence of Cit in labeled or unlabeled form.
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Affiliation(s)
- J S Pate
- Botany Department, University of Western Australia, 6009, Nedlands, W.A., Australia
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Romero F, L�pez-Ruiz A, Verbelen JP, Rold�n JM. Immunocytochemical localization of glutamine synthetase in Rhodobacter capsulatus E1F1 and Rhodopseudomonas acidophila. Arch Microbiol 1988. [DOI: 10.1007/bf00411651] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Joseph CM, Meeks JC. Regulation of expression of glutamine synthetase in a symbiotic Nostoc strain associated with Anthoceros punctatus. J Bacteriol 1987; 169:2471-5. [PMID: 2884210 PMCID: PMC212094 DOI: 10.1128/jb.169.6.2471-2475.1987] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
A characteristic of N2-fixing cyanobacteria in symbiotic associations appears to be release of N2-derived NH4+. The specific activity of the primary ammonium-assimilating enzyme, glutamine synthetase (GS), was found to be three- to fourfold lower in Nostoc sp. strain 7801 grown in symbiotic association with the bryophyte Anthoceros punctatus than in free-living Nostoc sp. strain 7801. Quantitative immunological assays with antisera against GS purified from Nostoc sp. strain 7801 and from Escherichia coli indicated that similar amounts of the GS protein were present in symbiotic (50 micrograms mg-1) and free-living (68 micrograms mg-1) cultures. The conclusion from these experiments is that GS is regulated by a posttranslational mechanism in Anthoceros-associated Nostoc sp. strain 7801. However, the results of comparative catalytic and immunological experiments between N2- and NH4+-grown free-living Nostoc sp. strain 7801 implied control of GS synthesis. A correlation was not observed between the level of GS expression and the extent of symbiotic heterocyst differentiation in Nostoc sp. strain 7801 associated with A. punctatus.
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