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Lichens to Gunnera — with emphasis on Azolla

  • G. A. Peters
  • R. E. ToiaJr.
  • H. E. Calvert
  • B. H. Marsh
Part of the Developments in Plant and Soil Sciences book series (DPSS, volume 21)

Summary

N2-fixing cyanobacteria occur in symbiotic associations with fungi (ascomycetes) as lichens and with a few green plants. The associated cyanobacterium is always a species of Nostoc or Anabaena. Only a small number of plant genera are involved but there is a remarkable range of host diversity. Associations occur with several bryophytes (e.g. Anthoceros, Blasia, Cavicularia), a pteridophyte (Azolla), cycads (nine genera including Macrozamia and Encephalartos) and an angiosperm (Gunnera). Except for Gunnera, where the cyanobacterium penetrates the plant cells, the cyanobacteria are extracellular with specialized morphological modifications and/or structures of the host plant organs providing an environment which facilitates interaction with the prokaryote.

Salient aspects of current knowledge pertaining to the establishment, perpetuation, and functioning of the individual symbioses are summarized. Where possible this includes information concerning recognition and specificity, mode(s) of infection, morphological modifications/adaptations of the host plant and a synopsis of morphological, physiological and biochemical changes common to the symbiotic cyanobacteria. The latter encompasses heterocyst frequencies, enzymes involved in ammonia assimilation, photosynthetic capability and metabolic interaction with the host.

The Azolla-Anabaena symbioses, which have potential agronomic significance as an alternative nitrogen source and maintain continuity with the endophyte through the sexual cycle, are emphasized.

Key words

Anthoceros Azolla Blasia Gunnera Macrozamia N2 fixation Peltigera Symbiotic cyanobacteria Symbiotic Nostoc and Anabaena 

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Copyright information

© Martinus Nijhoff Publishers, Dordrecht 1986

Authors and Affiliations

  • G. A. Peters
    • 1
  • R. E. ToiaJr.
    • 1
  • H. E. Calvert
    • 1
  • B. H. Marsh
    • 1
  1. 1.Battelle-C.F. Kettering Research LaboratoryYellow SpringsUSA

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