Reconstitution of the symbiosis of Gunnera manicata Linden: cyanobacterial specificity

Abstract

SUMMARYThe ability of various cyanobacteria to establish a symbiosis with Gunnera manicata Linden was examined under sterile conditions. Cyanobacterial strains were classified as infective if they could be found in a well‐defined infected area within the Gunnera gland tissue 40 d after inoculation. Nine out of 17 tested Nostoc strains were able to infect G. manicata. The infecting strains were all symbiotic isolates. These included six out of ten isolates from Gunnera spp., the isolate from the cycad Macrozamia sp., that from the hornwort Anthocerns sp., and that from the lichen Peltigera canina. None of the seven strains belonging to genera other than Nostne was capable of infection, even though the majority of them were also able to form motile hormogonia. Negative staining revealed fimbria‐like structures in both infective and non‐infective strains. In fact, two of the non‐infecting strains had the most abundant fimbria‐like filaments. No conspicuous structural or ultrastructural differences between infecting and non‐infecting strains were detected using light‐ and transmission electron microscopy. We conclude that selection between conceivable microsymbionts is exerted at the recognition and/or entrance stage.