THE INFECTION PROCESS AND ULTRASTRUCTURE OF THE GUNNERA-NOSTOC SYMBIOSIS

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SUMMARY

The two components of the Gunnera–Nostoc symbiosis were isolated, grown separately in culture and the association resynthesized in vitro. Both components develop normally when grown independently and Nostoc retains its ability to fix atmospheric nitrogen in symbiosis.

Infection by Nostoc is initiated when the alga grows on mucilage produced by an apical papillate gland. The alga develops rapidly, growing between the papillae and finally penetrating thin-walled meristematic cells at the base of the gland. Resulting nodules contain intracellular algal cells within a host membrane envelope. The algae are considerably modified in thylakoid distribution and shape, and have a very high heterocyst frequency. At later stages, the algae are enclosed in a thickened wall continuous with that of the host cell.

Ancillary

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