The marine lichen Lichina confinis (O. F. Müll.) C. Ag.: ultrastructure and localization of nitrogenase, glutamine synthetase, phycoerythrin and ribulose 1, 5-bisphosphate carboxylase/oxygenase in the cyanobiont

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SUMMARY

Thallus ultrastructure and the localization of proteins involved in photosynthesis, N2 fixation and ammonia assimilation was studied in the Lichina confinis (O. F. Müll) C. Ag.-Calothrix symbiosis. The lichen thallus showed profuse branching. Within this, the cyanobiont was located in the cortical zone. Haustoria were frequently observed in contact with vegetative cells of the cyanobiont but not with heterocysts. An extensive mucilage layer containing numerous vesicles occurred around cyanobiont cells. Immunolabelling showed nitrogenase to be exclusively located in heterocysts of the cyanobiont and the free-living Calothrix sp. Glutamine synthetase (GS) levels in the cyanobiont were found to be drastically decreased compared to the levels in free-living (cultured) Calothrix sp. Such a decrease was more prominent in mature parts of the thallus than in the apical region. Rubisco was mostly located in carboxysomes of the vegetative cells of the cyanobiont. There were relatively low levels of Rubisco in the cytoplasm of vegetative cells, while heterocysts showed negligible levels. In free-living (cultured) Calothrix sp., phycoerythrin (PE) was found to be located along the thylakoid membranes both in vegetative cells and heterocysts. Cyanobiont cells showed a similar pattern but the levels were relatively lower.

Abbreviations
GS

glutamine synthetase

PE

phycoerythrin

GDH

glutamate dehydrogenase

Mr

relative molecular mass

TEM

transmission electron microscopy

SEM

scanning electron microscopy

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